The Bridge and Structural Engineer Indian National Group of the International Association for Bridge and Structural Engineering
Contents :
Volume 4 : December 2013
Editorial • From the desk of Chairman, Editorial Board : Alok Bhowmick • From the desk of Guest Editor, A K Banerjee
Kolkata Symposium, 2013 • Highlights of 36th IABSE Symposium on “Long Span Bridges & Roofs: Development, Design and Implementation” held at Kolkata from 24-27 September 2013
1. Use of Bearings and Expansion Joints in Bridges & Flyovers – Issues of Concern AK Banerjee
1
2. Selection of Appropriate Bearing Type and Arrangement for Bridges Mahesh Tandon
4
3. Guidelines for Selection and Application of Expansion Joint Systems for Bridges Jitendra Rathore, Peter Gunther
12
4. Bearings & their Configurations within Bridge System VN Heggade
23
5. Bearing System of Signature Bridge, Delhi Jose Kurian, SK Rustagi
36
6. Case Studies on Bearings, Expansion Joints and STUs in Long Span Bridges N Bandyopadhyay
49
7. Application of Spherical Bearings with UHMWPE sliding material for Bridges Jitendra Rathore, Peter Gunther, Wolfgang W. Fobo
56
8. Recent Trends in Repair and Replacement of Bearings and Expansion Joints for Rehabilitation of Bridges Lakshmy Parameswaran
64
9. Importance of Quality Control Measures for Structural Bearings and Expansion Joints – An Introspection Achyut Ghosh, Santanu Majumdar
73
C o n te n ts
Special Topic : Bearings, Expansion Joints & STUs for Bridges
Information Section 1. Suspension Bridge in Bhopal CV Kand, Manish Karandikar
78
Research Papers 1. Mix Design Method for High Performance Concrete Dhirendra Singhal, Veerendra Kumar, Balkrishan
88
2. Design of Structural Light Weight Concrete Using Unconventional Light Weight Aggregates Part-II Experimental Study MC Nataraja, MC Sanjay
95
3. Effect of Clamping Force of Rivets on the Fatigue Life of a Riveted Connection Mohammed Adil Shaikh, NM Bhandari, Pradeep Bhargava
103
Panorama • About ING-IABSE • Office Bearers and Managing Committee Members 2013 • ING-IABSE Membership Application Form
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The Bridge & Structural Engineer
JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING
ING - IABSE
March 2014 Issue of the Journal will be a Special Issue with focus on BUILDING STRUCTURES SALIENT TOPICS TO BE COVERED ARE : 1. 2. 3. 4. 5. 6. 7.
1. 2. 3. 4. 5.
AA
Case Studies for Residential, Office/Commercial Buildings, Car Parkingg Structures,, Airport p Buildings, g , Metro Station Buildings. g Seismic Design & Detailing Issues for Buildings Structural Analysis, Design & Detailing Issues Alternative Structural Systems and Materials Status of Building Codes in Structural Engineering & their limitations
Those interested to contribute Technical Papers on above themes shall submit the abstract by 15th February and full paper by 28th February 2014 in a prescribed format, at email id : ingiabse@bol.net.in
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ING - IABSE
JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING
June 2014 Issue of the Journal will be a Special Issue with focus on
CODES & STANDARDS IN STRUCTURAL ENGINEERING (Developments & Needs for Improvement) SALIENT TOPICS TO BE COVERED ARE : 1. Limit State Code IRC:112 & its impact in Bridge Design – Objective & Comparison with Previous IRC Codes and International Codes. 2. Critical Appraisal of Existing Codes & Standards (Indian as well as International) 3. Format of Indian Codes & Basis of Design 4. Need for Improvement in the quality of Codes and Standards in India & the way forward. Those interested to contribute Technical Papers on above themes shall submit the abstract by 30th April 2014 and full paper by 30th May 2014 in a prescribed format , at email id : ingiabse@bol.net.in . ii Volume 43
Number 4
December 2013
The Bridge and Structural Engineer
December 2013
B&SE: The Bridge and Structural Engineer, is a quarterly journal published by ING-IABSE. It is one of the oldest and the foremost structural engineering Journal of its kind and repute in India. It was founded way back in 1957 and since then the journal is relentlessly disseminating latest technological progress in the spheres of structural engineering and bridging the gap between professionals and academics. Articles in this journal are written by practicing engineers as well as academia from around the world. The journal got a long deserving face-lift, with effect from September 2013 Issue.
Editorial Board
All material published in this B&SE journal undergoes peer review to ensure fair balance, objectivity, independence and relevance. The Contents of this journal are however contributions of individual authors and reflect their independent opinions. Neither the members of the editorial board, nor its publishers will be liable for any direct, indirect, consequential, special, exemplary, or other damages arising from any misrepresentation in the papers.
Chair :
The advertisers & the advertisement in this Journal have no influence on editorial content or presentation. The posting of particular advertisement in this journal does not imply endorsement of the product or the company selling them by ING-IABSE, the B&SE Journal or its Editors.
S C Mehrotra, Chief Executive, Mehro Consultants, New Delhi
Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt. Ltd., Noida
Members : Mahesh Tandon, Managing Director, Tandon Consultants Pvt. Ltd., New Delhi A K Banerjee, Former Member (Tech) NHAI, New Delhi Harshavardhan Subbarao, Chairman and Managing Director, CCP Ltd., Mumbai Nirmalya Bandyopadhyay, Director, STUP Consultants Pvt. Ltd., New Delhi Jose Kurian, Chief Engineer, DTTDC Ltd., New Delhi
Advisors : A D Narain, Former DG (RD) & Additional Secretary to the GOI N K Sinha, Former DG (RD) & Special Secretary to the GOI G Sharan, Former DG (RD) & Special Secretary to the GOI A V Sinha, Former DG (RD) & Special Secretary to the GOI S K Puri, Former DG (RD) & Special Secretary to the GOI R P Indoria, Former DG (RD) & Special Secretary to the GOI S S Chakraborty, Chairman, CES (I ) Pvt. Ltd., New Delhi
Front Cover : Top Right : Photograph showing Modular Expansion Joint with 25 gaps and 2000 mm movement capacity, installed in a bridge. Top Left : Schematic Sketch showing Single Strip seal Expansion Joint Bottom Right : Photograph showing installed Shock Transmission Units for Ganga Bridge at Allahabad, U.P. Bottom Left : Photograph showing Pot Bearing of 3.2m diameter with Vertical load carrying capacity of 209MN. Weight of Bearing is 15 tonnes.
B C Roy, Senior Executive Director, JACOBS-CES, Gurgaon Published : Quarterly : March, June, September and December Publisher : ING-IABSE C/o Secretary, Indian National Group of the IABSE IDA Building, Ground Floor (Room No.12) Jamnagar House, Shahjahan Road New Delhi-110011, India Phone: 91+011+23386724, 23782923 Telefax: 91+011+23388132 E-mail: ingiabse@bol.net.in, ingiabse@hotmail.com, secy.ingiabse@bol.net.in Submission of Papers : All editorial communications should be addressed to Chairman, Editorial Board of Indian National Group of the IABSE, IDA Building, Ground Floor, Jamnagar House, Shahjahan Road, New Delhi – 110 011. Advertising: All enquiries and correspondence in connection with advertising and the Equipments/Materials and Industry News Sections, should be addressed to Shri RK Pandey, Secretary, Indian National Group of the IABSE, IDA Building, Ground Floor, Jamnagar House, Shahjahan Road, New Delhi-110011.
The Bridge & Structural Engineer, December 2013
Disclaimer :
Journal of the Indian National Group of the International Association for Bridge & Structural Engineering
The Bridge and Structural Engineer
• Price: ` 500
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Volume 43 Number 4 December 2013 iii
From the Desk of Chairman, Editorial Board
The members of Editorial Board & Advisory Board of ING-IABSE are extremely happy to note that the September Issue of the journal, which focused on “Urban Flyovers”, has been very well received by the readers. Other than the normal circulation list, the journal was circulated to all the delegates of 36th IABSE Symposium on ‘Long Span Bridges and Roofs”, held at Kolkata in September 2013 and we have received several e-mails and telephone calls from the readers expressing their appreciation for the content, quality and presentation of this journal. We express our sincere thanks to all the readers for giving us this encouraging feedback. It gives us the much needed extra motivation to bring in further advancement in the journal. We also take this opportunity to request all the readers of the journal from the industry as well as academic and research institutions to promote the journal by wide circulation amongst the peers and encourage contribution of high quality technical, scientific and research papers for the journal, which has practical applications in bridge and structural engineering. The present issue is focused on ‘Bearings, Expansion Joints & shock transmission units (STU)’. These mechanical parts and
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supplemental features are vital components of the bridge structure, serving several important functions, such as transfer of forces from superstructure to substructure (after allowing for all translations in the direction as defined by the designer), allowing rotations of superstructure at support without affecting the substructure, force damping during earthquake etc. Selection of appropriate type, arrangement, positioning of these mechanical parts and proper installation & testing of these units are extremely important for ensuring proper functioning of the bridge as a whole. Our Guest Editor for this issue is Shri A K Banerjee, who is a well known personality in the field of bridge and structural engineering in India. We hope that this issue will help to disseminate the knowledge and information about Bearings, Expansion joints and STU’s, which are vital bridge components, among the structural engineering fraternity. Happy Reading !
ALOK BHOWMICK
The Bridge and Structural Engineer
From the Desk of Guest Editor
ING-IABSE had come out with their September, 2013 issue of the quarterly journal The Bridge & Structural Engineer on the topic of “Urban Flyovers” in a new improved format in line with the quarterly journal of the Parent Body IABSE, Zurich, during the last International Symposium on “Long Span Bridges and Roofs – Development, Design and Implementation” held at Kolkata in September, 2013. In a continuing trend, this December, 2013 issue has now come out on another important subject “Bearings, Expansion Joints and Appurtenances”, very relevant to bridges and flyovers. These products constitute vital components of bridges and flyover structures and yet their share in the cost of construction of the structures and especially of the highway project as a whole is very small. While the mechanism of Quality Assurance in design and construction of these structures is reasonably well established by standards and procedures in place and undergoes a proven system of monitoring and approval by the Supervision Consultant or Team Leaders of Independent Engineers in PPP projects, the same may not be the case during construction of many of these structures. There is a certain element of casualness and laxity on the part of the Team Leaders and Bridge Engineers, responsible for Quality Assurance of these vital components of
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the structures, presumably due to their lack of knowledge and awareness of the importance of Q.A of these products coupled with a total reliance on the Manufacturers/Suppliers in this regard by virtue of their empanelment with the Ministry of Road Transport & Highways. As a practicing Highway and Bridge Engineer, I am very happy that ING-IABSE has chosen a very topical subject for the December, 2013 Quarterly issue of the Journal of “The Bridge and Structural Engineer”. The topical relevance of the subject is all the more apparent, as there are concerns about the lack of Quality Assurance of bearings and expansion joints in construction of bridges and flyovers, although elaborate standards, specifications and guidelines for these products do exist in the relevant IRC Codes and Special Publications, keeping in view the state of the art products being used now. It is heartening to note the good response received from the Experts through a large number of papers, dealing with different aspects of bearings, expansion joints, STUs etc., covering selection of bearings and joints for new structures, as well as rehabilitation of old bridges, spherical bearings, case studies on application and performance of these products, importance of these manufactured products and also ways and means to improve their Quality Assurance for long term serviceability.
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In all, there are 9 papers dealing with these aspects, besides one paper on Suspension Bridge in Bhopal and 3 research papers related to concrete & steel construction. I am sure that this quarterly issue of INGIABSE Journal will elicit good response from the readers both in Public and Private Sectors, being topical in content and endeavouring to address the concerns of the users about the
need for stricter Quality Assurance of bearings, expansion joints and other appurtenances in the large number of bridges, including major bridges and flyover structures being constructed in the country and many more to be constructed in future.
A.K. Banerjee
Profile of A.K. Banerjee Mr. A.K. Banerjee is a Post Graduate in Civil Engineering from I.I.T, Delhi and has five decades of experience in planning, design, supervision and contract management of Highway and Bridge projects. He was Chief Engineer in the Ministry of Road Transport & Highways, Govt. of India and later Member (Technical) in the National Highways Authority of India (NHAI). He is currently Director (Technical) and Head, Bridge Division in URS Scott Wilson India Pvt. Ltd. During the career in the Ministry, he had been closely associated with planning, design, construction supervision and repair/rehabilitation of a large number of major bridges on National Highways. Mr. Banerjee had been the Convenor of the Committee on Bearings and Expansion Joints for empanelment of Manufacturers and Suppliers of bearings and joints in the Ministry from the year 1995 to 2002 and had been closely involved in the process of Quality Assurance of these products. He has been an active member of the Bearings, Joints & Appurtenances Committee (B-6) for nearly last 20 years and was the Convenor of the Sub Committee for drafting the Guidelines for Expansion Joints IRC:SP 69. He has dealt with several EPC contract projects, funded by Govt. and External Funding Agencies like World Bank, ADB etc. as Engineer as well as Independent Engineer for several DBFOT (PPP) projects in Highway Sector. Post retirement in the Private Sector, he has been continuing to deal with a large number of EPC/PPP projects in the Highway Sector, including construction of a large number of bridges as Engineer/Independent Engineer for last ten years. During his long career in the Ministry, Mr. Banerjee had been on Foreign Assignment for 5 years as Civil Engineering Expert with the Govt. of Iraq.
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Highlights of the 36th IABSE Symposium on “Long Span Bridges and Roofs – Development, Design and Implementation” held at Kolkata from 24th to 27th September 2013 The Indian National Group of the IABSE had organized the 36th IABSE Symposium on “Long Span Bridges and Roofs – Development, Design and Implementation” at Kolkata from 24th to 27th September 2013. The first time an IABSE event of this scale was hosted outside Delhi. Ministry of Road Transport and Highways, Government of India, was the nodal Ministry. The National Highways Authority of India, Public Works Department, West Bengal, Urban Development Department, West Bengal, Irrigation and Waterways Department, West Bengal, Central Public Works Department, Hooghly River Bridge Commissioners, Kolkata Port Trust, Maharashtra State Road Development Corporation Ltd, IL&FS Transportation Networks Ltd, Sadbhav Engineering Ltd, Second Vivekananda Bridge Tollway Co Pvt Ltd, DK Project Pvt Ltd, Transstroy India Ltd, Reliance Jio Infocomm Ltd, Reliance Infrastructure Ltd, IRB Infrastructure Developers Ltd, Land T BPP Tollway Ltd, Bharat Vanijya Eastern Pvt Ltd, Millenium Road Construction Pvt Ltd, Roads (India) International, SEW Infrastructure Ltd, PNC Infratech Ltd, Ashoka Buildcon Ltd, Hindustan Construction Co Ltd, Intercontinental Consultants & Technocrats Pvt Ltd, Shri Bajrang Power & Ispat Ltd, Dilip Buildcon Ltd, Bhopal, MC-Bauchemie (India) Pvt Ltd, KCC Buildcon Pvt Ltd, Oriental Structural Engineers Pvt Ltd, Faith Healthcare, JACOBS, Dineshchandra R Agarwal Infracon Pvt Ltd and RITES Ltd have contributed towards organization of the 36th IABSE Symposium 2013. The choice of the symposium theme was driven in part by the needs felt in India. The nation, in pursuit of economic growth and overall development, has launched itself on the path of infrastructure development, with investments nearly doubling in succeeding Five Year Plan periods. Transport improvement is recognized as the most intensely felt requirements. While
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there is a focus on the economic infrastructure like urban transport, water supply, sewage treatment etc. there is also a need for creating space for public and social activities, such as auditoriums, sports stadiums etc. Bridge and structural engineers are deeply involved and will continue to remain engaged in bringing about this major shift in the provision of transport and public facilities. The objective of the Symposium was to serve as a major international platform for exchange and dissemination of the experience gained. It addressed the future challenges and continuing search for optimal solutions. The IABSE Symposium 2013 was attended by more than 400 delegates from all over India and abroad, including some international experts as well as from Central/State Government Departments, PSUs Private Sector Organisations and Academic Institutes. The symposium carries two foci: one on large column free enclosed for covered spaces like convention centers, aircraft hangers and other transport terminals, industrial structures, sports stadium and others. The other focus was on long span bridges, both road and rail, across rivers, sea link, long viaducts crossing deep gorges and flyovers in urban areas. The IABSE Symposium 2013 was inaugurated on 24th September 2013 by Shri Sarvey Sathyanarayana, Hon’ble Minister of State for Road Transport and Highways by lighting the traditional lamp. Dr Sudarshan Ghosh Dastidar, Minister-in-Charge, PWD & Environment Department, West Bengal and Dr Amit Mitra, Minister-in-Charge, Finance and Excise Department, West Bengal, Shri P Popovic, President of IABSE and Shri C Kandasamy, Honorary Treasurer, ING-IABSE and Director General (Road Development) & Special Secretary, Government of India, Shri VL Patankar, Chairman, ING-IABSE and
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Additional Director General, Ministry of Road Transport and Highways, Shri RK Pandey, Secretary, ING-IABSE and Chief Engineer (Planning), Ministry of Road Transport and Highways, Dr BC Roy, Chairman, Scientific Committee and Vice President of IABSE and Shri Ueli Brunner, Executive Director, IABSE also graced the occasion. Shri C Kandasamy, Honorary Treasurer, ING-IABSE and Director General (Road Development) & Special Secretary, Government of India welcomed the dignitaries. Shri VL Patankar, Chairman, ING-IABSE and Additional Director General, also welcomed the delegates, invitees and guests to the IABSE Symposium 2013. Dr BC Roy, Chairman of the Scientific Committee and Vice President of IABSE gave an outline of the scientific contents of the IABSE Symposium. Shri P Popovic, President of IABSE and Shri Ueli Brunner, Executive Director, IABSE also spoke on the occasion. Shri Sarvey Sathyanarayana, Hon’ble Minister of State for Road Transport and Highways released the Souvenir on this occasion. Shri P Popovic presented the 2013 IABSE Awards. The Opening Ceremony concluded with a lively cultural programme presenting a variety of contemporary Indian music. During the Symposium, a Technical Exhibition was also organized which was inaugurated by Dr Sudarshan Ghosh Dastidar, Ministerin-Charge, PWD & Environment Department, West Bengal. In this technical exhibition about 71 exhibitors displayed their products, material technology, equipments, machinery, plants etc. From a total of 270 abstracts that had been received and 175 papers from 35 countries were submitted to the Scientific Committee, who selected 108 for oral presentations and 30 for poster presentations. From September 25 to 27, 2013, the programme offered 23 technical sessions, both plenary and parallel as per the following main topics:
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Planning Design Research and Development Implementation Operation and Maintenance In addition, three special sessions were held on Poverty Alleviation and Disaster Management as follow-ups to the discussions at Delhi in 2005 and Urban Transit and Metro. In a special session on Friday, September 27, 2013, Mamata Banerjee, Chief Minister of West Bengal, addressed the delegates and shared her thoughts on ‘West Bengal – Vision and Opportunities’. A special session for young engineers organised by young engineers was also included in the programme. It offered various presentations about working abroad, work done at IABSE and a technical paper on ‘Geometrical Influence on Transverse Thermal Stresses in Concrete Bridge Sections’, by Oskar Larsson, Sweden. After the session, some 40 young engineers joined the Young Engineers Social Event at the ITC Sonar. Eight Keynote Lectures and 124 contributions have been collected in the Symposium Report and on a CD. The book (498 pages) and CD can be ordered (e-mail: ingiabse@bol.net.in) at Secretariat of the Indian National Group of the IABSE at New Delhi. On Wednesday and Friday, half-day technical visits were organised to Kolkata East-West Metro Project, the first underwater metro project in India, being developed under the river Hooghly. The 16 km long project is partly underground and partly at grade with 6 elevated and 6 underground stations and a Depot. On Thursday, a tour was conducted to India’s first Aerotropolis located near Durgapur in West Bengal. It is being developed in association with Singapore’s Changi Airports International (CAI) and constructed by Bengal Aerotropolis Project Limited (BAPL). The airport city is constructed around an old airfield near Andal, Barhaman, previously used by USAAF during the World War II.
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A number of social events gave a fascinating glimpse of the rich Indian heritage. During the symposium, delegates and accompanying persons were offered the opportunity to join social tours to Kolkata, to explore its many landmarks and places of interest, such as the Victoria Memorial, Saint Paul’s Cathedral, Kali Temple, Mother Teresa’s Home and Swami Vivekananda’s House. The Concluding Session was held on 27th September 2013 (afternoon). Shri VL
Patankar gave the Valedictory Address. A number of recommendations emanating from the deliberations presented. Delivering his valedictory address, he expressed the hope that the outcome of the IABSE Symposium 2013 would have enriched the delegates professionally for development, design and implementation of long span bridges, roofs and other structures. Shri P Popovic proposed a Vote of Thanks.
Shri Sarvey Sathynarayana, Hon’ble Minister of State for Road Transport and Highways, Government of India, lighting the traditional Inaugural Lamp along with high dignitaries
Shri C Kandasamy, Honorary Treasurer, ING-IABSE and Director General (Road Development) & Special Secretary, Government of India Delivering his welcome address during the Inauguration
Shri Sarvey Sathynarayana, Hon’ble Minister of State for Road Transport and Highways, Government of India, releasing Souvenir of 36th IABSE Symposium along with high dignitaries
Shri VL Patankar, Chairman, ING-IABSE and Additional Director General, Ministry of Road Transport and Highways, Delivering his welcome address during the Inauguration
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Shri P Popovic, President of IABSE Delivering his address during the Inauguration
Dr BC Roy, Vice President of IABSE and Chairman, Scientific Committee Delivering his address during the Inauguration
Shri Sarvey Sathynarayana, Hon’ble Minister of State for Road Transport and Highways, Government of India, delivering Inaugural Address
Dr Sudarshan Ghosh Dastidar, Minister-in-Charge, PWD & Environment Department, West Bengal Guest of Honour, delivering his address
Dr Amit Mitra, Minister-in-Charge, Finance and Excise Department, West Bengal Guest of Honour, delivering his address
Shri RK Pandey, Secretary, ING-IABSE Proposing a Vote of Thanks
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A view of the Cultural Evening during the 36th IABSE Symposium
Another view of the Cultural Evening during the 36th IABSE Symposium
View of the audience during the Inaugural Function
Dr Sudarshan Ghosh Dastidar, Minister-in-Charge, PWD & Environment Department, West Bengal along with high dignitaries inaugurating the Technical Exhibition
View of the Technical Exhibition Hall
Mamata Banerjee, Hon’ble Chief Minister of West Bengal addressing during Special Session on “West Bengal – Vision and Opportunities”
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View of the audience during the Special Session
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View of the audience during the Valedictory Session
The Bridge and Structural Engineer
Use of Bearings and Expansion Joints in Bridges & Flyovers – Issues of Concern A.K. Banerjee Technical Director, Bridges URS Scott Wilson India Pvt. Ltd. 19th Floor, Tower C, Building 5, Cyber Terraces, DLF Cyber City - Phase-III, Gurgaon - 122002, Haryana, India asis.banerjee@urs.com A.K. Banerjee obtained his B.E (Civil) degree from B.E. College, Shibpur and M.Tech from I.I.T. Delhi. He had an illustrious career as Bridge Engineer in the Ministry of Road Transport & Highways, where he was Chief Engineer and later became Member (Technical) in the National Highways Authority of India. He had also been the Director, IAHE. He is presently Technical Director (Bridges) in URS Scott Wilson India Pvt. Ltd., Gurgaon and Convenor / Member of various Bridges Technical Committees, including the Committee on “Bearings, Expansion Joints & Appurtenances”.
1. Summary Over the years, there have been significant developments in the process of modernization of bearings and expansion joints in bridges and flyovers etc. and the relevant IRC codes, guidelines and specification have been framed conforming to International Standards, outlining in details the stringent acceptance criteria, based on elaborate tests to be performed on both the raw materials and finished products, as well as long term performance guarantee of the products supplied by the manufacturers. However, in practice, there are issues relating to conformance to the acceptance criteria in manufacture, supply and installation of bearings and joints vis-a-vis the experience of the personnel entrusted with ensuring the same for installation of the right products. This paper briefly addresses the issues involved and attempts to raise the level of awareness of the users and establish an effective system of Quality Assurance to ensure the desired level of performance of these products over their design service life.
2. Probable Causes Bearings & Joints
of
Failure
of
PTFE bearings. It has been seen that the failures of these bearings occur either due to: (a) deficient design; (b) materials not conforming to specification and (c)
improper process control in manufacture
In the case of elastomeric bearings, designs are generally done by the design consultant of the client or contractor and the same need to be proof checked or reviewed by an independent consultant in both EPC and PPP projects to ensure strict conformance to the relevant code IRC: 83 - Part II. In the case of POT and POT cum PTFE bearings, the design is generally done by the manufacturers, adopting the relevant IRC: 83 - Part III, based on the loads/forces, movements and rotations specified in the design, which could be checked and approved by the design/ review consultant. However, the credentials of the manufacturer and successful testing of both raw materials and the finished bearings are very important to ensure quality of these products and to prevent failure of the bearings during their service life, keeping in view the difficulties involved in replacement of bearings, when the structures are in service.
2.1 Bearings
2.2 Expansion Joints
Most commonly used bearings today are either elastomeric bearings or POT and POT cum
These are generally proprietary/patented products, conforming to established International
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Standards, based on rigorous testing and acceptance criteria. The expansion joints are designed to cater to varying gaps for movement due to expansion/contraction of the superstructure, conforming to the acceptance criteria specified in the relevant IRC Guidelines IRC:SP:69-2011, based on various tests of both raw materials and finished joints. While there are not many instances of complete failure of the expansion joints, but they do suffer major distress/damage under wheel loads mainly because of lack of quality assurance in use of materials, manufacturing and testing of the joints. This leads to a major problem of replacement of joints during service period of the structure. Some major causes of failures are a) improper alignment of edge beams, b) improper quality of neoprene seal element, and c) clogging of joints with debris.
Consultant in charge of supervision and quality assurance of the project. b)
3.2  Expansion Joints a)
In the case of expansion joints, the scenario is somewhat different. Till say 1990s, use of single strip seal joints was not much common and angle iron with copper strip joints were widely used for girder/box girder bridges with simply supported spans up to say 50 m having movements less than even 50 mm and the popular Finger Type Joints for long span continuous bridges with much larger joint movements. However, slab seal joints involving about 1m length of slab seals have been used in the past for balance cantilever bridges across some major bridges like Barak Bridge in Silchar. In the late 1990s, Manufacturers of both single and modular strip seal expansion joints abroad entered into the market in India with their patented products, including the edge beams and neoprene seal elements, conforming to International Standards & Specifications, imported from abroad. Eventually, local manufacturing of these joints was allowed by Companies in India with tie up with the parent companies holding the patent for these products in stages by MoRT&H with a view to economizing the cost.
b)
With the introduction of strip seal and modular seal joints and local manufacturing of these products, detailed guidelines and specifications were drawn up as IRC: SP
3. Present System of Quality Assurance & Issues of Concern 3.1  Bearings a)
Deficiency in the design of bearings is not much common, although there are issues about improper assessment of seismic forces and non-provision of adequately designed seismic restraining/isolation devices, which are invariably required when elastomeric bearings are proposed in Seismic Zone IV and V beyond certain span length. However, there are major issues of quality assurance both in regard to raw materials and finished products, particularly for elastomeric bearings. This is mainly because there is too much dependence on the reliability of the bearings obtained from the Manufacturers/Suppliers empanelled with Ministry of Road Transport & Highways (MoRT&H) and the Supervision Consultant/ Independent Engineers often fail to ensure testing of both raw materials and the finished bearings from an Independent accredited Agency and totally rely on the test certificates given by the Manufacturers/ Suppliers. Even the suppliers of the bearings do not always comply with this requirement unless insisted upon by the
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There have been instances of premature failure of mainly elastomeric bearings requiring their replacement within a short period of completion of the bridge. Such failures occur more due to use of substandard raw elastomeric rubber (sometimes beyond its shelf life) than deficiency in design under normal conditions. It has also been seen in many cases that while the external neoprene cover did conform to the specifications of elastomeric rubber, it was not so for the internal layers between the steel plates, although the finished bearing passed the specified tests.
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69-2005, which have since been revised during the last few years in IRC: SP: 692011. However, there are concerns of total reliability on the products of the Manufacturers/Suppliers by the Supervision Consultant/Independent Engineers without ensuring strict conformance to the Acceptance Criteria laid down in IRC:SP:692011, including Performance Bank Guarantee for these products, as required. More often than not, the Team Leaders tend to fully rely on the test certificates, both for the joints and anchorages, furnished by the Manufacturers/Suppliers, without insisting on testing by an Independent Agency having the required test facility. Even witnessing the Acceptance Criteria tests in the Manufacturers’ factories are sometimes given go by, either due to lack of knowledge of such tests or lack of awareness of the importance of conformance to the Acceptance Criteria specified in IRC:SP 692011, particularly with regard to a) Fatigue Test of Anchorages, b) Debris Expulsion Test, and c) Water Tightness Test etc.
4. Way Forward Broadly, it may be seen that the Bridge Engineers of the Supervision Consultant or Independent Engineer (DBFOT projects) need to be made accountable by the Team Leader for ensuring strict compliance to the Acceptance Criteria prescribed in the IRC Codes, Guidelines & Specification for both Bearings and Expansion Joints by insisting on Independent Testing of the raw materials and the finished products and ensuring Performance Guarantee in financial terms by the Manufacturers/Suppliers, as
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mere empanelment of these Firms does not necessarily guarantee Quality Assurance of the finished products. In the case of a BOT/ DBFOT project, a common logic/argument put forward by the Concessionaires is that he would be responsible for the entire project during the Concession Period and defects observed, if any, would be rectified by him. While it may be somewhat acceptable in case of long Concession Period of 20-30 years, but may not hold good for shorter periods considering the design life of these bearings, particularly POT and POT cum PTFE bearings and expansion joints. Also, any rectification/replacement/ resetting of the bearings and joints need closure of traffic and provision of diversions (for two lane bridges), which need to be avoided to the extent possible.
5. Conclusion The paper attempts to highlight the functional importance of the bearings and expansion joints in bridges and flyovers, which contribute to a relatively small cost, as compared to the cost of the structure itself and the total cost of the project as a whole, as well as probable causes of their failures. There are concerns about lack of both knowledge and awareness among the Bridge Engineers, responsible for Quality Assurance in bridge construction, of the specific provisions of Acceptance Criteria in the codes, guidelines and specification of these products and it would not be exaggerating to highlight some amount of laxity on the part of these Engineers in charge of supervision of the project in Quality Assurance, which could compromise with the serviceability of these structures over their long design life of 75 to 100 years.
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SELECTION OF APPROPRIATE BEARING TYPE & ARRANGEMENT FOR BRIDGES Mahesh TANDON Managing Director Tandon Consultants Pvt. Ltd. New Delhi, INDIA tandon@tcpl.com
Prof. Mahesh Tandon received his Bachelor degree in Civil Engineering from IIT Roorkee and Masters from University of Hawaii, USA He was appointed Distinguished Visiting Professor at the Indian Institute of Technologies at Kanpur and Roorkee by the Indian National Academy of Engineering (INAE) and the All India Council for Technical Education (AICTE).
Summary Bearings provide the vital link between superstructure and substructure. They ensure loads and deformations applied to the former is provided a safe passage to the latter. Many types of bridge bearings are available and the selection of the most appropriate ones including their arrangement are exceedingly important for the safety and serviceability of the bridge structure as a whole. This paper highlights some of the major design considerations in this regard. Keywords: Bridge Bearings, Stability, Elastomeric, Earthquake, POT-PTFE, Pier Cap, Integral Bridge
1. Introduction Bridge superstructures and substructures are almost always designed separately. The connection provided by bearings to the two can affect the bridge safety and economy significantly. The bearing selection is intimately connected with the overall concept of the bridge and has a profound influence on its overall behavior. While bearings almost always facilitate or atleast permit rotations, they can be made to restrain movements in one or all directions. The magnitude of forces from and movements of superstructure required to be transferred to the substructure are the deciding factor in the selection of bearing
4  Volume 43
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type and how arrangements can be organized on the pier cap.
2. Overall Dimensioning Equilibrium of the superstructure is an important consideration. The arrangement of bearings should be such that there is a generous lever arm that provides the required stabilising moments when live loads are placed at the extreme position of the deck. To ensure equilibrium the overturning moments must be less than the stabilising moments after applying appropriate factors of safety in different load combination (Ref. 1, 2, 3, 4, 5). Fig. 1 shows how the equilibrium can be affected by the different configurations of the superstructure. Reduced distance between bearings can result in smaller lever arm and thereby reduced stabilising moment. Fig. 1(a) shows the usual configuration of a 2-lane or 3-lane box girder superstructure. The stablising moment is provided by the permanent loads while the live loads induce overturning about the bearing on the right hand side. Contributing to the overturning action are the lateral actions like wind and/or earthquake. Further, in case the bridge is on a curve, not only do the permanent forces contribute to the over-turning moments but the centrifugal forces produced by the live loads further aggravate the same.
The Bridge and Structural Engineer
A steeper inclination of the box girder web, Fig. 1(b), from the vertical can lead to a reduced lever arm for the bearings. Similarly, a large deck width with a narrow box girder shown in Fig. 1(c) (made possible by supporting the cantilever tip with external struts connected to the bottom of the web) again results in a reduced lever arm. In such situations a careful evaluation of stability as well as minimum compression required for proper functioning of the bearing (Ref. 1, 2, 3) should be made.
Design loads on bearings are assessed by applying load factors to take account of the probability of occurrence of the individual design forces occurring simultaneously (Ref. 4, 5). In some codes this concept is applied by adjusting the allowable stresses in the bearing components when subjected to different types of load combinations. The present codes on bearings (Ref. 1,2,3) are based on the Working Stress Design method and are under revision so as to incorporate the Limit State Design method of design. Applied forces on bearings can be reduced by judicious selection of bearing releases and constraints as well as increasing the c/c distance between them in the transverse direction. The situations become more complex for arriving at an appropriate arrangement of bearings when the superstructure span is skewed or curved. (b) Elastomeric Bearings
Fig. 1: Stability of Deck is affected by C/C of Bearings
3. Selection of Bearing Type (a) Loads The loads from the superstructure are transferred to the pier cap or top part of the sub-structure through bearings, shear keys or integrally. Selection of the bearing type is intimately connected with nature and magnitude of the forces it is subjected to. The loads transmitted from the superstructure consist of permanent loads which are vertically downward while lateral loads may be produced by action due to wind, earthquake, traffic as well as restraint to strain related effects of temperature as well as creep and shrinkage of concrete superstructures.
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Elastomeric bearings are by far the least expensive type of bearings. These should generally be the first choice provided the calculated translations and rotations as well as the applied vertical and horizontal loads are within limits. The structural behavior of elastomeric bearings under shear, compression and rotation is shown in Fig. 2. For Conventional bearings based on Ref. 2, the weakest manifestation of structural behavior is under shear as well as friction on the top and bottom surfaces of the bearing under lateral loads. An example of unsatisfactory behavior is shown in Fig. 3.
Fig. 2: Elastomeric Bearing: Structural Behavior
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Fig. 3: Unseating of Girder Resting on Elastomeric Bearing During Bhuj Earthquake (New Surajbari Bridge)
In moderate to high seismic zones, such as IV and V in India (Ref. 4), some type of external restraint is necessary for resisting seismic forces to prevent unseating or dislodgement of superstructure. Restraints in the form of linkages such as cables are popular in some countries particularly when steel superstructures are involved. However, in India and many other countries restrainers in the form of concrete ‘reaction blocks’ protruding from the pier cap are more popular. An interesting arrangement for a Railway bridge in a high seismic zone in Algeria is shown in Fig. 4. As can be seen the restrained end of the span of the 2 girder simply supported span is restrained vertically as well as horizontally by prestressed cables. The lateral restraints at both restrained and free ends is provided by reaction blocks projecting from the pier cap. Elastomeric bearings on vertical interfaces of the reaction block and superstructure ensure that there would be no damage due to violent shaking caused by a major earthquake. Another interesting arrangement of seismic restraint when superstructure rests on elastomeric bearings is shown in Fig. 5. The end diaphragm of the box girder is extended down into a recess in the pier cap. The longitudinal restraint is provided at one end only while transverse restraint is provided at both ends. All restraints are created by means of elastomeric bearings on vertical faces of the recess.
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Fig. 4: Seismic Attachments for Superstructure: Benisaf – Ain Temouchent Line- Algeria
Fig. 5: Seismic Attachments: Box Girder Superstructure
The Eurocode EC 8 (Ref. 6) indicates a strong preference of using elastomeric bearings for vertical loads only while the earthquake forces are taken by other structural connections. This preference can be gauged by the following provisions: • Supporting member (i.e. substructures) connected to the deck should in general remain in the elastic range. Translated into earthquake forces in Ref. 4, this would amount to assuming R = 1 in Table 8 as no plastic hinges would develop in piers. Also, the large imposed deformations would have to be catered for. • In case the elastomeric bearings have to resist both non-seismic and seismic forces, they attract special provisions and testing applicable to seismic isolation devices. This issue is discussed in art. 7.0 of this paper.
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(c) Pot-Ptfe & Spherical Bearings Capacity to take vertical loads is limited in Elastomeric Bearings. The same applies to deformation capabilities. When either or both of them are “excessive” we have to resort to other types of bearings namely POT-PTFE bearings (Ref. 3) or Spherical Bearings.
of new ones in their position. If any temporary packings are required in case the loads on hydraulic jacks are to be retained for longer time, space for the same must also be planned. An example of the plan of the pier cap of a series of simply supported spans is shown in Fig. 7 and of a continuous structure in Fig. 8.
An example of the use of POT bearings in Zone V in consort with concrete restrainers for a 3 spans continuous bridge (32.5 m + 98 m + 32.5 m) is shown in Fig. 6. The longitudinal restraints are provided on only one of the piers as shown while the other supports are “free”. Transverse restraints have been provided on all the four piers. Elastomeric bearings are provided on vertical interfaces between deck and concrete restraints.
Fig. 7: Plan of Pier Cap Supporting Adjacent Simply Supported Spans
Fig. 6: Seismic Attachments: Continuous Superstructure for Bridge over Ravi
4. Bearing Replacement The design life of bearings is invariably smaller than that of the permanent structure. Hence, provisions are required in the permanent structure which envisage the methodology of replacement of the bearings. These provisions must form part of the original design/drawings. Basically, bearing replacement involves planning of the pier cap so that it can accommodate all the permanent features like pedestals, bearings and other appurtenances like rain water pipe or other drainage arrangements, etc, as well as, the hydraulic jacks which have to be positioned on the pier cap to lift the superstructure to enable removal of existing bearings and installation
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Fig. 8: Plan of Pier Cap for Continuous Structure
5. Slopes and Gradients Slopes and gradients are a part of bridge configuration for reasons of deck drainage and sometimes dictated by alignment (vertical or horizontal). In all cases, the bearings must be sandwiched between horizontal surfaces which must be provided by the pedestal on the pier cap and the soffit of the superstructure, Fig. 9.
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Slopes in the transverse direction of the bridge deck can easily be tackled by adjusting the vertical height of the pedestals. The top of pier cap should be provided with a mild slope parallel to the shorter direction to avoid stagnation of water. Gradients in the longitudinal direction of the bridge deck are more complex to handle. One solution is to provide small fillets while casting the girder as shown in Fig. 9.
Fig. 11: Inadequate Edge Clearances
Fig. 9: Bearings on Gradient & Slopes
6. Edge Distances Care is to be exercised while dimensioning the pier cap and position of bearings and/or other temporary supports so as to have adequate edge distances. Inadequate edge clearances (Fig. 10) can result in damage to both superstructure as well as pier cap. Examples of resulting damages are illustrated in Figs. 11 and 12.
Fig. 10: Pier Cap Plan Showing Inadequate Edge Clearances Note: Superstructure Shown Dotted 8  Volume 43
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Fig. 12: Damage due to Inadequate Edge Clearance
Fig: 13: Example of Integral Bridge: Panchsheel Flyover, Delhi
The Bridge and Structural Engineer
7. Special Issues
e)
Bridges present ‘soft targets’ for terrorists and vandals making them unserviceable with not too much difficulty, Refer example in Fig. 14.
f)
Sharply skewed superstructures have the possibility of uplift at the acute angle corner, which can be tackled with considerable difficulty and expense. If the deck rests on bearings.
(a) Integral Bridges Integral Bridges are characterized by monolithic connection between the deck and the substructure (piers and abutments). Such bridges are the answer for small and medium length bridges where bearings and expansion joints can either be eliminated altogether or reduced to a minimum. Fig. 13 shows an example of integral bridge construction for a flyover in New Delhi. By incorporation of intermediate expansion joints the Integral Bridge concept can be extended to long bridges and viaducts. The elimination or minimizing of Bearings and Expansion Joints is important as they are fragile elements and represent the weakest links in bridge structures. The provision of Bearings and Expansion Joints imply the following: a)
Increased incidence of inspection and maintenance required.
b)
Necessity of replacement during the service life of the bridge since their design life is much smaller than that of the rest of the bridge elements.
c)
Decrease in redundancy and difficulties in providing adequate ductility for resisting earthquake effects, leading to larger earthquake design forces.
d)
Possibility of dislodgement of superstructure during accidental loads, especially those due to earthquakes is a clear danger requiring expensive and clumsy attachments.
Fig: 14: Example of Damaged Pier Cap, Bearings & Superstructure due to Terrorist Action
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(b) Bearings in Consort with Seismic Devices Seismic devices can be effectively used in bridge structures for the following purposes: (i)
Reduce the seismic forces by increasing the natural period of vibration by base isolation using special bearings or those that increase damping. Example of such bearings are shown in Fig. 15.
(ii)
Distribution the earthquake forces to several sub-structures, so that the seismic forces do not get loealised on piers with restrained bearings only. A good example of the utilization of devices called “Shock Transmission Units” (STUs) is shown in Fig. 16. A 1020m long bridge could be provided with only one Expansion Joints (EJ2) in the center and two at the extreme ends (EJ1 and EJ3). The forces generated by the mass inertia of the deck could be shared between 3 piers in this arrangement. The photograph of the STU installation is shown in Fig. 17. It is highlighted that STUs do not reduce the total force generated but is only a means of resisting it as multiple locations.
Fig. 15: Base Isolation & Energy Dissipation Volume 43
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elastomeric bearings does reduce the effective length factor K quite significantly (from 2.3 to 1.3) it must be ensured that the superstructure is restrained from translation.
Fig. 16: NHAI’s Ganga Bridge at Allahabad Showing Application of STUs
Piers are subjected to both vertical and horizontal forces which can act simultaneously. Horizontal forces can include both seismic and non-seismic forces like braking and traction. In the case of a series of simply supported spans resting on elastomeric bearings it is seldom possible to create external restraint or bracing and consequently all piers sway in identical fashion when subject to horizontal forces. In such bearing arrangements case 7 of the Table in BS 5400 Part 4 becomes applicable and K=2.3 should be adopted. Since, our recent code IRC 112 has adopted the provisions of BS 5400 Part 4, a clarification along the above lines would be most helpful for the designer.
Fig. 17: NHAI’s Allahabad Bridge: Application of STUs
(c) Effective length of pier The physical pier length (height), L, is multiplied by an effective length factor K to compensate for the rotational and translational boundary conditions. KL represents the length between inflection points of a buckled column while K = 1 represents a column hinged at both ends.
Fig. 18: Eurocode EC2 cl. 5.8.3.2. : Figure 5.7
Contrary to general perception, bearings also have an effect on the design of piers in some cases. This is apparent from the effective length factors given in the Eurocode EC2, AASHTO code and BS 5400 Part 4 shown in Figs 18, 19 & 20 respectively. By and large all three codes have similar provisions and should be adopted in the absence of more refined analysis. The exception is the case of BS 5400 Part 4 in which a special provision exists for elastomeric bearings. The provisions shown in Figure 20 not only indicate the type of support at the upper end but also the connecting member or bracing, if any. When seen from this viewpoint it becomes clear that whereas supporting the superstructure on
Fig. 19: Aashto Code
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The Bridge and Structural Engineer
The arrangement of all elements over the pier cap require careful consideration. Bearing replacement during the life time of the structure and edge distances are some of these considerations. A generously dimensioned pier cap is highly recommended. Use of Integral Bridge concepts reduce the number of bearings and expansion joints and should be adopted where possible. In the present state-of-the-art bearings are often used effectively in consort with seismic devices like Shock Transmission Units and Dampers in order to design sub-structures economically with respect to lateral forces.
9. References
Fig. 20: BS : 5400 Part 4
8. Concluding Remarks The importance of careful planning of the general arrangement of bearings and the selection of bearing type has been highlighted in the paper. Elastomeric bearings should always be the first choice due to their low cost and excellent behavior when subjected to vertical loads. However, their behavior under lateral loads like earthquake requires external restrainers such as “reaction blocks” to ensure safety of the bridge. For larger vertical loads, POT-PTFE or spherical bearings need to be used.
The Bridge and Structural Engineer
1.
IRC 83 Part 1: Standard Specifications and Code of Practice for Road Bridges: Part IMetallic Bearings.
2.
IRC 83 Part 2: Standard Specifications and Code of Practice for Road Bridges: Part IIElastomeric Bearings.
3.
IRC 83 Part 3: Standard Specifications and Code of Practice for Road Bridges Part III- POT, POT-cum-PTFE, Pin and Metallic Guide Bearings.
4.
IRC 6-2010: Standard Specifications and Code of Practice of Road Bridges: Section II- Loads and Stresses.
5.
Amendment to IRC:6-2010. Notification no: 78 dated 28th July, 2012.
6.
Eurocode 8: Design of Structures for Earthquake Resistance: Part 2: Bridges.
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Guidelines for Selection & application of Expansion Joint Systems for Bridges Jitendra Rathore General Manager, Technical Mktg. Civil Engineer Sanfield (India) Limited jitendrarathore@sanfieldindia.in
Summary In analogy to Mother Nature, the evolution in bridge construction lead to a functional and thus to a differential construction method. This way, in avoiding constraints at critical (structural) locations, long-lived and robust structures emerged. This was and is being achieved with modern bridge bearings and expansion joints. Due to their relatively simple installation, long service life and low maintenance costs, these structures are economical and with low exposure to disruption. Environmentally friendly and recyclable material as well as the effortless replacement of smaller units contributes to sustainability. For years & decades, the Expansion Joint Systems has been an integral appurtenance of the Bridge Construction. Although significant advancement in the technology of this product has been made in the recent past. It is equally important to understand the key criteria that influence the selection, adoption and thereafter functioning, rather smooth functioning of these Expansion Joints in the Bridge Structure. Keywords: Expansion Joints, Differential Construction Method, Strip Seal Joint, Modular Joints, Equidistance Control Mechanism.
1. Introduction Expansion Joint is the mechanical system used to bridge the structural discontinuity (Expansion Gap) provided in between the Structural Elements that could either be the two adjacent deck segments or in between the Abutment and the first deck Slab of the Bridge Structure. 12 Volume 43
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Peter Gunther Sr. Manager, Intl. Sales Structural Protection Systems Maurer Sohne GmbH & Co. kG guenther@maurer-soehne.de
The basic desirable functions that an Expansion Joint system should perform are: 1.
Accommodating movements & rotations that caused by the Structure.
2.
Water Tightness by preventing ingress of the rain water to the structure underneath.
3.
Offering Smooth Riding Surface.
4.
Minimal Resistance to the Structure while causing the Movement.
In bridge construction, the construction method as well as the aesthetics are predominantly shaped by the structural elements. Due to the technical challenges of modern bridge construction on the one hand and the cost and environmentally related general conditions on the other hand there exists a continuous selection and optimization of the products employed. Some of these products display disadvantages caused by their function, for example a limited service life. However, such products can only be relinquished if the economical and ecological total balance does not become negative. An “Optimisation of the Necessary” is therefore the better alternative. The knee joint or the intervertebral discs are problem zones of the human body – however as parts of a body rather a result and not the cause of natural evolution. This paper is about normal bridges with bridge bearings and expansion joints as well as the possibilities of optimization. Thereby, the notion of a “Differential Construction Method”, which is an established notion in mechanical engineering, is being introduced.
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Bridge bearings and expansion joints are exposed to demanding strains. Therefore, only such products have to be employed which either withstand in a functional way to all the exposures over the total life time of the bridge or they shall be replaced only in the course of a defined maintenance period at the structure. This way, maintenance costs for such structural members can be kept relatively low. In India the use & selection of the Expansion Joints are governed by the MORT&H Revised Interim Specifications issued vide Circular Number RW/NH-34059/1/96-S&R with amendments time to time and IRC Special Publication SP:69 first published in the year 2005 and recently revised in the year 2011. The main categories of the Expansion Joints classified in the above specifications are: 1. Buried, Filler & Asphaltic Plug Joints
-
2. Compression Seal, Finger & Elastomeric Pad Joints
For small movements.
For small to medium movements.
3. Strip Seal Joints -
For medium to large movements.
4. Modular Joints
For large to very large movements.
-
While the above referred specifications deals in elaborated way for the selection criteria, advantages & disadvantages of these Expansion Joints. The key factors based on practical aspects are discussed in this paper.
2. Factors responsible for Joint Selection It is appropriate to summarize the selection criteria into two main aspects i.e. the demand of the structure and the aspect of technical & commercial viability. Depending on the design, geometry of the structure, location of the Joint and various other factors, the needed expansion Joint may require to serve various degrees of freedom (for movement and / or rotation) out of which the most common is the movement along the longitudinal direction of bridge and also the rotation about the transverse axis at the Joint location. The Table - 1 below gives a brief illustration of the capabilities of different expansion joint against the various degrees of freedom:
Table 1: Table showing possible degrees of freedom for different Expansion Joint Types Degree of Freedom
Buried Joint
Filler Joint
Movement in Very Very Longitudinal Limited Limited Direction
Asphaltic Plug Joint √
Finger Compression Elastomeric Joint Seal Joint Pad Joint √
√
Strip Seal Modular Joint Joint
√
√
√
√ (Depends on Design)
√
√ (Depends on Design)
Movement in Transverse Direction
X
X
X
Movement in Vertical Direction
X
X
X
X
Rotation about Transverse Axis
X
X
X
X
√
Very Limited
√
√ (Depends on Design)
Rotation about Longitudinal Axis
X
X
X
X
√
Very Limited
√
√ (Depends on Design)
The Bridge and Structural Engineer
Very Very Limited Very Limited Limited
√
Very Limited Very Limited
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Degree of Freedom
Buried Joint
Filler Joint
Asphaltic Plug Joint
Finger Compression Elastomeric Joint Seal Joint Pad Joint
Strip Seal Modular Joint Joint
Rotation about Vertical Axis
X
X
X
X
√
Very Limited
√
√ (Depends on Design)
Skew Movements
X
X
X
X
Very Limited
X
√
√ (Depends on Design)
2.1 Small movement Joints
2.4 Large to very large movement Joints
With the advancement in the design, engineering and techniques of construction, the Structures are becoming more and more demanding and as an effect, the requirements for small movement Expansion Joints is fading out.
Like the strip Seal Joints, this category is also not having many choices and mainly the Modular Expansion Joints fulfils the requirement for this range of movements. Apart from Modular Joints, isolated references of Finger Joints are also noticed but only for cases which falls within the category of freedom as per above Table 1.
2.2 Small to medium movement Joints For small to medium movements Joint range, although significant requirement exist for this category but due to the fact that on one hand the strip seal Joints are technically superior and on the other hand the joint systems falling in this category have one or the other limitation on their performance and also the factor that the cost of strip seal joints nowadays competitive due to quantum production phenomenon and standardization of production process, this category is also more or less dominated by the use of single strip seal Expansion Joint Systems only. 2.3 Medium to large movement Joints By & large Strip Seal Joint is the only Joint system which qualifies for this category of medium to large movement Joint range without any restriction or functional limitations.
3. Strip Seal Joints The specifications of IRC regards the strip seal joint applicable upto to movement & gap value (whichever is higher) of 80 mm. This is mainly because above this value of gap, the joint edges start suffering severe impact loadings affecting the long term durability not only of the Joint but also the supporting / adjoining structure. Also, the riding quality, comfort & safety to the moving vehicular traffic will be compromised. However, for cases where there is no direct contact of the moving vehicular traffic with the expansion Joint for e.g. in rail bridges and structures for carrying the services like pipeline etc. Application of strip seal joint can be stretched upto 150 mm gap value with using larger seal profiles.
Fig. 1: Strip Seal Expansion Joint (TYP) Cross section after concreting 14 Volume 43
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The Bridge and Structural Engineer
Although the strip Seal Expansion Joints are quite common and widely used. They do encounter some problems & issues in their performance at times which are as under: 1.
Clogging of the open Seal Profile with dust & debris.
2.
Leakage from the Joint
3.
Riding discomfort at the Location of Expansion Joint.
While the 1st point can be regarded as the characteristic deficiency of the Strip Seal Joint. The later two are more associated with either the faulty material, workmanship & Installation. The Elastomer seal profiles of Strip Seal Joint are generally V-shaped profiles which allows the movement of Joint by simple folding & opening action. The portion above the seal thus attracts dust & debris deposit over the period in performance. While to some extent the seals performs self debris expelling action in which the extra amount of dust is pushed out of the seal cavity as the Joint closes which is then washed / carried away by the suction effect of moving vehicular traffic but this alone is not sufficient. The other remedial measures to this problem are the periodical cleaning of the elastomeric seal profiles or otherwise the use of special elastomeric seals with multilayer configuration thus not allowing any or less space for dirt accumulation. For the leakage through the Expansion Joint which in most of the cases due to damaged seal profile but sometimes also through the interlocking of the elastomeric seal with the steel edge beams. This problem is minimized if the dimensions of the steel profile cavity and the ear shaped projection of the elastomeric seal are within tolerances to provide air tight connection. This could be checked with the seal pull out and ponding test on the representative samples of the expansion joints at the manufacturers workshop. In addition, the ponding test shall also be applied at random at the job site on actual installed Expansion Joints. In addition, use of special grade lubricant-cum-adhesive material during the seal insertion process is also advisable. Riding discomfort at the expansion Joint is the next but most common problem specially The Bridge and Structural Engineer
encountered with Strip Seal Expansion Joints. The problem not only occurs with fresh installed Expansion Joints but worsens in the old structures where the road surfacing is re-laid over time & again. This itself is the root cause of the problem as this riding discomfort is not mainly due to the gap between the expansion joint but due to the incompatibility of the wearing coat layer with the backfill joint block-out concrete. At times, due to urgency of speeding up the construction work, the Expansion Joints are installed before the wearing coat is done and later on the wearing coat is laid but the portion of asphalt next to the block-out concrete remains un-compacted. This asphalt once compacted under the regular traffic movement creates a hump which is the main reason for the level difference and riding discomfort.
Fig. 2: Settlement in un-compacted asphalt adjacent to block-out concrete creating hump
The simple remedy of this problem is to always have the expansion Joints installed after the wearing coat is done. The wearing coat is first laid continuously over the bloc-out recess putting sand bags inside and then properly compacted wearing coat is saw cut to the required width and Joints are installed using conventional string-line method matching with the finish wearing coat level. Also for future relaying, it is to be ensured that atleast 5 meter long portion of the wearing coat on both sides of the structure shall be chipped and the fresh wearing coat is re-laid with proper compaction and matching with the existing Joint level to minimize the level difference & hump effect.
4. Modular Expansion Joints Modular joints consist of several steel beams that are arranged parallel along the axis of the joint Volume 43
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and sealing elements are located in between these steel sections to seal the individual gaps from ingress of water and dirt. Control elements have to take care that the individual gap openings receive their equal share of movement of the total movement of a joint. Another function of the control elements is to transfer the horizontal forces that occur, for example, due to braking forces of a wheel, safely into the edges of the joint. Of the many proprietary brands of modular joints that are on the market, their fundamental difference lies mainly in the support system and functioning of equidistance control mechanism. This portion of the paper discusses the criteria that distinguish the different types of modular joints in terms of their functioning. 4.1 Mechanism of Modular Expansion Joint Depending on the support and the control mechanism of a joint, the following design characteristics can be discerned. The terms “rigid” and “resilient” hereby should not be interpreted literally, but are meant to depict a relative measure for the deformations of the respective element. 1.
Vertical support of the center beam and/or the support bar
(s..) rigid
(e..) resilient
2.
Horizontal support of the center beam on the support bar
(..s..) rigid
(..g..) sliding and resilient in torsion
3.
Control mechanism
(..s) rigid
(..he) sequentially arranged and resilient support
(..pe) parallel support
arranged
and
resilient
A combination of such design characteristics discern the individual design types of modular joints that, as stated earlier, are mostly of proprietary nature. For example, a movement joint that is composed of the characteristics “e.s.he” shows the relevant characteristics “resilient vertical support”, “horizontal support sliding and resilient in torsion” and “control mechanism sequentially arranged with resilient support”. A further distinctive characteristic is the way the control elements and the support elements are located. They can be arranged both at separate locations and also functionally separated at the center beam. However for further elaborations this is only of secondary nature. The figure 3 below shows possible combinations of the characteristics that were pointed out above:
Fig. 3: Functional principles of modular joints (1 = scissor construction, 2 = sliding lamella type, 3 = MAURER girder grid type, 4 = MAURER swivel joist movement joint)
On the one hand, rigid control mechanisms guarantee an exact allocation of the total movement to the individual gaps, and this 16 Volume 43
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mechanism also employs a clearly defined support system. But on the other hand such a rigid control is prone to strains that are caused The Bridge and Structural Engineer
by unnoticed movements, such as dimensional tolerance, difference in temperature in the respective members of the joint, and deviations from the designed movement. The support system that neither accepts dimensional tolerance nor is pre-stressed resiliently, gives cause to strong noise emission and high wear. For this reason, modern modular joints employ a resilient control system. Usually this is achieved by plastic springs that are either being deformed along their longitudinal axis or by means of shear deflection. The individual center beams are connected by such springs. Thus we have several chains of sequentially arranged springs. As it is the case with such a system, the total resulting stiffness is a function of the number of center beams, or modules, that are connected by this way. One exception is the MAURER swivel joist system, that is being controlled by guided and shear-resilient torsion joints. This system has all the advantages of the exact scissor control system, but, due to its shear resilience, in addition the MAURER swivel joint system can also compensate dimensional tolerances and strains. Because each center beam is controlled individually, the stiffness of the horizontal support system is independent of the number of modules, or center beams. A swivel joist system employs a control mechanism with parallel arranged springs. 4.2 Design principle of control mechanism with sequentially arranged springs (Type 2 System “e.g.he�) By means of vertical support of the center beams, that is per each support bar, a series of sequentially arranged springs is arranged. The stiffness of each individual spring depends on the speed of its movement (i.e., a function of the load that acts on the spring). The stiffness can be of linear or nonlinear nature. Depending on the design system of the modular joint, the control springs will be without strain, thus undeformed, either in closed state, at medium gap opening or at maximum gap opening. Because the center beams and their support bars are supported by sliding bearings, being also prestressed, a certain sliding resistance must be overcome to move the center beams. This sliding resistance gives rise to a so called imperfect control, that The Bridge and Structural Engineer
although partially being balanced by dynamic vibrations under traffic, never can be totally ruled out. With the springs being arranged sequentially, the system will become the weaker in horizontal direction, the more center beams a movement joint employs. This results in an increase of the imperfect control of the gap openings.
Fig. 4: Imperfect control of sequentially arranged springs, sliding lamella type
The Fig. 4 above illustrates that if the relative movement is 320 mm (that is, gap width per seal should increase from 40 mm to 80 mm), arriving at the maximum design movement of 640 mm, the share of movement of the 1st seal is 133 mm, with an imperfect control component of 53 mm. The 7th and the 8th seal experience no movement, that is, they remain in their original position. 4.3 Case study of imperfect control mechanism of Modular Joint using sequentially arranged springs Tsing Ma Bridge, Hongkong 5 March 2001 1:30 p.m.
Tsing Ma Bridge, Hongkong 6 March 2001 3:00 a.m.
Tsing Ma Bridge, Hongkong 6 March 2001 4:30 a.m.
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A typical example that confirms in practise what the theory of this paper conveys is the Tsing Ma Bridge in Hongkong, where a 25 seal modular joint of type “sliding lamella” was installed. According to the theory presented here, friction in the control mechanism of a sliding lamella type would be that large that control of the gap width can no longer be guaranteed for all gaps. Rather, only the modules next to the moving bridge deck will move, and the center beams (i.e. modules) further away from the action will not be subject to any movement. Taking a look at this 25 seal joint. The gap openings were photographed in the afternoon at 1.30 pm, and then again twice in the night, at 3.00 am and 4.30 am. •
Gaps close during daytime (thermal expansion of the bridge deck). Clearly it can be seen that the first 3 gaps, counting from right, are totally closed. Gap #4 is partially opened.
•
13 ½ hours later, at 3 a.m., due to thermal contraction of the bridge deck the gaps open. Again, this applies only to the first 3 gaps, and the 4th gap already remains at its position that it had during daytime, and same it is with all gaps further left.
•
Another picture was taken at 4.30 am, the (probably) coldest time of a day. This picture shows that now gap #4 also opened up to some extent, but gap #5 and all other gaps further left do not appear to have undergone any movement.
Fig. 5: Cross section of a Girder Grid Expansion Joint
A big advantage of this system lies in the rigid connection between the support bar and the center beam, and the use of 1 support bar per each center beam. If we assume the same friction coefficients at the left and right edge of a joint, the friction forces will offset each other, and there is no imperfect control mechanism. This is independent of the pretensioning force, spring constant and friction.
Fig. 6: Imperfect control of girder grid joints
4.4 Design principle of control mechanism with sequentially arranged buffer springs (Type 3 System “e.s.he”)
The Fig. 6 above illustrates that all center beams will relatively early participate at the movement of the joint. The maximum gap without stoppers will be 97 mm, with a difference of gap openings of 4.8 mm. The stoppers that part of design will be activated at the first gap itself at the theoretical individual gap width of 65 mm.
The gap openings of girder grid joints are controlled by sequentially arranged buffer springs. If the gap is closed, these buffers are without any strain. With increasing gap opening, these control buffers will be compressed. The characteristic of the buffer spring constant is non-linear, that is, the bigger the gap opening, the stiffer the buffer spring constant.
As a result, we can establish that both the sliding lamella type Modular Joints utilizing sequentially arranged springs and the Girder Grid Modular Joints utilizing control buffer mechanism gives imperfections in uniform gap openings which is comparatively lesser in case of later Joint type. Such modular joints are therefore not suitable over 8 modules joint system.
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The Bridge and Structural Engineer
4.5 Design principle of control mechanism with parallel arranged springs (Type 4 System “e.g.pe”) The MAURER swivel joist joint is the only system that employs a control mechanism of the center beams with parallel arranged springs. Due to
the specific arrangement of the support bars as well as the connection between support bar and center beam, both the load carrying function and the control function can be achieved in a simple way, without need of a specific control mechanism.
Fig. 7: Cross Section of MAURER Swivel Joist Joint
The center beams will be supported by the support bar allowing sliding along the axis of the support bar. They rest on shear-torsionsliding elements with guidance elements along the support bar. The support elements are supported at the center beam and at the support stirrup respectively, allowing torsion around their vertical axis. Thus, their distances are fixed. If the superstructure moves, the support bars will be pushed through the swivelling guiding bearings and thus experience a swivel movement. Due to the fixed distances of the torsion elements, this swivel movement gives rise to an almost even allocation of the total movement to the individual gap openings.
help of shear-rigid support elements at the edge beams, which then leads to an exact control mechanism. The functioning of the control mechanism is independent of the number of modules.
Fig. 8: Control of a 4 modules joint having shear-rigid (left) and shear-resilient (right) support system
The control mechanism of MAURER swivel joist joint employ all advantages of an exact push and pull control. But in addition this MAURER design can also compensate unnoticed or unwanted movements like dimensioning tolerances in manufacturing, or different deformation of the edge beam and the center beams due to temperature differences. This can be owed to the shear-resilient torsion joints. The shear resilience of the support elements affects a certain incomplete control of the individual gaps. This effect can be offset with the The Bridge and Structural Engineer
Fig. 9: Imperfect control of MAURER swivel joist joints Volume 43
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The figure - 9 above illustrates the behaviour of a imperfect control in parallel arranged swivel joinst joints with least impact. If each gap experiences a theoretical movement of 40 mm, 7 of the 8
Effectiveness of Control mechanism in sequentially arranged springs control
center beams are activated. When the 8th center beam is activated, the imperfect control at the 1st center beam is 11 mm. This value remain almost constant up to the total opening of all gaps.
Effectiveness of Control mechanism in MAURER swivel joist expansion joints
Fig. 10: Photos showing the effectiveness of two different type equidistance Gap control mechanisms
4.6 Summary The essential characteristics of the 3 control systems described in this paper are summarised in Table 2 below. Also Fig. 11 below shows the individual gap openings at the time of the
maximum opening of the movement joint. The numbers between the profiles reflect the respective deviation from the expected ideal value and thus indicates the amount of imperfect control of the respective center beam.
1.
Sliding Lamella type Modular Joint System equipped with sequentially arranged control springs control mechanism
2.
Girder Grid type Modular Joint System equipped with sequentially arranged buffer springs control mechanism
3.
Maurer Swivel Joist type Modular Joint System equipped with parallel arranged springs control mechanism
Fig. 11: System comparison at maximum gap opening 20  Volume 43
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The Bridge and Structural Engineer
Table 2: Overview of design characteristics Sliding lamella sequential control mechanism
Girder Grid Joint
Swivel Joist Joint
sequential control mechanism
parallel control mechanism
number of modules ~ 5 under safe number of modules ~ 8 under safe unlimited number of modules application application direction of movement fixed
direction of movement fixed
direction of movement arbitrary
Large control problems, increasing Medium control problems, Little control problems, with number of modules increasing with number of modules independent of number of modules Stoppers required
Stoppers required
Stoppers not required
Failure of 1 control spring inhibits total control of gap openings
Failure of 1 control spring inhibits total control of gap openings
Failure of 1 sliding bearing affects only the respective center beam and not the total system
High friction force due to high pretensioning (V = 20 kN) and summation of the sliding surfaces (µ ~ 10%)
Little friction force due to double support (V = 2 x 12kN) and the their partially balancing effects (∆µ ~ 0-8%)
High friction force due to high pretensioning (V = 20 kN), however only 1 pair of sliding elements (spring and bearing)
Default position of sequentially arranged springs is in middle position, there being without prestressing, and consequently being subject to vibrations
When gap is closed, control springs are without strain. Prestress starts with gap opening. The bigger the opening, the more the stabilising effect of the control springs
No sequential chain of springs. System is stabilised independently from number of modules and size of gap opening
Spring constant (stiffness) low and of linear nature. Stoppers will be activated at an early stage, thus leading to emission of noise
Spring constant (stiffness) in the middle range and of nonlinear nature. If gap opens, control springs get increasingly stiff and so support the stoppers
High spring stiffness, and also high stiffness of the system, particularly for large movement joints
Transmission of horizontal forces dependent on number of modules. The higher the number of modules, the weaker the total system, leading to large movement of center beams. Horizontal force must be transferred via the spring chain
Transmission of horizontal forces dependent on number of modules. The higher the number of modules, the weaker the total system, leading to large movement of center beams. Horizontal force must be transferred via the spring chain
Transmission of horizontal forces independent on number of modules. Horizontal force will be transferred from the center beam via the support bar directly to the edges of the joint
Permissible spacing of support bars depending on number of modules
Permissible spacing of support bars depending on number of modules
Permissible spacing of support bars independent of number of modules (STP system)
Tilt-resilient support with high strain onto the sliding bearing
Tilt-rigid support by means of a stiff connection, resulting in little strain onto the sliding bearing
Tilt-rigid support by means of a pair of forces acting in the guidance of bearing and springs, resulting in a medium strain onto the sliding bearings
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5. Conclusion It will be not inappropriate to conclude this paper by saying that the Expansion Joints are unavoidable evils. While serious efforts have been made by the designers and construction engineers across the globe to avoid or atleast minimize their usage in Bridge Construction, the task is still distant as performance of such innovative construction & design will only be proven with the passage of time. Hence, it is reasonable that we should learn for the state of the art technologies & advancements in the field of Expansion Joints and to better adopt & apply the right type of Expansion Joint in most suitable way so as to get the longitivity and durability in its performance during service. In combination with appurtenances like expansion joints of long service life, bridges are being economic and sustainable. Modern Expansion joints can be designed in a way that they need to be maintained or replaced only in the course
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of general maintenance procedures that are planned ahead. Procurement and installation costs for expansion Joints can reach 2% of the total costs of the bridge structure while the cost for their repairs & replacements, if needed could cost fortune plus the disruption of traffic & services for long time. For this, the slightly increased procurement costs for such long life products can easily be justified.
6. References 1.
IRC:SP:69-2011: “Guidelines & Specifications for Expansion Joints”, 2011.
2.
MORT&H Revised Interim Specifications issued vide Circular Number RW/NH34059/1/96-S&R with amendments.
3.
Dr. Christian Braun, “The differential construction method in Bridge Construction – Structures entailing bridge bearings & expansion joints”, paper at symposium, Leipzig 2011.
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BEARINGS & THEIR CONFIGURATIONS WITHIN BRIDGE SYSTEM V. N. Heggade Member-Board of Management Gammon India Ltd, Mumbai venkat.heggade@gammonindia.com
V.N. Heggade, presently is Member, Board of Management of Gammon India Limited. He has more than 28 years experience of Designing and Constructing Bridges, Energy structures like Chimneys & Cooling towers, Marine structures and Hydraulic structures etc. He is the first engineer to receive ‘IABSE-Prize’ (International Association for Bridge & Structural Engineering, Switzerland) from developing countries in addition to National awards like Pt Jawaharlal Nehru Centenary award from IRC; Pre stressed concrete design award from Institution of Engineers, and ICI awards for best publications.He has more than 70 papers to his credit and is a member of various IRC (Indian Roads Congress) and BIS (Bureau of Indian Standards) committees. He is also a member of Indian Member Committee of Federation Internationale Du Beton, IMC fib. He has been an invited and a keynote speaker in National and International Seminars, Symposiums and Congresses. He has a passion for tall and long structures and he is an ardent advocate of sustainability and aesthetics in construction.
Key words: Bearings, Bridge system, Translation. Rotation, Deformation, Seismic Transmission, Teflon, Elastomeric.
Summary Since the introduction of bridge bearings, prominently by railways somewhere in 18th century, the bridge bearings have come long way being in perpetual evolution from Plane Bearings to Rotation Bearings to Deformation Bearings. Till the use of elastomer and Teflon in particular as a part of the bearing, the translation and rotation was achieved by pure steel components in Rocker and Roller bearings which increased construction depths of bridges. The induction of elastomer being confined in a pot allowed rotation by deformation and the less than 5% coefficient of friction of Teflon allowed smooth translation and the same can be termed as paradigm shift in Bridge Bearing Technology. The bridge bearings help the engineers to minimize the restraints in boundary conditions and the engineers can configure them with in the bridge system to channelize the forces to follow the functions. However Bridge Bearings require regular maintenance and becoming expensive
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as such whether there will be another paradigm shift in technology or elimination of bearings altogether will be resorted to in coming days is to be seen.
1. Historical Evolution Until the late eighteenth century, virtually all major structures were built in stone, brick or mixed masonry, which is strong in compression and weak in tension. Consequently, the commonest structure built were arches, in which any expansion or contraction would change in the radius of arch, or accommodated by plastic flow within the very weak mortar used in between masonry blocks, without any distress. These structures, generally of load bearing and massive in nature, are little affected by environmental factors. While arch bridges were dominant form of iron bridge building for larger spans till early 19th century, the engineers were very inventive in the case of suspension bridges that seemed to be the most feasible solution of conventional materials like wood, stone and cast iron were used. However, for larger spans in early 19th century chain or cable bridges were built. Changing forms of cables due to moving loads and changing lengths
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due to temperature fluctuations necessitated shifting saddles normally placed on pylon top made of stone. The shifting saddles ensured that cables could permanently take shape without inducing significant horizontal force on pylon top. The structural make up of these devices were perhaps the precursors for the bearings later to be used in girder bridges.
other hand from shifting saddle examples of suspension bridge, simultaneously there were attempts to achieve free supporting by roller bearings. (Fig. 2) The plane bearings had inherent problems for the superstructure under deflection. The load would have reduced to a smaller bearing area or a like load affecting the structural system of bearing substructure and strength of superstructure. (Fig. 3)
Fig. 3: Damage of lattice girder due to plane support (Culmann 1852)
Fig. 1: Shifting saddles for suspension bridges-precursors to bearings
Meanwhile it was realized that wooden bearings normally used for girder bridges were ineffective and costly due to repeated replacements as such girders were directly made to rest on cast iron plates. Thus first form of iron bridge bearings in technological terms was “plane bearings” meaning upper and lower part shared a planar area of direct contact.
This led to the invention of rotating bearings allowing the deflection of superstructure in the form of rocker bearings and knuckle bearings. In many railway bridges in eighties, riveted truss joints were the state of the art, knuckle pins were the bearing technology which worked as pivot. These typical knuckle bearings (Fig. 4) were extensively used up to twentieth century.
Fig. 4: Typical knuckle pin bearings Fig. 2: Ballysimon Bridge 1846-7, resting on rollers (Osborne 1849)
Though the issue of material expansion was known to engineers by the experience of arch and suspension bridges, it took some time to understand that the same is required for girder bridges as initially girders were rigidly connected to abutments and masonary supports. On the 24 Volume 43
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In case of rocker bearings, upper part rocksoverthe lower part (Fig. 5) and the sliding friction at knuckle locations is transformed into rolling friction where the contact could be flat to curved or curved to curved. The available bearing technologytill now was able to cater for temperature change and low deflection for small to medium spans. However, The Bridge and Structural Engineer
apart from increase in spans further the deck widths had begun to be doubled and tripled to cater for 2 and multiple tracks. This warranted facilitation to absorb longer movements and higher deflections in longitudinal directions and also the same in transverse direction.
of bearings configuration / arrangement to cope with the movements in all direction.
Fig. 7: Arrangement of the bearings within the bridge system (Mehrtens 1900)
There were also other solutions attempted like ball bearings with freedom of movement in all directions and multi roller bearings with rollers of small diameter arranged in two orthogonal rows to allow movement in all directions (Fig. 8) to reduce the height and bulkiness of bearings.
Fig. 5: Typical rocker bearings with flat/curved & curved/curved contacts
The example of spherical sliding curved bearings allowing the rotation in every direction could be seen in the bridges along the railway like between Halle and Huber of Germany via Sorave as back as 1871 (Fig. 6).
Fig. 8: Multi ball (Left) and multidirectional (Right) bearings
Path breaking breakthrough in bearing technology is the introduction of rubber as bearings by railways to absorb vibration. This gave rise to the evolution of new family of bearings called “Deformation bearings”. Fig. 6: Example of spherical curved bearings in 1875
Transitional and rotational mechanism in longitudinally and transversely to be inbuilt at different levels made the bearings taller and bulkier. In an attempt overcome this, way back in 1891 engineer Claus Koepke employed single layer of rollers diagonally as shown in Fig. 7, providing a sort of breakthrough in the direction
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Thus from 1840 to world war – II, the plane bearings, rotational bearings in the form of the steel dominated bearing technology. From mid 1950s new generation of bridge bearings outdated conventional steel bearings gradually. The conventional rubber confined in a pot replacing the sand in the pot could only allow rotational movement, but still rollers were to be resorted to accommodate longitudinal
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and transverse translation as such the newly synthesized polytetrafluoroethylene (PIFE or Teflon) completed this generation. This new Teflon offered friction resistance lesser than 5% of bearing pressure vis-à-vis steel to steel contact of 40%. Teflon based sliding bearings enabled small construction depth apart from being anticorrosive and resistant under high pressure. The superstructure rotation had to be accommodated by rocker mechanism that is where, pot sliding bearings, deformation sliding bearings (Fig. 9) and point rocker sliding bearings came from.
Fig. 9: Deformation sliding bearing, Pot sliding bearing, Point rocker sliding bearing
In spherical bearings, the rotation of the superstructure was enabled by means of sliding inside a ball joint. The increase in radii combined with Teflon with reduced friction loss has improved the load transfer capacity to the tune of 17,000tons in case of Signature Bridge bearing which is under construction. In recent development Disc bearing, which is modified version of POT bearings is in vogue. In this, elastomer element is provided in a ring from surrounding the centrally located shear restriction mechanism of steel catering for the horizontal loads acting on the bearing. Another type of mechanism, shock transmission unit, which absorbs the effect of regular thermal movement and also distribute the load equally throughout the bridge in case of sudden load like earthquake is being talked about. This is very useful for multi-span continuous decks where the load sharing results into smaller design section for the substructure and foundations. 26 Volume 43
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2. Function & Types The function of bearing is to transfer the forces from one part of the bridge to another i.e. superstructure to the substructure. Bearings also relieve constraints i.e. movement and rotation, which may generate additional forces in the substructure and foundation. Sometimes bearing is provided to remove indeterminacy of structure, as in the case of cantilever construction with suspended spans. We may say, bearing is a component, which safeguards the structure against, all external forces, effects due to thermal movements and other adverse weather conditions (creep and shrinkage) during the lifetime. The judicious arrangement or configuration of bearings may be used to direct or guide the strain of the structural element in a predefined fashion. In a way bearings are the powerful structural tool of a designer to dictate the flow of forces in the whole idealization. Structural engineer in the past as described earlier had to struggle with the design of substructure and foundation for accommodating stresses due to thermal strains. Larger the length of structure, higher this movement, necessitated the development of modern bearings. While deliberating on the historical evolution, though most of the bearing types are touched upon, the bearing types can be broadly summed up as below: • Roller bearings. • Rocker bearings. • Knuckle pin bearings. • Leaf bearings. • Link bearings. • Hinge bearings • Sliding bearings. • Elastomeric bearings • Pot bearings • Disc bearings • Spherical bearings In the recent past, elastomer and especially Teflon has become the integral part of all modern bridge
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bearings by its combination allowing translation and rotation in the desired directions outdating pure steel bearings which were in vogue till 1960s. Some aspects of modern bridge bearings are discussed in succeeding paragraphs. The use of elastomer and PTFE is illustrated by an example of Pot-PTFE bearing (Fig. 10). The main types of elastomer used in bridge bearings are natural rubber, HDRB (High Density Rubber), Neoprene, SBR, EPDM and NBR. This elastomer are normally durable, high in impact absorption, good bonding with metal if required, high resistance to ageing, good tearing properties, good physical properties and high resistance to oil and chemicals.
Fig. 10: Pot-PTFE bearing components & their functions
In the pot bearing, the elastomer which is confined in the pot enables rotation by shear deformation of elastomer and as elastomer is confined within the pot compression as well as translation does not happen. The translational component is provided on top which is enabled by Teflon. Teflon is a linear chain polymer of high molecular strength, chemically inert, very less friction coefficient, not easily oxidisable, stable under all environments and resistant to all common solvent. The key component of a disc bearing is the disc at its centre (Fig. 11), which carries the load of the structure above and allows rotations about any horizontal axis. The disc is moulded from high-strength Polyether Urethane (PU), an aromatic thermoplastic with excellent mechanical properties. The allowable compressive stress on the disc is as high as 35 MP, and it does not require confinement, as does, for example, the elastomeric pad at the heart of a pot bearing.
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The disc is also highly resistant to environmental impacts, and remains effective at a very wide range of temperatures. Further parts of the bearing allow fixing to the structure, and resist horizontal loading or permit sliding movements as necessary.
Fig. 11: Typical Disc bearings
Spherical bearings (Fig. 12) consist of an assembly of precision-machined steel components with spherical concave and convex elements in its centre designed and sized according to the specific requirements of the project. These bearings transfer large vertical loads while accommodating the structure’s relative movement. Whether they are fixed, unidirectional or multidirectional, spherical bearings transfer vertical and horizontal load combinations as well as longitudinal and transverse movements. They can also be equipped with an uplift restraint device.
Fig. 12: Various components of spherical bearings
The design principle of the spherical bearing is that of a fixed bearing that allows rotation in any direction, the characteristic feature being that rotational movements of the bridge superstructure about any axis (point-type tilting) are transformed into sliding movements between the convex and concave plates of the bearing. The bottom component is a regular steel plate
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with a spherically concave top face. This concave face is covered with a recessed PTFE sheet. The top component is a solid anodized aluminium or stainless steel plate with a spherically machined convex bottom face. When sliding components are added, the fixed bearing becomes a mobile bearing that can accommodate horizontal movement. This horizontal movement can be multidirectional or unidirectional if a guiding system is provided. These sliding components consist of a polished stainless steel sheet welded to the underside of a steel plate and a PTFE disc bonded to the upper surface of the convex plate. In order to increase its load-bearing capacity, the PTFE disc is recessed into the steel to a depth equal to approximately one-half of its thickness. The PTFE disc has small cavities (lubrication dimples) that contain a special lubricant to ensure permanent lubrication of the sliding surfaces.
should include check for smooth movement and damage due to undue rotation. The physical forms of the bearings shall be devoid of crevices, recesses that can house or entrap moisture, dirt and oil. The bearings also should not be made up of dissimilar materials, which can give rise to corrosive currents. Generally the present structures are constructed with provision of future replacement. Another special condition, where the structure is expected to settle or hog due to creep, provision should be kept for the insertions of shims under the bearing, this do not affect structure adversely however it provides smooth riding surface. The different types of bearings are symbolically reproduced on the basis of their functions universally as given in the Fig. 14.
The currently under construction Signature bridge at Delhi has two fixed spherical bearings to support its peculiar pylon whose capacity whose capacity under service conditions is as high as 17,000 metric tonnes ( Fig. 13).
Fig. 14: Symbolic representation of bearing functionality
Selection Criteria
Fig. 13: 17,000 t capacity fixed spherical bearing being tested for Signature Bridge, Delhi
The longevity of bearing depends upon the material constitution as steel bearing last up to lifetime of structure whereas elastomeric bearing may require to be replaced many times in the lifetime of a structure. The maintenance is very important factor for durability and regular maintenance and inspection is necessary. For the purpose of the regular maintenance, the provision of cage ladder to access the location of maintenance gallery / platforms should be made in the piers and abutments. Maintenance
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The forces on the bearings depend upon the construction methodology, its position, degree of indeterminacy and geometry of structure. The bearing should be designed for all permanent loads, time dependent loads, displacements, rotations and transients loads. Following are the forces, which may act coherently, or separately: • Permanent load including superimposed load. • Pedestrian and vehicular load, including dynamic effect. • Transient load such as earthquake load and vehicular impact load. • Wind load (Transient)
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• Erection load • Forces developed structure.
due
to
restraint
of
• Due to settlements. Along with these forces, bearings would experience movements and rotations, in different directions due to following actions: • Thermal actions – uniform temperature cause linear movement only, whereas temperature gradient may cause rotation also at bearing location. • Creep effect. • Shrinkage effect. • Structural configuration. • Tilt, settlement or movement of ground. • Axial and flexural strains arising from dead load live load and pre stressing etc. Permanent load also includes forces developed due to pre stressing effect in continuous construction or cantilever construction.
Fig. 15: Selection of bearing on functionality
The location of bearing has great influence on the structure as well as forces and movements developed in the structure. If a continuous bridge has a fixed bearings at one abutment and free / roller bearings at other abutment, free bearings would require combination of very large movement with less vertical load, whereas fixed bearing for intermediate pier would require heavy horizontal forces for the design of sub structure and foundation in seismic case.
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The structure governs bearing and bearing governs structure, both are true. The designer should keep in mind, the type of bearing, while designing substructure, for example, the elastomeric bearing, which attracts additional force (Vr . lt) due to shear rating, may have considerable effect specially if there is difference of height of substructure or erection condition governs design. The deflection of the substructure, especially slender and very long, may require additional provision of movement in the free bearing. The designer should do the correct analysis of the bearing reactions, by modeling the bearings at the points where they are actually situated and in combination with structure, as sometimes the stiffness of the bearings has influence on the structural behavior. Bearings initially may be decided on the basis of span, however detail analysis should be carried out keeping in mind structural requirement, durability and maintenance / inspection. Therefore in very inaccessible terrain, it is apt to provide metallic bearings or POT / PTFE bearings. Generally tar paper or felt layer is adequate for simple spans on rigid supports up to 7.5 m, mild steel or neoprene bearings are adequate between span range of 7.5 m to 15 m. For spans in excess of 15 m, other types of bearings may be used or adequately designed laminated neoprene bearing can be provided. In special case, use of neoprene bearing is not recommended such as suspended spans on flexible cantilever ends, where metallic or POT / PTFE bearings are appropriate to cater for large deflections, movements and rotations. Also hinge bearing is provided between two cantilever ends, where bearing is required to take very large rotations and movements, allowing transfer of shear without transferring any moments. However smooth functioning of hinges isvery imperative for the successful behavior of structure. Pendulum hinge or Plunger plate type central hinge bearings (Fig. 16) have traditionally been used at the hinge location, but have exhibited severe fatigue distress in practice due to continuous load reversal. In a conventional
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plunger type hinge bearing, the load transfer takes place through line contact of metallic components. The hinge bearings (i.e., the line contact zones) are subjected to quick reversal of stress during the passage of vehicles, resulting in continuous hammering action.
Fig. 16: Top left: Conventional plate type central hinge, Top right: Modified central hinge, Bottom: Installation of modified central hings
The line contact zones are also subjected to wear and tear caused by frequent reversible longitudinal movements of the bridge deck due to sway during the passage of each vehicle. This dynamic effect aggravates the continuous impact, which together with the wear and tear at the line contact zone quickly produces a gap between the plunger and the plate due to fatigue. The dynamic behaviour of the cantilever arm due to the semi-hinged condition (resulting from the gap between plunger and plate) will further aggravate the fatigue and thereby the distress. The gap then grows quickly, producing a ‘no hinge’ condition within a short period. The effect of continuous impact also produces continuous and quick reversal of both shear and tensile stresses on the bolts which anchor the plunger plate type bearings, often resulting in failure of the bolts due to fatigue. In order to overcome these problems of central hinges, a special central hinge bearing consists of interlocking male and female parts, which are anchored tothe tips of the cantilevering deck sections by means of tensioned high strength Macalloy or equivalent PC bars are developed and successfully used in 2nd Varanasi bridge and Shitalakshya bridge in Bangladesh. Special
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bearing devices are housed at the top and bottom of the male hinge, which slides over the stainless steel plate provided in the female hinge. The special bearing devices also feature precompression applied during bearing assembly in order to ensure perfect contact throughout the proposed service life. The problem of cantilever mating or articulation is overcome by a smart arrangement of bearings in Nivedita Setu extradosed bridge in Kolkotta. A pair of structural steel box girders is placed inside the concrete box girder and they span between the cantilever ends of the two units. They are fixed to one unit with fixed disc bearing while the other end rests on sliding bearing. Thus the longitudinal differential movement between two superstructure units freely takes place. The girders are roughly 12 m long. It can be observed from Fig. 17 that with the arrangement of disc bearings at top and bottom face of the steel box girders, differential vertical displacement or rotation between the two units is eliminated. Therefore longitudinally the units act like one continuous beam. A modular expansion joint is provided at the bridge deck level. Movement of vehicular traffic would not produce any undesirable deformation at the expansion joint. Figure 6 shows a photograph of the joint location during construction.
Fig. 17: Top left: Articulation arrangment in Nivedita Setu, Bottom: Installation of Articulation in Nivedita Setu, Kolkotta
In crux the following are the some of the criteria for the selection of bearings: • The functions to be performed. (Fig. 15) • Simply supported or continuous decking.
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• Straight or curved decks. • Flexibility of conditions.
substructure
and
climatic
• Prescription as to the constraining manner of superstructure. • Vertical and lateral axial capacities. • Compatibility requirements with deck joint movements in vertical and transverse directions. • Locations, e.g. in an inclined superstructure, the fixed bearing are preferably located @ lower ends.
Positioning and Layout of bearings with in bridge system The urban flyover and also some bridges have longitudinal gradients from the functional requirement. In such cases, the bearings could be aligned (Fig. 18) horizontally irrespective of sloping superstructure or could be aligned parallel to sloping superstructure. Both alignments have its ownmerits and demerits. The horizontal alignment transfers only vertical reactions and no permanent horizontal reactions on bearing. Despite being on the slope, since there is no dead load horizontal reaction, the clamping of the spans may not be necessary during erection of superstructure. However, this arrangement requires steps at the locations of expansion joints to cater for movement and greater the elongation and movement, bigger is the step.
However, this arrangement requires steps at the locations of expansion joints to cater for movement and greater the elongation and movement, bigger is the step. Also in case of pre-cast construction, the provision of groove or wedge in the girders or segments in an inclined manner, to accommodate top bearing plates becomes cumbersome, in the casting yard. On the other hand, the inclined bearing arrangement has the slope of the expansion joint independent of movement and the provisions of grooves / wedges in the pre cast construction at the casting yard are quite simpler. However, the permanent horizontal force may cause crooked piers due to displacement by creep of concrete and soil. Though, both types of arrangement are in practice, the IRC strictly advocates for horizontal alignment. Hitherto, for the simply supported bridges up to two lanes, fixed bearings (rocker) with a small play provision on one end and free bearings (roller) in the longitudinal direction having fixity in transverse direction has been successfully used for straight superstructure. This arrangement for the bridges with small deck widths can be still successfully adopted as the expansion / contraction taking place in superstructure and pier caps in transverse direction are same. Nevertheless, to avoid the transverse restraint likely to be caused by thermal effects and wind force, the practice of providing statically determinate systems as shown in Fig. 19 is replacing the earlier system.
Fig. 18: Bearing positioning for sloping bridges
Also in case of pre-cast construction, the provision of groove of wedge in the girders or segments in an inclined manner, to accommodate top bearing plates becomes cumbersome, in the casting yard.
The Bridge and Structural Engineer
Fig. 19: Top I: Arrangement for lesser width decks, Bottom: Arrangement for large width decks
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In the classical layout, shown Fig. 20 as the left hand bottom corner bearing is restrained in the longitudinal direction, it becomes difficult to estimate the internal forces due to the external lateral loadings.
Proper layout of bearings on a curved span along with estimation of movement is a critical and important activity for the durability of the structure. Due to continuity in superstructure the longitudinal forces due to braking, tractive effect, temperature, creep & shrinkage movement will be transferred to the bearings, not only depending on the shear rating of the bearings but also on the stiffness of the pier and foundation. In case of straight continuous span the distribution of horizontal force can be carried out effectively with relative simple computation. Whereas for curved continuous span the transverse stiffness of deck due to curvature along with the location and direction of movement of bearing becomes an important factor. All stresses in the bearing and as well on the superstructure will be of normal nature and the system can be effectively designed for all loading conditions. The span length and the loading pattern will determine the size of bearing. Similar to that of straight continuous girders, for a stiff system single bearing guided in all directions can be provided on intermediate piers of curved spans.
Fig. 20: Classical & Determinate systems
For straight continuous bridges, normally two bearings are used at abutment and piers location. If the torsional stiffness of the deck is very high like in box girder, intermediate piers can have single bearing (Fig. 21). As shown in the same figure, for curved continuous bridges, the longitudinally guided bearings shall be placed in such a way that the main movement of bearing should be in the axis of the traffic. The movement of other bearings shall have the same angle between the polar line and moving direction.
Fig. 21: Bearing Layout for straight/curved continuous spans
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Shock Transmission Units (STU) or Lock Up Devices (LUD) In case of multispan continuous bridges, the horizontal forces due to seismic in longitudinal direction is mainly absorbed by fixed pier as such there is no uniform distribution of horizontal forces among the piers. One way of achieving this is by integral bridge without bearings so that seismic distribution is uniform on all piers. But this gives rise to provision of very large expansion joints which may not be feasible. The shock transmission units designed to connect the superstructure with substructure( Fig. 22) to form a temporary rigid link provides an opportunity to distribute the sudden loads due to seismic and braking etc. uniformly on all piers apart from allowing the movement for slowly induced loads due to temperature, creep and shrinkage. Within the cylinder provided in STU as shown in the Fig: 22, viscous fluid passes from one compartment to another through a small designed passage. Under the sudden load like seismic and braking it gets locked as the
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fluid cannot pass from one compartment to another suddenly as such superstructure and substructure is integrated for structural response. For other slowly applied loads like temperature, creep and shrinkage, there is little resistance for the passage of fluid as such the movement is accommodated in STUs. The STU was first used by Steinman for Carquinez Bridge in California in 1927 and in India first time; the same was used for 2ndBassien Road Bridge in Mumbai.
Fig. 22: STUs for Brahmaputra bridge at Gouhati under construction
The effective utilization of STUs is illustrated below by the example of Brahmaputra Bridge (Fig. 23) under construction at Guwahati. The total length of the main bridge of 1.50 km is conceptualized by a single girder between piers P6 to P18 having 12 spans (2*105 + 2*150 + 4*130). The example provision at P6 & P18 locations being 450 mm, the construction is being done by cantilever construction method. The central pier P12 is equipped with fixed and longitudinally guided bearingswithout STUs, while the other piers are provided with 3 numbers STUs of 4.5 MN capacity and 2 numbers longitudinally guided bearings. As the structure is idealized to originate expansion and contraction from pier P12, on either side as the piers are moving outwardly, longitudinal movement absorption capacity of STUs as well as bearing keeps on increasing as can be seen from the Fig. 24. In the absence of STUs, the central pier would have to be catered for approximately 80 MN instead of 6.3 MN and the expansion provision requirement at P6 and
Fig. 23: Bearing & STU Layout Brahmaputra bridge at Gouhati under construction
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Fig. 24: Top left: Girder C/S of Brahmaputra bridge, Top right: Longitudinal section of STU showing the location of viscous liquid with in cylinder. Bottom: Bearing forces & movements
P18 locations would have been unmanageable. Perhaps the largest single girder bridge of 1.5Â km in India would not have been possible without the provision of STUs.
Management and Standardization Formerly, when neoprene, rocker and rockercum-roller and PTFE (sliding) bearings were popular, the same used to be designed and drawn by the bridge designer himself and the vendors were chosen only for manufacturing. Since different vendors have their own type of arrangements or configuration for POT / POT cum PTFE bearings, the design is done by the vendors for the given forces, rotations and movements. This warrants very high lead-time. Generally, forces, translations and rotations are supplied to approved vendors. Designs and drawings are obtained from them and necessary approval for the same is sought from clients. Once the drawings are approved from the clients, bearings are ordered for fabrication and load testing is carried out in the presence of clients. Especially, in item rate jobs it is imperative to realize the importance of lead-time required
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for bearing manufacturing and the details of forces, translations and rotations are supplied to the contractors in the inception of the project itself. Bearing designer shall be also apprised with the grade of the concrete in the pedestal and superstructure as the same determines the sizes of the bottom and top plates apart from the position of pre stressing cables or strands to avoid the clashing of studs and sleeves with the cables / strands. The early finalization of bearing size is essential to size up pier cap dimensions, though in cast-in-situ construction, it is not necessary to standardize top and bottom plate dimensions and bolt positions. Just to highlight the complexity, in a particular project of pre cast segmental construction, there were 32 types of bearings aggregating to 468 nos. of bearings to be bolted to 234 nos. of segments. If all these 32 types bearings have different top and bottom plate dimensions and also different bolt positions, it is almost impossible to monitor and control the mismatching of bearings with segments at casting yard. Hence it is imperative to standardize the top and bottom plate dimensions and bolt platforms from the constructability point of view.
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Bridge, IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, August 8-10, 2010, Dhaka, Bangladesh.
Conclusion The application of synthetic materials like elastomer and Teflon led to the evolution of 3rd generation of bearing technology since 1950s outdating pure steel bearings extensively developed for railways later used for road bridges too. The combination of elastomer and Teflon in various ways sliding, rolling and rocking of steel bearings by deformation which was a paradigm shift in a way. Will there be a 4th generation of bearings in the form of new materials or will it be dispensed with as the analysis of the structures without bearings has become easier these days and also manufacturing and maintenance of bearings have become expensive?
References 1.
Volker Wetzk, From the German by Barthold Pelzer, Berlin, pp 3333 to 3355.
2.
V N Heggade & Sandeep Pattiwar, Bridge Bearings, National seminar on Bridge Appurtenances, Pune-2003.
3.
T. Spuler & G. Moor, C. Ghosh, Supporting economical bridge construction – the central hinge bearings of the 2nd Shitalakshya
The Bridge and Structural Engineer
4.
N. Bandyopadhyay, A. Ghoshal & A. Sengupta, Relevance of bearings and expansion joints – case studies for indeterminate bridges, IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, August 8-10, 2010, Dhaka, Bangladesh.
5.
‘Gunter Ramberger’, Structural Bearings and Expansion Joints for Bridges by IABSE Publication.
6.
‘JE Long’ Bearings in structural Engineering, Newnes-Butterworths Publication.
7.
‘David J. Lee’, Bridge Bearings and Expansion joints, E & FN SPON Publication.
8.
‘Dr. V.K. Raina’ Concrete Bridge Practice, Tata McGraw-Hill Publication.
9.
‘V.N. Heggade’ Key note address on Bridge bearings, IABSE-ING work shop on Bridge Bearings & Expansion joints @ Bhopal on 29th September 2002.
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BEARING SYSTEM OF SIGNATURE BRIDGE, DELHI Jose KURIAN Chief Engineer, Delhi Tourism & Transportation Development Corporation Ltd., New Delhi, India jose1.kurian@gmail.com Jose Kurian graduated in Civil Engineering from the National Institute of Technology, Calicut in1968 and later took M. Tech in Structures from IIT, Delhi. He also holds a post Graduate Diploma in Earthquake Engineering from the International Institute of Seismology and Earthquake Engineering, Japan. He belongs to CES and joined CPWD as AEE. Presently, he is the Chief Engineer, DTTDC, Delhi.
S.K. RUSTAGI Chief Project Manager, Delhi Tourism & Transportation Development Corporation Ltd., New Delhi, India skrustagi2004@yahoo.co.in
S.K. Rustagi received his Bachelor degree in Civil Engineering from Delhi College of Engineering and Master’s degree from IIT, Delhi. He belongs to CES 1980 batch and joined CPWD & promoted to Chief Engineer in June 2012. Presently, he is the Chief Project Manager, Wazirabad Bridge Project, DTTDC, Delhi.
1. Background of the Project
2. Description of the Project
There is a pressing demand for additional EastWest corridor over river Yamuna in Delhi. The existing two lane wide barrage-cum-bridge at Wazirabad, has been serving as a vital link between Delhi and U.P. areas for the last sixty years. The tremendous increase in the volume of traffic using this bridge has far exceeded its designed capacity. A new bridge is therefore, under construction on the downstream of existing barrage-cum-bridge to connect NH-1 (Road No. 45) on the Western Bank and Wazirabad Road (Road No. 59) on the Eastern Bank of the river Yamuna. The under construction East-West corridor over river Yamuna would cater to the needs of the commuters from Yamuna Vihar, Gokulpuri, Nandnagri, inter-state traffic from Ghaziabad, Sahibabad on the eastern side and Timarpur, Burari, Mukherjee Nagar, Mall Road and North-West Delhi etc., on the western side. It was also decided in the initial planning that this area would be developed as a Tourist Destination by creating a water body and State of the Art Bridge.
Proposal to construct a new 8 lane unique bridge (Signature Bridge) across river Yamuna 600m downstream of the existing barrage-cumbridge at Wazirabad, Delhi was an outcome of the decision of Delhi Government, for making a landmark structure in Delhi, and to develop the surrounding area into a Tourist Destination. The proposed bridge will join Marginal Bund Road at Khajuri Khas intersection on eastern side and will join Road No. 45 (Outer Ring Road) on the western side.
Based on the traffic studies and topographical survey, various alignments were considered and after lot of deliberations, it was decided that the proposed bridge will be constructed 600m downstream of the existing barrage-cum-bridge.
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Fig. 1: Key Plan
The project also includes construction of Approaches (Western as well as Eastern) on both sides of proposed Signature Bridge. The
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key plan of the scheme is shown in Fig. 1. The scheme developed was not only to provide approaches to the Signature Bridge but also to eliminate traffic congestion along the road no. 45 (Outer Ring Road) on western side and at Khajuri Khas crossing on eastern side. On Western side, grade separators comprising of flyovers, loops and ramps are being constructed to ensure signal free traffic movement at proposed intersection of bridge with Road No. 45 and existing intersection at Timarpur, Nehru Vihar and Wazirabad, The view of Western Approach is shown in Fig. 2. Road widening, construction of footpath, storm water drains, cycle track and subways are also part of Western approach.
track, storm water drains etc. In addition, 6 lanes flyover is also being constructed at Khajuri Khas intersection with a rotary at ground level to ensure signal free movement. The view of Eastern Approach is shown in Fig. 3.
Fig. 3: Model view of Eastern Approach
3. Main Bridge (Cable Stayed)
Fig. 2 Model view of Western Approach to Signature Bridge
Eastern approach includes construction of about 2 km long embankment, river training works, river protection works, widening of existing roads, construction of roads, footpaths, cycle
The proposed main bridge across river Yamuna is a cable stayed bridge having main span of 251 m and nine approach spans of 36 m each (2 spans on western side and 7 spans on the eastern side of the bridge). The total length of the bridge is 575 m. This is an un-symmetrical cable stayed bridge with stay cables on one side and back stays on other side. The pylon is bow shaped having a height of 154m from the deck level. There are dual carriageways of four lanes each (14 m wide) with central verge (1.20 m), maintenance walkway and space for anchorage of cable stays. Fig. 4 shows the longitudinal section of the bridge and Fig. 5 shows the cross section of the bridge.
Fig. 4: Longitudinal Section of the Cable Stayed Bridge
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Fig. 5: Cross Section of the Cable Stayed Bridge
The outer to outer width of the bridge is 35.20 m (with additional width at pylon and back stay anchorage location). The bow shaped pylon would be in high strength steel and superstructure deck would be of combination of steel girders and precast/cast-in-situ RCC deck. The height of longitudinal girder is 2.30 m.
The cable stay span (Main span of 251 m) will be counterbalanced by the backstays at axis 23C (centre of the deck at pier P23). There will be tension of the order of 63800 KN in this bearing and therefore a specially designed Rocker (Pendulum) Bearing has been provided at this location.
At each support location, two piers (one at axis A and another at axis B) supported on open foundation / well foundation has been provided.
One bearing at every pier location (axis A and B at P1, P2 etc.) is to be provided to carry the vertical load of the structure under various combinations of loads as per IRC 6:2000. The bearings allow free rotation and displacement in both directions (longitudinal as well as transverse direction).
4. Bearing System of the Bridge The two legs of steel pylon are supported on two large bearings at axis 19. The bearings are installed on two piers (P19A & P19B). These bearings allow free rotation while displacement is restrained in both ‘X’ (longitudinal) and ‘Y’ (transverse) direction. The stiffness of the pier is small enough to allow displacement under temperature by flexibility of the piers.
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The guide bearings that allow displacement only in ‘X’ direction (longitudinal direction) are proposed to be installed at axis1 and 26 of the bridge (at either ends of the bridge). The bearing scheme is shown in Fig. 6.
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Legend for Bearing
Fig. 6: Bearing scheme of the Cable Stayed Bridge
5. Selection of Type of Bearing The design consultant for this project proposed state of art spherical bearings for this bridge. There is no IRC code for spherical bearings. Therefore, it was decided to follow EN codes for design and manufacturing of spherical bearings.
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Though spherical bearings are costlier than the Pot cum PTFE bearings, but spherical bearings are much preferred to Pot cum PTFE bearings from its functional requirement and durability. The general comparison of Pot cum PTFE and Spherical bearings is as under:
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Sl. No.
Parameter
Pot cum PTFE bearings
Spherical bearings
1
Elastomeric Sealing
The sealing element around the elastomeric pad is subject to wear due higher magnitude & frequency of rotation and translation. Hence has limited performance life.
Spherical bearings have no elastomeric pad and hence no sealing. Thus, longer trouble free performance life is expected.
2
Restoring Moments
The elastomeric pad gets deformed along with structural rotation; the pad works like a spring and produces a ‘restoring moment’. This restoring moment has to be accommodated by sliding material and results in extreme edge stresses and failure problem of PTFE like cold flow etc.
Spherical bearings produce a nominal rotation moment due to friction at sliding interface. Hence no significant edge stresses development at the PTFE, thus ensuring longer & trouble free performance.
3
Rotational capacity
Being governed by the edge strain in the elastomeric pad, these have limited capacity of rotation. Hence not ideal for long span and high rotational requirements.
Provides high rotation abilities to the bearing being consisting of concave & convex sliding components, without causing stress and / or strain to its components.
4
Durability
The expected life span is 10-20 years because of several components in the assembly having variable characteristics, limitation to perform repetitively. High rotation causes wear & damage to sealing ring. These needs regular check and maintenance.
The expected life span is much more as compared to Pot Bearings as these have sturdy and rigid steel assembly with PTFE/MSM layers providing rotation and translation without any damage/significant wear. Interval of check and maintenance gets increased.
5
Frictional Forces
Friction of the sliding part is negatively affected because of elastomeric pad having permissible design pressure less than that of PTFE. Thus higher frictional forces are developed at the sliding interface that is to be resisted by the bearing at the fixed end. Hence the bearings are to be designed for higher forces at the fixed ends, thus becomes costlier.
Since these bearings have PTFE / MSM material, therefore, has higher compressive strength as compared to the elastomer pads, the horizontal friction forces are less than for pot bearings. Hence much economic design of the bearings at the fixed ends.
6
Inspection
There is no possibility to inspect from outside to know the status of wear as elastomeric pad and sealing rings are confined. Only the measurement of the tilting gap and settlement is an assumption of the wear. As such the assessing the status of wear and its reporting is approximate.
Being openly visible, condition of curved and flat sliding surfaces can be inspected and examined from outside. As such, precise analysis of bearing condition is possible.
6. Design and Loads of Bearings The loads for each bearing have been worked out under various combinations of loads as per
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IRC 6:2000. The bearing schedule for the bridge is as under:
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Axis
Direction
Dead Load + Superimposed Load + pre-stress (KN)
Maximum (KN)
1A, 1B
Z
2900
5400
1A, 1B
X&Y
0
1C
Y
2A, 2B
Axis
Direction
Dead Load + Superimposed Load + pre-stress (KN)
Maximum (KN)
21A & 21B
X&Y
0
0
0
22A & 22B
Z
9100
12500
0
5500
22A & 22B
X&Y
0
0
Z
10000
11000
23A & 23B
Z
6400
9000
2A, 2B
X&Y
0
0
23A & 23B
X&Y
0
0
3A, 3B
Z
7900
15800
23C
Z
-48100
-63800
3A, 3B
X&Y
0
0
24A & 24B
Z
6700
10000
19A & 19B
Z
139100
171000
24A & 24B
X&Y
0
0
19A & 19B
Y
5400
27100
25A & 25B
Z
8900
12500
19A & 19B
X
0
19700
25A & 25B
X&Y
0
0
20A & 20B
Z
10800
14000
26A & 26B
Z
2900
5000
20A & 20B
X&Y
0
0
26A & 26B
X&Y
0
0
21A & 21B
Z
8900
13000
Y
0
5300
26C
7. Spherical Bearings for Approach Spans
the maximum load to be carried by the bearings. The detailed dimensions of the bearing are as given below. The typical details of bearing are shown in Fig. 7.
The spherical bearings are grouped in three types (except bearings at P19), depending upon Type
Bu (mm)
BGL (mm)
Lu mm)
LGL (mm)
HB HP (mm) (mm)
Vmax (KN)
Hmax (KN)
B1
470
570
470
1146
128
B2
670
790
670
1334
B3
850
990
850
1490
Location / Axis
Max Movement Max Movement (X) mm (Y) mm
22
5000
0*
26A & 26B,
± 270
± 40
152
22
10000
0*
1A, 1B, 23A, 23B, 24A & 24B
± 250
± 40
180
22
16000
0*
2A, 2B, 3A, 3B, 20A, 20B, 21A, 21B, 22A, 22B, 25A & 25B
± 230
± 40
*Without bearing friction
Fig. 7: Details of Spherical Bearings B1, B2 & B3 type
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8. Guide Bearings These bearings are proposed to be provided at axis 1 and axis 26 so as to allow displacement only in the longitudinal direction. The design parameters and details are shown in Fig. 8a to Fig. 8c.
Type Location / Axis B4
1C & 26C
Fig. 8a: Guide Bearing
Max Movement (X) mm
Max Movement (Y) mm
± 270
± 40
Fig. 8b: Guide Bearing
Fig. 8c: Guide Bearing
9. Spherical Bearings for Axis P 19 The maximum vertical load on this bearing is 171000 KN. The maximum longitudinal force is 19700 KN and transverse force is 19700 KN. The bearings are designed for free rotation and no displacement in either direction (longitudinal as well as transverse direction) after completion of erection. However, the bearing at P19B is
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designed in such a way that it allows translation upto 40 mm during erection only and no translation afterwards. During installation, the bearing at P19A would be placed 20 mm away from the centre of pier towards outer side of the bridge and bearing at P19B would be placed 20mm away from the centre line of the pier towards centre line of the
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bridge. It is expected that there would be a displacement of 40 mm during erection of pylon at P19B towards outer side of the bridge. Thus, after erection both the bearings would be 20 mm away from the centre of the pier, towards outer side of the bridge. The bearing P19A is a circular spherical fixed bearing which does not allow movement in either direction. However, bearing P19B is a rectangular/ circular spherical bearing consisting of additional sliding surface to allow movement of 40 mm only in transverse direction during erection. Fig. 9 shows the details of bearing at P19A and Fig. 10 shows the details of bearing at P19B.
Fig. 9: Spherical Bearings for axis P19A
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Fig. 10: Bearing at P19B
10. Rocker (Pendulum) Bearings Eight backstays are anchored in axis ‘C’ at P23 to counter balance the forces of 15 pairs of cable stays of the main span. One rocker (pendulum) bearing is proposed for each backstay cable, hence there are eight rocker (pendulum) bearings anchored in axis ‘C’ at P23 location. The design load on each bearing is as under: ULS Loads Vertical Load = 1750MT (Tension) Horizontal Load = 20MT (in both directions) SLS Loads Vertical Load = 1250MT (Tension) Horizontal Load = 50MT (in both directions) Fig. 10 indicates the function of rocker bearing. 44 Volume 43
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Fig. 11: Typical Rocker (Pendulum) Bearing
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Each bearing mainly consists of the following components: a)
Top bearing plate (80 mm thick) with 2 nos., welded BOSS plates 1280 x 1480 x 60 mm with hole of diameter 560 mm.
b)
Bottom bearing plate(120 mm thick) with 2 nos., welded BOSS plates 1280 x 1480 x 60 mm with hole of diameter 560 mm.
c)
Tension bar out of 2 nos. plates 1040 x 60 with 4 nos. welded BOSS plates 1200 x 920 x 60 mm with holes of 420 mm diameter.
d)
Two pins of 420 mm dia. with material 34 Cr.NiMo6V. Each pin is secured by 2 nos. caps of tube 508ø x 20 with head plate ø 508 x 20 and 2 nos. bolts of dia. 24 mm.
e)
48 nos. anchors with free tendon duct out of DYWIDAG/DSI single plane bars 36WS material quality 950/1050 with heat shrinking sleeve.
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Fig.12 shows the manufacturing of bearing in the workshop of M/s Maurer Sohne in Germany and Fig. 13 shows the typical details of rocker (pendulum) bearing.
Fig. 12: Manufacturing of Rocker (Pendulum) Bearing
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Fig. 13: Section of Rocker (Pendulum) Bearing for axis 23
4
Fig. 14: Testing of Bearing in laboratory
11. Standards & Codes Followed for Manufacture of Bearings by M/s Maurer Sohne 1
General
Quality management System
ISO 9001
2
Design
Structural bearing part 1 General design rules
EN 1337-1
5
Structural bearing part EN 1337-2 2 sliding elements
3
Material
46 Volume 43
Welding
Lubricant – Silicon grease
EN 10204
Quality requirements for fusion welding
EN ISO 3834
Qualification test of welders-Fusion welding
EN 287
Part-7 steel Structures: Execution and constructor’s qualification
DIN 18800
Welding-Fusion welded joints in steel, nickel, titanium and their alloys (beam welding excluded) – Quality levels for imperfections
EN ISO 5817
Corrosion Paints & Varnishes – Protection Corrosion protection of steel structures by protective paint systems
EN ISO 12944
12. Workmanship of Bearings
European Technical Approval Spherical bearing with special sliding material
ETA 06/0131
Metallic productsTypes of inspection documents
EN 10204
Hot rolled products of structural steels: General technical delivery conditions
EN 10205
The bearings shall be marked by the manufacturer either with the type numbers stated in the schedule of bearings or with the manufacturer’s own type or other numbers. A schedule shall be provided which relates the manufacturers own type or other numbers to the type numbers stated in the schedule of bearings. The design
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The contract provisions are as under: 12.1 Marking of Bearings
movement directions and magnitudes and the axis of bearing shall be marked on the upper faces of bridge bearings to facilitate checking of the installation. The manufacturer shall provide detailed drawings as well as workshop drawings along with method statement for its installation. The manufacturer shall provide a declaration of compatibility stating that the bearings are suitable for functioning under the actual conditions in respect of support and general arrangement of the adjacent structure 12.2 Storage of Bearings Bearings shall be stored off the ground on level supports and in a manner which will not result in damage or deformation to the bearings or in contamination of the bearings. 12.3 Corrosion Protection Bearings shall be protected against corrosion by a protective coating to suit the environment of the site conditions and the required life of the bearings. The manufacturer shall provide an evidence of the satisfactory use of the proposed protective coating in a similar environment and subject to similar use elsewhere. 12.4 Grouting Grout for grouting base plates and holding down bolts shall be a proprietary non-shrink cementitious type. The grout shall not bleed or segregate. The suitability of the grout and grouting procedure proposed by the manufacturer shall be verified by a test grouting in an arrangement where the dimensions and positions are the same as will be experienced in actual use. The test shall demonstrate an undisturbed grouting operation and a complete filling of the total bearing area. Grout shall also be tested for strength. 12.5 Installation The bearings shall be installed as recommended by the manufacturer & approved by the consultant and to the standards. Bridge bearings which have been pre-assembled shall not be dismantled. The levels of substructures on which bridge bearings will be installed shall be adjusted to suit the thickness of the bearing so that the superstructure will be at the specified level after The Bridge and Structural Engineer
completion. In case of having temporary locking devices for the bridge bearings, they shall be removed before post-tensioned superstructures are stressed. Installed sliding bearings shall be provided with a cover to prevent harmful materials from damaging the sliding surfaces of the bearings. 12.6 Tolerances The centreline of bridge bearings shall be within 5 mm of the specified horizontal position. The level of bridge bearings shall be within ±20 mm of the specified level. The relative levels for two bearings on the same pier shall be within 2 mm of the specified value. The inclination of bridge bearings shall be within 1 in 500 from the specified inclination. The horizontal axis of bridge bearings shall be within 0.002 radian of the specified alignment. 12.7 Inspection and Testing 12.7.1 Load Tests At least one or a pair of bearings (depending on the requirement) from each batch selected at random shall be load tested at manufacturer laboratory in presence of client. A batch of bearing is defined as bearings with the same size and sliding properties. Vertical and horizontal load test shall be carried out on the selected bearing. The test loads shall be the serviceability limit state loads. If required additional tests with test loads up to the ultimate limit state loads shall be carried out. The method of testing and test results shall comply with DIN 1072. 12.7.2 Friction Tests At least one bearing from each batch selected at random from each batch of sliding bearings and from each batch of other types of bridge bearings which contain sliding parts shall be selected for friction test. The friction tests shall be carried out to determine the coefficient of friction, flatness, bonding properties and resistance to mechanical damage. One finished bearing shall be presented for approval by the Client before mass production of the bearings commence. The finished bearing arrangement shall represent the actual access and inspection conditions of the function of the bearings including sliding guides,
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adjustment, pointer scale and coverings. Erection and exchange procedure of the bearing shall be demonstrated. The Contractor shall document the friction values of the sliding bearings at the actual stress level for temperatures ranging from +40°C to -1°C. The results of the friction tests shall comply with the following requirements:
12.7.3 Durability Tests
• The coefficient of friction in any test position shall not exceed the value specified by the manufacturer.
The project is being executed by Delhi Tourism & Transportation Development Corporation (DTTDC) as a deposit work of Delhi Government.
Bearings shall be durability tested for the number of sliding’s expected in the specified life time of the bearing.
13. Credits
Structural Consultants
JV of M/s Schlaich Bergermann Und Partner (sbp), Germany for Superstructure works & M/s Construma Consultancy Private Limited (CCPL) for Foundation & Sub-structure works.
The bearings shall be with low friction behaviour (µ< 2.0% with T≥ 0°C). Constant low friction of the used sliding material to be confirmed by a long term test of an independent testing institute with the following conditions:
Proof Consultants
JV of M/s SYSTRA, France for Super-structure works & M/s Tandon Consultants Private Limited (TCPL) for Foundation & Sub-structure works.
• Average test contact pressure p = 60 N/mm2
Contractor
JV of Gammon-Construtora Cidade- Tensacciai
Supplier of Bearings
M/s MAURER SOHNE
Contract Amount
Rs. 631 Crores
Duration of work
45 Months
Target date of Completion
December 2014
• The flatness of the stainless steel shall be within the specified limits after testing • The bond to the backing plate shall be unaffected by the friction test • The PTFE shall be free from mechanical damage after testing
• Constant test sliding velocity 15 mm/s • Test sliding path 50 km Maximum sliding coefficient during the test: µ < 3.5% with -35°C. Characteristic permissible pressure of the sliding material fk = 180 N/mm2. The supplier has to certify his third party control.
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Case Studies on Bearings, Expansion Joints and STUsâ&#x20AC;&#x2122; in Long Span Bridges N. Bandyopadhyay Director STUP Consultants P. Ltd New Delhi nbandyo@stupmail.com
N. Bandyopadhyay received his Civil Engineering degree from Calcutta University in 1974. After completing his post graduate studies, he has been working in Consulting Engineering profession and engaged in design of Bridges and other Major Structures.
Summary Forces from bridge superstructure are transferred to the substructure through bearings. Disposition of bearings & expansion joints in a statically indeterminate structure controls the manner in which forces are transferred to multiple substructures as well as development of secondary forces in the superstructure. It is important for the designer to select the appropriate arrangement of Bearings, Expansion Joints and Shock Transmission Units (STU) for effective passage of vertical as well as seismic & thermal effects to substructure. This paper presents case studies of arrangement of bearings & expansion joints in two medium span bridges Keywords: Bearing; Expansion Joint; Shock Transmission Units; Continuous Girder; Scour.
1. Introduction Traditionally Bridge superstructures were designed as statically determinate structure to exclude all secondary effects. The standard bearing arrangement in such type of bridges is Rocker (Fixed) bearing on one end and Roller (Free) bearing at the other end. The span and bearing arrangement of this type ensures that vertical as well as horizontal forces are uniformly distributed on all substructures and secondary stresses do not develop in the superstructure. Deck expansion joints are provided at every pier. Selection of this configuration leads to heavier
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and costlier structure than statically indeterminate configurations for longer spans. The large number expansion joints create potential source of corrosion initiation besides adversely affecting riding comfort. Long span bridges are mostly statically indeterminate structure and often have locked-in forces due to the method of construction. Adoption of continuous girder configuration, for example, generally results in lighter & economic design as the moments in a continuous beam are distributed over the span. Continuous or integral bridges, on the other hand, develop secondary forces and moments due to daily & seasonal temperature changes and may cause severe local stress concentration. Secondary forces are also generated in concrete girders due to creep and shrinkage effects. In the regions with high design seismic coefficient, the effect of the horizontal seismic force on superstructure as well as substructure depends on the arrangement of bearings. Bearings, in continuous bridges, can be arranged to transfer horizontal forces to selected piers. Bearings, Expansion Joints as well as Shock Transmission Units (STU) can be effectively configured to manage the passage of Seismic and Thermal forces to foundation and thereby control the structural behaviour of bridge superstructure under different loads. Layout of bearings in continuous curved girders, in addition, requires caredul analysis to mitigate the effects of thermal, shrinkage & creep effects.
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Bearing & Expansion Joint arrangement in two medium span bridges are described to illustrate effective application of articulation in indeterminate structures.
2. Third Karnaphuli Bridge 2.1 Description of the Bridge The third Karnaphuli Bridge is located near the city of Chittagong in Bangladesh. The three navigational spans of the 950m long bridge are 200m. This first major cable supported bridge in Bangladesh was opened to traffic in the year 2010. The four lane bridge project was executed by Bangladesh Roads and Highways Department under joint funding by Kuwait Fund for Arab Economic Development (KFAED) and Government of Bangladesh. It was constructed by MBEC-ACL-COPRI JV on design and construct basis. HighPoint Rendel Ltd. (HPR) of UK were the designer of the bridge. KEI-BCLTAEP-STUP JV were Supervision Consultants in this project. The project site lies in the coastal region of Bay of Bengal in the soft alluvial plain. The top layer of river bed consists of recently deposited fine sand and silt and prone to scour. The effect of scour
was estimated to be 34m from Design Highest Water Level. The saturated sandy bed material is also susceptible to liquefaction during seismic event. The site is located in a potentially active seismic zone with major documented fault zones all around. As per Bangladesh National Building Code it is located in Zone-2 which corresponds to a 100 year return period peak ground acceleration of 0.05g. The site also experiences a number of cyclones every year. The design wind at the site is 210 km/hour. 2.2 Bridge Configuration The length of the bridge is 950m. It consists of a six span continuous120m approach Viaduct (16m + 4x22m + 16m) on northern end and 830m long (115m + 3x200m + 115m) main bridge. The main bridge is a single plane extadosed prestressed concrete box girder bridge. The single box four lane deck is 24m wide with depth varying from 6.75m at pier to 4.0m at midspan. The pylons are 25.75m tall. There are six single plane stay cables located at distances between 36m and 76m from the pylon. These cables pass through saddles in the pylon located at heights between 19m and 24m and are anchored on the deck. Expansion Joints are located at the two ends of the 830m long bridge.
Fig. 1 : Schematic Elevation of Main Bridge
Fig. 1 & 2 shows the schematic configuration of the main bridge. The vertical and horizontal forces from the superstructure are transferred to substructure through a set of bearings on pier cap. The substructure consists of four inclined circular columns that directly transfers loads from superstructure bearings to piles. Each of the piers is founded on four 3.0m diameter bored castinsitu RCC piles of 75m length.
Fig. 2 : Bearing Arrangement on Pier Cap 50â&#x20AC;&#x192; Volume 43
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2.3 Effect of Variable Scour Essentially, the superstructure is a continuous five span girder. The support reactions in a continuous girder are dependent on the relative stiffness of the supports. In case of horizontal forces the foundations of the bridge derives their lateral stiffness from the soil support. In river bridges on erodible strata the soil around the foundation that has not been scoured away provides the same. A stiffer support would attract more horizontal force compared to a nearby foundation that has lesser stiffness.
The global analysis was carried out considering a number of such possible scoured river bed (Fig. 3). The design forces in bearings and STUs were arrived from there. 2.4 Bearing & STU Arrangement The 830m main bridge has expansion joints at two ends (Fig. 4). The superstructure box girder along with the pylons is connected to the piers through a set of bearings. As the bridge is located at a high seismic zone, besides bearings & STUs, concrete shear keys have been provided in a central opening of the pier cap.
Fig. 3: Variable Scour along Bridge length
Fig. 4: Longitudinal Support of Superstructure under Normal & Seismic Condition
Although the main channel of Karnaphuli river is about 300m wide, typically like the rivers in soft alluvial plains, the flood channel between the banks is almost one kilometre wide. The river flows in “braided” form within the “khadir”. These channels flow around often unstable sand bars called “chars”. These unstable chars formed by deposition of sediments frequently change their location and shape and thereby the shape, location and flow depths in the channels changes often. Generally, during rainy season, a number of chars get inundated due to increase in discharge. The top layer of river bed consists of recently deposited fine sand and silt that are prone to scour. The saturated sandy strata are also susceptible to liquefaction during seismic event. It had been considered in design that top 30m of the river bed may not provide any support to foundation due to soil liquefaction, river scour, dredging. Due to the characteristics of fluvial deposit, depth of soil that cannot be relied upon will be non-uniform across the width of the river.
In terms of theoretical support arrangement, the five span girder is pinned at P8 with roller supports at other piers. Expansion Joints are provided at P6 and A2. Expansion/ contraction of 515m bridge length takes place at A2. The modular expansion joint have been designed for 500mm movement. Normally with such arrangement, horizontal force developed or applied anywhere on the span will be transmitted to the fixed pier P8. As the design seismic forces are very high, it would have been extremely uneconomical to design the foundation and pier at P8 to resist the horizontal seismic forces developed within superstructure weighing little more than 30,000 MT. Besides the superstructure girder would also be subjected to large axial force and designed accordingly. Instead, Shock Transmission Units (STU), also known as Lockup Device has been provided at P7, P8 and P9, which would lockup and therefore, share fast acting forces like seismic or vehicle breaking. By design, these devices will allow slow movement like thermal
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expansion. The superstructure girder would, under normal circumstances, not develop thermal stresses. The behaviour of the bearings & STUs under normal and seismic condition are shown in Fig. 4. Horizontal forces in transverse direction are shared by all piers through the
direction. The four bearing arrangement on pier cap also permits transmission of small amount of bending moment from the superstructure to substructure. Fig. 6 shows the photograph of a pier cap. Fig. 7 shows the photograph of the completed bridge.
Fig. 5 : Layout of Bearings, STUs and Shear Keys
sliding guided bearings. A number of analysis with different combinations of scoured and unscoured piers and piers partially founded on liquefied and non-liquefied soil under seismic loading were carried out to find the maximum effect at any location. Fig. 5 shows the layout of bearings, STUs and shear keys to achieve the structural behaviour stated above. Four POT / PTFE-POT bearings are provided on each pier cap. A central cut-out is provided to house the concrete shear key. A Pin bearing is provided at the shear key location at the fixed pier P8. This bearing can only resist horizontal forces. Vertical force at each pier is carried by the POT bearings. All four bearings at P8 at free-free type as the pin is located at that pier. At piers P7, P9 and P10 there are three free-free POT bearings that take only vertical loads along with one longitudinally guided PTFE-POT bearing. This bearing would allow free movement of the deck in longitudinal direction but would restrict movement in transverse direction and thereby transmit transverse horizontal forces to the pier. STUs provided at P7, P9 and P10 will contain fast acting horizontal forces in the longitudinal
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In high seismic zones, it is a practice to provide a second line of defence against span dislodgement under extreme seismic event, whose intensity is higher than that considered in design. Concrete shear keys on the soffit of superstructure girder are provided to cater to this requirement. These shear keys are physically enclosed in a cutout on the pier cap. The space in-between are packed with elastomer to act as buffers.
Fig. 6: Karnaphuli Bridge - Pier Cap
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weigh more than 150MT. Uniform depth of the prestressed concrete box girder is 3.45m. The superstructure girder is made integral with the pier (Fig. 8).
Fig. 7: Third Karnaphuli Bridge (2010)
3. Nivedita Setu 3.1 Description of the Bridge Nivedita setu across river Hooghly is located at the northern end of Kolkata. It forms a part of the 6.1 km Tollway to provide a critical improved connectivity between the National Highway systems on eastern and western banks of Ganges. The Tollway including the bridge has been built and being operated by Second Vivekananda Bridge Tollway Company P. Ltd since 2007 under a thirty year concession from NHAI. The 880m (55m + 7x110m + 55m) extradose bridge has been designed by International Bridge Technologies Inc, USA in association with CES, India & PB, USA. The bridge along with all other components of the Tollway has been constructed by L&T Ltd. 3.2 Structural Configuration The pylons of this bridge are 14m tall. The superstructure girder is a single cell concrete box girder with 30m wide deck carrying 6-lane traffic. There are six cables in single plane passing through saddles in the pylon. The bridge has been constructed by precast segmental construction method by cantilevering from the pier. The individual 30m wide segments
Fig. 8: Integral Pier, Superstructure & Pylon
In terms of structural arrangement the bridge consists of four 220m units (See Fig. 9) that are connected at the midspan through longitudinal expansion joints. They are like portal frames connected at overhang tips. The expansion joint has been detailed in such a manner that it permits only longitudinal movement between the units allowing thermal movement. The shear force is transferred between the units through the expansion joints. This arrangement of articulation only in longitudinal direction allows the superstructure to behave as a single continuous girder eliminating any ‘kink’ associated with midspan connection.
Fig. 9 : Typical 220 m unit of Nivedita Setu
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3.3 Arrangement of Articulation at Midspan The primary elements of the expansion joint arrangement are shown in Fig. 10, Fig. 11 and Fig. 12. A pair of structural steel box girders is placed inside the concrete box girder and they span between the cantilever ends of the two units. They are fixed to one unit with fixed disc bearing while the other end rests on sliding bearing. Disc bearing features a highly durable moulded polyether urethane rotation element at its core, which can be subjected to very high stresses while facilitating significant rotations. This type of bearing is smaller in size compared to POT bearings. The longitudinal differential movement between two superstructure units freely takes place. The girders are roughly 12 m long. It can be observed from Fig. 10 that with the arrangement of disc bearings at top and bottom face of the steel box girders, differential vertical displacement or rotation between the two units is eliminated. Therefore longitudinally the units act like one continuous beam. A modular expansion joint is provided at the bridge deck level. Movement of vehicular traffic would not produce any
undesirable deformation at the expansion joint. This being essentially an integral bridge there are no other bearings excepting at the abutments. Fig. 13 shows a photograph of the joint location during construction while Fig. 14 shows a photograph of the completed bridge.
Fig. 10: Longitudinal View of Expansion Joint
Fig. 11: Steel Beam
Fig. 12: Cross section at Expansion Joint
Fig. 13: Nivedita Setu : Mid Span Expansion Joint
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Fig. 14: Completed Nivedita Setu (2007)
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4. Conclusion The internal forces as well the support reactions in an indeterminate structure depend upon the imposed boundary conditions. An indeterminate structure can be solved for different combinations of boundary conditions. Out of all those sets, one or two sets yield desirable design results in terms of minimum secondary forces as well as manageable support reactions. Bearings
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and expansion joints translate to the boundary conditions for stress analysis. Therefore, it is necessary to give careful consideration to bearing layout in continuous bridges. The examples cited demonstrate the same.
5. References Ramberger, G, 2002, Structural Bearings and Expansion Joints for Bridges â&#x20AC;&#x201C; IABSE SED 6.
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Application of Spherical Bearings with UHMWPE Sliding material for Bridges
Jitendra Rathore General Manager Technical Mktg. Civil Engineer Sanfield (India) Limited jitendrarathore@sanfieldindia.in
Peter Gunther Sr. Manager, Intl. Sales Structural Protection Systems Maurer Sohne GmbH & Co. kG guenther@maurer-soehne.de
Summary Over the past years in Indian Bridges, various types of Bearing systems viz. Steel Sliding Bearings, Rocker Roller, Elastomeric, Spherical & Pot-PTFE Bearings have been used. In recent past time, the Elastomeric Bearings for small to moderate and Pot/Pot-cum-PTFE Bearings for moderate to large span structures are being adopted quiet commonly. However, with the advancement in Construction Techniques and also the fact the Designers being innovative are working on the edge of engineering. As a result, longer spans & thinner superstructures combined with day-byday increasing traffic load pose more & more severe performance requirements for the Bridge Bearings to deliver. Although the performance of Pot/Pot-cumPTFE Bearings in Indian bridges has found to be satisfactory till now, but the fact remains that their exposure to the Indian Bridges is not as old as in other developed countries. On the other hand, the bridge designers have often felt the requirement of a Bearing System sturdy enough to sustaining adverse combination of heavy horizontal forces with moderate vertical loads that common in earthquake condition & yet at the same time flexible to accommodate large rotation & sliding displacements occurring with high velocity, frequency & magnitude.
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Wolfgang W. Fobo Regional Director, Asia/Pacific Structural Protection Systems Maurer Sohne GmbH & Co. kG fobo@maurer-soehne.de
The required Bearing system thus need to posses both the Strength & Flexibility Characteristics combined in one package to cop up with the dynamic loading, rotation & movement requirements of the present day structures & tomorrow. For such demanding cases, when comparing the different Bearings options available, Spherical Bearings have been found to be advantageous that not only overcome the limitations of Pot & other conventional Bearing forms, yet able to provide higher rotations while accommodating the higher magnitude of loads & forces. Keywords: Spherical Bearings, MSMÂŽ (Maurer Sliding Material), PTFE: Poly tetra fluoro ethylene, UHMWPE: Ultra High Molecular Weight Polyethylene.
1. Introduction to Spherical Bearing The Spherical Bearing consists of a set of concave & convex mating steel components with a low friction sliding interface in between thereby permitting rotation by curved sliding. For the purpose of providing the movement ability and controlling the degrees of freedom, the bearing system is combined with flat sliding elements, guides and restraining rings. Spherical Bearings are applicable for all types of structures but especially for non-rigid structures with relatively large and frequent displacements
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& rotations caused by variable loads, next for superstructures that induce fast sliding displacements in bearings, e.g. in case of Rail Bridges and Soft Structures like Cable Stay, Continuous & Suspension Bridges etc.
Fig. 1: Spherical Bearing overview
2. Characteristics of Spherical Bearings The spherical bearing transfers force reliably and rotates smoothly. It not only has great bearing capacity, large rotation ability etc. v/s the pot bearing, also it is more suitable for bridges having high torsion. Compared with the pot bearing, it has the following advantages: 1)
2)
3)
The bearing transfers force through the spherical surface, so no contraction / unequal force distribution will occur and the reacting force on concrete is relatively even. The Spherical bearing rotates through the sliding of the spherical surface thus inducing less moment compared to restoring moment by the elastomeric pad inside Pot Bearing due to rotational deflection. Whatever moment generated is only influenced by the radius of curvature of the spherical face and the friction coefficient at the sliding interface but totally independent to the angle of rotation, so it is especially suitable for large rotation angles. The design rotation angle therefore could be 0.02 radians or even more. Non-the-less, the moment inside the spherical bearing that due to sliding friction will be decreasing with the increase in loads & comparatively lot lesser than
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the restoring moment of Pot Bearing elastomeric pad that increasing with the increase in deflections. 4)
The rotation of the bearing is consistent in all directions so it is suitable for wide and curve bridges. The in-plan rotation, although not required normally but if desirable is also possible in Spherical Bearings which to some extent is a limitation with Pot Bearing.
5)
No rubber is used in the bearing so there is no problem of rubber ageing affecting the bearing rotational performance. Also the Bearing is least affected due to extreme temperature variations and thus especially suitable for areas exposed to extreme weather conditions.
The Concept of Curved Surface Bearing Devices, precisely Cylindrical & Spherical Bearings is not new and the provision in general for these Bearings are covered in IRC: 83 (Part I) first published in 1982 and revised in 1999, further detailed specifications for their designing, manufacturing etc. is covered in European Codes EN: 1337-7 & AASHTO LRFD Specifications.
3. Use of UHMWPE (Maurer special sliding material MSM®), inside Spherical Bearings MSM® is an innovative sliding material developed by Maurer Söhne for meeting the challenging performance requirements set up by the German Transrapid Consortium for application inside the guideway bearings for the “Transrapid” magnetic train – Maglev Train tracks. The condition posed for the sliding material of these bearings was the capacity to move as fast as 15 mm/s and yet maintaining long service life in excess of 50 years. Maurer Söhne accepted the challenge and developed a sliding material named MSM® (i.e. MAURER Sliding Material) that even exceeds the requirements set up by the Transrapid Consortium. The new sliding material employs a several fold lifetime as compared to the conventionally used sliding material PTFE.
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PTFE
MSM
Fig. 2: Disc of MSM® & PTFE side by side
In addition to the application in bridge bearings. MSM® is also suitable for other applications, such as incremental launching bearings, earth quake devices, or sliding bearings in buildings. MSM® is a modified polyethylene, featuring enhanced sliding characteristics and an increased load bearing capacity. MSM® contains no regenerated or filling material. Like PTFE, it is also a thermoplastic resin, insensitive against chemical and ageing, without environmentally hazardous components, e.g. like fluorine or chlorine. 3.1 Advantages of MSM® (UHMWPE) over PTFE The use of special sliding material MSM®, respectively UHMWPE in place of conventional PTFE gives the following advantages: 1. Sliding velocity With the observations from various Tests & Studies conducted on the sliding behaviour of PTFE, the maximum sliding velocity of PTFE equipped bearing is restricted to 2 mm/sec. PTFE when exposed to a sliding velocity over 2 mm/sec, will demonstrate increased wear, which further reduces the life time of the bridge bearing. In certain demanding cases, the sliding displacement in bridge bearings could exceed this velocity. Similarly, relatively soft structures like large suspension bridges, cable stay bridges often perform movement velocities which by far exceed the sliding velocity of 2 mm/sec. In contrast, UHMWPE can perform sliding velocities of up to 15 mm/sec without wearing effects. 2. Temperature sensitivity Full strength of UHMWPE (MSM®) can be utilized 58 Volume 43
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without any reduction upto a temperature of 35°C while the same is limited to 30°C for PTFE according EN: 1337-2. Likewise in extreme cold climate, UHMWPE again demonstrates superior performance. While PTFE cannot be used at temperatures below –30°C, MSM® can be employed at temperatures reaching down to –48°C. As the ambient structure temperature in India goes as high as 46 to 48°C. MSM® proves out to be a better choice than PTFE as able to sustain higher temperature. 3. Commercial Aspect: Size The permissible stress of the wearing material is normally the limiting factor for the design & sizing of the bridge bearings. For the permissible stresses of the sliding material, we have to take into account the maximum ambient temperature. Let us assume a maximum temperature at the bridge structure to be 46°C. According to EN1337-2, the permissible stress in the PTFE has to be reduced by 2% per degree rise in temperature beyond 30°C. Since, 46°C is 16°C over the maximum allowable limit of 30°C for PTFE up to which we can have the full strength for designing, so we have to reduce characteristic strength of PTFE which is 90 MPa by 32% which comes to 61.2 MPa. Further, using the partial safety factors of 1.4 for the material and 1.35 for the loads (assumed), the permissible pressure of PTFE works out to 61.2 / (1.4 x 1.35) = 32.4 MPa. For MSM® (UHMWPE), similar calculation applies based on the European Technical Approval ETA 06-131, which confirms the temperature limit of 35°C for MSM®. As, 46°C is 11°C over the maximum temperature of 35°C, required reduction will be 22%. The characteristic strength value of MSM® being 180 MPa, when reduced by 22% comes to 140.4 MPa. Again, using the partial safety factors of 1.4 for the material and 1.35 for the load, the permissible pressure of MSM® is reduced to 140.4 / (1.4 x 1.35) = 74.3 MPa. The Bridge and Structural Engineer
Comparing the permissible pressures of the two sliding surfaces duly applying the reduction factor due to rise in temperature upto 460C, UHMWPE can be stressed up to 74 MPa, whereas PTFE cannot go beyond 32 MPa under similar conditions. Consequently, the base area of an UHMWPE Spherical Bearing is substantially less than that of the Pot/Pot-cum-PTFE or even PTFE-Spherical Bearing, and thus smaller and economical to manufacture. This also provides the freedom to Bridge designer for economizing the dimensions of structure adjacent to Bearings. Or otherwise, could safely fit inside the limited spaces where other bearings cannot be accommodated.
also while deforming to accommodate the load & rotation produces restoring moment. For Sliding Bearings, this restoring moment affects the sliding surface. The restoring moment not only occurs during live load rotation but still present as long as the Pad is deformed. This restoring moment has to be accommodated by the sliding material and when combined with the temperature effects, the edge failure in the form of creep or cold flow of sliding material is even likelier. Thus, the restoring moment from elastomeric pad results in early wear of the sliding material inside a Pot Bearing and therefore a decisive factor in determining the life of these Bearings.
4. Commercial Aspect: Friction
4.2 Wear of sliding material (PTFE or MSM®)
Compared to PTFE, UHMWPE displays a much smaller friction coefficient at all temperatures and stresses. Consequently, the horizontal force caused by friction which is introduced into the substructure is much less, which may have beneficial effects onto the design and cost of the substructure.
Performance of any Bearing system is governed by the service life of its sub-components. Safe service life is the period within which the component is deemed fit for its normal functioning and beyond which it may still function but causing significant distress / adverse actions or may not function at all.
4. Spherical Bearings over Pot Bearings: life expectancy
In respect to their material characteristics, PTFE and MSM® were thoroughly tested at the National Material Testing Institute of the Stuttgart University of Technology (MPA). The test arrangement was identical as it is required for friction tests according to EN: 1337-2 but the performance parameters for MSM® were set quite above than those applied for PTFE.
Pot Bearings are serving the Infrastructure project in India for quite some time now and has not shown any significant problem that could be categorised as their characteristic deficiency. However, on the basis of research & experience gained from the usage of Pot Bearings for over 40 years worldwide. The following emerged as the main concerns of Pot/Pot-cum-PTFE bearing system: 1.
Restoring moment due to tilting stiffness of Elastomeric Pad
2.
Wear of components; Sliding material & sealing system
4.1 Restoring moment due to tilting stiffness of Elastomeric Pad The fact is well known that every elastic material when deformed produces strain or rebound effect trying to regain its original shape & condition of unrestrained. This counter force is directly proportional to the deformation, i.e. higher the deformation, higher will be the resultant strain or restoring moment. Elastomeric disc of Pot bearing
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As can be seen, the disc of PTFE has cold flown and settled on the mating S/S surface. Dimples flattened. Also the S/S surface turned black indicating there is no much sliding capacity left in this interface
Little scars on the MSM® disc but no significant wear noticed. The dimples on the disc of MSM® is still intact and the mating S/S surface shining means more sliding capacity left in this interface. The test stopped after 50,000 m slide path
Fig. 3: Long Term Sliding Test on the Disc of PTFE & MSM® by DIBt, Stuttgart Germany
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The long term sliding test on MSM® did not generate any significant signs of wear. Since the 50 km slide path testing satisfied the projected performance requirements for most severe requirement conditions, the test was simply stopped. Hence, it can well be said that the sliding performance limits of MSM® has not been reached yet. Below paragraph cites the conclusion of MPA Stuttgart investigation on the two sliding surfaces: “To summarize, it can be noted that, compared to the regulations for the use of white PTFE as component in structural bearings, no reservations can be made for the use of the Maurer Sliding Material MSM®. In addition, MSM® can cover performance requirements in areas where PTFE has fallen short. Even under relatively high strain (contact pressure “p” to a maximum of 200 N/ mm2 – static load, respectively 60 N/mm2 – dynamic load, speed v up to 15 mm/s), only limited deformations due to creep and relatively low coefficients of friction can be noted. Further, practically no signs of wear or other relevant damages could be detected in the contact area”. On the other hand, the PTFE-standard tests refer to a total sliding path of 10,000 m although some initial tests are available for 20,000 m. The limit of sliding ability to 10,000 m for PTFE can be verified from the long term friction test parameters that discussed in EN: 1337-2 where a total slide path of 10242 m is mentioned. Example: For better understanding of the above and also the impact, which the difference in the sliding ability of PTFE & MSM® can cause on the performance of a bearing, we take the example of single girder often used in Railway Bridges, which has a main span of 26.4 meters. Assuming the Bridge bearings have to accommodate a vertical load of 5,000 kN in Service Condition. The frequent movements of the bridge bearings in a single girder are largely caused by the rotation at the end girder – a translation that also occurs is however neglected.
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Fig. 4: Movement of a bridge bearing caused by rotation
As above figure shows, the translation of the sliding support of a single girder which is caused by the rotation of the end girder can be calculated as follows: Δl = θ.h + θf.hf The suffix “f” thereby stands for the rotation at the fix end, which has to be superimposed onto the displacement caused by rotation at the sliding end. If we can assume a uniform load “q” to be acting on the single girder, the rotation at the fix end and at the sliding end will be identical, which leads us to: Δl = 2 θ.h In order to calculate the possible translation of a single girder due to frequent end rotation under the variable load actions, let us assume a rotation “θ” of 0.005 radians which is the maximum rotation allowed for Pot Bearings under “frequent load combination actions” as per EN: 1337-5. Assuming, the total height of the girder 5.0 m and neutral axis “h” say = 2.5 m. So the translation at the Bridge Bearings with every load cycle in that case will be: Δl = 2 * 0.005 * 2,500 = 25 mm Since with each load cycle we would have a “back and forth” situation, the total translation caused by rotation would therefore amount to two times Δl i.e. 50 mm per cycle. In case of spherical bearings, the translation at the sliding surface has to be increased to account for the shift that caused due to sliding of the spherical part (the calotte). At a radius of 450 mm, this would add 2.25 mm, or 4.5 mm per cycle.
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So pot bearings would perform a sliding movement of 50 mm per cycle, and spherical bearings would slide 54.5 mm per cycle. Independent Test carried out at DIBt, Institute of Civil Engineering in Germany revealed that the maximum accumulated sliding capacity of PTFE under certain parameters of performance is 10,000 meters before being damaged. Thus the number of cycles to reach the maximum sliding ability of PTFE which is 10,000 m, would thus be limited to 10,000,000/50 = 200,000 cycles for pot bearings, respectively 10,000,000/54.5 = 183,000 cycles for Spherical bearings equipped with PTFE. As, it appears that Spherical-PTFE bearings demonstrate a lower life time than Pot-PTFE bearings. This however holds only if they are not fully utilised. For spherical bearings, there is no rotational limitation specified as it is there in EN1337-5 for pot bearings. Only when the Spherical-PTFE bearings should be compared within the limits of Pot-PTFE bearings, such a conclusion may be justified. On the contrary, if the spherical bearing should be installed upside down, the sliding component caused by the rotation of the spherical part will act against the sliding displacement, thus reducing the total movement of the sliding element. In the above example, the 2.25 mm of the calotte movement should have to be subtracted from the 25 mm, and so in total we would arrive at a total sliding displacement of 45.5 mm per cycle (as compared to 54.5 mm in conventional design). This would increase the life time of the very same spherical bearing to 1,000,000/45.5 = 220,000 cycles which then exceeds the limit of the pot bearing at 200,000 cycles. Under the same assumptions, sliding material MSM®, generic termed as UHMWPE which is also tested and certified by DIBt to last at least 50,000 m, will be good for at least 915,000 cycles. Although the actual results may vary depending on the accuracy of the assumptions made in above calculations viz. the actual rotation under the live load, stress concentration over PTFE / MSM®, sliding velocity, Girder Height & eccentricities etc.,
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yet these calculations as using the phenomenon that actually takes place in a bridge structure, illustrates the near actual number of cycles for the sliding material (PTFE or MSM® respectively UHMWPE) of a bridge bearing, in other words the performance life of the Bearing before it gets due for repair or replacement. 4.3 Wear of sealing system Like the Sliding material, sealing system that used inside the Pot Bearings for effectively confining the elastomeric disc also wear-out with its usage. Among all the acceptable form of sealing systems under EN: 1337-5, Brass sealing lifetime is confirmed with approval tests of 1 km sliding path, for PTFE-Carbon or POM Sealing this is comparatively higher but limited to maximum 2 km sliding path. After this distance, the Sealings are worn out. This directly put under question, the Long-term fitment & performance of the Pot Bearings that subjected to higher magnitude & frequency of rotation & translation. Below is an extract of the EN1337-5 which is the European Standard on pot bearings. It is regulated that “under frequent combination of actions”, that is, under traffic load, the maximum rotation caused by this traffic load Δα2 shall not exceed 0.005 rad.
Fig. 5: Extract of the EN1337-5 about permissible rotation in Pot Bearings due to live load actions
Considering the POM or Carbon-PTFE sealings which employ the maximum service lifetime of 2,000 m. So, after how many cycles the 2,000 m maximum slide path will be reached? A pot bearing for a vertical load of 5,000 kN would require approximately a diameter of the elastomeric pad of
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5,000,000/32.0 = 156,250 mm2, or a diameter of 446 mm, so let’s make it 450 mm. Given the maximum permissible rotation caused by traffic to be 0.5%, per each cycle the sealing element would use 2 x (450/2) mm x 0.005 = 2.25 mm up and down movement per cycle Lifetime of the sealing element would thus calculate to 2,000,000/2.25 = 888,000 cycles. For spherical bearings which have no sealing Component
Pot-PTFE bearing
Sealing element of pot bearing
888,000 *
elements, this limitation would not apply.
5. Summary The following table illustrates the maximum number of cycles of bridge bearings which has a maximum vertical load of 5,000 kN. The maximum structural temperature is 46°C, the rotational angle in the end girder caused by traffic loads as 0.5%. The life time of the wearing parts thus calculates to the following numbers of cycles:
Spherical-PTFE bearing installed conventionally
Spherical-PTFE bearing Spherical-MSM® installed upside down (UHMWPE) bearing
This limitation does not This limitation does not This limitation does applies applies not applies
* The Pot Bearing Sealing element cycles is calculated in favourable situation. For larger elastomeric pads and utilizing other forms of sealing elements like Brass, Stainless steel etc, the number of cycles reduces significantly. Also, for structures with relatively large rotations caused by variable loads that exceeding 0.005 radians which often the case with structures like steel bridges, cable stay, continuous & suspension bridges and most importantly Rail Bridges etc, the number of cycles reduces further.
Sliding element of the bridge bearing
200,000
183,000
5.1 Number of cycles and number of trains For the sake of simplicity, we assume that each passing train counts only one cycle. Of course it is possible that different weights of the coaches of the train may cause minor rotations which also should add up, but this is neglected for the above illustration purpose. If for example we can assume a daily traffic of 50 trains, the life time of the wearing parts of the bridge bearings shall be reached as following: • Pot-PTFE Bearing: 200,000/50 = 4,000 days or around 11 years • Spherical-PTFE: 183,000/50 = 3,660 days = 10 years in conventional installation mode • Spherical-PTFE: 220,000/50 = 4,400 days = 12 years when installed upside down • Spherical-UHMWPE = 915,000/50 = 18,300 days = 50 years
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220,000
915,000
Indeed, the life time of UHMWPE-Spherical bearing is attributed to be at least 50 years, which is also written inside the approval documents for the MSM® Spherical Bearing ETA 06-131.
6. Conclusion To conclude, while the adoption of SphericalPTFE Bearings in place of Pot-PTFE eliminates the concerns that arises due to the functional behaviour of Elastomeric Pad and that associated with service life limitations of the sealing elements as discussed above. A step ahead, replacement of PTFE sliding material with the Sliding material, MSM® (UHMWPE) further eliminates the concerns of limited sliding path, displacement velocities & load carrying ability that exists with PTFE and thus results a Bearing system that would perform almost for the entire life of the structure without requiring any major repair or replacement exercise.
The Bridge and Structural Engineer
7. References
5.
European Technical Approval, ETA 06 / 0131 on Maurer MSM® Spherical Bearings with Special Sliding Material.
1.
IRC: 83 - Part I: “Metallic Bearings”, 1999.
2.
EN 1337 - 2, “Structural bearings - Part 2: Sliding Elements”, March 2004.
6.
AASHTO LRFD Specifications, Fourth Edition 2007.
3.
EN 1337 - 5, “Structural bearings - Part 5: Pot bearings”, March 2005.
7.
4.
EN 1337 - 7, “Structural bearings - Part 7: Spherical and Cylindrical PTFE bearings”, March 2004.
Dr. Christian Braun & Dr. Christiane Butz, “Static and Dynamic Friction in Curved Surface Sliders”, IABSE paper, Venice March-2010.
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RECENT TRENDS IN REPAIR AND REPLACEMENT OF BEARINGS AND EXPANSION JOINTS FOR REHABILITATION OF BRIDGES Dr. Lakshmy Parameswaran Chief Scientist, Bridges & Structures Division CSIR-Central Road Research Institute, New Delhi-110025 lakshmy.crri@nic.in Lakshmy Parameswaran, born in 1962, received PhD (Civil Engineering) from IIT Roorkee. She has more than 26 years experience and is currently working in CSIR-CRRI as a Chief Scientist. Her main areas of research are bridge management, health monitoring of bridges and bridge aerodynamics.
Abstract Bearings and expansion joints are important elements of bridges with service life lower than that of bridges. In most of the existing bridges, distresses are often seen in these components mainly due to improper installation, lack of periodic inspection and maintenance. Therefore, during the service life of bridge, these elements are to be repaired and replaced number of times, resulting in huge expenditure of exchequer. Therefore, in this paper attempts have been made to discuss the common defects observed in these components, repair and replacement methods and precautions to be taken. Some key issues with respect to modular joints and seismic isolation bearings are brought out to improve their usage in bridge design and retrofitting. Keywords: bridges, bearings, expansion joints, distress, repair, replacement, spalling, leakage, functionality, monitoring
Introduction Bearings and expansion joints are used for translating the boundary conditions assumed in the bridge design into reality. Bridge bearings are mechanical systems placed between the superstructure and the substructure. They not only transfer loads from superstructure to substructure, but also ensure the structure functions as intended so that no part is under excessive stress and/or deformation. In typical girder bridges, the bearings must allow free 64â&#x20AC;&#x192; Volume 43
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translations and rotations of the span in the specified directions. In addition, bearings must also restraint the span in predetermined positions or directions. Many of the existing bridges in our country were designed as simply supported bridges. The bearing arrangement in these bridges is rocker (fixed) bearing on one end and roller (free) bearing at the other end, for example, old ITO Bridge over River Yamuna in Delhi. The span and bearing arrangement of this type of bridges ensures that vertical as well as horizontal forces are uniformly distributed on all substructures and secondary stresses do not develop in the superstructure. Also, in simply supported spans, deck expansion joints are provided at every pier. Selection of this statically determinate structures leads to heavier and costlier structure in comparison to continuous bridges or statically indeterminate configurations especially for longer spans. Also, in simply supported spans, the large number expansion joints create potential source of corrosion initiation besides adversely affecting riding comfort. Another type of bearings widely used in small and medium span bridges, is the elastomeric bearing, due to their low initial cost, easy installation and low maintenance, which make them an alternative to traditional metallic bearings. Realizing the advantages of continuous bridge configuration, recently most of the bridges and flyover built in our country have number of continuous units, for example, Second Thane The Bridge and Structural Engineer
Creek Bridge at Mumbai. In continuous bridges the bending moments are distributed over the span which leads to lighter and economic designs. However, in these bridges secondary forces and moments are generated due to diurnal and seasonal temperature changes, creep and shrinkage effects and may cause severe local stress concentration. The bearing arrangement in bridges is also influenced by plan geometry of deck. Bearing layout in a straight continuous bridge is relatively simple, whereas it is complex in curved continuous span as the estimation of bearing movement becomes very important. Due to continuity in superstructure, apart from vertical and lateral forces, longitudinal forces due to braking and tractive forces, temperature, creep and shrinkage, wind and seismic will be transferred to the bearings, depending on the shearing rating of bearing and flexibility of pier and foundation. In continuous bridges POT bearings are generally used at fixed piers and POT-PTFE bearings at free and expansion piers. In the regions with high seismic risk such as earthquake zones IV and V as per Indian seismic map, the effect of the horizontal seismic force on superstructure as well as substructure depends on the arrangement of bearings. Bearings, in continuous bridges, can be arranged to transfer horizontal forces to selected piers such as fixed piers. In some of the bridges, bearings, expansion joints as well as Shock Transmission Units (STU) have been effectively configured to transmit the seismic and thermal forces to foundation and thereby control the structural behaviour of bridge superstructure under different loads, for example Basin Creek Bridge. In modern bridges, bearings and expansion joints are the problematic components with respect to performance and maintenance issues. In some situations their performance can lead to the closure/failure of major bridges, and their maintenance can be extremely difficult and costly to implement. Most of these problems can be overcome if robust design rules are implemented to ensure that their design and construction delivers highly durable and reliable bridge components, and that designers make due consideration for their future maintenance
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so that it can be undertaken in an appropriate and affordable manner.
Defects, Malfunctioning and Failure of Bearings and Expansion Joints The main problem with metallic bearings has been corrosion of the steel, particularly at the sliding interfaces leading to a frozen bearing (Fig. 1). The metal-to-metal contacts in metal bearings easily trap dirt and moisture, thus causing corrosion and leading to freezing of bearing components, which is one of the most common failures of this type of bearing. Lubricants have been used and found to trap debris and moisture and also cause corrosion to develop. Apart from this, cracking and spalling of concrete under the bearing plate is also often seen. For example, the sliding bearings of Ghaggar Bridge were found to be rusted as no maintenance and greasing was done after the construction of bridge. Sliding plate bearings were rusted and allowed no movements, which resulted in spalling of the concrete over the bearings and cracking of superstructure as discussed by Ghosh (2000) and these bearings were replaced by elastomeric bearings. Other major problems are tilting of bearings (Fig.2), displacement of roller bearing during earthquake (observed in many RC-T-girder after the 1988 earthquake in East west Highway) and spalling of pier top during earthquake (Fig. 3).
Fig. 1: Rusted Roller Bearing Surrounded by Dirt and Debris
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Fig. 2: Tilting of bearing
Fig. 4(b): Crushing of Elastomeric Bearing
The severely strained elastomeric bearing and the damaged pedestal of New Surajbari Bridge during Bhuj Earthquake is shown in Fig. 5 and 6 respectively. The slippage of neoprene bearing of Louisiana Bridge has been discussed with field investigation including video monitoring by Heymfield etal (2001).
Fig. 3: Spalling of Concrete due to Improper Steel Restrainer (Tarkhola Bridge, Sikkim Earthquake, 2006)
The failure modes of elastomeric bearings include cracking, splitting, slippage, crushing and bulging as shown Fig.4 (a) and Fig. 4(b). Elastomeric bearings will have to be replaced, if they exhibit excessive bulging, tearing of elastomer or damaged steel laminate.
Fig. 4(a): Bulging of Elastomeric Bearing
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Fig. 5: Severely Strained Elastomeric Bearing of New Surajbari Bridge during Bhuj Earthquake (2001)
Fig. 6: Damaged Pedestal of Elastomeric Bearing of New Surajbari Bridge
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In the case of POT bearing, extruding of the confined rubber bearing pads as shown in Fig. 7 is identified as the most common failure mode. Premature wearing of the PTFE at the PTFE and stainless steel slide interface can also be a common failure or in-service maintenance problem. Poor installation techniques also contribute significantly to failures and reduce longevity of these bearings. Other reasons for defects are poor design of component which leads to little space for installation, inspection and maintenance, use of inappropriate material for bearing accessories, poor quality corrosion protection layer, excessive lateral load or rotation and inadequate lubrication of elastomeric pad. Corrosion protection can be achieved by hot dipped galvanisation of metallic parts or by using stainless steel for bearing manufacture.
with respect to direction of movement, excessive movements of piers, abutments or foundation, manufacturing defects (fabrication tolerance error, use of poor quality material), improper installation of bearings, lack of maintenance leading to accumulation of debris dirt and water, failure of expansion joint system that leads to water accumulation around or underneath the bearings, unforeseen events like impact /flood, chemical attack, fire and so on. In USA, even there was a catastrophic failure of rocker bearings, which led to the collapse of four bridge spans occurred due to the rockers becoming unstable at fairly mild angles of tilt as reported by Fyfe et al. (2006). Periodic inspection and monitoring of bearings helps in identifying the visible defects, movement of bearing, condition of bedding and bolts, etc. Subsequent to the inspection a decision is to be taken about its repair or replacement. The severity of damage can be assessed during condition survey. The functioning of bearings can be ascertained by monitoring its movement on an hourly basis for two to three days as shown in Fig. 9.
Fig. 7: Extrusion of Rubber from POT Bearing due to Broken Seal
Fig. 9: Measurement of Movement of POT-PTFE Bearings Fig. 8: Broken Seal in POT Bearing
The defects of bearings are mainly caused when (i) movements of bridge deck due to temperature, seismic/wind action, creep or shrinkage not accurately addressed in the design (ii), misalignment or improper orientation of bearing The Bridge and Structural Engineer
During the inspection of bridge expansion joint, look out for (i) damage of concrete deck or dirt wall near the joint, (ii) debris or vegetation growth, (iii) any loose fixture or anchorage (iv) corrosion of metal parts, (iv) torn or pulled out seal or missing seal, (v) loose strip seal, (vi) shoving of joint or joint
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coming out and (viii) leakage of joint. Joint damage can be due to improper installation, unsound concrete in the vicinity of joint or due to heavy traffic. Corrosion of metal parts can be due to leakage of joints and loose strip seal can be due to puncturing of seal or seal pulling out of anchorage. To ascertain the functioning of expansion joints, the expansion gap at the road level needs to be measured and compared with the value estimated during the design of bridge. The translational movement of expansion joint can be measured by installing LVDT, on an hourly basis, for two to three days. By comparing the recorded translational and rotational movements of expansion joints with the design values, helps to conclude about the functionality and on repair/replacement of these joints. The common defects found in expansion joints are shown in Fig. 10-11.
Fig. 10(c): Strip seal torn Fig. 10: Common Defects in Expansion Joints
Other expansion joints such as asphaltic plug joints develops cracks along the edge which leads to water leakage, debonding or depression of joint, potholing and loss of aggregates. In the case of compression seal joints defects such as dislodgement or damage of seal and cracked or broken edge beams are often seen. Finger plate joints develop distress due to fatigue of finger plates, bolts and anchorages due to their working as cantilevered elements under repeated traffic loading, filling of debris between combs, corrosion of metallic joint, low skid resistance and failure of concrete anchorage.
Fig. 10(a): Worn out and broken seal
Fig. 10(b): Malfunctioning of joint 68â&#x20AC;&#x192; Volume 43
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Fig. 11: Compression Failure of Expansion Joint During Earthquake
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serious section loss that might require bearing replacement.
Fig. 12: Tensile Failure of Joint during Earthquake
In the case of modular bridge expansion joints (MBEJ), distresses are due to debris accumulation in seal, fatigue crack, corrosion of metal parts, water leakage at seal splice and reflective crack in concrete directly above support boxes.
Repair of Bearing From the above discussions, it is seen that in many bridges, even the distress of superstructure is often due to the defective bearings. Therefore, bearings need periodic inspection and routine maintenance. The function resistance to moving parts and condition of the bearing are the deciding considerations in replacement of a bearing. Uncoated steel if used in sliding bearings will corrode. The corrosion will cause the bearing surfaces to become rough. The coefficient of friction between the plates will increase due to the corrosion, and the bearing will cease to function. This condition can be improved and avoided by lubricating the bearings or by providing bearing materials with low coefficients of friction. Bearings are either externally lubricated or self-lubricated through the selection of special materials. Low viscosity penetrating grease such as graphite grease grade conforming to IS 508 may be applied externally to existing sliding plate or rocker bearings. Extreme deterioration from corrosion can cause a bearing to lose section and, in the worst case, failure of the bearing to transmit loads to the substructure as designed. Routine maintenance cleaning (removal of accumulated debris) and cleaning and painting (power tool or blast cleaning and recoating) can protect and prevent The Bridge and Structural Engineer
The repair of metallic bearings include replacement of rocker pin, correction of overrun of roller (either by realignment if overrun is <25mm or by welding additional base plate if overrun >25mm), replacement of missing anchor bolts/ nuts of base plate, epoxy grouting of anchor bolts etc. Tilting of the bearing can be corrected by repositioning/realigning the top plate of bearing by dismantling and recasting in the girder and replacement of anchor bolts. However, if anchor bolts are not damaged or deteriorated, they can be reused. Also, during the repair of bearing, there is a need to monitor the movement of expansion joint to ensure proper realignment and lubrication of bearing. Bearing seat repair may be required, even if the bearings are functional. Jacking is required to accomplish bearing seat repairs. If there is spalling /cracking of concrete beneath the bearing plate is noticed, then appropriate repair needs to be carried out depending on the depth of spall, width of crack and area of spall/crack. For repair of spall, epoxy sand mortar (1:7) or polymer modified concrete can be used. In case depth of spall is more than 50mm, an appropriate reinforcing mesh (chicken mesh) fixed with V-nails prior to placing cement-sand mortar or concrete. Similarly, crack sealing needs to be done injecting low viscosity epoxy material at high pressure. In case of rusted exposed steel reinforcement, the same shall be treated by application of two coats of alkaline rust converting primer after duly cleaning the rebar surface free from loose materials, dirt etc., If the corrosion has resulted in loss of cross-section of rebar, the same shall be replaced with new bars of same diameter and shall be welded/spliced to the existing reinforcement.
Bearing Replacement Jacking and resetting of a bearing is usually required due to misalignment, which may occur on elastomeric, sliding plate, or rocker bearings. This can be accomplished by jacking from the bearing seat area or by constructing
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a jacking frame supported on the footing of the substructure or on soil under the bridge. When jacking frames with cross bracings are used, subsurface investigation shall be performed. When all bearings in a substructure unit are replaced, the replacement bearing can be of different type rather than the same type as that of existing bearing. For example, Lee et al (1999) have discussed the replacement of existing mechanical bearings with Elastomeric beatings in Ahmad Shah Bridge, Malaysia. Resetting of bearings may introduce eccentricity of load into the substructure. Therefore, all new bearing plates must be designed for the reorientation of loads. The designer should also consider the new load path and the effects of jacking and resetting on the new bearing plate on the substructure. The designer should consider seismic design in the analysis for bearing replacement. Rob North (2011) described the design of temporary works for the girder jacking system, including the constraints and difficulties encountered, demonstrating the significance of providing adequate girder jacking provision as an integral part of permanent design. Deflection analysis for all spans has been emphasized to ensure the adequacy of jacking system requirement and shop detailing of the steel work. Replacement of bearings below prestressed concrete girders needs to be done very carefully. The space constraint also needs to be considered during the selection of appropriate jacks and jacking operation. Also, the end diaphragm of longitudinal girders should have sufficient flexural/ shear capacity to withstand the jacking operation. Park, et al (2001) have discussed about the jacking procedure for the replacement of PSC I-girder bearings without damaging the superstructure. The FEM based analysis procedure to compute jacking force and overall jacking sequence for a 4-span continuous unit has been proposed. The method takes into account the stress concentration at the loaded area on the girder and the behaviour of superstructure during the jacking. Also, an analytical equation is
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proposed to compute the allowable jacking force considering the bursting stress induced at the loaded area of the girder.
Replacement of Expansion Joints The replacement of expansion joints should be taken up only after the repair/replacement of bearing, as jacking of the deck is necessary for repositioning/replacement of bearings. It involves the following steps. Step-1: For replacement of expansion joints, concrete at the edge of deck slab should be dismantled to expose the reinforcing steel to a distance of at least 300mm on either side of expansion gap. Step-2: If there is any deficiency of existing steel in the vicinity of expansion joint, then additional reinforcement along its length or in perpendicular direction shall be provided by welding with the existing reinforcement, maintaining a lap length of at least 5 times the diameter of bar. Step-3: Provision of additional steel to hold the edge beams of expansion joint assembly in position, by means of steel studs welded to the existing/ new reinforcement. Step-4: After the placement of reinforcement concreting is done for which concrete of same grade as that of deck slab or 5Mpa higher grade needs to be used. Also, concreting has to be done either in the morning hours or late night hours, when the atmospheric temperature is almost same as that of bridge temperature. For concreting, ready mix concrete (RMC) can be used. It may be noted that RMC shall be poured with minimum possible lapse of time; otherwise its workability will be reduced, affecting the strength of concrete.
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Care must be taken, if mastic overlay of wearing course is done after the replacement of expansion joint. It should not lead to the clogging of expansion joint or formation of trough shaped profile at the expansion joint. Monitoring of post repair movement of expansion joints is an important step to ensure the functionality of bearings and expansion joints and can be easily achieved by measuring the gap between the expansion gap at hand rail level.
Other Key Issues The following aspects need to be further studied, investigated or implemented: • There can be problems when permanent bearings are used as launch bearing during increment launch of a post-tensioned concrete box girder bridge as reported by Paul (1999) • Accessibility to bearings and expansion joints for condition assessment and repair • Minimal disruption of traffic during repair/ replacement of bearings and expansion joints • Selection of bearings for bridges located in high seismic risk regions • Behaviour of sliding POT bearings of curved box girder bridge • Adaption of seismic isolation bearings for new bridges and for retrofitting demands development of guidelines for seismic isolation design and test facilities for evaluation of isolation bearing (Imbsen, (2001), IRC:62010) • Precautions during design and installation of bearings on sloping span • MBEJ shall be designed for strength, fatigue and fracture limit state under vertical and horizontal loads. Fatigue testing of modular expansion joints for traffic load prevailing in our country • Antiskid treatment for metal surface wider than 200mm exposed to vehicular traffic Fig. 13: Different Stages of Replacement of Expansion Joint
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• Expansion joints to be designed accommodate ULS movements Volume 43
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Concrete Institute, Farmington Hills, MI, USA.
Conclusion Bearings and expansion joints are important components and their premature failure affects the performance of the bridges. There is a need to analyse the reasons for failure and develop long lasting bearings. Also, there is a need to implement the bridge maintenance management system to enhance the service life by periodic repair and replacement of bearing and expansion joints, the perpetual trouble shooters of bridges.
Acknowledgement
4.
Imbsen, R.A., (2001), “Use of isolation for seismic retrofitting of bridges”, Journal of Bridge Engineering, ASCE, Vo.6, No:6, pp. 425-438.
5.
Ghosh, S., (2000), “Bearings and expansion Joints-Key contributors to durability of bridge structures, The Bridge & Structural Engineer, Vo, 30, pp.137-154.
6.
Paul. A., (1999), “Problems encountered during incremental launch of a post tensioned concrete box girder bridge”, Proceedings of International Conference on Current and future trends in bridge design, construction and maintenance, Eds. Das, P.C., Frangpool, D.M., and Nowak, A.S., pp.271-279.
7.
Lee., H.S., Ng, S.K., Yap, C.L.,Voon, Y.L., Lim, B.T.,(1999), “Replacement of existing mechanical bearings with elastomeric bearings for Ahmad Shah Bridge, Temerloh, Malysia, Proceedings of International Conference on Current and future trends in bridge design, construction and maintenance, Eds. Das, P.C., Frangpool, D.M., and Nowak, A.S., pp. 403-414.
8.
IRC: 6-2010, “Standard Specifications and Code of Practice for Road Bridges”, Section-II, Loads and Stresses, Fifth Revision, IRC, New Delhi.
9.
Rob North (2011), “Riverside ExpresswayStructural Support for Bearing Replacement”, Queensland Roads, No. 10, pp. 17-26.
The paper has been published with the permission of Director, CSIR-CRRI, New Delhi.
References 1.
Heymfield, E., McDonald, J., and Avent, R., (2001), “ Neoprene bearing pad slippage at Louisiana Bridges”, Journal of Bridge Engineering, ASCE, Vol. 6, No. 1, pp.3036.
2.
Park.S.K.,Kim,H.Y.,and Kim, J.H., (1998), ”Bearing replacement for prestressed concrete I-Girder bridges”, Journal of Bridge Engineering, Vol. 6, No. 4, pp.271275.
3.
Fyfe, ER, Milligan, P & Watson, S.C., (2006), ‘A discussion of failure modes on high load bridge bearings which have resulted in the current design methods, philosophy, and guidelines for disc bearings’, World congress of joints, bearings, and seismic systems for concrete structures, 6th, Halifax, Nova Scotia, Canada, The International Joints & Bearings Research Council & American
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The Bridge and Structural Engineer
IMPORTANCE OF QUALITY CONTROL MEASURES FOR STRUCTURAL BEARINGS AND EXPANSION JOINTS – AN INTROSPECTION Achyut GHOSH Technical Advisor (International) mageba SA Bulach, Switzerland ghosh.achyut@gmail.com
Born 1941, Engineering Graduate in Mechanical Engineering from Calcutta University, Bengal Engineering College, Sibpore, West Bengal, Exdirector Metcogroup of Companies, Designer of various equipment like Pile Driving Machine, Railway Traverser, Transfer Cars, Designer of Bridge Bearings & Expansion Joints, Ex-member IRC Bridges Committee, Member IRC Bearing Committee (B6) & Steel Structure Committee (B5), Ex-member ACI Bearing Committee 554, Visiting Professor IIT’s & other colleges in India and abroad
Santanu MAJUMDAR Chief Executive Officer mageba Bridge Products Pvt Ltd Kolkata, India smajumdar@mageba.in
Santanu Majumdar, the CEO of mageba India, is a graduate in Civil Engineering from Jadavpur University, Kolkata, in the year 1991. He started his career as a bridge and structural engineer has served the industry of Bridge Bearings and Expansion Joints for the last 20 years.
Summary
1. Why Introspection
There is a misconception in our country that quality of the bearings and expansion joints are assured due to the final inspection by client/ agency. Nothing can be further from the truth. Quality of the product is assured during all stages of manufacturing i.e., from raw material to intermediate processing to final assembly and load testing where applicable. The quality assurance methods are to be followed to reduce/ eliminate costly rejection of the end product due to failure in quality. The quality assurance methods when followed for the various stages in manufacturing and acceptance provides pointers to the way the quality is moving, so that corrective methods can be adopted, before exceeding the stage tolerance limits. This is the only way to produce good quality bearings and expansion joints economically and in the shortest period of time.
1.1 There is a misconception in our country that quality of the bearings and expansion joints are assured due to the final inspection by client/ agency. In this article we want to show that nothing can be further from the truth, quality of the product is assured during all stages of manufacturing i.e., from raw material to intermediate processing to final assembly and load testing where applicable.
Keywords: Bearings and Expansion Joints,Quality assurance, Raw material control, Process control, All stages ofManufacturing, Eliminate costly rejection of the end product.
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1.2 What if a bearing fails in the final inspection? Such possibilities are negated, when appropriate quality assurance i.e., quality control measures are adopted.
2. Quality Assurance 2.1 The encyclopaedic reference for Quality Assurance is as follows: Quality assurance (QA) refers to administrative and procedural activities implemented in a quality system so that requirements and goals for a product, service or activity will be fulfilled. It is the systematic measurement, comparison
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with a standard, monitoring of processes and an associated feedback loop that confers error prevention. This can be contrasted with quality control, which is focused on process outputs. Two principles included in QA are: “Fit for purpose”, the product should be suitable for the intended purpose; and “Right first time”, mistakes should be eliminated. QA includes management of the quality of raw materials, assemblies, products and components, services related to production, and management, production and inspection processes. Suitable quality is determined by product users, clients or customers, not by society in general. It is not related to cost, and adjectives or descriptors such as “high” and “poor” are not applicable. For example, a low priced product may be viewed as having high quality because it is disposable, where another may be viewed as having poor quality because it is not disposable. 2.2 The purpose of Quality Assurance is as follows: • Increasing the safety of the product. • Increasing the service life i.e., durability of the product. • Reducing the maintenance requirement of the product. • Reducing the cost of production by reducing/ eliminating in process rejections and eliminating rejections at final stage, thereby reducing the cost to the society. 2.3 The Control on Quality is achieved in the following two main spheres: • Material control. • Process control.
3.1 The quality control starts with the input materials. 3.2 They are to precisely match the laid down specifications. They must match some Indian standards or foreign standards or the manufacturer’s standard.
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3.4 There are laid down procedure for collection of test samples from the body of the material being tested as per Indian standards or foreign standards. The test piece for cast steel has to be integral to the casting. 3.5 The main physical tests are as follows: • Yield, Ultimate tensile strength (UTS) and elongation test. • Bend test. • Charpy impact at room and low temperature where applicable. 3.6 In addition to the main physical tests as above there are ultra-sonic and radioactive tests for determination of internal flaws in rolled, forged and cast products: 3.7 The main chemical tests are as follows: • Determination of percentage of Carbon, Manganese, Silicone, Sulphur & Phosphorus and other important elements in steel, both forged and cast. • Determination of percentage of main alloying elements for non-ferrous forgings and castings. 3.8 Metals and alloys can be tested by spectroscopy for accurate determination of percentage of all constituents. 3.9 In addition to the MTC, there are various tests for non-metals like elastomer, POM, PTFE, Poly-Urethane etc.
4. Process Control
3. Material Control
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3.3 There preferably has to be a manufacture’s test certificate (MTC). In addition they must pass a physical and or chemical confirmatory test form the producers’ in-house laboratory or dependable out-sourced laboratory.
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4.1 The following Process Controls are used in the workshops and included laboratories of manufacturer for the production of structural bearings and expansion joints: • Fabrication process control. • Corrosion protection process control.
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• Rubber products process control.
5. Fabrication Process Control
• Assembly process control.
The various fabrication processes are as under.
• Factory production control tests.
5.1 Flame cutting
4.2 The following Process Controls Type Tests are used in the workshops and included laboratories of manufacturers for the development of various types of Structural Bearings and Expansion Joints. This is to be clearly noted that Type Tests are done during development of the product and is not for routine demonstration:
Oxy-acetylene flame cutting in workshop is mostly done by portable linear cutting machines. The torch nozzle size and linear speed is set depending on the thickness of the material being cut. However the flame cut surface is usually machine finished prior to further processing or application
• Fatigue test for the lip welded beams for expansion joints- This is a very expensive test and may consume a very long period in arriving at the result. Till date these tests are performed in University/ Institute laboratories inside and outside the country. This test is done to confirm the material selection and corresponding welding procedure. • Fatigue test components of expansion joints for defined number of load cycles o simulate life. • Test for the welding effectiveness of thin stainless steel plate to thick steel plate- This being a difficult process, it is done to establish the electrode used, the procedure and the parameters of welding. • Test on Elastomer- The finished elastomer in Elastomer bearings or Pot bearings needs to maintain some physical properties as noted in the codes. Though these are type tests, however these tests as per relevant parts of IS 3400 are repeated from time to time depending on the raw materials supply. • PTFE sliding specification
material-
Relevant
• Robo®Slide or any similar UHMWPE (Ultra High Molecular Weight Poly Ethylene) sliding material should be governed by ETA (European Technical Approval) • POM (Poly Oxy Methylene) sealing material – Relevant specification • Trials for various corrosion protection application towards compliance to applicable codes
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5.2 Welding Welding used in workshop should follow the guidance provided by EN 1090 and ISO 3834 and preferably the manufacturers shall be certified accordingly ISO 3834 and also EN 1090. 5.3 Fitting It is manual process and quality of fitters and supervision is the check. 5.4 Machining Machining also is manual process. The quality and economics depends on maintenance, permissible tolerance level, use of cutting fluids, choice of right type of machine etc. The quality of operator and supervision is the check. 5.5 Grinding Grinding quality will be as is required, however it is a precursor to Sandering. Polishing and Lapping. 5.6 Sandering, Polishing & Lapping These processes are required to provide the quality of surface finish required for appropriate performance of the bearing parts, for long life, say the inside of the pot in a pot bearing, the sliding surface in a sliding contact
6. Corrosion Protection Process Control The corrosion protection provided to these products are processed as under with controlling of: 6.1 Environment While the items are passing through the various stages of corrosion protection some
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environmental controls like dew point etc are maintained within an acceptable limit for the applied corrosion protection to have a long life. 6.2 Consumables
a calendaring process to feed the mould for vulcanizing. 7.3 Moulding
• Chemical etching.
The proper moulding of rubber to achieve uniform vulcanization throughout the matrix a lot of operator control and supervision. The plan sizes, the thickness, the mass of the end product vary, the type of heating (electrical or steam). This requires alteration in the mould geometry, permitting oozing out of raw mix to create internal pressure in the mould, maintaining the tolerance on elastomer layer thicknesses, introducing the company brand, lot nr etc and precise control of time-temperature cycle
6.4 Surface coating treatment using
7.4 Reinforcing Plates
The various consumables used in the corrosion protection like grits, zinc wire eic., must have acceptable quality to achieve the desired end results. 6.3 Surface cleaning using • Power tools. • Grit blasting.
• Metalizing. • Painting. • Hot dip galvanizing. • Hard chromium coating
7. Rubber Production Process Control The mixing, moulding/ vulcanizing of rubber compound requires careful supervision. The raw rubber (both poly-isoprene & poly-chloroprene particularly the later) has got limited shelf life. It is the responsibility of the quality control personnel to keep track of the manufacturing date of the raw material in stock. About 12 nr of additives (mostly in fine powdered form, whereas some are liquid) are added during mixing the rubber to achieve the required qualities of ultimate tensile, shear, aging, bonding compression set, antioxidation, anti-ozone etc etc. 7.1 Mixing The mixing/ kneading of the additives with the raw rubber (gum) is a mechanical process. The gum is a malleable fibrous structure. To achieve uniform mechanical properties in the vulcanized end product, the additives must be spread uniformly in the interstices of the fibres to get proper and uniform bonding, which require plenty of operator control and supervision. 7.2 Calendering The mixed rubber raw material must go through
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The required bond between the vulcanized elastomer and the steel reinforcing plates is achieved by two coat bond material application. The first coat is applied within a short period of time of the finished and grit blasted steel plates. The second coat is applied on the dried first coat. 7.5 Finishing The oozing vents in the mould and a few other elastomer extrusions are to be removed and the bearing is to be dressed.
8. Assembly Process Control The assembly process control consists of the following: 8.1 The parts to be assembled are identified as per drawing. 8.2 Name plate, Indicator, Scale & Clamping devices are fitted. 8.3 Packing is done to ensure that the bearings reach the site safely without any contamination.
9. Factory Production Control Tests The following factory production control tests are done: 9.1 Each finished elastomeric bearing is load tested and the result is compared with the average values to check odd result if any.
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9.2â&#x20AC;&#x192; Other type of bearings and expansion joints are tested for dimensions, surface corrosion protection, marking etc for compliance:
10. Conclusion Quality control measures when followed rigorously as described above, ensures that the quality of the product is assured during all stages of manufacturing i.e., from raw material to intermediate processing to final assembly and
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load testing where applicable, there by almost eliminating the chances of rejection of the end product, assuring good quality product at the end and ultimate economy. These measures provides pointers to the way the quality is moving, so that corrective methods can be adopted, before exceeding the stage tolerance limit. This is the only way to produce good quality bearings and expansion joints economically and in the shortest period of time.
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Suspension Bridge in Bhopal C.V. Kand BE (Civil), Msc (Bridges)-UK, PhD, Chief Engineer Designs (Retd.) M.P. India cvkand@yahoo.co.in Dr. C.V. Kand, born 1930, received his civil engineering degree from the College of Engineering, Pune in 1955, MSc Bridges in 1977 and PhD in 2006. His consulting organization was started after retirement in 1988.
Summary Suspension bridges for pedestrians are being constructed in India since last 2000 years or more in Kashmir, Assam, Himachal Pradesh, Uttarakhand, Sikkim and some part of North Bengal. These were made of wire ropes. Kashmir is reported to have made steel suspension bridge in 16th century. Lakshman Jhoola a pedestrian suspension bridge of 137 m was constructed in 1932. However, long suspension bridges are not done in India for vehicular traffic. There is no IRC code on suspension bridges. There are several ideal situations for suspension bridges. The paper describes a pedestrian suspension bridge at Bhopal across the channel of a large lake, constructed for a recreation centre on the other side of the lake.
Manish Karandikar Consulting Engineer manishkarandikar@yahoo.com
Manish Karandikar, born 1969, received his civil engineering degree from the Univ. of Indore in 1991 and Master Degree in 1995 from the Univ. of Indore
areas have adopted various means of transport such as tall trees tied together, rope suspension bridges and corbel type of bridges. The ropes used to be manufactured from natural shrubs. A community used to make such long ropes. Such communities are available all over India. The ropes also used to be made from plants grown along rivers and the structure made from the ropes across streams was called jhulla and chinkar (Fig. 1).
Keywords: Suspension Bridge, Anchor block, Hanger rod.
1. Introduction Communication in hilly areas of India from Kashmir, Himachal Pradesh, Uttarakhand, North U.P., North Bengal, Sikkim and other hilly areas up to Nagaland was often disrupted by formidable natural obstacles. Ferry boats were not possible in many areas since the river valley used to be deep with high velocity currents. Mode of conveyance such as horse cart and bullock carts or horse ride used in plain areas before advent of automobiles was not possible in the hilly areas. Therefore, the people of mountain 78â&#x20AC;&#x192; Volume 43
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Fig. 1: Jhullas in Himalayan Region
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In Maharashtra area particularly in Konkan, scrapers grown on trees were used to make such bridges and called sakava. Such jhullas are still being used on streams to approach a temple on the other side. These were also called chinkas. Cane and bamboo with ropes have also been used for the bridges and with these bridges up to a hundred meters span were made. Iron chain suspension bridge on Trinchu River in Bhutan was constructed in 1783. It has a span of 45 meters and width of 1.8 meters (Fig. 2). It is also reported that iron rope suspension bridge was constructed in 15th century by Tibetian saint Thongton Gylpo (1385-1464). He is reckoned as the earliest known suspension bridge builder with steel rope. First long Suspension Bridge was constructed in Kerala in 1877, the Bridge is 120Â m long across the River Kallada in present Kerala State by the British (Ref. 3, Photo 1). Another long suspension bridge in 20th century with steel wire ropes was constructed in India at Rishikesh in 1932 called as LAKSHMAN JHOOLA. Its length is 137 m and width is 1.8 m (6 feet). The bridge was constructed for the benefit of pilgrims going to Kedarnath and Badrinath along Ganga River. It was constructed in 1932.
Fig. 2: Iron Chain Suspension Bridge, Thinchu River Bhutan 1783
There are many suspension Bridges constructed in Himachal Pradesh, Sikkim state along the rivers for pedestrian traffic and some are for also vehicular traffic.
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Photo 1: Suspension Bridge across the River Kallada, Kerala
2. Locations for Long Span Bridges In India, towns were normally established in past along water bodies such as rivers and lakes so that drinking water is available nearby for the people. Initially towns might have been established on one side of the water body. Later, the towns were spread to the other side of the water body. To have a communication between the two sides a bridge has been build across the water body. Later, when the town grew many such bridges were built on the water body for communication. Towns like Pune, Nasik, Ahmadabad, and Banaras have many such bridges in the same town. When the width of the water body was small and the depth of water was not much, normal road bridges are constructed. However in case of lakes with depth of water more than 6-10 meters the cost of foundation would be high. Therefore in such spots a long span bridge with one span from bank to bank are ideal. These do not obstruct the water and the view of the lake. On the contrary they add to the aesthetics of the lake and of the town and do not affect the environment. Bhopal town was developed by Raja Bhoj in the 11th century on one side of the large lake. The water level was raised by constructing a bund which is known as Kamala Park Bund for crossing the lake and also for recreation purpose. Another bund was made about a kilo meter away on the downstream side to make Chota Talab. This was about 250 years ago. Earlier proposal was to build
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a bridge, however to enhance the beauty of the lake a solid bridge was made. This is called Pul Pukhta. Bhopal town has spread on both sides of the large and small lakes. The Kamala Park Bund and Pul Pukhta are the only connections between the old town and the new town established on the other side. The old two passages that are Kamala Park and Pul Pukhta are not able to meet the needs of the present traffic of the growing town. Therefore with a view to enhance the beauty of the lakes and the town on both sides it has become necessary to construct long span bridges at three locations. The spans will be 1000 meters, 500 meters and 700 meters. A suspension bridge, a cable stayed bridge or Long Span Single Arch Bridge will be the ideal solutions. These are yet to be constructed.
3. Suspension Bridge at Bhopal At the end of the large lake about 1km from
the waste weir, a suspension bridge has been constructed across the lake. This location is about 2-3 km away from the main habitation. It was proposed to establish a tourist spot for the town on the other side of the lake which has a hilly area. Moreover, the proximity of the lake will attract the people of the town to relax at a spot near the water body. This project was taken up by Tourism Department of Madhya Pradesh and the spot is known as Sair Sapata, which is an ideal spot for loitering .With a view to make the spot aesthetically beautiful it was proposed to make this bridge as a suspension bridge with its pillars on the banks of the lake. A road bridge to cross the lake has already been built by the Public Works Department on a road connecting Bhopal to Sehore. Many educational institutes have been built beyond the lake and this road bridge serves the needs of vehicular traffic. Details of this suspension bridge are as below (Fig. 3).
Fig. 3: General Arrangement Drawing, Bhopal Suspension Bridge 80â&#x20AC;&#x192; Volume 43
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•
The walk way 3.5 m wide with steel railings on both sides.
•
Loading on the walk way 560 kg/m2.
Hydraulic Data of the Lake
Photo 2: Google Image of the Site
Bed level lowest
RL 499.250,
Highest bed level
RL 508.900 at the anchor block.
HFL
RL 510.501
Design discharge when the west weirs are opened 2802 cumecs. Design velocity 3 m/s Soffit level of the bridge
RL 513.082
Foundation level of pylon
RL 486.440
Foundation level of anchor block
RL 502.830
Bottom of Curtain wall
RL 500.330
Number of wire ropes provided on each pylon
6 No. which are anchored in the End Block
Photo 3
Silent Geometric Data of Bridge • Total length and span: Central span 80m between piers • Side span: 40 m on either side • Overall length: 160 m with length of anchor block overall length is 183.20 m. • Clear pedestrian width: 3.5 m, Overall width: 4.1 m • Anchor blocks on either side beyond a distance of 160 m • Foundations for pylons: Pile foundations with 6 piles anchored in rock. • Depth of foundation: about 13 m below bed level. • Details of pylons: 2 columns spaced at 5.9 m centre to centre and laid on the pile cap. The columns stiffened by cross girders. Height of pylon from pile cap level is The Bridge and Structural Engineer
Photo 4
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4. Some Technical Aspects of the Bridge The Tender document did not give any design criteria. There is no code of practice issued by Indian Road Congress on suspension road bridges, therefore various design issues were discussed with well known designers of suspension bridges in India. A document (Reference 2) was referred to while finalising the design. The design aspects of this bridge are explained in paragraph 5 below. However there were several other problems associated with the construction of this bridge and maintaining quality control. These are explained here below. 4.1 Hydraulic aspects It was thought that since this bridge is across the lake there will be no velocity or scour depth. However this bridge is located hardly 1km on the upstream of waste weir in the tail- end channel. There are 11 gates for the west weir. The lake level rises during monsoon due to discharge coming from the catchment area of 365 km2. The maximum water level at the lake is 510.501 m. When the water level in the lake reaches to this level or a little lower, the gates are opened gradually. However, when the rainfall is high all gates have to be opened. This is the worst condition for the design of pylons of the suspension bridge. It was therefore ascertained from hydraulic calculations the following data. Maximum flood level
RL 510.501
Maximum discharge
220.9 cumecs
Catchment area
365 km2.
Design velocity
3 m/s
Scour Depth at pylon
RL 495.500
Scour Depth at abutment (anchor block)
RL 500.830
At the abutment foundations have to be taken by 2m in soil below the scour level of RL 500.320 However instead of abutment there is an anchor block which will anchor the stress cables therefore it was desired to limit the open excavation for the Number 4
4.2 Safe Bearing Capacity for Anchor Block The contractor proposed 50 tonnes/m2 as the safe bearing capacity. However load bearing test was carried out and a bearing capacity of 28 tonnes/m2 was adopted. The size of anchor block as per design requirement came to 12 x 6.5 m. The curtain wall was taken 2.5 m deeper below the foundation level of anchor block. The anchor block structure was a hollow structure with 1000 mm thick RCC walls on all four faces. The hollow portion of 10 x 4.5 m was filled by M15 concrete. 4.3 Permissible Stresses in Wire Ropes The factor of safety for wire ropes is considered as 2.5 for the breaking load of the wire rope in China and other countries. According to Indian Codes clause 506.4.1 of IRC 24 of 2001, Table 6.2 stipulates basic permissible stress that is axial tension in the wires. This is equal to 0.6 x Fy, where Fy is the yield stress. The yield stress = Proof stress divided by 1.63 Proof stress = Breaking load divided by 1.43
Since rock is available at the level higher than the calculated scour level of RL 495.500 the pylons are socketed 0.6 m in hard rock that is RL 498.830
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anchor blocks and not go up to designed scour depth but to provide a curtain wall and apron to limit the scour depth. This technique has been adopted in a number of bridges and found to be quite successful. IRC Codes also permit this practice. Foundations of RCC box type of bridges are also laid hardly 300-600 mm below the bed level and scour is limited by providing curtain wall and apron. A drawing for the anchor block is enclosed for reference (Fig. 4). Besides this stone pitching are provided at the anchor block as shown in Fig. 4.
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Permissible stress = Breaking load divided by (1.63 x 1.43) = Breaking load divided by 2.4 Therefore, factor of safety on the breaking load is 2.4 which is rounded off to 2.5 4.4 Test of 32 mm Hanger Rods The walk way of the suspension bridge is fixed to the wire ropes by 32mm hanger rods. It was decided to ascertain holding down capacity of 32mm diameter hanger rods. The hanger rods are anchored in the concrete of deck. The load The Bridge and Structural Engineer
on the hanger is 10 tonnes. Considering a factor of safety of 2 it was decided to test the anchor boards by 20 tonnes (factor of safety 2). A drawing showing the test procedure is enclosed (Fig. 5). The test results are also enclosed.
Pressure in kg/cm2
Load in kg
Pressure in kg/cm2
Load in kg
140 150 160 170 180 190 200 210 220 230 240 250 260
8727.60 9351.00 9974.40 10597.80 11221.20 11844.60 12468.00 13091.40 13714.80 14338.20 14961.60 15585.00 16208.40
330 340 350 360 370 380 390 400 410 620
20572.20 21195.60 21819.00 22442.40 23065.80 23689.20 24312.60 24936.00 25559.40 38650.40
4.5 Dynamic Test On Piles Clause 709.2.4 of IRC 78 stipulates routine load test on one pile with a test load of 2.5 times the designed load. However amendment in IRC 78 permits Dynamic Load Test and this was carried out. Ms Geodynamics were engaged to carry out load tests on piles with a purpose to carry out load capacity of piles and also measure the settlements under the maximum load. The factor of safety for the load was 2.5. The test results shows that pile can take that load. 4.6 Testing of Materials and Quantities of Materials Wire ropes, mild steel deform bars; cement and aggregates used in the work have been tested. The following quantities of materials are used in the work.
Pull Out Test of 32 mm Suspender Pressure in kg/cm2
Load in kg
Pressure in kg/cm2
Load in kg
10 50 80 100 120 130
623.40 3117.00 4987.20 6234.00 7480.80 8104.20
270 280 290 300 310 320
16831.80 17455.20 18078.60 18702.00 19325.40 19948.80
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• Concrete • Deform bars • Wire ropes • Structural steel for parapet walls 4.7 Mishaps in the Construction There were two mishaps during the construction work which occurred generally due to some faults in the construction procedure.
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• Horizontal cracks in the pylon on Law Academy side at about 5m above the bed level occurred. Water spray was continuously done for 24 hours due to which some of the cracks closed. This is autogenous healing of concrete which has been done in several bridges. However, glass tele-teles were fixed at the cracks for a period of one month. The glass did not break and therefore the cracks were not widening.
4.9 Quantities of Work
•
Total weight of cable with hanger and suspender: - 45.5 MT
During stressing operation of the cables the cable slipped due to collapse of winch. This was then replaced
Main suspension cable: - 186.5 m x 6 Numbers
On u/s and d/s, seamless galvanized
48 mm dia steel core 6 x 37
1570 N/m2
Total hanger : - Type I 28 No.
As already stated, the defects are due to inexperienced technicians at the site.
Type II 128 No.
4.8 Period of Construction
32 mm dia – 132
The work was started on 7th October 2008 and was completed on 27th January 2011.
Rope : - 1200 m @ 10 kg/m- 12 Ton
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Total suspender : - 40 mm dia – 28
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RCC Decking : - Type I – 18 No. Type II 18 No. Central span – 01 No. Cast in situ – 02 No. Total Cost project (from final bill)
:- Rs. 3.705 Crores
w: Dead Load Total weight (Including Weight of Suspenders)
App. Quantity of concrete: M15 base concrete and plumb concrete : - 701 cum
v: Vertical Component of Cable Tension i
M20 concrete of ramp : - 21 cum
T: Cable Tension = w L2/ 8f
M25 concrete of anchor block, curtain wall and apron
: - 532 cum
M35 concrete of pylon deck slab : - 574 m3 App. Quantity of mild steel used in RCC - 100 tons
5. Structural Analysis for Suspension Bridge Structural Analysis for Bridge was done using FEM and final model cross checked on STAAD for all the load cases as mentioned below and the results of deflections were computed and after ascertaining that these deflections are in permissible limits the Design of components was done. The structural model analyzed on STAAD is shown as below.
H: Horizontal Component of Cable Tension φ: Angle with horizontal of tangent to cable n: Angle with horizontal of chord line joining end of span L: Length of Cable in Main span, n = f/K= 0.111 (ii)
Horizontal forces due to live loads were calculated as per following relations given in above text.
Denominator N = 8/5 + 3 Iz / (A x f2 ) x (1 + 8 n2) + 6 Iz / (A x f2 ) x K1 / K x sec f Live Load Tension TL = p’ x K / (5 x N x n) (iii) Horizontal forces due to temperature Temperature Strain ε = αt x (T2 – T1) Tension Force = ε E Acables Live Load : Pedestrian Live load of 560 kg/m2 considered as per IRC:6. Case 1. Live Load on full span
Case 2. Live Load on half span
Case 3. Live Load on quarter span Horizontal Force in cables (i)
Horizontal forces in cables were calculated as per classical theory presented in Reference – 2.
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Seismic Forces Seismic forces were calculated as per provisions of IRC:6, The applicable seismic zone is zone-2. Response spectrum analysis was carried out as per spectrum provided in IRC: 6 2010. Construction Sequence Analysis The construction sequence analysis (Forward analysis) was performed to find out tension force generated in top suspension cables. After building the pylons in the traditional way and erecting cable at place over pylons saddles, the bridge deck is constructed by lifting the bridge deck segments from river floor. In order to retain the “correct” geometry of the bridge deck, all deck sections are continuously elevated and connected to the hangers. A temporary connection between the deck sections was installed after all segments were launched in place. Preliminary hinged connections with minimum possible spacing between the segments in order to kinematically allow movements without inducing impermissible constraints, and avoiding the segments to bang against each other uncontrollably. The procedure of connecting the different girder segments with stiffening truss was started to the respective deck units. This stiffening truss connection to respective girder units caused correcting induced deflection and the change in tension of the suspension cables in accordance with the weight of the actually mounted segments and truss. The displacement of previous stage were multiplied by respective directional stiffness to found out misfit forces to be applied at each stiffening truss construction stage. This tension was superimposed with previous found tension in cable due to SIDL and temperature forces to find out final tension in cable. Wind forces The major challenge in the design of long suspension bridges is their vulnerability to wind induced vibrations. Long-span bridges requires correctly ascertaining Dynamic behavior namely Vortex shedding, Buffeting and flutter. The section is subjected to wind static forces (a) Horizontal Tension T (b) Vertical lift N (c) Torsional
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Moment M. These loads are derived from the design wind speed by multiplying the respective dynamic pressure with the dimensionless steady-state drag, lift, and moment coefficients CT, CN and CM respectively with wind pressure q. Thus Forces T = CT q Aarea, N = CN q Aarea, M = CM q B L where B & L are deck width and Length respectively and Aarea is the projected side deck area. The dimensionless coefficients are dependent on Reynolds number Re = VB/ν and Strouhal Number S = f h / V Dynamic vibrations are caused by three mechanisms. (1) Buffeting - These fluctuations are called “turbulence intensities” which describe the deviations of the actual wind from the steady state. (2) Flutter - The self induced girder/deck vibrations due to change in wind force due to self motion. Classical flutter comprises only the coupling of lift and moment terms (i.e. coupling between first few vertical modes and low Torsional modes). (3) Vortex Shedding - A phenomenon closely related to flutter is the lock-in of the vortex shedding frequency. Normally, the shedding frequency increases linearly with wind velocity. In near field region the natural frequency of the structure is imposed to the vortex shedding frequency, which is nearly independently of the wind velocity. Dynamic Wind analysis was carried on FEM software and results were within accepted limits.
6. Conclusion IRC has not finalized any code of practice for suspension bridge. There are several situations particularly in hilly areas where suspension bridges will be more suitable. Moreover these are aesthetically beautiful. Suspension bridges are ideal on large lakes with considerable depth of water. These also enhance the beauty of the lakes. If these are constructed during construction of dams, access from one high bank to other is easy. Such bridges are constructed in Himalayan area.
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7. Credits The contract for this bridge was a lump sum contract awarded to RAMDIN ULTRA TECH, PVT LTD a firm based in Indore who have engaged INVICTUS CONSULTANCY SERVICES as consultants for design. Madhya Pradesh Tourism Department engaged Dr. C.V. Kand and Dr. Dindorkar for proof checking the design and sorting out technical and construction problems.
of Madhya Pradesh, in charge of the work and Shri. Brajesh Tiwari Assistant Engineer for their valuable assistance in preparation of the paper.
9. References 1.
The Ancient Bridges of India by Jean Deloche.
2.
Practical Treaties on Suspension Bridges, their Design, Construction, and Erectionâ&#x20AC;? by D.B.Steinman, Published by John Wiley & Sons.
3.
Google Image.
8. Acknowledgements Acknowledgements are viewed to Shri. A.A. Bhoraskar Chief Engineer Tourism Department
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Mix Design Method for High Performance Concrete
Dhirendra Singhal
Veerendra Kumar
Balkrishan
Professor of Civil Engineering Deenbandhu Chhotu Ram University of Science and Technology Sonepat-131039 chairmancivil@dcrustm.org
Professor of Civil Engineering Indian Institute of Technology BHU, Varanasi-221005 Vkumar1655@yahoo.co.in
Associate Professor Department of Civil Engineering PTU GZS Campus Bathinda-151001 balkrishandr@yahoo.com
Dr. Singhal, graduated from Bhopal University in 1986 in Civil Engineering. He did his Ph.D. in 1993 from Insitutte of Technology, BHU, Varanasi. He was also awarded Post Doctrate from Japan Society for the Promotion of Science in 1995. He also received award for the best research paper by The Institution of Engineers (India) in 2000. He has guided number of M.Tech and Ph.D. students. Dr. Singhal is a member of many International and National professional bodies.
Dr. Veerendra Kumar who graduated from IIT Kanpur did his Ph.D from BHU, Varanasi. He has deep interest in research and academics. Dr. Veerendra has guided many M.Tech and Ph.D. students and published several research papers in International/ National journals/proceedings. His research interest included Design and Analysis/Concrete Technology/Special Concretes.
Dr. Balkrishan joined GZS, PTU campus Bathinda after completing his B.Tech and M.Tech from PEC Chandigarh. He did his Ph.D. on Steel fibre reinforced concrete from Punjab Technical University, Jalandhar. He has guided number of M.Tech students and actively involved in research and consultancy work.
Summary As the name suggests, it is hoped that high performance concrete performs better than conventional concrete. High performance concrete is that concrete which performs better during fresh state as well as in hardened state and provides strength according to the structural requirements. Many additives as well as admixtures such as fly-ash, silica fumes and plasticizer/super-plasticizer are added into it in order to achieve these requirements. However, the basic mix design methods available do not consider the inclusion of these admixtures.
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This detailed study was undertaken to investigate the effects of addition of silica fumes into concrete and suggest a best possible mix design method. For this purpose, different mix design methods were studied in two stages to include possible variation in ingredients and it was found that Indian Standard Method provided with best results i.e. high strength at minimum cement content. Keywords: Silica fumes; high performance concrete; mix design; ACI method; IS method; COST method; Generalized approach method; compressive strength; tensile strength.
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1. Introduction High performance concrete can be defined as that concrete whose ingredients, proportions and production methods are specifically chosen to meet special performance and uniformity requirements that cannot be always achieved by using only conventional materials like cement, aggregates, water and chemical admixtures, and adopting normal mixing, placing and curing practice. Since any structure which is to be built will require these basic properties, therefore, it can be understood that high performance concrete is a futuristic material. In order to achieve all these properties, admixtures are often used in high performance concrete. The admixtures which are often added in order to produce high performance concrete are silica fumes, fly-ash, plasticizer, super-plasticizer, etc. If concrete requires enough ductility and toughness, fibres will also be required to be added in concrete. The design methods available such as IS Codes [1-2], ACI Method [3-4] COST [5] (Concrete Optimization Software Tool) Method and Generalized Approach Method [6] do not include the provisions of all these admixtures. Through the present study, the effects of all these admixtures have been investigated and a best suitable mix design method has been suggested. The study has been conducted in two stages. Firstly, the effects of addition of silica fumes have been investigated since silica fumes is the main admixture which is added in order to fill the transition zone and to obtain the strength and durable concrete. Thereafter, two mix design methods i.e. Indian and American Mix Design Methods were compared. In the second stage various admixtures such as silica fumes, fly-ash, super-plasticizers were added and all the four mix design methods named above were intentionally compared with different mix proportions so that the suitable mix design method should come out as best under different conditions and independently.
2. Experimental Programme Since silica fumes is the main ingredient added in high performance concrete to solidify the transition zone and hence to achieve better durability, in
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the first set of this study, the effects of addition of silica fumes were studied on the properties of cement. For this, cement was replaced partially with silica fumes and normal consistency, initial and final setting time, soundness and compressive strength were studied. Further, two mix design methods i.e. Indian Standard mix design method and American Concrete Institute Mix design methods were studied. It was found that Indian Standard Mix Design Method offered better results. In the second stage of this study, all the basic ingredients i.e. cement, aggregate and admixtures were changed and the four named mix design methods were studied. The properties of the materials used in this study in first stage were as under: The cement used confirmed the requirements of IS: 8112 [7] with specific gravity 3.14 and compressive strength 43.74 MPa. Fine and coarse aggregate used confirmed the requirements of IS: 383 [8] and had fineness modulii 3.015 and 6.68 and specific gravity 2.60 and 2.70, respectively. The silica fumes used could be obtained only from one source had the properties as detailed in Table-1 and remained unchanged in both the stages of the testing. The properties of the materials used in this study in second stage were as under: The cement used confirmed the requirements of IS: 8112 [7] with the specific gravity 3.15 and compressive strength 46.50 MPa. Fine and coarse aggregate used confirmed the requirements of IS: 383 [8] and had fineness modulii 2.21 and 6.91 and specific gravity 2.53 and 2.71, respectively. In the first set of testing, Sulphonated Naphthalene based super-plasticizer was used while in the second set Polycarboxylate based super plasticizer was used.
3. Results and Discussions 3.1 Effects of addition of silica fumes 3.1.1 Normal Consistency The variation of normal consistency of cement
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replaced partially with different percentages of silica fumes has been shown in Fig. 1. The figure clearly shows that the normal consistency increases gradually with the increase in silica fumes contents. Therefore, it becomes obvious that the addition of silica fumes in cement required more water to hydrate. The reason was that the addition of silica fumes added more cementitious material because the unit weight of silica fumes is appreciably less than cement and thus required more water to hydrate for normal consistency.
Fig. 2: Variation of Setting Times with Addition of Silica Fumes
3.1.3 Soundness The results of soundness through Le-Chatelier’s expansion with partial replacement of cement by silica fumes have been plotted in Fig 3. It is obvious from Fig. 3 that the addition of silica fumes has gradually decreased the soundness of cement upto 7% and significantly beyond 7%. However, this needs further investigation as to how this significant decrease in soundness would affect the durability of concrete.
Fig. 1: Variation of Normal Consistency with the content of Silica Fumes
Table 1: Properties of Silica Fumes used Parameters
Specifications
Analysis
SiO2
Minimum 85%
89.7%
Moisture Content
Maximum 3.0%
0.80%
Loss on Ignition
Maximum 6.0%
1.70%
Carbon
Maximum 2.5%
0.90%
Specific Surface
Minimum 15 m2/g
20.40 m2/g
Bulk Density
500-700 Kg/m3
660 Kg/m3
Specific Gravity
—
2.22
3.1.2 Setting Times The effects of addition of silica fumes on setting times of cement have been shown in Fig 2. It is clear from the figure that both initial and final setting time decreases with the increase in silica fumes percentage in cementitious material. The reason for the reduction of setting times seemed to be the acceleration of hydration provided by high silica content with high specific surface area of silica fumes. 90 Volume 43
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Fig. 3: Variation of Soundness with the Addition of Silica Fumes
3.1.4 Specific Gravity The effects of addition of silica fumes on the specific gravity of cement have been depicted in Fig 4. Specific gravity of cementitious material decreased with the increase in partial replacement of cement by silica fumes. It was found that the decrease in specific gravity with the increase in silica fumes was almost linear. It was 3.14 in case of pure cement and the same reduced to 2.77 with 12.5% silica fumes. The reason seemed to be obvious that silica fumes had specific gravity 2.22 whereas cement had 3.14. Therefore, the increase in content of silica fumes decreased the specific gravity of the mixture.
Fig. 4: Variation of Specific Gravity with the Addition of Silica Fumes
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3.1.5 Compressive Strength
3.2 Mix Design Methods
The compressive strength with partial replacement of cement at the ages of 3 days, 7 days and 28 days has been shown in Fig. 5. It can be seen from the figure that there is no significant difference in compressive strength up to 12.5% replacement. One of the reasons while choosing optimum silica content was this fact in further study.
After studying the preliminary properties of cement, two mix design methods were tried and water-cement ratio was kept constant since compressive strength is mainly governed by the water-cement ratio. The details of mix proportions are in Table 2.
Fig. 5: Effect of Addition of Silica Fumes on Compressive Strength of Cement
Cubes of 100 mm in size were cast to determine the compressive strength at the ages of 7, 28, 60 and 90 days. However, tensile and flexural strengths were determined at the ages of 28 and 90 days. The tensile strength was determined through these cubes only by applying load along the diagonally opposite edges. Flexural strength was determined through the prismatic specimens 100 x 100 x 500 mm in size. The specimens were tested over the span of 400 mm and a point load was applied centrally.
Table 2: Details of Mix Proportions Coarse Fine Water Cement (Kg/m3) (Kg/m3) Aggregate Aggregate (Kg/m3) (Kg/m3)
Super-plasticizer (2% by weight of cement-Fly-ash)
Silica Fumes (Kg/m3)
1215
11 litre
----
422
1215
11 litre
66
550
772
851
11 litre
----
484
772
851
11 litre
66
Mix Design Method
Designation
Indian Standard Method
M1
192.50
550
422
M2
192.50
484
American Concrete Institute Method
M3
192.50
M4
192.50
The compressive strength of the four mixes designed by Indian Standard and American Concrete Institute has been shown in Fig. 6. The details of the mixes used appear in Table-2. It can be seen from the figure that the strength of M2 remained always higher than M1. Further, the percentage increase in compressive strength of Mix M1 from 28 days to 90 days was 23.26% while for Mix M2 was 25.78%. Mix M3 designed by American Concrete Institute Method although gained higher 90 days compressive strength yet the compressive strength with silica fumes (Mix M4) remained lower than the mix proportions designed by Indian Standard Method (M2).
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Fig. 6: Compressive Strength of Concrete by IS and ACI Methods
Fig. 7 shows the variation of tensile strength at the ages of 28 and 90 days obtained for different mixes designed by the two methods. It can be seen from the curves that the mixes containing silica fumes provided more tensile strength than
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the mixes without silica fumes irrespective of mix design methods. However, the mix designed by Indian Mix Design method showed 20% more tensile strength (Mix M2) than the mix designed by American Concrete Institute Method (M4).
Fig. 7: Tensile Strength of Concrete by IS and ACI Methods
The flexural strength of the four mixes designed by Indian Standard and American Concrete Institute has been shown in Fig. 8. The remarkable difference which was observed here was that there was significant increase in flexural strength with the addition of silica fumes and by using Indian Standard Mix design method. However, the flexural strength reduced significantly with the addition of silica fumes by American Concrete Institute Mix Design Method (Mix 3 & Mix 4).
Fig. 8: Flexural Strength of Concrete by IS and ACI Methods
Therefore, it is obvious that Indian Standard Mix Design Method offered maximum compressive, tensile and flexural strength with silica fumes and the method can be relied upon. The reason for the differences in behaviour as discussed above lies in mix proportions, if Table 2 is observed carefully. It is clear from the table that water, cement, water-cement ratio, silica fumes and super-plasticizer are same when the mixes are designed by the two methods. However, the mixes designed by American Concrete Institute have significantly higher content of fine aggregate and thus less content of coarse aggregate. In the second stage of testing as has been discussed above, the ingredients of concrete except silica fumes were totally changed and 92â&#x20AC;&#x192; Volume 43
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following four methods of mix design were tried. i)
Indian Standard Mix Design Method
ii)
American Concrete Institute Mix Design Method
iii)
Concrete Optimization and Software Tools Mix Design Method
iv)
Mix Design by Generalized Approach Method
The approach of mix design method was also totally changed. In this mix design procedure fly-ash was also added as admixture and the optimum replacement of fly ash and silica fumes based on results of 28 days compressive strength was determined. The optimum dosages of super-plasticizer and possible reduction of water content was also determined. The optimum contents were as under Fly-ash = 7.50 % Silica Fume = 12.50 % Super-plasticizer = 2 % by weight of cement Optimum water reduction = 15% A mix for M 30 was designed by the four methods with the contents of admixtures as discussed above. The details of the mixes and compressive strength at 28 days appear in Table 3. It can be seen in the Table that an attempt was made to maintain water-cement ratio constant in all the methods i.e. 0.45. The compressive strength attained in COST, ACI, IS and Generalized Approach Method was 35.33 MPa, 36.53 MPa, 39.67 MPa and 38.55 MPa, respectively. It has been observed that the compressive strength in Generalized Approach Method and IS method was maximum. In Generalized Approach Method, concrete mix was designed in four trials as detailed in Table 3. The trial mix (Mix A) was obtained using the American Concrete Institute method. The method was targeted for medium workability and 28 days target strength was 38.25 MPa. Silica Fume has been considered as part of cementitious material. This mix resulted in a compaction factor of 0.87 and 7 and 28 days compressive strength of 23.85 and 39.45 MPa, respectively. Based on data of this mix, another plain concrete mix (Mix B) was proportioned using The Bridge and Structural Engineer
the Generalized Approach. This was proportioned to obtain a compacting factor of 0.87 and 7 days compressive strength of 23.85 MPa. (0.67 times of Mix A). This mix resulted in compacting factor 0.87 and 7 days strength of 22 MPa. These values were fixed as the target workability and 7 days strength of the fly ash cement concrete mix.
The effect of fly ash on workability and strength had to be taken into account. Hence, a trial mix (Mix C) was made with proportions similar to the above Mix B, except that cementing materials were made up of cement and fly ash. Cement to fly ash ratio of 92.5: 7.5 was used.
Table 3: Comparison of Different Mix Design Methods 28 days Water Coarse SuperType of Water Silica Fine (Kg/m3) Cement Fly Ash Compaction Compressive Method Cement Fumes Aggregate Aggregate Plasticizer Strength (Kg/m3) (Kg/m3) Factor (Kg/m3) (liter/m3) Ratio (Kg/m3) (Kg/m3) (MPa) ACI
0.453
206.32
364.36
56.94
34.16
595.30
1112.37
9.11
0.90
36.53
COST
0.456
282.56
495.62
77.44
46.46
513.08
827.60
9.60
0.91
35.33
IS
0.453
191.58
338.33
52.86
31.72
496.48
1217.67
8.46
0.87
39.67
GENERALISED APPROACH METHOD MIX A
0.453
206.32
398.60
56.94
--
595.30
1112.37
9.11
0.87
39.45
MIX B
0.423
219.59
454.25
64.89
--
581.44
1079.81
10.38
0.87
31.33
MIX C
0.423
219.59
415.31
64.89
38.93
581.44
1079.81
10.38
0.85
46.22
MIX D
0.471
219.45
372.74
58.24
34.94
573.09
1113.57
9.32
0.85
38.55
When the cementitious material used (cement: fly ash) is in the ratio 92.5: 7.5 (Mix C), the 7 days compressive strength obtained was much less than the targeted value. The final mix D was proportioned using the Generalized Approach for mix proportioning. The Mix D was obtained based on data of Mix C. The Mix D resulted in 28 days compressive strength of 38.55 MPa. From the results obtained, it was concluded that the IS method is the best method for the mix design of high performance concrete which provided maximum strength including all the admixtures at the minimum cement content. Since the Indian Standard [9] for mix design has been revised in the recent past which provides better strength than the earlier version due to better homogenous mix [10], it is hoped that the new version will provide further better strength.
4. Conclusions Based on the above results and the discussions, the following conclusions are being drawn 1.
The amount of water required for hydration increases with the increase in silica fumes
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content as indicated by the increase in normal consistency 2.
Initial and final setting times decreases with the increase in silica fumes content.
3.
Specific gravity of the cementitious material decreases with the increase in silica fumes content.
4.
Soundness of cementitious material decreased slightly with the increase in silica fumes content.
5.
The mix designed by Indian Standard Method provided best results with the minimum cement content.
Acknowledgement The authors are highly thankful to ACC Limited for supplying cement, SIKA India Pvt. Limited, New Delhi for providing super-plasticizer Viscocrete, and to Elkem India Private Limited, Mumbai for providing silica fumes. It is duly acknowledged that these companies provided a great support in the implementation of this project by arranging all the materials free of cost. The authors are Volume 43
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further highly thankful to Ms Kumari Asha and Mr. Avtar Singh, M.Tech. students for their support provided during this study.
References 1.
IS: 10262-1982, Recommended Guidelines for Concrete Mix Design, Bureau of Indian Standards, New Delhi.
2.
SP: 23-1982, Handbook of Concrete Mixes, Bureau of Indian Standards, New Delhi.
3.
ACI Committee-211, Recommended Practice for Selecting Proportions for Normal and Heavy Weight Concrete, Journal of American Concrete Institute, Vol. 66, 1969, pp. 612-629.
4.
ACI Committee-211, Recommended Practice for Selecting Proportions for Normal and Heavy Weight Concrete, Journal of American Concrete Institute, Vol. 74, 1977, pp. 59-60.
5.
http://ciks.cbt.nist.gov/cost/specify.html
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6.
SHASHIPRAKASH S. G., NAGARAJ T. S., RAVIRAJ S. and YENAGI B. V., Proportioning of Fly-ash Cement Concrete Mixes, ASTM, Vol. 16, 1994, pp. 104-109.
7.
IS: 8112-1989, Specifications for High Strength Ordinary Portland Cement, Bureau of Indian Standards, New Delhi.
8.
IS: 383-1970, Specifications for Coarse and Fine Aggregates from Natural Sources of Concrete, Bureau of Indian Standards, New Delhi.
9.
IS: 10262-2009, Recommended Guidelines for Concrete Mix Design, Bureau of Indian Standards, New Delhi.
10. SINGHAL D., AGGARWAL S. K. and BRAR J. S., “Concrete Mix Design IS:10262 2009 Vs IS:10262 1982”, Proceedings of Innovations in Concrete Construction, UKIERI International Congress at NIT Jalandhar, 5-6March 2013, pp 454-460.
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DESIGN OF STRUCTURAL LIGHT WEIGHT CONCRETE USING UNCONVENTIONAL LIGHT WEIGHT AGGREGATES PART II - EXPERIMENTAL STUDY M.C. Nataraja Professor, Department of Civil Engineering, Sri Jayachamarajendra College of Engineering, Mysore-570 006, India nataraja96@yahoo.com Dr. M.C. Nataraja has authored/coauthored more than 150 publications in journals and conferences at national and international level. He has many awards and distinction to his credit which include ICI-outstanding concrete technologist award for the year 2012-13 and best technical paper awards by ICI and International council for FRC.
Summary
M.C. Sanjay Research Scholar, Department of Civil Engineering, Sri Jayachamarajendra College of Engineering, Mysore-570 006, India sanjaygowdamc@gmail.com M.C. Sanjay is pursuing his Ph. D at Sri. Jayachamarajendra College of Engineering, Mysore. His research interests include value added materials in concrete, materials characterization and structural behavior.
slag, Strength, Water absorption.
This study into the use of “unconventional light weight aggregates” for making structural light weight concrete is in two parts. The first part deals with a parametric study on the structural light weight concrete mix design as per ACI 211.2. For the parametric study two types of aggregates namely burnt coal cinder (light and heavy) and broken paver blocks from unexploited sources are used. Details of the first trial mix for two grades of concrete M20 and M30 are presented in Part I which was published in March 2013 issue of this journal. The Part II deals with the experimental studies on workability and strength properties of these concretes. Set of laboratory tests including slump, compaction factor, compressive strength, split tensile strength and flexural strength were conducted and catalogued. The water absorption test has also been conducted to study the effects of concrete in respect of durability. The investigation revealed that compressive strength obtained is higher compared to the required target values. Hence 50% and 30% of FA and GGBFS as a partial replacement to cement is tried and test results are discussed.
With increasing concern over the excessive exploitation of natural aggregates, synthetic lightweight aggregate produced from environmental waste like burnt coal cinder (light and heavy) and broken paver blocks is a viable source of structural aggregate material. When these lightweight aggregates are used, we can expect not only the reduction of selfweight and other positive effects for concretes but also the reduction of environmental pollution through recycling of waste resources. The use of lightweight aggregate will contribute significantly to sustainable development and promote the ability of future generations to meet their own needs. Essentially, lower modulus of elasticity (Ec) value for lightweight concrete results in a reduced stiffness, as defined by the product of modulus of elasticity and moment of inertia (EI). Reduced stiffness can be beneficial in cases requiring improved flexural response, such as bridges and in structures where differential settlement may occur [17].
Keywords: Light weight cinder (LWC), Heavy weight cinder (HWC), Broken paver blocks (BPB), Fly ash, Ground granulated blast furnace
Earlier researchers have investigated experimental study on workability and strength properties of light weight aggregate concrete
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1. Introduction
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(LWAC). The fracture path in light weight aggregate concrete most often has been observed through the aggregate than around [16]. The usual methods of mix design for proportioning of light weight concrete (LWC) are not suitable as the fracture would not be through the transition zone. Re-proportioning of concrete mix can be done by law of mixtures if the fracture is through the aggregate [14-15]. Chia and Zhang [4] studied the effect of superplasticizer on the rheological behavior of fresh lightweight aggregate concrete and the stability of the concrete under vibration. Their results indicated that an increase in superplasticizer content in the concrete reduced the yield stress, but did not have a significant effect on the plastic viscosity. They also showed that the segregation resistance of LWAC was decreased with increasing the dosage of superplasticizer in LWAC mixes. Wasserman et al [20] have reported that physical structure of light weight aggregate and its effect on the aggregate-matrix interfacial bond have a marked influence on the compressive strength of concrete. Lo and cui [13] have reported that porous surface improved the interfacial bond between the aggregate and cement paste by providing interlocking sites for cement paste forming a dense and uniform interfacial zone. Hence enhancing the 7 day strength to 90-92% compared to 70-80% of normal weight aggregate concrete and the wall effect does not exist on the surface of porous lightweight aggregate resulting in a better bond than the normal weight aggregate. Al-Khaiat and Haque [3] have reported that lightweight concretes with porous aggregates (high water absorption) are less sensitive to poor curing as compared to normal weight concrete especially in the early ages due to the internal water supply stored by the porous lightweight aggregate. Holm and Bremner [6] have stated that water absorbed within the LWA does not contribute to the w/c ratio however it reduces plastic shrinkage and enhances hydration through extended internal curing. Internal curing not only contributes to a more efficient hydration of the cement in a concrete mixture, but also promotes enhanced performance of SCMs such as fly ash and slag, both seen as major material sources for â&#x20AC;&#x153;greenerâ&#x20AC;? and more sustainable concretes. The principle reason for low permeability and 96â&#x20AC;&#x192; Volume 43
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excellent durability of lightweight concrete is the general absence of microcraks in the aggregatecement paste interfacial transition zone, which according to Holm and Bremner [6], is due to similarities of elastic moduli between the lightweight aggregate and the mortar fraction. Ries et al. [18] has observed that when pozzolans are added, the high quality micro structure of the contact zone of concrete containing light weight aggregate is moderately enhanced. In contrast, when high quality pozzolans are used in concrete containing normal weight aggregates this zone of weakness is significantly improved. Shannag [19] have observed that the addition of silica fume at 5 to 15% in the LWC can improve the strength properties while, replacements of 10% fly ash instead of cement in concrete can decrease strength as compared to without fly ash. From this it is very that there are distinct advantages of using LWA in concrete. Keeping this in mind and also to explain the feature of ACI code, the present work is framed. This paper presents the experimental study on workability and strength properties of structural light weight aggregate concrete produced from burnt coal cinder (light and heavy) and broken paver blocks as a coarse aggregate for M20 and M30 grades of concrete as per ACI 211.2 [1].
2. Experimental investigation The experimental part of the investigation has been planned in the following three stages. Procuring of materials and testing, casting the specimens and testing of specimens. Initially all preliminary tests on materials are conducted as per guidelines of the standards. In the present experimental study, the following materials were used: 2.1 Materials 2.1.1 Cement In this investigation, 43 Grade OPC conforming to IS: 8112 [11] with 28 day compressive strength of 52N/mm2 is used. Properties of cement are presented in Table 1. 2.1.2 Light weight coarse aggregates Three types of light weight coarse aggregate have been used. These aggregates are Light weight cinder (LWC), Heavy weight cinder (HWC) The Bridge and Structural Engineer
and Broken paver blocks (BPB). The aggregates passing through 20 mm and retained on 4.75 mm are used with 60:40 proportion which satisfies the requirements of IS: 383 [10]. Properties of aggregates are presented in Table 2. The aggregates are tested as per IS: 2386 [9]. The broken LWC, HWC, BPB aggregates can be seen in Fig 1.
LWC
HWC
BPB
Fig. 1: 20 mm down LWC, HWC, BPB coarse aggregates
2.1.3 Fine aggregate Naturally available river sand confirming to zone II as per IS: 383 [10] have been used as fine aggregate. Specific gravity, fineness modulus and water absorption of fine aggregate is 2.61, 2.85 and 0.48 % respectively.
Table 2: Properties of light weight aggregates as obtained in the laboratory Properties
Type of Aggregates LWC
HWC
BPB
2.1.4 Water
Specific gravity
1.92
2.40
2.42
Tap water is used for mixing and curing of concrete and mortar cubes.
Dry rodded density (oven dry), kg/m3
869
1039
1359
2.1.5 Superplasticiser
Dry rodded density (ssd), kg/m3
947
1087
1443
Water absorption, %
9.01
4.71
6.20
void’s, %
54.08
56.70
40.09
Impact value, %
52.60
48.18
35.81
Crushing value, %
50.96
45.59
32.34
In the present investigation, Conplast SP 430 super plasticizing admixture is used, which complies with IS: 9103:1979 [12]. Conplast SP 430 is based on sulphonated naphthalene polymers and is supplied as a brown liquid instantly dispersible in water. It has been specially formulated to give high water reduction up to 25% without loss of workability. Its specific gravity is 1.145 (at 30°C) and chloride content is Nil. Air entrainment is approximately 1%. Table 1: Physical properties of cement and recommendations for 43 grade cement Properties Standard Consistency, %
Test Results
IS:8112-1989 Requirements
31.50
No standard value
Setting time in minutes Initial setting time
120
Not less than 30
Final setting time
265
Not greater than 600
Specific gravity
3.14
-
Compressive Strength (MPa) 3 days
32.67
23
7 days
43.20
33
28 days
56.67
43
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Based on the properties of materials used, trial mix proportion for two concrete mixes of M20 and M30 grade as per ACI 11.2 [1] has been designed for certain design requirements. Trial mix details are presented in Tables 3 and 4. The concretes were named as Light weight cinder concrete (LWCC), Heavy weight cinder concrete (HWCC) and Broken paver block concrete (BPBC). Table 3: Trial mix details for target strength of M20 Yield Cement Water Sand LWA w/c (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3)
M20 LWCC
367
202
821
663
0.55
2054
HWCC
367
202
895
761
0.55
2225
BPBC
367
202
634
1010
0.55
2214
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Table 4: Trial mix details for target strength of M30 M30
Table 6: Workability in terms of slump and compacting factor for M30
Yield Cement Water Sand LWA w/c (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3)
LWCC
462
202
743
663
0.43
2071
HWCC
462
202
816
761
0.43
2242
BPBC
462
202
556
1010
0.43
2230
Casting and curing of specimens are done as per IS: 516-1959. For each mix 9 cubes of size 100 x 100 x 100 mm, cylinders of size 100 x 200 mm and flexure beams of size 100 x 100 x 500 mm are casted for various curing periods 7, 28 and 90 days. At the end of each curing period, three specimens were tested to know the compressive strength, split tensile strength and flexural strength. 2.2 Tests performed on fresh concretes The workability of the fresh concrete mixes is tested in terms of slump and compaction factor (CF) as per the IS: 1199-1959 [8]. The test results are presented in Tables 5 and 6 respectively. First trial mix may not satisfy the workability requirements. This may be due to high absorption capacity and rough surface texture of cinder aggregates. In any mix design, getting the required workability is not a problem as long as admixtures are permitted. Only thing is that suitable dosage for the given w/c is to be identified. Addition of 1% superplasticizer increases the slump of concrete as shown in Fig. 2 and 3.
M30
Type of concrete
Slump (mm)
CF
LWCC
25
0.92
HWCC
30
0.93
BPBC
100
0.98
2.3 Tests performed on hardened concretes 2.3.1 Compressive strength The concrete cubes were prepared and tested for compressive strength as per IS: 516-1959 [7]. Strength development at the age of 7, 28 and 90 days are determined and presented in Tables 8 and 9. Seven, 28 and 90 days strength results are based on average of strength of 3 samples.
Fig. 2: Effect of superplasticizer on slump of M20
Table 5: Workability in terms of slump and compacting factor for M20 Type of concrete
Slump (mm)
CF
LWCC
20
0.93
HWCC
25
0.90
BPBC
100
0.98
M20
Fig. 3: Effect of superplasticizer on slump of M30
Table 8: Average compressive strength at various ages for M20 Average compressive strength, MPa Days 7 28 90 Weight, kg 2.109 M20 LWCC 21.46 37.00 45.03 HWCC 31.60 46.30 54.33 2.312 BPBC 24.34 39.46 48.08 2.341
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Table 9: Average compressive strength at various ages for M30
Table 12: Average flexural strength at various ages for M20 Average flexure strength, MPa
Average compressive strength, MPa Days 7 28 90 Weight, kg M30 LWCC 33.26 44.80 49.33 HWCC 41.67 48.33 53.66
2.146 2.324
BPBC 35.80 45.53 51.00
2.367
2.3.2 Split tensile strength For some purposes, such as the design of highway and airfield slabs, the shear strength, resistance to cracking; the tensile strength is of interest [17]. The concrete cubes were prepared and tested for split tensile strength as per IS: 516-1959 [7]. Strength development at the age of 7, 28 and 90 days are determined and presented in Tables 10 and 11. Seven, 28 and 90 days strength results are based on average of strength of 3 samples. Table 10: Average split tensile strength at various ages for M20 Average split tensile strength, MPa
M20
Days
7
28
90
LWCC
2.41
2.91
3.35
HWCC
2.48
3.51
4.56
BPBC
2.40
3.49
4.16
Table 11: Average split tensile strength at various ages for M30 Average split tensile strength, MPa
M30
Days
7
28
90
LWCC
2.29
4.13
4.33
HWCC
3.49
4.76
4.96
BPBC
2.73
4.25
4.90
M20
Days
7
28
90
LWCC
3.28
6.06
7.14
HWCC
5.12
7.30
8.40
BPBC
4.90
7.16
8.04
3. Discussion of test results The first trial mix for M20 and M30 concretes developed compressive strength of 21.46 and 37.00 MPa for LWCC, 31.60 and 46.30 MPa for HWCC & 24.34 and 39.46 MPa for BPBC at 7 and 28 days for M20 and, 33.26 and 44.80 MPa for LWCC, 41.67 and 48.33 MPa for HWCC and 35.80 and 45.53 MPa for BPBC at 7 and 28 days of M30 respectively. It is the common opinion that concrete with light weight aggregate will have low tensile strength. This can be improved by improving the strength of concrete itself by decreasing the w/c ratio. In the present work, the light weight concrete exhibit reasonably high compressive strength with satisfactory tensile strengths as found from the Tables 8-12. These values are high compared to the required target values M20 and M30. In addition the mixes possess reasonably good splitting and flexure strengths for any application. These mixes can be used straight away, if the minimum required tensile strengths are satisfied. Otherwise, these mixes can be further economized to get the target strength. For this w/c ratio cannot be increased due to the limitation of durability. In such cases use of SCM is the top priority. Hence 50% and 30% of FA and GGBFS as a partial replacement to cement is tried.
2.3.3 Flexural strength
4. Reproportion of M20 with LWC and HWC as aggregate with 30% and 50% of FA and GGBFS
The concrete cubes were prepared and tested for flexure strength as per IS: 516-1959 [7]. Strength development at the age of 7, 28 and 90 days are determined and presented in Table 12. Seven, 28 and 90 days strength results are based on average of strength of 3 samples.
Compressive strength results are presented in Tables 13 and 14. Initially 30% of SCMs are used. For 30% replacement, the compressive strength at 28 days is slightly more than the target compressive strength and hence the mix can be further economized by increasing
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the replacement level to 50%.The variation of results can be seen in Figures 4 to 7. From these graphs the exact replacement level for any target strength can be identified. Table 13: Average compressive strength at various ages of M20 LWCC with FA and GGBFS Light weight Cinder concrete, M20 Cement Cement Cement Cement Days Cement + 50% + 50% + 30% + 30% FA SLAG FA SLAG 7
21.46
13.34
15.47
17.20
16.73
28
37.00
25.00
29.60
30.93
28.60
Fig 6: Variation of compressive strength with age for M20 HWCC containing FA
Table 14: Average compressive strength at various ages of M20 HWCC with FA and GGBFS Heavy weight cinder concrete, 20 MPa Days Cement Cement Cement Cement Cement + 50% + 50% + 30% + FA SLAG FA 30% SLAG 7
31.6
13.67
16.47
18.14
20.12
28
46.3
23.73
26.15
28.60
30.84
Fig. 7: Variation of compressive strength with age for M20 HWCC containing GGBFS
4.1 Water absorption Water absorption is an important factor due to the porous structure of the LWAC. The purpose of this test is to identify the capability of the concrete to absorb water. This property is particularly important in concrete durability. Water absorption measurements in hardened concrete were carried out according to ASTM C 642-06 [2] Standard. The initial weight (saturated specimen) is taken as M1. The final weight (oven dry) is taken as M2. % Water absorption = (M1-M2) / M2
Fig. 4: Variation of compressive strength with age for M20 LWCC containing FA
Table 15: Average water absorption at various ages of M20 LWCC with FA and GGBFS Days 50% FA Light weight cinder (LWCC)
50% 30% 30% FA GGBFS GGBFS
7
10.28
8.675
9.60
8.94
14
9.75
7.99
9.37
8.66
21
9.75
7.85
9.19
8.32
28
9.75
7.61
9.03
7.97
Fig. 5: Variation of compressive strength with age for M20 LWCC containing GGBFS
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Table 16: Average water absorption at various ages of M20 HWCC with FA and GGBFS Days 50% FA Heavy weight cinder (HWCC)
50% 30% 30% FA GGBFS GGBFS
7
8.37
6.73
7.87
7.24
14
8.17
6.50
7.62
7.07
21
8.16
6.43
7.58
6.92
28
8.16
6.02
7.39
6.73 Fig. 9: Water absorption versus age of curing for M20 HWCC containing FA and GGBFS
Fig. 8: Water absorption versus age of curing for M20 LWCC containing FA and GGBFS
Water absorption results are presented in Tables 15 and 16. Though light weight aggregate has higher absorbing capacity, the concrete counterpart has lesser permeability similar to any other normal weight concrete. In light weight aggregate concrete, the aggregates are surrounded by dense impermeable matrix due to low w/c ratio. Thus the continuous porosity in the matrix is eliminated and the water cannot reach the aggregates. As seen from the Tables 15 and 16, the absorbed water at 7 day is higher and it decreases gradually with age and at 28 day the water absorbed is significantly less. Though 50% FA and GGBFS has higher absorption the value decreases at 28 days compared to 30% FA and GGBFS. The variation of results can be seen in Fig. 8 and 9.
5. Conclusions This study discusses an experimental program on workability and strength properties of structural light weight aggregate concrete produced from burnt coal cinder (light and heavy) and broken paver blocks as a coarse aggregate for M20 and M30 grades of concrete as per ACI 211.2. The following conclusions can be drawn according to the results of this study: The Bridge and Structural Engineer
• Light weight aggregate due to their inherent porous nature will absorb large quantity of water and hence it is difficult to adjust the water content. First trial mix may not satisfy the workability requirements. Using suitable dosage of admixture for the given w/c, the required workability can be obtained. • The light weight aggregate concrete exhibit reasonably high compressive strength. These values are high compared to the required target values M20 and M30. In addition the mixes possess reasonably good splitting and flexure strengths for any application. These mixes can be used straight away, if the minimum required tensile strengths are satisfied. Otherwise, these mixes can be further economized to get the target strength. FA and GGBFS can be used to economize the mixes. These mixes will have enhanced durability properties with significant increase in strength at 90 days. • Another concern with light weight aggregate concrete is its porosity. Though light weight aggregate has higher absorbing capacity, the concrete counterpart has lesser permeability similar to any other normal weight concrete. In light weight aggregate concrete, the aggregates are surrounded by dense impermeable matrix due to low w/c ratio. Thus the continuous porosity in the matrix is eliminated and the water cannot reach the aggregates. Hence the aggregates considered namely light weight cinder; heavy weight cinder and broken paver block from unexploited sources have good potential for producing structural light weight aggregate concrete for M20 and M30 for any Volume 43
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application. Though the grade is specified based on cylindrical strength as per ACI, in the present work small cubes of size 100 mm are used for compression testing.
6. References 1.
ACI 211.2-98(1998), Standard Practice for Selecting Proportions for Structural Lightweight Concrete, American Concrete Institute, Detroit, Michigan.
2.
ASTM C 642-06, Standard test method for density, absorption, and voids in hardened concrete, West Conshohocken, PA, American Society for Testing and Materials, 2006.
3.
AL-KHAIAT H., and HAQUE M.N., “Effect of initial curing in early strength and physical properties of a lightweight concrete”, Cement and Concrete Research, Vol. 28, No 6, 1998, pp. 859-866.
4.
5. 6.
CHIA K.S., and ZHANG M.H., “Effect of Chemical admixtures on Rheological Parameters and Stability of Fresh Lightweight Aggregate Concrete”, Magazine of Concrete Research, Vol. 56, No. 8, 2004, pp. 465-473. FOSROC, Product Brochure, Conplast SP 430, India. HOLM T.A., and BREMNER T.W., “Moisture dynamics in light weight aggregate and concrete”, Expanded Shale Clay and SlateInstitute, Publication-9340, 2004.
7.
IS: 516-1959, Method of Tests for Strength of Concrete, Bureau of Indian Standard (Eleven reprint), New Delhi, April 1985.
8.
IS: 1199-1959, Methods of sampling of Analysis of Concrete, Bureau of Indian Standard (Eleven reprint), New Delhi, November, 1991.
9.
IS: 2386-1963, Method of Tests for Aggregate for Concrete, Bureau of Indian Standards, New Delhi, 1982.
10. IS: 383-1970,Specification for Coarse and Fine Aggregate from Natural Sources for Concrete, Bureau of Indian Standard, New Delhi, 1993. 102 Volume 43
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11. IS: 8112:1989,Specification for 43-grade Ordinary Portland Cement, Bureau of Indian Standards, New Delhi, 2001. 12. IS: 9103-1979, Concrete AdmixturesSpecifications, Bureau of Indian Standard, New Delhi, 1991. 13. Lo T.Y., and CUI H.Z., “Effect of porous lightweight aggregate on strength of concrete”, Materials Letters, Vol. 58, No. 6, 2004, pp. 916-919. 14. NATARAJA M.C., NAGARAJ T.S., BAVANISHANKAR S., and RAMALINGA REDDY B.M., “Proportioning cement based composites with burnt coal”, Materials and Structures, Vol. 40, No. 6,2007, pp. 543552. 15. NATARAJA M.C., and LELIN DAS., “A simplified mix proportioning for cement based composites with crushed tile waste aggregate”, Journal of Scientific and Industrial Research, India, Vol. 70, No. 5, 2011, pp. 385-390. 16. NEWMAN J., and OWEN P., Properties of lightweight concrete, Advanced Concrete Technology Set. Butterworth-Heinemann: Oxford, 2003, pp. 3-29. 17. NEVILLE A.M., Concrete Technology, Fourth edition, Pearson Education, New Delhi. 18. RIES J.P., SPECK J., and HARMON K.S., “Lightweight weight aggregate optimizes sustainability of concrete through weight reduction, internal curing, extended service life and low carbon footprint”, Concrete Sustainability Conference, 2010, National Ready Mixed Concrete Association. 19. SHANNAG M.J., “Characteristics of Lightweight Concrete Containing Mineral Admixtures”, Construction and Building Materials, Vol. 25, 2011, pp. 658-662. 20. WASSERMAN R., and BENTUR A., “Interfacial integrations in lightweight aggregate concretes and their influence on the concrete strength”, Cement and Concrete composites, Vol. 18, 1996, pp. 67-76. The Bridge and Structural Engineer
EFFECT OF CLAMPING FORCE OF RIVETS ON THE FATIGUE LIFE OF A RIVETED CONNECTION
Mohammed Adil Shaikh Design Engineer Spectrum Techno-Consultants Pvt Ltd
Navi Mumbai, India adil.kpdy@gmail.com adil.shaikh@spectrumworld.net Mohammed Adil Shaikh, born 1986, received his M.Tech in Structural Engineering from IIT Roorkee in 2013. He has been working with Spectrum TechnoConsultants Pvt. Ltd as a Design Engineer from the year 2008. His area of expertise includes the design of bridges, flyovers, metro viaducts, station buildings, industrial buildings etc.
N.M. Bhandari Emeritus Fellow Indian Institute of Technology, Roorkee, Uttarakhand, India nmbcefce@iitr.ernet.in
Pradeep Bhargava Professor Civil Engineering Indian Institute of Technology, Roorkee, Uttarakhand, India bhpdpfce@iitr.ernet.in
N.M. Bhandari, born 1946, received his Ph.D from University of Roorkee in 1983. He has teaching & research experience of 44 years at undergraduate and postgraduate level at a UOR and now IIT Roorkee. His major areas of research are: Post cracking/Non-linear analysis of reinforced concrete and masonry structures, Computer aided analysis and design of reinforced concrete buildings and bridges, Health monitoring and retrofitting of structures, etc. He has provided consultancy services on many important projects.
P. Bhargava, born 1962, received his Ph.D from the Swansea U.K. He has teaching and research experience of 27 years at undergraduate and postgraduate level at UOR, now IIT Roorkee. His major areas of research are: Finite Element Analysis of Structures, Structural Fire Engineering and Health Monitoring of Structures. He currently holds the position of Dean, Sponsored Research and Industrial Consultancy, IITR.
Synopsis This paper is concerned with developing a methodology for evaluating the fatigue life of a rivet in stringer-to-cross-girder connection of a truss bridge by finite element method in ABAQUS, incorporating the local connection geometry and estimating the fatigue life using S-N method.
Abstract Stringer-to-cross-girder connections in riveted bridges have been found to be susceptible to
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fatigue damage. Due to multiple cycles of loading on the stringers, these connections are one of the most fatigue critical connections in steel bridges. It is a well-documented fact through experiments carried out on riveted connections that the clamping force in a rivet plays an important role in its fatigue behaviour. In this paper, the global analysis of the truss bridge using beam elements is performed in SAP-2000. Modelling of riveted connections and application of clamping force of rivet in ABAQUS was also studied using some benchmark studies. A stringer-to-cross-girder
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connection was modelled using finite element method in ABAQUS by incorporating the detailed local geometry of the connection. The fatigue life of the connection was evaluated using the S-N curve and Palmgren-Miner linear damage hypothesis. The effect of clamping force of the rivet on the fatigue life of the connection was then studied. Keywords: Fatigue damage, Finite element method, Life assessment, Riveted connections, Steel bridges, S-N method.
1. Introduction The fatigue life assessments carried out in the past on steel bridges have primarily concentrated on evaluating the fatigue life of primary bridge members by modelling the bridge using beam elements. However, most of the fatigue damage that has been reported on riveted bridges has been observed on the riveted connections between primary members (Imam, et al. 2007). It is not possible to evaluate the fatigue life of connections using empirical methods. Hence there is a need to find out new strategies for carrying out this task. Previous studies have shown that finite element method can be used to carry out the detailed investigations of such riveted connections by modelling the exact geometry of the connection. Several commercially available software packages like ABAQUS, ANSYS etc. can be used for performing this task. Al-Emrani and Kliger (2003) have performed experimental investigation on the rigidity of stringer-to-floor-beam connections and analysed the same connections using finite element method. Fatigue damage susceptibility due to appreciable restraint in the connections was studied. Imam et al., (2007) have analysed a stringer-to-floor-beam connection of a plate girder bridge using ABAQUS. Having modelled the connection in true sense by modelling the rivets and connection angles, the bridge was analysed for different rivet defect scenarios like loss of rivet head, loss of clamping force in rivet, complete loss of rivet, presence of gap between rivet and rivet hole, partial loss of rivet head due to corrosion etc. Based on the analysis, several damage critical points in the rivets, connecting
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angles and girders were identified as hot-spots for cracks to originate. de Jesus et al., (2010) have analysed a similar stringer-to-floor-beam connection using ANSYS. Fatigue and fracture assessments were made. Different crack propagation scenarios were investigated.
2. Clamping Force in Riveted Connections The contraction of the plate in the longitudinal direction produces tensile force in the rivet and applies a compressive force on the outer plates. This compressive force is known as clamping force. The clamping force of a rivet is not reliable as it is difficult to control during the riveting process. Previous studied has shown that increase in the grip length of the rivets increases the clamping force (Åkesson, B. 1994). This is due to the fact that with increase in length of the rivet, during cooling the tendency to contract is greater than that of a short rivet. But this contraction is restricted by the plates and the residual force generated due to restricted contraction is transferred as a compressive force on the plates. The compressive stress generated in plates is hence known as clamping stress. The dispersion angle of the clamping force applied by the rivet head on the plate is assumed to be 30– 45° from the outermost part of the rivet head to the mid-plane of the plates (Åkesson, B. 1994). The clamping force is directly dependent on the driving temperature. A low driving temperature will lead to a low clamping force. Also, the surface treatment and surface finish is of great important to obtain good clamping force (Åkesson, B. 1994). Clamping force in a group of rivets in the same connection may vary depending on various reasons. Åkesson, B. (1994) carried out certain experiments to find out the clamping stress in the rivets extracted from old bridges which were in service for more than 50 years. Among the nine rivets tested, the maximum clamping stress was found to 189 MPa and minimum was 110 MPa. The average value was 151 MPa. This shows that, the actual clamping stress in a rivet usually lies between 100 MPa and 200 MPa. The average clamping stress in a rivet can be considered to be 150 MPa. Over a period of time, there can be
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a loss in the rivet clamping force. The causes of this loss can be corrosion, faulty workmanship, etc. A plastic deformation of a rivet also can lead to a release or in a worst case a total loss of clamping force, which drastically lowers the fatigue endurance (Imam et al., 2006).
will snap off the connection. Mostly, it is one rivet at the extreme corner that fails first. But it will lead to overloading of the other rivets present in the connection, thereby exceeding their design capacity.
3. Fatigue Critical Locations in Stringerto-Cross-Girder Connections For the same passage of train, different locations in a truss bridge may experience totally different kind of fatigue stresses. The stress range at the two locations may be same but the number of cycles of a particular stress range may be different at the two locations. The influence length of a truss member is equal to the span of the truss bridge. However, in comparison to this, the influence length of a stringer which is simply supported between cross girders, is equal to the c/c distance between the cross girders which is in fact the span of the stringer. Due to this, a stringer will be subjected to a substantially high number of stress cycles for the same train as compared to that of a truss member. The number of stress cycles for the truss member will be one whereas for the stringer, it can be the same as that of the number of axles in the vehicle crossing over the bridge (Ă&#x2026;kesson, B., 1994). The stringer-to-cross-girder connection is one of the most difficult non-moment resistant joints to design for failure. The connection is bound to have certain flexural stiffness in lieu of making the connection more shear resistant. Hence the connection will resist some longitudinal bending moment additionally. Due to this, it has been a major practice to connect only the stringer web, to the web of cross girder with the help of connecting angles. The common mode of failure of a stringer-to-cross-girder connection is the shear failure of rivets, cracking of connection angle at the angle fillet, cracking of stringers at the cope, cracks originating from rivet holes, etc. The fatigue critical locations listed above are shown in Fig. 1. Failure of rivets is one of the most critical aspects of the stringerto-cross-girder connection. After being subjected to sufficient number of repetitive cyclic loading, the rivet shank will fail in shear and the rivet head
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Fig. 1: Fatigue critical locations in a Stringer-to-cross-girder connection
The other critical failure pattern in a stringerto-cross-girder connection is the failure of connection angles. Imam et al., (2007) have shown that the angle fillet and rivet holes are the most critical locations for origination of fatigue cracks in case of connecting angles. Imam et al., (2007) have observed that with the increase in the clamping stress of rivet, the angle fillet becomes more susceptible to fatigue damage and if the clamping stress is less, the rivet and rivet holes are more prone to fatigue damage. Failure of the stringer beam itself is the third scenario in the fatigue failure of stringer-to-cross-girder connections. The cope of a stinger is a location of high stress concentration. The fatigue crack tends to grow from this location. To avoid such a scenario, curved cope shall be used instead of right angled ones. However, even in curved copes, crack is seen to develop and propagate in radial direction.
4. Analysis of Global Bridge Model The roadway bridge considered for analysis is a single lane truss bridge located in Ranikhet in Uttarakhand. The bridge is composed of two equal trusses. The structural system of each truss is shown in the Fig. 2. The cross section of the bridge including the carriageway details is shown in Fig. 3. Although it is a relatively new bridge, it was considered for analysis since the structural
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drawings were easily available. The purpose of this study being to develop a methodology for assessment of residual fatigue life of old riveted steel bridges, the methodology proposed in this study can be applied to any bridge with similar configuration henceforth. The same riveted truss bridge was previously analysed by Ghule, V.V (2012) and the fatigue life of the main truss members was assessed. It was concluded that
the fatigue life of the bridge is governed by the most critical member in the truss which turned out to be an inclined tie member U4-L5. The fatigue life of the inclined tie member was found to be 237 years. Hence it was concluded that the fatigue life of the bridge is 237 years which was way beyond the expected service life of the bridge which is 100 years.
Fig. 2: General details of the truss bridge
Fig. 3: Cross Section of the bridge
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The global model of the truss bridge was modelled in SAP-2000. The truss members, stringers, cross girders and bracings were modelled as frame elements. The slab was modelled using 200 mm thick thin shell area elements. Since the structural drawings were available, the actual member properties were assigned to each element. Dead Load (DL) of the structure was assigned using self-weight multiplier command available in SAP-2000. The Super Imposed Dead Load (SIDL) was assigned using the loading features available in the software. The loads of wearing coat, crash barrier and services were applied under SIDL case. The load of wearing coat was assigned as a surface pressure on the slab and the load due to services and crash barrier was assigned as concentrated load on the external nodes of the slab. It was observed that out of the three stringers running longitudinally
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along the bridge, the central stringer is most critical. The stringer-to-cross-girder connection in the mid-span of the bridge was considered for the detailed fatigue analysis. The values of deflection due to DL and SIDL were obtained. These displacement values will be applied in the local connection model prepared in ABAQUS to obtain the deformed shape of the connection due to DL and SIDL before the application of live load. Live load on the bridge is the major contributor towards fatigue. The vehicular load moving in and out of the bridge causes cyclic stresses in the bridge members. Therefore, for fatigue analysis it is very important to have the exact vehicle types, axle loads, axle distances and frequency of the vehicles. The details of axle loads of the trucks plying on Indian roads are available in SP-37:1991 of IRC. Four different types of trucks have been defined in the code. The actual traffic density on the bridge was not available for the present study due to which the traffic data was assumed. The average number of vehicles of each type assumed to ply over the bridge in a single day has been listed in Table 1. Table 1: Type of vehicles [IRC - SP-37:1991] Sr. No. 1 2 3 4
Type of vehicle Standard Truck Heavy Truck 35.2 Ton Truck 44 Ton Truck
No. of repetitions per day 200 150 100 50
The vehicular load is applied as a combination of two trucks of the same configuration, moving back to back with a distance of 18 m between the two vehicles. This was done to ensure maximum response. The width of the axle was considered to be 1.8 m c/c. The live load was applied using the multi-step static command available in SAP2000. A total of 80 load steps were generated for each vehicle type. An impact factor of 1.12 was considered for the analysis. For worst condition, the eccentricity of live load with respect to the central stringer was considered to be zero. This means that both the wheels in an axle of the vehicle are equidistant from the stringer.
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The values of the shear force in the stringers on either side of the cross girder at the critical connection were extracted from the analysis of global model. Out of the 80 load steps generated for each vehicle type, the load steps relevant for the critical connection were sorted. The shear force history was extracted from the analysis for each vehicle type at the end of the stringer on the left side of the connection and at the start of the stringer on the right hand side of the connection along the longitudinal axis of the bridge. The shear force history of the left and right stringer for heavy vehicle load case is shown in the figure 4. Likewise, the shear force histories under other vehicle types were also obtained.
Fig. 4: Shear force history of left and right stringer under heavy vehicle load
5. Modelling Riveted Connections in Abaqus-Cae Before advancing into modelling a riveted connection in its actual form in ABAQUS, we should understand the nuances involved in such modelling. It is important to understand the method of incorporating the clamping force of rivet and frictional contact between different components like connection angle–cross girder, connection angle–stringer, connection angle– rivet, etc. To tackle this situation, previous researchers Imam et al., (2007) and de Jesus et al., (2010) have used a simple double lap joint as a benchmark study. In the present study, the same double lap joint has been modelled and the results obtained were compared with the results of previously stated literature to validate the methodology adopted. It was also required to ensure that the finite element model of the connection prepared in ABAQUS-CAE behaves as expected. Therefore a benchmark study on Volume 43
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effect of clamping stress of rivet on rigidity of the connection was also carried out.
direction. All the three plates were restrained against translation in the transverse direction.
5.1 Riveted Double Lap Joint
To model the frictional contact between the plates, the contact properties available in ABAQUS was used. The contact properties were assigned to the model using the interaction module. The “SURFACE-TO-SURFACE” interaction was used to model the frictional contact between the plates and the rivets. Surface-to-surface contact interactions describe contact between two deformable surfaces or between a deformable surface and a rigid surface. It is required to define the master and slave surfaces for interaction. In case of the interaction between rivet and plates, rivet surface was considered to be master and the plate surface was considered to be slave. In case of interaction between the plates, the surfaces of the inner plate were considered to be master and the surfaces of the outer plates were considered to be slave. The friction models available in ABAQUS include the general form and modified versions of the classical isotropic Coulomb friction model.
A finite element model of a riveted double lap joint having a single rivet and three plates is discussed in this section. The dimensions of the lap joint have been taken to be same as that considered by Imam et al., (2007) and de Jesus et al., (2010). The details of the lap joint are shown in Fig. 5. The thickness of the top and bottom plate is 9.5 mm each and that of the middle plate is 11.1 mm. The diameter of the rivet is 25.4 mm. The width of the cap was considered to be 1.6 times the diameter of the rivet and the depth of the cap was considered to be 0.7 times the diameter of the rivet. Therefore, the width of cap was taken as 40.64 mm and the depth of the cap was taken as 17.78 mm.
Fig. 5: Dimensions of the riveted double lap joint
The assembly of the riveted lap joint model is shown in the Fig. 6. The meshing of rivet and plates was carried out using the “SWEEP” meshing technique in ABAQUS. ABAQUS uses swept meshing to mesh complex solid and surface regions. In this technique, a mesh is created on one side of the region, known as the source side and the nodes of that mesh are copied along the sweep path, one element layer at a time, until the final side, known as the target side, is reached. The finite element mesh consists of 21382 nodes and 17088 elements. C3D8 brick element was used for all the parts. Linear elastic behaviour is considered for the finite element analysis. Young’s Modulus (E) for steel was defined as 2 x 105 MPa and Poison’s ratio (ν) of 0.3 was considered. The top and bottom plates were restrained against translation in the longitudinal
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Fig. 6: Finite element model of the riveted double lap joint
A contact interaction property can be used to define tangential behavior (friction and elastic slip) and normal behavior (hard, soft, or damped contact and separation).For tangential behaviour, the “PENALTY” friction formulation was adopted. The penalty friction formulation permits some relative motion of the surfaces (an “elastic slip”) when they should be sticking. While the surfaces are sticking, the magnitude of sliding is limited to this elastic slip. ABAQUS continually adjusts the magnitude of the penalty constraint to enforce this condition. The friction coefficient between
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the plates was considered to be 0.3. The type of contact behaviour in the direction normal to the face i.e. normal behaviour can be defined by defining the proper pressure overclosure relationship. In the present study, it is important that the two surfaces do not penetrate into each other. Hence “HARD CONTACT” pressure overclosure relationship was adopted. The “HARD CONTACT” relationship minimizes the penetration of the slave surface into the master surface at the constraint locations and does not allow the transfer of tensile stress across the interface. Apart from this, the surfaces were allowed separation after contact. The clamping stress of the rivet was varied to get the response of the lap joint to the variation in clamping force of the rivet. The clamping force of the rivet was assigned on a surface at the centre of the rivet using the “BOLT LOAD” command. Bolt load is used to model tightening forces or length adjustments in bolts, rivets or fasteners. The tension in the tightened bolts can be modelled by applying a bolt load in the first step of the analysis. The load can be defined in terms of either a concentrated force or a prescribed change in length, and applied across the rivet cross-section surface that has to be specifically created while modelling the rivet. The force to be applied is obtained by multiplying the clamping stress required with the area of rivet cap in contact with the outer plate. An external load in the form of uniform surface pressure P = 30 MPa was applied on the middle plate in longitudinal direction, opposite to that of the restraints in the outer plates. Multiple models having clamping stress of 0MPa, 1 MPa, 25 MPa, 50 MPa, 75 MPa, 150 MPa and 200 MPa were analysed and the results were extracted. The results obtained for the lap joint are presented in the form of Stress Concentration Factor (SCF). “Stress Concentration Factor is defined as the ratio between the maximum stress at the surface of the rivet hole, in the loading direction, and the uniform net stress, evaluated in the plate cross section containing the rivet axis and is normal to the loading” ( Rodrigues et al., 2011). As per the above definition, the SCF is given by the following expression.
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smax SCF = –––– sn
Equation 1
Where, σmax = maximum stress at the surface of the rivet hole, σn = uniform net stress, The values of SCF were computed for different clamping stress and the results obtained were compared with the results of de Jesus et al., (2010). The comparison of the results is shown in Fig. 7.
Fig. 7: Stress Concentration Factor vs Rivet clamping stress in the middle plate for externally applied load P
5.2 Stringer-to-Cross-Girder Connection Using the modelling techniques discussed above for a riveted lap joint, a local bridge connection model is developed. The details of the truss bridge are shown in Figs. 2 and 3. The total width of the bridge is 5.4 m. The bridge has three stringers running longitudinally with c/c distance of 2 m. The cross girders are spaced at 5 m c/c. Therefore the length of each stringer is 5 m and that of the cross girder is 5.4 m. The stringer is connected to the cross girder with the help of two connection angles ISA 75 x 75 x 10. The stringer is of ISMB 500 and the cross girder is of ISWB 600. The connection between stringer and cross girder is predominantly a shear connection. The rivets here are susceptible to fail under shear. The nominal diameter of the rivet is 22 mm. The outer diameter of the cap is 35.2 mm and the depth of the rivet cap is 15.4 mm. A similar analysis of a riveted stringer-to-cross-girder connection was performed by Imam et al., (2007). Same
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approach is applied here. The full length of the stringer was considered for the analysis and was modelled. The cross girder was modelled up to the adjacent stringer. The details of the connection are shown in the Fig. 8.
node and the associated solid nodes acting as the coupling nodes. Each internal constraint distributes the forces and moments acting at its shell node as forces acting on the related set of coupling surface nodes in a self-equilibrating manner. The resulting line of constraints enforces the shell-to-solid coupling. Only displacement degrees of freedom in the solid elements and displacement and rotation degrees of freedom in the shell elements are coupled in shell-to-solid coupling. Shell-to-solid coupling does not couple other degrees of freedom such as temperature, pressure, etc.
Fig. 8: Details of the connection
Linear elastic behaviour is considered for the finite element analysis. Young’s Modulus (E) for steel was defined as 2 x 105 MPa and Poison’s ratio (ν) of 0.3 was considered. The rivets and connection angles were modelled using 8-node (C3D8) solid elements. A part of the stringer and cross girder, 500 mm on either side of the connection is modelled using the same 8-node solid elements. The rest of the stringer and cross girder is modelled using 4-node (S4) shell element. The “SHELL TO SOLID” coupling constraint available in ABAQUS was used to model interface between the shell and solid elements. Surface-based shell-to-solid coupling allows for a transition from shell element modelling to solid element modelling. It is most useful when local modelling requires the use of a full threedimensional analysis but other parts of the structure can be modelled as shells. It uses a set of internally defined distributing coupling constraints to couple the motion of a “line” of nodes along the edge of a shell model to the motion of a set of nodes on a solid surface. The coupling nodes located on a solid surface lying within a region of influence are automatically selected. Any alignment between the solid and shell element meshes is not required. For each shell node involved in the coupling, a distinct internal distributing coupling constraint is created with the shell node acting as the reference 110 Volume 43
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Fig. 9: Assembly of the stringer-to-cross-girder connection showing only the solid element mesh
The FE model of the connection is shown in Fig. 9. The entire local analysis model of the connection comprising of the full length of stringers and the cross girder is shown in the Fig. 10. A combination of “SWEEP” and “STRUCTURED” meshing technique was used to mesh the components according to the geometry to obtain a consistent mesh. The structured meshing technique generates structured meshes using simple predefined mesh topologies. The mesh of a regularly shaped region such as a square or a cube is transferred onto the geometry of the region to be meshed. The finite element mesh comprises of 117983 solid elements 9(C3D8),
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2864 shell elements (S4) and 149210 nodes. The stringers and cross girder are bound to have certain rotational fixity at the joints. Hence the boundary conditions applied to the model are restraint against translation in the three global directions at the extreme edges of the stringers and cross girder.
hence the deflection decreases. This is seen as a positive result and is comparable to the results obtained in previous studies by Imam et al., (2007) and de Jesus et al., (2010). The exact values of the deflection could not be compared with the previous studies since the dimensions were different.
Fig. 10: The finite element mesh of the entire assembly
Fig. 11: Assembly of the connection model for checking the joint rigidity
5.3 Joint Rigidity
6. Analysis of Local Connection Model
Once the modelling of the connection in ABAQUS is complete, it was necessary to check the rigidity of the joint and the behaviour of the connection under different clamping stresses. The connection model discussed in the previous section was modified to perform this check. Imam et al., (2007) have performed a similar analysis where one stringer was modelled as a cantilever and the rest of the members were considered to be rigidly fixed at the extreme ends away from the connection. Same approach was employed in the present study. The shell element portion of the left stringer was removed and the left stringer was made to behave as a free cantilever with a span of 500 mm. The assembly of the connection model is shown in Fig. 11. A vertical point load of 1 ton acting in the direction of gravity was applied at free end of the cantilever. The boundary condition at the far end of the stringers and cross girders is same as that of the complete connection model discussed in the previous section. The clamping stress in all the rivets was varied and the maximum deflection at the connection was obtained for each case of rivet clamping stress. The variation of deflection for different clamping stress is shown in Fig. 12. The results obtained show clearly that with increase in clamping force of the rivet, the rigidity of the joint increases and
The modelling of the local stringer-to-crossgirder connection in ABAQUS was discussed extensively in the previous section. A total of three load steps were created for the analysis. The first step was created for the application of rivet clamping force. The second step for the application of displacement due to dead load and super imposed dead load. The third load step for the application of fatigue load history generated due to the vehicular live load. The scope of the study was to understand the behaviour of a stringer-to-cross-girder connection due to different clamping force of the rivet and to obtain the fatigue life of the connection. The analysis was carried out for three different clamping stresses 150 MPa, 100 MPa and 50 MPa. The deflection due to dead load and super imposed dead load at the connection is applied as displacement at the connection location in ABAQUS. However while modelling in ABAQUS, the extreme ends of the cross girder and the stringers were considered to be hinged. Hence relative displacement at the joint was calculated to be input in the analysis. The displacement at the far end of the connection, i.e. at the previous cross girder was 52.04 mm whereas the displacement at the connection was 54.50 mm. Therefore the relative displacement turned out to be 2.46 mm. This displacement
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was input as a boundary condition in the dead load step in ABAQUS. The displacement was applied on a patch at the connection location.
Fig. 12: Deflection vs Rivet clamping stress for joint rigidity check
For live load, the loading history obtained for the SAP-2000 analysis was in the form of shear force in the left and right stringer. The connection between stringer and cross girder being a shear connection, the live load is transferred to the cross girder from the stringer by shear action. Therefore a patch of 180 mm x 50 mm was created at the end of each stringer. The shear force history obtained from the SAP-2000 analysis was then converted into patch load and applied on both the left and right stringers. The vehicular live load history was applied using the ‘AMPLITUDE’ command available in ABAQUS. Amplitudes allow us to specify arbitrary time or frequency variations of load, displacement, and some interaction attributes throughout a step using step time or throughout an analysis using total time. The load history was input as tabular amplitude having the same variation as that obtained from SAP-2000 analysis. The patch load to be applied was given a magnitude of 1 MPa in the gravity direction and the amplitude previously defined was assigned to this patch load. Since there were four different vehicle classes and three different clamping stresses, a total of twelve different models were created and analysed. The top most rivet on the left stringer was found to be the most critical rivet in the connection. On detailed study of the rivet in question, it was observed that maximum shear stress in the rivet occurred at the interface of the connection angle and the stringer. The critical section of the rivet and the elements considered for post-processing are highlighted in the Fig. 13. Maximum variation
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in the shear stress due to vehicular live load was observed in the second quadrant of the rivet cross-section. It is proven through previous studies that among the three stages of fatigue failure, the crack initiation phase is the most time consuming phase. Crack propagation and fracture can be sudden. An opinion was made that the stress fluctuation in the first quadrant (having same order as trigonometric quadrants) will lead to crack initiation. Hence it was decided to perform the fatigue analysis of the elements in the first quadrant and estimate the life of the rivet based on this analysis. The elements selected for fatigue analysis are highlighted in the Fig. 14. The stress history obtained for each element was then averaged out and the final stress history for the first quadrant was obtained.
Fig. 13: Critical location for maximum shear stress in the rivet
Fig. 14: Elements selected for fatigue analysis in the cross-section of the rivet (2nd quadrant)
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7. Fatigue Analysis The shear stress history at the critical section of the rivet was obtained for different vehicle classes under different clamping forces. The stress history obtained was of variable-amplitude type as expected under fatigue loading of bridges. From the obtained results, the stress range histograms as well as the number of cycles for each stress range were derived. The process of fatigue analysis and damage calculation for heavy truck loading has been discussed in detail. For other vehicle types, same approach is followed. Stress range is a function of maximum and minimum peaks in a stress history plot which mean that the intermediate values are of no importance. Neglecting the intermediate points, the stress history obtained was sorted to get the maximum and minimum peaks. The sorted shear stress history diagram under heavy truck loading for three different clamping stresses is shown in Fig. 15.
flow is the stress range and is assigned a half cycle. The half cycles of similar magnitude shall then be combined together. The working diagram of rainflow counting method for heavy truck loading under 100 MPa clamping stress is shown in Fig. 16. A rainflow starts from the top most point i.e. point A where the value of stress is zero. The rain progresses towards B and crossed point B where the value of stress is 3.81 MPa. Now as the rain flows towards D, it encounters a new flow which has started from C having the value of stress as 14.08 MPa. Since the value of point C is greater than that of point A, the flow from A terminates just after B and the flow from C moves ahead beyond D. So the first stress range is obtained by the difference of the stresses at point B and A, which turns out to be 3.81 MPa. The number of cycles is 0.5. Now, D has the maximum value on the negative side of the spectrum. So the flow which had started from C and crossed D will not encounter any other obstruction. Hence the second stress range is the difference between the stresses at D and C, which turns out to be 19.36 with half cycle. Similarly the other stress ranges are obtained. To
Fig. 15: Sorted shear stress history under heavy truck loading for different clamping stresses
To obtain the stress range and corresponding number of cycles, rainflow counting method was adopted. The methodology of using rain flow counting method is as follows. The horizontal time history shall be rotated clockwise by 90 degrees. Now, imagine the time history graph to be Japanese pagoda roof and allow the rain to flow down from the top. Count the number of half cycles. Terminate the flow of the rain when either the rain reaches the end of time history or the rain encounters a trough of greater magnitude or the rain encounters a previous flow. The stress difference between the start and end of a rain
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Fig. 16: Working diagram for rainflow counting for 100 MPa clamping stress under Heavy truck loading
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ease the calculations, the stress ranges having closer values can be grouped together and their number of cycles can be added up. If we observe the stress range histogram of 100 MPa clamping stress under heavy truck loading (Fig. 18), it can be seen that stress range 43 has 1 full cycle. This is obtained by adding two half cycles having an approximate value of 43. Similarly, for stress range 1, three half cycles have been added up to obtain 1.5 cycles. By this procedure, the rest of the stress range histogram can be worked out. Based upon the above methodology, the stress ranges under the four different vehicle classes for different clamping stresses were obtained. Stress histogram was then plotted from the stress ranges and corresponding number of cycles obtained by rain flow counting method. The number of cycles obtained thus far is for the passing of two vehicles back to back. The stress range histograms for one crossing of two heavy trucks back to back for 150 MPa, 100 MPa and 50 MPa clamping stresses is shown in Figs. 17 - 19.
is computed by using ‘Palmgren-Miner linear damage hypothesis’ which can be stated as “The damage at a certain stress range is proportional to the number of cycles”. In simple words, the ratio of number of cycles (ni) at a certain stress range (Δs) and maximum allowable number of cycles (Ni) for that particular stress range gives the damage caused to that particular stress range (Δs).
Fig. 19: Stress range histogram for 50 MPa clamping stress under heavy truck loading
Damage for a particular stress range (Dsi) n = i Equation 2 Ni Where, n i Ni
Fig. 17: Stress range histogram for 150 MPa clamping stress under heavy truck loading
Fig. 18: Stress range histogram for 100 MPa clamping stress under heavy truck loading
8. Damage Calculation The fatigue damage caused in the rivet due to single passage of two back to back vehicles 114 Volume 43
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is the number of cycles occurring at stress range magnitude, Δsi of a stress spectrum is the number of cycles corresponding to particular fatigue strength at stress range magnitude, Δsi
The value of Ni can be determined by Wöhler’s curves for the corresponding value of Δs. For a particular material, the Wöhler’s curve shall be developed by performing fatigue experiments on the material samples obtained from the structure. This will ensure that the fatigue analysis carried out is accurate and that it gauges the current condition of the structure. However if the material samples of the bridge are not available, one can use the Wöhler’s curve available in the relevant standard codes or any other data available in relevant literature, for material similar to the material of the bridge under study. BS 5400: Part 10:1980 specifies different S-N curves based on detail classes defined in the code. A riveted connection falls under detail class D. For the current study, the Wöhler’s curve was obtained using the following expression given in BS 5400: Part 10:1980 for detail class D.
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Log10N = Log10[1.53 x 1012] – 3 Log10S Equation 3
Table 3: Total damage per day for 100 MPa rivet clamping stress
The expression given in equation 3 corresponds to a probability of failure of 2.3% within the design life of the structure. The S-N curve corresponding to a 50% probability of failure within the design life of the structure for detail class D as per Annexure 1 of BS 5400: Part 10:1980 is given by the following expression.
Rivet Clamping Stress = 100 MPa
Log10N = Log10[3.99 x 1012] – 3Log10S Equation 4 The damage calculated for each type of vehicle in the above section was for the passing of two vehicles back to back. The bridge will experience a number of such repetitions again and again in a single day. This number will depend on the traffic density. The frequency of different vehicles assumed is tabulated in table 1. The damage calculated for the passing of one set of vehicles is multiplied with the number of repetitions and the total damage caused due to each vehicle per day is calculated. The total damage per day is then added together to obtain the total damage per day for all type of vehicles. The damage in the rivet for different rivet clamping stress is presented in Table 2, 3 and 4. Table 2: Total damage per day for 150 MPa rivet clamping stress Rivet Clamping Stress = 150 MPa Vehicle type
Damage No. of vehicle Damage per due to combinations day combination per day of two vehicles
Vehicle type
Damage No. of Damage per due to vehicle day combination combinations of two per day vehicles
Standard 1.0011E-08 Truck
100
1.0011E-06
Heavy Truck
4.02627E-08
75
3.0197E-06
35.2 Ton 2.42728E-08 Truck
50
1.21364E-06
44 Ton Truck
25
8.61914E-07
3.44766E-08
Total damage per day =
6.09636E-06
Table 4: Total damage per day for 50 MPa rivet clamping stress Rivet Clamping Stress = 50 MPa Vehicle type
Damage No. of vehicle Damage per due to combinations day combination per day of two vehicles
Standard 2.08569E-08 Truck
100
2.08569E-06
Heavy Truck
5.88964E-08
75
4.41723E-06
35.2 Ton 2.64453E-08 Truck
50
1.32227E-06
44 Ton Truck
25
8.83768E-07
3.53507E-08
Total damage per day =
8.70895E-06
Standard 6.37378E-09 Truck
100
6.37378E-07
9. Fatigue Life Evaluation
Heavy Truck
2.55296E-08
75
1.91472E-06
The residual fatigue life can be computed from the following equation
35.2 Ton 1.13235E-08 Truck
50
5.66175E-07
44 Ton Truck
25
2.14358E-08
Total damage per day =
5.35895E-07 3.65417E-06
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Residual fatigue life (in days) = Df - Da Dp Where,
Equation 5
Df is the fatigue damage sum at failure which is taken as unity in Palmgren-Miner linear damage hypothesis
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Da is the fatigue damage produced by past traffic. It would be zero if the S-N curves are generated for undamaged component Dp is the fatigue damage produced by traffic during 24 hours The present study has been carried out considering 50% probability S-N curve. Based on previous research and statistical study it has been indicated that if 50% probability S-N curves are used, then to assess safe working life Df should be taken as 0.3 in place of 1 (Lassen, T. and Récho, N., 2013). If the curve is assumed to be prepared by testing totally undamaged sample of material same as the one used in actual bridge, Da becomes equal to zero. Thus modified equation is n Df = ∑ i = 0.3 Ni
Equation 6
Hence residual life of members in years is determined by following expression: Residual life in years =
Df 0.3 = Dy Time in Days x 365
Equation 7
The fatigue life of rivet obtained for different clamping force of rivet is presented in the Table 5. The results tabulated in table 5 clearly show that the fatigue life of a rivet is directly proportional to the clamping stress. As the clamping stress is reduced, the fatigue life also decreases. The failure of first rivet in the connection was considered to be end of life of the connection because failure of one rivet will lead to overloading on other rivets of the connection which will lead to total failure of the connection. Table 5: Fatigue life in years for different clamping stress Rivet Clamping Stress
Total damage in one day TD
Total damage in one year TDy
Fatigue life
150 MPa
3.65417E-06 1.3338E-03 224.9 Years
100 MPa
6.09636E-06 2.2252E-03 134.8 Years
50 MPa
8.70895E-06 3.1788E-03 94.37 Years
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10. Conclusions Stress range concept is a very simple and useful method to predict the residual life of steel bridges. Residual life assessment of steel bridges is done using conventional method of S-N curves. The global model of the truss bridge was analysed in SAP-2000 and the load history due to different vehicle combinations was obtained. A local model of the riveted connection was modelled in ABAQUS. Load history obtained from SAP-2000 was applied as an external load and analysis was performed for different clamping force in the rivets. The top most rivet of the stringer was found to be the most critical rivet. The effect on fatigue life of the rivet due to variation in clamping force was studied. It was observed that the fatigue life of the rivet decreases with decrease in the clamping force. It also leads to loss in fatigue life of the connection. This behaviour of the connection can be attributed to the fact that, under high clamping force, the friction between the plate’s increases and the load is actually transferred through friction between the plates. Due to partial loss in clamping force, the plates get loosened and there is partial loss of frictional contact. In this case, the load is transferred primarily through shear than friction, due to which more damage in the rivet is caused. There is a drastic reduction in the fatigue life when the clamping stress reduces to 100 MPa from 150 MPa. It further reduces when the clamping stress is 50 MPa. This shows the importance of clamping force in riveted connections. Since roadway bridges are subjected to less stress cycles their fatigue life is generally more as compared to railway bridges. Hence railway bridges are more critical for fatigue failure.
References 1.
ABAQUS Version 6.8 (2008), Dassault Systems Simulia Corp, United States.
2.
“Assessment of Residual life of Ganga Bridge No. 110 Dn. (Near Kanpur) Lucknow Division Northern Railway” Report no. - BS70, December 2004, RDSO Lucknow.
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3.
Åkesson, B. “Fatigue life of riveted railway bridges”, PhD Dissertation, 1994, Chalmers University of Technology, Sweden.
4.
Al-Emrani, M. and Kliger, R. “FE analysis of stringer-to-floor-beam connections in riveted railway bridges” Journal of Constructional Steel Research, 2003, pp. 803-818.
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Banerji, P. and Chikermane, S. “Structural health monitoring of a steel railway bridge for increased axle loads”, IABSE Structural Engineering International, February 2011, pp. 201–216. Chaminda, S.S., Ogha, M., Dissanayake, R. and Taniwaki, K. “Different approaches for remaining life estimation of critical members in railwaqy bridges” Steel Structures, July 2007, pp. 263-276. de Jesus, A.M.P. and Pereira, R.M.G. “FEM analysis of riveted connections aiming fatigue and fracture assessments”, Iberian Conference on Fracture and Structural Integrity, March 2010, Porto, Potrugal. Dwivedi, A. K., Bhargava, P. and Bhandari, N.M. “Thermal Gradients in Concrete Box Girder bridges” The Bridge and Structural Engineer, ING-IABSE, Vol. 34, No. 1, March 2004, pp. 53-72. Dwivedi, A. K., Bhargava, P. and Bhandari, N.M. “Thermal Stressess in Concrete Box Girder bridges” The Bridge and Structural Engineer, ING-IABSE, Vol. 34, No. 1, Dec. 2004, pp 31-56.
10. Fisher, J.W., Struik, J.H.A., and Kulak, G.L. “Guide to design criteria for bolted and riveted joints “ John Wiley & Sons, New York, NY, 1974. 11. Ghule, V.V. “Health and residual life assessment of steel bridges “, M.Tech Dissertation, 2012, Indian Institute of Technology, Roorkee, India. 12. Haghani, R., Al-Emrani, M. and Heshmati, M. “Fatigue-prone details in steel bridges” Buildings, 2, 2012, pp. 456-476. 13. Helmerich, R., Kuhn, B. and Nussbaumerx,
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A. “Assessment of existing steel structures. A guideline for estimation of the remaining fatigue life” Structure and Infrastructure Engineering, Vol. 3, No. 3, September 2007, pp. 245 – 255. 14. Imam, B.M., Righiniotis, T.D. and Chryssanthopoulos, M.K. “Fatigue assessment of riveted railway bridges” Steel Structures, 5, 2005, pp. 486-494. 15. Imam, B.M., Righiniotis, T.D. and Chryssanthopoulos, M.K. “Fatigue reliability of riveted connections in railway bridges” 3rd International ASRANet Colloquium, July 2006, Glasgow, U.K. 16. Imam, B.M., Righiniotis, T.D. and Chryssanthopoulos, M.K. “Numerical modelling of riveted railway bridge connections for fatigue evaluation” Engineering Structures, 2007, pp. 3071– 3081. 17. Imam, B.M. and Righiniotis, T.D. “Fatigue evaluation of riveted railway bridges through global and local analysis” Journal of Constructional Steel Research, 2010, pp. 1411–1421. 18. Imam, B.M., Righiniotis, T.D. and Chryssanthopoulos, M.K. “ Performance of steel structures under fatigue cyclic loading” Journal of Civil Engineering and Architecture, Vol. 5, No. 8, March 2011, pp. 265-272. 19. IRC:24-2001 “Standard specifications and code of practice for road bridges - Section: V – Steel road bridges” The Indian Road Congress, New Delhi, India. 20. IRC:6-2000 “Standard specifications and code of practice for road bridges - Section: II - Loads and stresses” The Indian Road Congress, New Delhi, India. 21. IRC:SP-37-1991 “Guidelines for evaluation of load carrying capacity of bridges” The Indian Road Congress, New Delhi, India. 22. Kuehn, B., Lukić, M., Nussbaumer, A., Guenther, H. P., Helmerich, R., Herion, S., Kolstein, M.H., Walbridge, S., Androic, B.,
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Dijkstra, o., and Bucak, Ö. “Assessment of existing steel structures: recommendations for estimation of remaining fatigue life” JRC Scientific and Technical Reports, 2008. 23. Kumar, P. and Bhandari, N.M. “Mechanism Based Assessment of Masonry Arch Bridges” IABSE quarterly publication Structural Engineering International, Zurich. Vol.16, No. 3, August 2006, pp. 226-234. 24. Kumar, P. and Bhandari, N.M. “Non Linear Finite Element Analysis of Masonry Arches” –Structural Engineering International, Journal of IABSE,SEI Volume 15, Number 3, August 2005, pp. 166-174. 25. Larsson, T. “Fatigue assessment of riveted bridges” PhD Dissertation, 2009, Luleå University of Technology, Sweden. 26. Lassen, T. and Récho, N. “Fatigue Life Analyses of Welded Structures: Flaws” John Wiley & Sons, 2013 27. Oka, V.G, Hopwood, T. and Harik. I.E. “Fatigue analysis of steel bridges using a portable microcomputer based strain gage
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system” Computers & Structures, Vol. 31, No. 2, 1989, pp. 151-186. 28. Pipinato, A., Pallegrino, C. and Modena. C. “Fatigue assessment of highway steel bridges in presence of seismic loading” Engineering Structures 33 (2011) - pp. 202–209. 29. Pipinato, A., Pallegrino, C., Bursi, O.S. and Modena. C. “High-cycle fatigue behavior of riveted connections for railway metal bridges” Journal of Constructional Steel Research, 2009, pp. 2167-2175. 30. Rodrigues, M.P.G., de Jesus, A.M.P. and Silva, A.L.L. “Comparison between alternative fe modelling strategies for riveted connections concerning fatigue assessments” Revista da Associação Portuguesa de Análise Experimental de Tensões, Vol. 19, 2011, pp. 19-31 31. Vermes, W.J. “Design and Performance of Riveted Bridge Connections” International Bridge Conference, June 2009, Pittsburgh, USA.
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About ING - IABSE
About IABSE
The Indian National Group (ING) of the IABSE was set up in May 1957 under the patronage of the Government of India, Ministry of Road Transport and Highways and State Governments, as a non-official learned body with the participation of engineers and professional from both the public and private sectors as well as from various research and academic institutions. The Group organizes lectures, conferences, colloquia and workshops on topical subjects and publishes a quarterly technical journal “The Bridge and Structural Engineer.”
The International Association for Bridge and Structural Engineering (IABSE) was founded in 1929. Today, IABSE has about 4,000 members in over 100 countries. The mission of IABSE is to promote the exchange of knowledge and to advance the practice of structural and bridge engineering worldwide in the service of the profession and society. To accomplish the mission, IABSE organises conferences and publishes the quarterly journal “Structural Engineering International” (SEI), as well as reports and other monographs. IABSE also presents annual awards for outstanding achievements in research and practice that advance the profession of structural engineering. IABSE deals with all kinds of structures, materials and aspects of structural engineering.
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Indian National Group of the IABSE Office Bearers and Managing Committee members 2013 Chairman 1.
Shri VL Patankar, Additional Director General, Ministry of Road Transport and Highways Vice-Chairmen
2.
Shri BN Singh, Member (Projects), National Highways Authority of India
3.
Shri Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt Ltd Past Chairmen
4.
Shri C Kandasamy, Director General (Road Development) & Special Secretary, Ministry of Road Transport and Highways
5.
Shri AV Sinha, Former Director General (Road Development) & Special Secretary
6.
Shri RP Indoria, Former Director General (Road Development) & Special Secretary Honorary Treasurer
7.
The Director General (Road Development) & Special Secretary Honorary Members
Past Member of the Executive Committee and Technical Committee of IABSE 12. Prof SS Chakraborty, Past Vice-President, IABSE & Chairman, Consulting Engineering Services (India) Pvt Ltd 13. Shri CR Alimchandani, Past Member, Technical Committee, IABSE & Chairman and Managing Director, STUP Consultants P Ltd 14. Dr BC Roy, Vice President, IABSE & Past Member, Technical Committee, IABSE, Senior Executive Director, JACOBS-CES Honorary Secretary 15. Shri RK Pandey, Secretary, ING-IABSE & Chief Engineer (Planning), Ministry of Road Transport and Highways Members of the Executive Committee 16. Shri VK Gupta, Director General, Central Public Works Department 17. Shri AD Narain, Former Director General (Road Development) & Addl. Secretary 18. Shri AK Banerjee, (Technical), NHAI
Former
Member
8.
Shri Ninan Koshi, Former Director General (Road Development) & Addl. Secretary
19. Shri G Sharan, Former Director General (Road Development) & Special Secretary
9.
Prof SS Chakraborty, Past Vice-President, IABSE & Chairman, Consulting Engineering Services (India) Pvt Ltd
20. Shri SK Puri, Former Director General (Road Development) & Special Secretary
Persons represented ING on the Executive Committee and Technical Committee of the IABSE
21. Dr Nirmalya Bandyopadhyay, Director, STUP Consultants Pvt Ltd Secretariat
10. Dr BC Roy, Vice President, IABSE & Past Member, Technical Committee, IABSE, Senior Executive Director, JACOBS-CES
22. Shri RK Pandey, Secretary, ING-IABSE & Chief Engineer (Planning), Ministry of Road Transport and Highways
11. Dr Harshavardhan Subbarao, Member, Technical Committee of IABSE & Chairman and Managing Director, Construma Consultancy Pvt Ltd
23. Shri Ashish Asati, Director, Indian National Group of the IABSE
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24. Shri KB Sharma, Under Secretary, Indian National Group of the IABSE
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Members of the Managing Committee 2013 Rule-9 (a): A representative of the Union Ministry of Road Transport and Highways 1.
Shri VL Patankar, Additional Director General, Ministry of Road Transport & Highways
Rule-9 (b): A representative each of the Union Ministries / Central Government Departments making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time 2.
CPWD - nomination awaited
3.
Shri BN Singh, Member (Projects), National Highways Authority of India
4.
Ministry of Railways - nomination awaited
Rule-9 (c): A representative each of the State Public Works Departments/ Union Territories making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time 5.
Shri G Jagannatha Rao, Chief Engineer, R&B (PPP), Govt of Andhra Pradesh
6.
Govt of Arunachal Pradesh - nomination awaited
7.
Shri AC Bordoloi, Commissioner & Special Secretary, Govt of Assam, Public Works
8.
Shri Bablu Kumar Deputy Director (Training), Training and Research Institute, Govt of Bihar
9.
Govt of Chattisgarh - nomination awaited
10. Shri Dinesh Kumar, Chief Engineer, Project Zone, M-I, Govt of Delhi, Public Works Department
11. Shri UP Parsekar, Chief Engineer (NH, R&B) Govt of Goa, Public Works Department 12. Govt of Gujarat - nomination awaited 13. Shri Mahesh Kumar, Engineer-in-Chief, Govt of Haryana, Public Works (Buildings & Roads), Department 14. Govt of Himachal Pradesh - nomination awaited 15. Govt of Jammu & Kashmir - nomination awaited 16. Govt of Jharkhand - nomination awaited 17. Shri AN Thyagaraj, Chief Engineer, Communication & Buildings (South), Govt of Karnataka 18. Govt of Kerala - nomination awaited 19. Shri BP Patel, Chief Engineer (Bridges), Govt of Madhya Pradesh, Public Works Department 20. Shri SB Tamsekar, Chief MMRDA, Govt of Maharashtra
Engineer,
21. Shri Ram Muivah, Principal Secretary (Works), Govt of Manipur 22. Shri Lambok Passah, Chief Engineer, PWD (Roads), Govt of Meghalaya, (R&B) 23. Shri John Rammawia, Chief Engineer (Roads), Govt of Mizoram, Public Works Department 24. Govt of Nagaland - nomination awaited 25. Govt of Orissa - nomination awaited 26. Govt of Punjab - nomination awaited 27. Govt of Rajasthan - nomination awaited 28. Govt of Sikkim - nomination awaited 29. Govt of Tamil Nadu - nomination awaited 30. Govt of Tripura - nomination awaited 31. Govt of Uttar Pradesh - nomination awaited 32. Govt of Uttarakhand - nomination awaited
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33. Shri Partha Gangopadhyay, Suptd Engineer, Survey and Design Circle, Govt of West Bengal, PW & PW (Roads) 34. Shri SK Chadha, Chief Engineer, Engineering Department, UT Chandigarh Administration Rule-9 (d): A representative each of the Collective Members making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time 35. Major VC Verma, Director (Mktg), Oriental Structural Engineers Pvt Ltd Rule-9 (e): Ten representatives of Individual and Collective Members 36. Shri AK Banerjee, (Technical), NHAI
Former
46. Shri MV Jatkar, Executive (Technical), Gammon India Ltd
Director
47. Shri M Thirpath Reddy, Director, SEW Constructions Ltd 48. Shri T Srinivasan, Vice President & Head – Ports, Tunnels & Special Bridges, Larsen & Toubro Ltd 49. vacant Rule-9 (g): Two representatives of the Engineering Colleges / Technical Institutes / Universities / Research Institutes 50. Dr K Ramanjanelu, Structural Engineering Research Centre, Madras 51. Prof RR Sandhwar, Cambridge Institute of Technology, Ranchi
Member
37. Dr VK Yadav, VSM, Addl Director General, Border Roads Organisation 38. Shri SK Puri, Former Director General (Road Development) & Special Secretary 39. Dr CK Singh, Former Engineer-in-Chiefcum-Addl.Commissioner-cum-Special Secretary
Rule-9 (h): Four representatives of Consulting Engineering Firms 52. Dr Raghuram Ekambaram, Sr. Associate Director, Jacobs-cEs 53. Shri AD Narain, President, ICT Pvt Ltd 54. Dr N Bandyopadhyay, Director, STUP Consultants Pvt Ltd 55. Dr GP Saha, Executive Director, Construma Consultancy Pvt Ltd
40. Shri RV Chakrapani, Chief Consultant, Aarvee Associates Architects Engineers & Consultants Pvt Ltd
Rule-9 (i): Honorary Treasurer of the Indian National Group of the IABSE
41. Shri G Sharan, Former Director General (Road Development) & Special Secretary
56. The Director General (Road Development) & Special Secretary to the Govt of India
42. Shri Amitabha Ghoshal, Vice President & Director, STUP Consultants P Ltd 43. Shri Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt Ltd 44. Shri RK Dhiman, VSM, Director (Works & Budget), Border Roads Organisation 45. Shri Rakesh Kapoor, General Manager, Holtech Consulting Pvt Ltd Rule-9 (f): Four representatives of Bridge and Structural Engineering Firms The Bridge and Structural Engineer
Rule-9 (j): Past-Chairman of the Society, for a period of three years, after they vacate their Chairmanship 57. Shri AV Sinha 58. Shri RP Indoria 59. Shri C Kandasamy Rule-9 (k): Secretary of the Indian National Group of the IABSE 60. Shri RK Pandey Volume 43
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December 2013 123
Rule-9 (l): Persons who have been awarded Honorary Membership of the Parent Body 61. Shri Ninan Koshi 62. Prof SS Chakraborty
64. Dr Harshavardhan Subbarao Rule-9 (n): Past Members of the Executive Committee and Technical Committee of the IABSE 65. Prof SS Chakraborty
Rule-9 (m): Persons represented ING on the Executive Committee and Technical Committee of the IABSE
66. Shri CR Alimchandani 67. Dr BC Roy
63. Dr BC Roy
CONSULTING ENGINEERS ASSOCIATES (Approved by Govt. of India MORT&H) All Civil engineering consultancy services under One Roof at Chandigarh
Project Management(PMC), Supervision & Q.C. Consultant Design / DPR of Roads & Bridges Pavement evaluation & Traffic Studies Total Station, GPS Survey & GIS Services Pre/Post - Tendering Services
Material Testing Lab. , Geotechnical investigations and Environment Impact Studies Practical training on Highways & Bridges and live demonstration of tests in Lab.
Civil Engineers Academy & Research Centre
“A Society registered for practical training and skill development for Civil Engineers and Technicians”
Reg. Office CEA&RC Institute SCO 51, Swastik Vihar MDC, Sec 5, Panchkula (Haryana). Plot No. 40, Ind. Area Phase 1, Panchkula (Haryana.) Phone : 0172-2555529,6545529(O), +91-9888498951(M) Phone: 0172-2581140 Website: www.consultingengineers.in Email: ceapkl@gmail.com
124 Volume 43
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"
INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION FOR BRIDGE AND STRUCTURAL ENGINEERING Form A. Application for Membership The undersigned* public authority* Association* Firm* Organisation* desire to join the Indian National Group of the International Association for Bridge and Structural Engineering as an Individual Member/Collective Member. ** We shall be represented by…………………..……………………….….. Name and Designation…………………………………………..……….….. Profession……………………………………………………………………... Organisation………………………………………………………………..…. Address………………………………………………………………………... ………………………………………………………………………………….. Place……..……………………Pin……………….Date……………………... STD Code ……..Phone (O)….……….Fax.….…….…Phone (R)..……..… E-mail………………………………………Mobile….……………………….. * **
Cross out the words not applicable Applicable to Collective Members only Signature Particulars
Date of birth………………………………………………………………...….. Academic qualifications……………………………………………..…...…… Brief details of professional carrier with dates………………..……………. Research experience and Papers, if any…………………………………… Membership of other Scientific for Technical Institutions…..……………... ……………….………………………………………………….……………….
"
Interests-steel work or reinforced concrete, etc…………….……………… From my personal knowledge of the applicant and in consideration of his qualifications as stated above, I recommended him as being in every respect a fit and proper person to be admitted to the Indian National Group of International Association for Bridge and Structural Engineering.
Applicable in case of Individual Members only
Signature Supporting Individual Member (Roll No ) C:\Documents and Settings\a\Desktop\MembershipForm.doc
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INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION FOR BRIDGE AND STRUCTURAL ENGINEERING No.ING/IABSEForm C-Declaration on Election
I………….……..……………………………………… have been elected as an …………………………….Member of the ING/IABSE agree to be governed by the Rules and Regulations of the said Society, as they now stand or as they may hereafter be altered or added to according to law and I undertake to promote the objectivities and interests of the Society so far as lies in my power provided that whenever I shall signify in writing eight months in advance to the Secretary that I am desirous of withdrawing from the Society, I shall, after the payment of any arrears which may be due from me, be free from the above mentioned obligations.
Witness my hand this………………day of………………..2014
Signature Also please furnish the Information overleaf.
C:\Documents and Settings\a\Desktop\MembershipForm.doc
126 Volume 43
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DETAILS OF ENTRANCE FEE AND SUBSCRIPTION I
Individual Membership* with Publications
Rs
Entrance Fee
100/-
i)
Less than 35 years
4000/-
ii)
Between 35 to 65 years
8000/-
iii)
Above 65 years
5500/-
II
Collective Membership** Entrance Fee
1000/-
Subscription with Publications
40,000/-
(Demand draft/Pay Order etc may be drawn in favour of “The Secretary, Indian National Group of IABSE, New Delhi”
* **
For qualified personnel For Government/Departments, Local Authorities, Firms etc.
Applications form duly filled in alongwith fees may be sent at the following address: The Secretary Indian National Group of the IABSE IDA Building, (G/F), Room No.12 Jamnagar House, Shahjahan Road New Delhi-110 011, INDIA Phone:011-2378 2923, 2338 6724 Fax: 011-2338 8132 E-mail: ingiabse@bol.net.in
C:\Documents and Settings\a\Desktop\MembershipForm.doc
The Bridge and Structural Engineer
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December 2013 127
With Best Compliments from
MANUFACTURER OF BRIDGE BEARINGS, EXPANSION JOINTS, STU,& STEEL GIRDER FABRICATION EXPERTISE IN REHABILITATION, P. T. SLABS, POST TENSIONING, ROCK ANCHORS & REBAR COUPLERS
SANFIELD is proud to become a Group Company of MAURER SOHNE WORLD LEADERS IN EXPANSION JOINTS, BEARINGS AND STRUCTURAL PROTECTION SYSTEMS SINCE 1876
13-A, SECTOR D, INDUSTRIAL AREA, GOVINDPURA, BHOPAL 462023, INDIA Ph: +91 755 4233535 (30 Lines) Fax: 2602663/4270730 E-mail: sanfield@sanfieldindia.in; sanfieldindia@gmail.com Web-site: www.sanfieldindia.in
128 Volume 43
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FRANKFURTER RING 193, 80807 MUNICH, GERMANY Ph: +49 89 32394-0 Fax: +49 89 32394-306 e-mail: ba@maurer-soehne.de Web-site: www.maurer-soehne.de
The Bridge and Structural Engineer