The Bridge and Structural Engineer

B&SE_Volume 46_Number 1_March 2016

The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION FOR BRIDGE & STRUCTURAL ENGINEERING

Enabling works, Formworks & Scaffolding Systems

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Volume 46 Number 1 March 2016  i

ii  Volume 46

Number 1 March 2016

The Bridge and Structural Engineer

The Bridge & Structural Engineer

Indian National Group of the International Association for Bridge and Structural Engineering ING - IABSE

Contents :

Volume 46, Number 1 : March 2016

Editorial • From the Desk of Chairman, Editorial Board : Mr. Alok Bhowmick vi • From the Desk of Guest Editor : Mr. Mohan Jatkar viii

Highlights of ING-IABSE Event • Highlights of the ING-IABSE Workshop on “Bridge Bearings, Expansion Joints & Seismic Devices” held at Bhopal on 15th & 16th January 2016

xi

Special Topic : Enabling Works, Formworks & Scaffdding Systems

2. ASCE/SEI 37-14 Design Loads on Structures during Construction Standard Robert T. Ratay, John F. Duntemann

6

3. Slipform System for Construction of Highrise Hollow Concrete Structures 11 Vijay M. Dharap, S. Abhilash Kumar 4. The Right Climbing System for every Highrise Project 21 Thorsten Kirchweger 5. Construction Design of Signature Bridge in Delhi Mario DE Miranda

26

6. Construction of 120m Span Arch Bridge using Cantilever Form Traveller Alok Panday

36

7. Temporary Works Paves Way to Permanent Profit 41 Raja Rajan. K. 8. Enabling Works for India's First Double Decker Bridge "Santacruz Chembur Link Road" – A Case Study Rakesh Kumar Mehta 9. Launching Systems for Precast Segmental Bridges Vinay Gupta

50

Contents

1. Challenges in Management of Temporary Works 1 Mohan V. Jatkar

62

Research Papers 1. Seismic Analysis of Well Foundation by Forced and Displacement Method RNP Singh, Hemant Kumar Vinayak

66

2. Steel Fibre Reinforced High Performance Concrete Exterior Beam Column Slab Joints under Reverse Cyclic Loading Ganesan N., Indira P.V., Nidhi M.

74

3. Seismic Behaviour of Concrete Barrel shell Structures under Static & Dynamic Loads Raana Pathak, Rakesh Khare

81

The Bridge and Structural Engineer

Volume 46 Number 1 March 2016 iii

The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING

June 2016 Issue will be a Special Issue with focus on TALL STRUCTURES

(Tall Buildings, Chimneys, Silos, TV Towers, Cooling Towers, Transmission Towers)

SALIENT TOPICS TO BE COVERED ARE : 1.

2.

3.

4.

5.

6.

Structural System & Forms Green Building & Smart Cities Wind induced response & EQ resistant design of tall structures Critical Appraisal of Existing Codes & Standards (Indian as well as International) New Construction Materials and Techniques.

Case studies for Design, Construction and Rehabilitation

The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING

September 2016 Issue of the Journal will be a Special Issue with focus on STEEL & COMPOSITE BRIDGES SALIENT Topics to be covered are : 1. Design Codes & Practices : National and International – A critical appraisal.

2. Analysis, Design and Construction practices in Steel as well as Composite Bridges.

3. Fabrication & Erection aspects for Steel Bridges 4. Repair and Rehabilitation Practices 5. Maintenance of Steel / Steel-Composite Bridges 6. Case Studies.

Those interested to contribute Technical Papers on above themes shall submit the abstract by 31st July 2016 and full paper latest by 30th September 2016 in a prescribed format, at email id : ingiabse@bol.net.in .

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Number 1 March 2016

The Bridge and Structural Engineer

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.

Disclaimer :

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.

Director, STUP Consultants Pvt. Ltd., 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 & MD, Construma Consultancy Pvt. Ltd., Mumbai Nirmalya Bandyopadhyay, Jose Kurian, Former Chief Engineer, DTTDC Ltd., New Delhi S C Mehrotra, Chief Executive, Mehro Consultants, 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

Front Cover :

S S Chakraborty, Former Chairman, CES (I ) Pvt. Ltd., New Delhi

Top left : Dome construction with one sided climbing formwork at ISKON temple, Mayapur, W.B.

B C Roy, Former Senior Executive Director, JACOBS-CES, Gurgaon

Top right: Temporary support system for pylon, Signature Bridge at Delhi Middle left: Slipform system for chimney shell construction Bottom left: Erection of steel girders for ROB portion, Santacruz Chembur Link Road, Mumbai Bottom right: Construction of arch bridge with temporary stay cable system at Parvati Bridge near Kullu, H.P.

Published : Quarterly : March, June, September and December Publisher : ING-IABSE C/o Secretary, Indian National Group of the IABSE IDA Building, Ground Floor (Room Nos. 11 and 12) Jamnagar House, Shahjahan Road New Delhi-110011, India Phone : 91+011+23388132 and 91+011+23386724 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 – 110011.

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.

Journal of the Indian National Group of the International Association for Bridge & Structural Engineering

March 2016

The Bridge & Structural Engineer, March 2016

The Bridge and Structural Engineer

• Price: ` 500

The Bridge and Structural Engineer

Volume 46 Number 1 March 2016 v

From the Desk of Chairman, Editorial Board

As you may be aware, this journal ‘The Bridge & Structural Engineer’ has gained immense popularity in recent times. Members look forward to getting the latest issue in hand.

Many non-members have also shown interest in getting copies of this journal. We, the members of the Editorial Board, strongly believe that these developments motivate current as well as future authors to publish more and more articles of their research and construction projects in ‘The Bridge & Structural Engineer’. This issue of the journal is focused on the theme of “Enabling works, Formworks & Scaffolding Systems".

Enabling works, formworks and scaffolding systems are integral part of any construction activity. Formworks and scaffolding also contributes to a substantial share of cost in concrete constructions. However, it is often seen that design and erection of these structures do not get the desired attention by Clients as well as Consultants. This is amply demonstrated by global statistics, which reveals that structural failures during construction stage is several times more than the failure during service stage. Analysis of catastrophic events of the past indicates for temporary works, there is a steady increase in the events in recent past. This

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is primarily due to following : a. Structures and buildings are becoming more and more complex in geometry and difficult to construct. b. The generation, who were conversant with hand calculations and who have the pulse of the structure, are either retiring or have already retired. The new generation of engineers are more computer savvy but have less feel for structure. Over dependence on computers and changes in industry practice have led to the loss of fundamental understanding of engineering behaviour. The experienced field engineers and general foreman at site who would often have the pulse of the structure even if they have not designed the structure, and would know there was a problem just by looking at it, are hardly available now. c. Though there are 15 lakh engineers graduating every year in India, only 20% are employable. There is an acute shortage of engineers at the front line with extensive broad experience. d. The change in codes and standards with more complex analysis, is giving rise to increased risk of errors in design.

The Bridge and Structural Engineer

Considering the above, the editorial board thought it prudent to bring out this special issue with the objective of improving the present safety standards in temporary works and familiarising and enriching the construction industry in this important but neglected field.

Our Guest Editor for this issue is Mr M V Jatkar, who is a towering personality in the industry and currently holding the position of Executive Director (Technical) in Gammon India Ltd. overseeing the functions of construction planning, HSE and Quality Management.

The Bridge and Structural Engineer

There could not have been a better choice for Guest Editor for us & we are thankful to Mr. M.V. Jatkar for having accepted our proposal to Guest edit this issue of the journal.

Happy Reading !

(ALOK BHOWMICK)

Volume 46 Number 1 March 2016  vii

From the Desk of Guest Editor

At the outset I thank the Editorial Board of INGIABSE for inviting me to serve as Guest Editor for this special issue on “Temporary Structures”. This is a much neglected and misunderstood subject which needs attention of all engineers: academicians, project authorities, practising engineers from designers to field engineers & system formwork providers.

Temporary structures cover a very wide range of structures in construction which cater to the need for providing support till the permanent structure becomes self supporting, provides access to work fronts, etc. As there can be wide variation in the sequence, actual loading, etc. resulting from the actual activities necessary for a project site, the designer has to derive the design basis itself by understanding the planned construction process thoroghly. This itself is a big challenge for the designer as there can be frequent changes in planning due to a variety of unforseen circumstances and constraints.

Proper implementation of the temporary structure design at site is a bigger challenge considering the pressure of time, cost, unskilled manpower, etc. Moreover it involves a number of agencies right from designers, fabricators, site supervisors, specialised agencies supplying system formwork and so on. Coordination with so many agencies requires a Temporary Works Coordinator for major sites for proper communication. Unfortunately there is an accute shortage of professionals who will

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be able to shoulder this onerous responsibility. A lot needs to be done right from introducing this subject in degree courses to training professionals. Merely mentioning this requirement in codes or contracts will not help.

The papers received for this special issue cover a various aspects of temporary structures through general papers covering design & construction issues, specialised structures for specific applications and some case studies. In the first paper, I have attempted to initiate the topic through an overview of various aspects of Temporary Structures.

Dr. Robert T. Ratay & Mr. John F. Duntemann, renowned experts in this field, have presented a paper on ASCE/SEI 37-14 “Design Loads on Structures during Construction” elaborating the design loads, load combinations and safety factors to be used in the analysis and design of structures during transient stages of construction, as well as of temporary structures used in construction operations.

Mr. V.M. Dharap & Mr. Abhilash Kumar in their paper “Slipform system for construction of high rise hollow concrete structures” have explained the principles and various components of slip forms.

They have explained all aspects of this technique covering construction, saftety, concrete mix requirements, etc. through some case studies.

Mr. Thorsten KIRCHWEGER has contributed a paper on “The right climbing system for every

The Bridge and Structural Engineer

high rise project”. He describes various climbing systems for high rise buildings and stresses the need to involve specialist formwork supplier right from the initial planning stage of the project.

Mr. Mario de Miranda in his paper “Construction Design of Signature Bridge in Delhi” describes detailed construction engineering of the landmark cable-stayed bridge on the Yamuna River in Delhi. This case study illustrates how to overcome complex problems through an integrated study of all aspects including construction methods and temporary structures.

Mr. Alok Panday has presented an interesting case study for construction engineering of an arch bridge in his paper “Construction of 120m Span Arch Bridge using Cantilever Form Traveller”. Mr. Raja Ranjan has, in his paper “Temporary works paves way to permanent profit”, has given a number of case studies to show that efficient temporary structures can result in cost effective solutions for a project.

The Bridge and Structural Engineer

Mr. Rakesh Mehta has presented a paper titled “Enabling works for India’s first Double decker bridge - Santacruz Chembur Link road” which describes in detail as to how extensive evaluation of various construction schemes helps in successful completion of such mega projects. Mr. Vinay Gupta in his paper has explained various types of launching systems for precast segmental bridges using span by span technique.

I am grateful to Mr. V.M. Dharap, who has vast experince in the field of Temporary Stuctures, for meticulously reviewing all papers and giving valuable suggestions. Finally I would like to thank ING-IABSE Secretariat- Mr. R.K. Pandey, Mr. K.B. Sharma & the Chairman-Editorial Board Mr. Alok Bhowmick and all the authors for their cooperation & guidance in making this issue a success.

(MOHAN JATKAR)

Volume 46 Number 1 March 2016 ix

Brief Profile of Mr Mohan Jatkar Mr. Mohan Vasant Jatkar got his Civil Engineering degree in 1977 and Masters in Structures in 1979 from College of Engineering, Pune (COEP).

He joined Technical Management Section of Gammon India Ltd. in 1980 as Design Engineer. In his initial career he worked on a various assignments like software development for structural design; design of natural draught cooling towers, chimneys and a variety of bridges. In later half of his career, he got an opportunity to work in design of temporary structures. As the department head he led the team in dealing with design of temporary structures & developing construction engineering for all types of infrastructure projects. Some of his challenging assignments include design of navigation spans for Pamban Bridge across Palk Strait, front end engineering for Signature Bridge, Marine Intake Works at Kalpakkam & Vaizag Thermal Power Project, etc.

Presently he is Executive Director (Technical) in Gammon India Ltd. overseeing the functions of construction planning, HSE and Quality Management. His main interests are in front end engineering, resolving interface technical issues & training.

Mr. Jatkar is a member of various professional bodies like IRC, ICI, etc. and is a member of work group (WG-6) for Bridge Erection Equipment of the International Association for Bridge & Structural Engineering (IABSE). He is also MemberSecretary for IRC committee on Temporary Structures (IRC:87).

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The Bridge and Structural Engineer

HIGHLIGHTS OF THE ING-IABSE WORKSHOP ON “BRIDGE BEARINGS, EXPANSION JOINTS & SEISMIC DEVICES” HELD AT BHOPAL ON 15TH & 16TH JANUARY 2016 The Indian National Group of the IABSE in association with Government of Madhya Pradesh, PWD and MP Road Development Corporation Ltd successfully organised two day Workshop on “Bridge Bearings, Expansion Joints and Seismic Devices” at Bhopal on 15th and 16th January 2016.

The Workshop was well attended by more than 200 delegates from various Govt Departments, Consultants, Contractors and representatives of the Manufacturers/Suppliers of products as well.

The aim of the Workshop was to disseminate the knowledge in the field of bearings, expansion joints and seismic devices in bridges, flyovers etc. and introduce the various products, their applicability and design standards, besides testing and acceptance criteria so far as application in Bridge and Structural Engineering is concerned. Some case studies on repair and rehabilitation of bearings and expansion

Shri D.O. Tawade, Chairman , ING-IABSE lighting the traditional Inaugural Lamp along with high dignitaries

Shri D.O. Tawade, Chairman, ING-IABSE delivering his address

The Bridge and Structural Engineer

joints was also presented during the Workshop.

Participation of delegates in floor intervention and discussions was very encouraging.

The Workshop was inaugurated by Shri D.O. Tawade, Chairman, ING-IABSE and Chief Engineer (Coordinator-II), Ministry of Road Transport and Highways by lighting the traditional lamp.

Shri C.P. Agrawal, Secretary, Govt of Madhya Pradesh, PWD extended warm welcome to the participants of the Workshop. Shri D.O. Tawade, delivered his address during the Inauguration. Shri RK Pandey, Secretary, ING-IABSE proposed Vote of Thanks.

The Workshop on "Bridge Bearings, Expansion Joints and Seismic Devices” was addressed by the following eminent experts covering the following themes:

A view of the Dais during the Inaugural Function

Shri R.K. Pandey, Secretary, ING-IABSE delivering his address

Volume 46 Number 1 March 2016 xi

15th January, 2016 Session-1 – Bridge Bearings 1

Dr Christian Braun, Maurer AG

– Key Note Address

2

Shri Alok Bhowmick

– Elastomeric Bearings

3

Shri Chinmoy Ghosh

– POT/PTFE/Smart Bearings

4

Shri Jitendra Rathore

– Spherical Bearings

5

Shri VN Heggade

– Bearings for Signature Bridge at Delhi – Case Study

6

Shri PY Manjure

– Repair and Rehabilitation of Bearings – Case Studies

16th January, 2016 Session-2 – Expansion Joints 7

Dr Sougata Roy, Mageba SA

– Key Note Address

8

Shri Peter Gunthur, Maurer AG

– Expansion Joints

9

Dr Lakshmy Parameswaran

– Evaluation, Testing and Acceptance Criteria of Expansion Joints

10 Shri Shibnath Lahiri

– Repair and Rehabilitation of Expansion Joints

Session-3 – Seismic Isolation / Restraining Devices 11 Dr Christian Braun, Maurer AG

– Key Note Address

12 Shri Vinay Gupta

– Seismic Isolation Devices

13 Shri Santanu Adhikary

– Seismic Isolation Devices – Case Study

Shri A.K. Banerjee, Chairman, Scientific Committee delivering his address

xii Volume 46 Number 1 March 2016

A view of the audience during the Inauguration

The Bridge and Structural Engineer

The concluding remarks of the Workshop were presented by Shri AK Banerjee, Chairman, Scientific Committee on 16th January 2016. He expressed the hope that the outcome of the Workshop would have enriched the delegates. The delegates who attended the Workshop mentioned that the subject matter of the Workshop is very timely. Shri Anil Chansoria, Chief Engineer (BOT), Govt of Madhya Pradesh proposed Vote of Thanks.

Another view of the audience during the Inauguration

A light music with dinner was organized in the evening of 15th January 2016 for the participants who rejoiced the evening.

The Workshop was a great success.

The Bridge and Structural Engineer

Volume 46 Number 1 March 2016  xiii

With Best Compliments From :

Reliance Infrastructure Ltd Mumbai

xiv  Volume 46 Number 1 March 2016

The Bridge and Structural Engineer

Challenges in Management of Temporary Works

Mohan V. Jatkar Executive Director (Technical) Gammon India Ltd. Mumbai mohan.jatkar@gammonindia.com

Summary Temporary structures present many challenges to construction agencies on a variety of fronts: cost effectiveness, speed of construction, safety of the permanent structure as well as personnel, etc.

This paper is a brief overview of the various aspects related to temporary structures.

Keywords: temporary works, falsework.

1. Introduction The term ‘temporary’ structure itself unfortunately invokes a sense of complacency in those who have not had an opportunity to understand the subject. This is probably the single most reason that the subject has never got the attention and importance it deserves.

IRC:87-2011 [5] defines temporary structure as parts or the works those allow or enable construction to protect, support or provide access to the permanent works and which may or may not remain in place at the completion of works.

BS:5975:2008 [2] gives a broader definition as an “engineered solution” used to support or protect either an existing structure or the permanent works during construction, or to support an item of plant or equipment , or to the vertical sides or side slopes of an excavation during construction operations on site or to provide access.

“Falsework” is a major subset of temporary works which is used to support a permanent structure while it is not self-supporting. Formwork is used to contain The Bridge and Structural Engineer

Mohan Jatkar, born 1955, received his civil engineering degree from the University of Pune, India. He has since worked for Gammon India Ltd. in design & front end engineering. His main area interest in construction planning & temporary works, HSE and training.

and give poured concrete the required shape and dimensions till it is able to support itself. Formwork consists of the material, like plywood or steel plate, immediately in contact with concrete and its back up members which stiffen it.

Success of temporary works is not just good design but depends on many aspects such as proper understanding of construction procedure, need to achieve target time cycles, following relevant procedures at site, safety, cost effectiveness and so on. This article attempts to give an overview of the challenges involved in the management of temporary works.

2. Background After a spate of accidents related to falsework failure in the UK, the government appointed a committee headed by Professor Stephen Bragg to investigate.

The final report (HSE 1976), known as the ‘Bragg Report’, had a large influence on the BS 5975: Code of practice for falsework first published in 1982. The committee analysed various falsework failures to determine direct technical reasons for failure and also the contributory procedural failures which allowed the technical faults to go undetected.

One of the primary causes of failures was found to be missing out on horizontal forces, which can be due to wind or arising out of construction activities, etc. in the design of falsework.

Reasons for failure of falsework, those can be directly attributed to technical issues, are: i)

Loads coming on the structure at site are not the Volume 46 Number 1 March 2016 1

same as those considered in the design basis.

This can happen when there are changes in methodology or sequence of work or changes in dimensions of the permanent structure itself. ii) The design itself is inadequate for the specified loads iii) The falsework erected at site is not according to the design. There can be last minute changes in the structure as per the material available at site without consulting the designer.

of vertical members of the falsework, inclination of soffit of the formwork, uneven settlement of foundations of vertical members, etc.

BS 5975 Clause 6.4.4 (Ref. 3) recommends that ALL falsework should be designed to be able to resist at each phase of construction the applied vertical loads AND the greater of either: a)

The first and the third are more of coordination or procedural issues whereas the second is a purely a design matter.

3.

Challenges in design

The basic principles of analysis and design for temporary structures are naturally the same as for a permanent structure. However there are several significant differences in the application to temporary structures; some of the important issues are mentioned below.

3.1 Uncertainty of loading Falsework is mainly subjected to the following loads: i)

Dead loads

ii) Imposed loads- construction personnel, static or mobile plant & equipment, stacking of materials, prestressing, etc. iii) Environmental loads like wind, earthquake, water, etc.

Definite guidelines are available in relevant codes for dead loads and environmental loads. Imposed loading has to be derived from construction methodology finalised in consulation with the contractors. It is to be noted that a temporary structure will be subjected to the design imposed loading everytime unlike a permanent structure which may be subjected to maximum imposed loading rarely over a long design life.

Horizontal forces on falsework can arise due to external factors like wind / earthquake, vehicular movements, impact of concrete bucket, use of vibrators for compaction, effect of prestressing, etc. These forces can be identified from the proposed methodology and calculated. There are some horizontal forces induced due to unforeseen factors like deviation in verticality 2  Volume 46

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A horizontal force equivalent to 2.5 % of W where W is the sum of the applied vertical forces at the time considered. This minimum force is considered to act at the point of contact between vertical loads and supporting falsework or

b)

Sum of horizontal forces that can arise from wind loads, erection tolerance forces (taken as 1% W), intentionally designed non-verticality of members, concrete pressure forces, water and waves, dynamic / impact forces and the forces generated by permanent works. It is to be noted that the provision of 1 % of vertical loads towards erection tolerance is applicable in situations where the recommended tolerance limits are achieved at site. In repetitive work these tolerances have to be achieved each time the falsework is erected. In situations where the limits are not likely to be achieved, suitable allowance has to be made by increasing the horizontal force.

Bragg report had recommended a minimum horizontal force of 3 % of the vertical loads for checking stability of the falsework. IRC:87 sticks to this value.

3.1 Lack of site information Many times adequate site information necessary for design is not available. Design done for one typical location may not be valid for another location at the same site even if the permanent structure is the same.

In many cases soil data is not known for designing footing for falsework. Information available for permanent structure may not be applicable due to excavation, backfilling, etc. If the bed profile is inclined, its effect has to be considered. Presence of underground utilities, flooding, etc. can result in local settlements.

3.2 Avoidance of progressive collapse As many connections exist in temporary structures, The Bridge and Structural Engineer

detailing of connections should be foolproof to reduce dependence on workmanship and inspection at site. Also a local failure should not lead to progressive collapse of the entire system which can be catastrophic.

3.3 Design Review To avoid mistakes in design, the BS code recommends independent design review within the design office for moderately complex designs. Design review by third party are recommended for complex and innovative designs involving significant departures from standards or which require considerable exercise of engineering judgment. Some contracts specify proof checking of design even for temporary structures.

4. Health, Safety & Environment (HSE) considerations Each construction project is unique and has its own hazards due to factors like work fronts spread out over large areas, exposure to extreme weather conditions, tight schedules resulting in psychological & physical pressures and moreover many unskilled labours. The construction industry recognises the hazardous nature of its activities which result in relatively high toll of accidents, which lead to serious injuries or fatality or result in substantial loss of time, compared with other industries. Some of the causes are related to temporary works.

The Building and Other Construction Workers Act 1996 deals with regulations to provide for workers' safety, health and welfare measures and for other matters connected therewith or incidental thereto.

Two of its chapters deal with 'structural frame and formwork' and 'scaffold'.

Temporary structures fall in two basic categories.

The first provide support for a permanent structure during construction or slopes of excavation, etc. The other category consists of structures which provide access and working area for the personnel to the work front. Incidents related to the first category are relatively less frequent but can result in significant fatalities. The issues involved are mainly structural design or coordination related and are discussed in the elsewhere in the article.

The number of incidents in the second category are more common. General causes of injuries or fatalities in construction are mainly fall from height, striking by The Bridge and Structural Engineer

objects, electrical shocks, overexertion, etc. A major cause of fatalities is fall from heights. Care needs to be taken to provide proper guardrails and toe board of adequate strength to prevent fall. Proper details should be included in the drawings for the access and working platforms.

IRC:87-2011 recommends preparation of a comprehensive site manual to define the main requirements of Safety, Health & Environment Management associated with the Employer, Contractor / sub-contractor or any such agencies to avoid accidents, occupational illness and harmful effects on environment during construction. The guidelines also recognise that existing Rules or Acts in India are not adequate to cover all aspects.

It recommends to include all relevant aspects, even though they are not covered by existing regulations, be included in the site manual.

5.

Management challenges

5.1 Design stage There is an acute shortage of engineers with experience in design of temporary structures as many of the engineers who had passed through a long learning curve and learnt from past mistakes have now retired. Current recession in the industry and consequent trimming of organisations has not helped matters. Most contractors no longer have an in-house design department for such structures and tend to outsource or depend on technical back up from proprietary systems. Under graduate courses do not offer even an introduction to this subject and there is nobody around to guide them in their professional career.

Temporary structures constitute a sizable percentage of the project cost particularly for complex structures or when the contract period is too short, which is the case for most of the current projects. At the same time these are not billable items. This puts a lot of pressure on the temporary works designer to design just adequate structures resulting in minimum material quantity and thereby minimum initial investment on the project. But the real cost effectiveness comes out of repetitive use of the system over similar projects, proper detailing to minimise erection & dismantling time and so on. This requires a robust system and may be a slightly higher initial cost.

Volume 46 Number 1 March 2016  3

5.2 Site operations

schedule & sequence of work, proposed methods of construction, access requirements, equipment & material available for temporary works and any other relevant data. If any deviations are proposed from the assumptions related to sequence or method of construction, loading or strength restrictions, etc. then the same have to be reviewed and approved by the designer of permanent works.

Some of the major challenges faced at project sites are: -

General reduction in skills of workmen and supervisors & particularly the loss of experienced foreman cadre

-

Most of the systems are reused over many projects. Rough handling & lack of maintenance at site can damage the components and reduce the expected life thereby increasing project cost.

-

Reuse of material requires proper inspection for rusting, cavitation, weld fatigue, bent or damaged members, etc. and necessary repairs or replacement

-

Many agencies are involved in various stages of temporary works: designer, main contractor, subcontractors, system suppliers, clients engineer / project management team, etc. Proper coordination and communication is required to ensure that necessary requirements are met at all stages and for each cycle of use.

-

Sites sometimes make deviations from the design drawings as per availability of material.

Sequence of construction also may be changed to suit site conditions without realising the design implications. Proper sketches should be made at site clearly showing the proposed changes. Such changes should be made only after confirmation from the designer.

It is to be ensured that a satisfactory design of temporary works is carried out. Depending on the complexity, the design & drawings are to be reviewed to check the concept, structural adequacy & compliance with the design brief.

ii) Communication & documentation- After recording the design document & drawings, they are to be made available to all concerned. iii) Site operations- Before being put to use for every construction cycle, the erected temporary structure is to be inspected to ensure that it is as per the final drawings. If any change in specifications or detail are noticed at any stage, the same are to be got approved from the designer. After the permanent structure gains required strength, the temporary structure can be permitted to be dismantled as per the specified sequence. When not in use, components of the temporary structure are to be stored properly after necessary repairs and maintenance.

5.3 Procedural controls

5.4 Roles & responsibilities

Proper implementation of temporary works is largely dependent on management of various activities from concept to erection / dismantling as well as maintenance& storage. In view of this BS 5975 describes design / technical requirements as well as procedures for controlling all activities as recommended by Bragg committee. IRC:87 has generally adopted the same approach. The procedures can be considered for controlling the three phases:

As in BS:5975, the IRC:87 recommends appointment of a separate person at all major projects for proper planning, implementation, monitoring, coordination and supervision of all temporary works related procedures as outlined above. He is the first point of contact between designer and the site team. However looking at the number of projects already under construction and those in the pipeline, a lot of efforts will have to be taken to develop this cadre due to accute shortage of trained manpower.

i)

Design- Initially a design brief is to be prepared giving all data required for design of temporary works for the project. This includes drawings & specifications for permanent work, codes &contractual specifications as per which design of temporary works is to be carried out , soil investigation & environmental data, construction

4  Volume 46

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6.

System formwork & responsibilities

Good proprietary falsework systems are now available particularly for the building sector. Since they have 'manufactured' rather than site fabricated components, site can get better time cycles in terms The Bridge and Structural Engineer

of faster erection and dismantling. In turn they can be more cost effective and are now being widely used in the building as well as other sectors. Basically three types of falsework systems are available: Type 1 Aluminum support legs with aluminum frames assembled into falsework systems, Type 2 Individual aluminum or steel props, either with proprietary timber beams or proprietary panels & Type 3 Heavier steel falsework systems.

IRC:87 gives a fairly detailed list of information to be given by manufacturers of proprietary systems to the user. Design of such systems is initially carried out by the suppliers themselves. However problems can arise if the basic assumptions made in the design are not properly communicated or understood by the user. Particularly, the issues of transfer of lateral forces and stability of falsework & erection to lerances are critical. Various international standards specify different criteria for tolerances to be achieved in erection and in turn how the effect of imperfections or deviations are to be accounted for in the design. Many times it is assumed such forces will be transferred to the already constructed portion of permanent structure. This has to be ascertained in the detailing and implementation at site.

With wide use of proprietary system, contractors now rely on supplier’s design establishment and at best carry out some random checks on the scheme and design provided with the system. The implications of shift in perception of design responsibility have to be clearly understood. When the system is reused for similar project the supplier’s technical inputs may or may not be available. It has to be understood that similar projects may not be exactly identical in terms of technical requirements.

Some vendors may quote low and a contractor may be tempted to accept the lowest quote to reduce his initial investment on the project. There are instances where there are differences in the specifications given with the quotation and the material actually supplied at site.There are some 'copied' systems available in the local market as well. There can be subtle shortfalls like

The Bridge and Structural Engineer

inferior specifications, lack of QA and technical back up in such cases. To avoid this, it is important to prequalify vendors for proprietary systems. It should be based on their experience, past reference projects, technical back up and quality assurance systems implemented in their organisation. Technical considerations should be given due weightage in the procurement process so that commercial considerations do not take precedence over safety risks.

7. Conclusion Proper implementation of temporary works requires various activities to be effectively managed & coordinated right through their value chain. This covers all aspects like design, specification, procurement, erection & dismantling as well as maintenance & storage. Increased awareness and steps to increase the competence of those engaged in temporary works design, management and implementation will greatly help in reducing the associated risks in the construction industry.

References 1.

RATAY, R.T. “Temporary Structures in Construction.” Third Edition, 2012, McGrawHill.

2.

BS 5975:2008. “Code of practice for temporary works procedures and the permissible stress design of falsework”.

3.

Bill Hewlett et al. “Revisiting Bragg to keep UK's temporary works safe under EuroNorms”,

Proceedings of the Institution of Civil Engineers, Forensic Engineering 167 May 2014 Issue FE2.

4.

Eur Ing P.F. Pallett et al, “Investigation into aspects of falsework”, HSE Contract Research Report 394 /2001.

5.

IRC:87-2011 “Guidelines for formwork, falsework and temporary structures”.

6.

IS:14687-1999 “Falsework Structures- Guidelines”.

for

Concrete

Volume 46 Number 1 March 2016 5

ASCE/SEI 37-14 DESIGN LOADS ON STRUCTURES DURING CONSTRUCTION STANDARD*

Robert T. RATAY, PhD, PE Consulting Structural Engineer Adjunct Professor, Columbia University New York, USA Structures@RobertRatay.com

John F. DUNTEMANN, PE, SE Senior Principal Wiss Janney Elstner Associates, Inc. Northbrook, IL USA jduntemann@wje.com

Robert T. Ratay’s long-time engineering practice is focused on investigation of structural and construction failures. He is the founding and current Chair of the ASCE/SEI 37 Standard Committee, and of the IABSE Working Group on Forensic Structural Engineering.

John Duntemann has over 35 years’ experience in the assessment of structural performance, including the failure analysis of buildings, bridges and other structures. He is one of the subcommittee chairs of ASCE/SEI 37, and member of the IABSE Working Group on Forensic Structural Engineering.

Summary Standards by themselves do not eliminate construction failures, they do not substitute for experience, good judgment and care, but do provide minimum criteria for desired performance and safety. ASCE/SEI 37, Design Loads on Structures During Construction Standard specifies design loads, load combinations and safety factors to be used in the analysis and design of structures during transient stages of construction, as well as of temporary structures used in construction operations. This paper is a brief presentation of the purpose, substance, and selected details of the Standard that has been developed and in use in the United States.

Keywords: design, construction, load, load factor, temporary structures, standards.

1. Introduction More failures of structures occur during construction than after the completion of projects; and most

construction failures result from temporary structures.

Advances in construction technology, new materials, more refined design methods with less margin for error, the construction of innovative (and perhaps more daring) structures, as well as the pressure of time, and the cost of construction financing appear to contribute to the proliferation of failures during construction.

In building construction, the situation is chronic not only in the United States but in other countries as well. The proximate causes of the failures appear to be non-adherence to good practices, break-down of organization, management and communication in the field, and the lack of a comprehensive and definitive design standards that address performance criteria, temporary loads, strengths and stability during construction.

Design codes and standards are mostly silent on the subject of construction loads, or give such general statements as “Proper provisions shall be made for stresses . . . during erection . . . of the building” and “Adequate temporary bracing shall be provided

*An earlier version of this paper, dealing with the now-superseded ASCE 37-02, was presented by the authors at, and published in, the proceedings of the Joint IABSE - fib Conference on Codes in Structural Engineering in Dubrovnik, Croatia, May 3-5, 2010.

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The Bridge and Structural Engineer

to resist wind loading . . . during the erection and construction phases.” The questions, of course, are: what is adequate and what are proper provisions?

The answers often depend on who defines them: the designer, the contractor, the owner, or the building official.

In the U.S., as in many other countries, there are manuals, guides and other forms of information published by federal and state government agencies, public authorities, and industry organizations. ([1], [2], [3]) There is a definite need in the US – and for that matter in many countries – to adopt and enforce unified design criteria, loads, load combinations and load factors for the design and inspection of structures during their transient construction stages and of temporary structures that are used as support, access, and protection during construction. While standards by themselves will not eliminate construction failures, and they are not a substitute for experience, good judgment and care, they provide minimum criteria for safety and proper performance.

2. Background ASCE/SEI 37-02 Design Loads on Structures During Construction Standard [4] took over fourteen years, from 1987 through 2002, to be developed by a seventy-member standards committee of the American Society of Civil Engineers. Members of the standards committee had experience in design, construction, manufacturing, inspection and testing, as well as from academia. The Committee has been chaired since its inception by the first author, its subcommittee on Loads and Load Combinations by the second author. Following the American National Standards Institute's (ANSI) procedures for consensus standards, including public balloting, the document was published in 2002. It has been in active use since then. A thorough review, updating and revision of the standard have been going on since 2007, the revised edition, ASCE/SEI 37-14 [5], underwent committee and public balloting, and was published in early 2015.

temporary structures used in construction operations.

The intent is that “Partially completed structures and temporary structures shall possess sufficient structural integrity, under all stages of construction, to remain stable and resist the loads specified herein.” Unique to the provisions is that “The construction loads, load combinations and load factors contained [in the Standard] account for the often short duration of loading, and for the variability of temporary loads.”

(All quotes in this paper are from the text of the document.)

Along with numerical load requirements, the document also offers some practical design and construction considerations, such as “Structural integrity shall be provided: by sequencing the construction so as to avoid creating vulnerable partially completed portions of the structure; by completing the system to support lateral loads as the dependent portion of the structure is erected or by providing suitable temporary lateral bracing; by avoiding conditions that result in loads that exceed the capacity of structural elements; and by promptly completing connections for all installed elements.” It also warns that “[f]or some configurations, the loads on a structure during construction may exceed the loads in the finished condition, and hence will govern the design of the structure.”

“The standard is intended for use by engineers knowledgeable in the performance of structures.”

Importantly, “The requirements contained [in the standard] are not intended to adversely affect the selection of a particular construction material or type of construction.” Also important in that the document “does not assign responsibility...”

The standard is composed of six chapters: 1.

GENERAL (general introduction identifying the purpose and scope of the document)

2.

LOADS AND LOAD COMBINATIONS

3.

DEAD AND LIVE LOADS

4.

CONSTRUCTION LOADS

3. The Standard’s Provisions

5.

LATERAL EARTH PRESSURE

The objective of the standard, ASCE 37, Design Loads on Structures During Construction, is to present design loads, load combinations and safety factors to be used in the design and analysis of structures during the transient stages of construction, as well as of

6.

ENVIRONMENTAL LOADS

The standard is printed in two-column format: the “standard” on the left side of the page in mandatory language, and the parallel “commentary” on the right side in explanatory language.

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Volume 46 Number 1 March 2016 7

3.1 Construction Loads, Load Factors and Load Combinations

Equipment reactions (CR): reactions from heavy equipment (rated or nonrated).

The construction loads, load combinations, and load factors in the document account for the relatively short duration of other than permanent dead load, variability of loading, variation in material strength, and the recognition that many elements of the completed structure that are relied upon implicitly to provide strength, stiffness, stability, or continuity are not present during construction. The load factors are based on a combination of probabilistic analysis and expert opinion.[6] The concept of using maximum and arbitrary point-in-time (APT) loads and corresponding load factors is adopted to be consistent with ASCE 7, Minimum Design Loads for Buildings and Other Structures.[7]

Since there is little statistical information available on which to base the selection of construction load factors in strength design, initial selection of load factors was based on those in ASCE 7. Adjustments to these factors were made based on an understanding of the nature, both physical and statistical, of these loads.

Particular load categories are designated to facilitate logical load combinations in order to accommodate a variety of realistic loading situations that occur during construction. A brief summary of the load categories is as follows: Dead Load (D): total vertical weight of all completed permanent construction.

Live Load (L): loads produced by the planned occupancy of the completed portions of the structures.

Fixed dead load (CFML): construction material loads, which are assumed constant during a certain phase or all of the construction period.

Variable dead load (CVML): construction material loads, which vary in magnitude during the construction period.

Worker and light equipment loads (Cp): loads due to workers and light equipment, such as tool boxes, and the like.

Lateral pressure of concrete (CC): loads resulting from concrete pressures on formwork during moving, pouring, pumping, or placing.

Lateral earth pressures (CEH): horizontal load effects resulting from soil pressures.

Horizontal construction loads (CH): any horizontal loads arising from worker and/or equipment operations.

Erection and fitting forces (CF): forces resulting from erection of equipment including alignment, fitting, bolting, bracing, guying, etc.

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The load factors for strength design (Table 2.2.2 in the Standard) are reproduced here in Table 1. For each type of load, a factor for the maximum load value is indicated and, where applicable, an arbitrary point-in-time (APT) load factor is also shown. There are a number of loads for which no APT load factor is provided; they should only be considered in load combinations when they are actually present and are therefore at their full or maximum value.

Table 1: Construction Load Factors Load

Load factor (Cmax)

D

0.9 (when counteracting wind or seismic loads) 1.4 (when combined with only construction and material loads) 1.2 (for all other combinations 1.6 0.9 (when counteracting wind or seismic loads) 1.4 (when combined with only construction and material loads) 1.2 (for all other combinations 1.2 1.4 1.6 1.3 (full head) 1.6 (otherwise) 1.6 1.6 2.0 2.0 (unrated) 1.6 (rated)

L CD

CFML CVML Cp CC CEH CH CF CR

Arbitrary pointin-time load factor (CAPT) ---

0.5 ---

--By analysis 0.5 ---0.5 By analysis 0 0

Several basic load combinations are also listed in the standard.

The Bridge and Structural Engineer

3.2 Environmental Loads and Load Factors The following environmental loads are considered in the Standard: Wind load (W) Thermal load (T) Snow load (S) Earthquake load (E) Rain load (R) Ice load (I) The basic reference for the computation of environmental loads is also ASCE 7. However, modification factors have been adopted to account for reduced exposure periods. For example, the design wind speed is taken as the basic wind speed in ASCE 7 modified by the following duration factors for the period of exposure: Construction/Exposure Period

Factor on design wind speed

Less than six weeks

0.75

From six weeks to one year

0.8

From one to two years

0.85

From two to five years

0.9

More than five years

1.0

ASCE 7 specifies an importance factor that adjusts the basic loads upward or downward depending upon the end-use occupancy and on the consequences of failure of the structure. (Critical structures, such as emergency facilities and places of assembly, are designed for greater loads than are most office buildings. Other structures, such as agricultural buildings that have low human occupancy, can be designed for lower loads.) For this construction loads standard, the importance factor is assigned a value of 1.0 for all structures, regardless of their end-use occupancy.

4. Conclusions During its construction a structure is subjected to loads some of which are different in nature, magnitude and duration from those during its service life. The ASCE/SEI 37 standard provides a rational method for determining the loads to which structures should be designed during their construction. While the authors and the Committee recognize that standards alone do not eliminate construction failures, this standard is intended to provide minimum criteria for safety and performance. A brief but good discussion of the designer's use of the ASCE/SEI 37 standard is Reference 8.

References

Certain loads in combinations with wind or snow may effectively be ignored because of the common practice of shutting down job sites during excessive snow and wind.

The load factors for the environmental loads (from Table 2.2.2 of the Standard) are shown here in Table 2.

1.

DUNTEMANN, J.F., and RATAY, R.T. 1997.

“Review of Selected U.S. and Foreign Design Specifications for Temporary Works-Part I.” In Proceedings of the ASCE Structures Congress ’97, Portland, Oregon, 1997, pp. 985-990.

2.

DUNTEMANN, J. F. 1996. Standards, Codes and Regulations, Chapter 2. In R. T. Ratay, Handbook of Temporary Structures in Construction, 3rd ed., McGraw-Hill, Inc., New York, 2012.

3.

DUNTEMANN, J. F. 2000. Design Codes and Standards, Chapter 2. In R. T. Ratay, Forensic Structural Engineering Handbook, 2nd ed., McGraw-Hill, Inc., New York, 2010.

4.

ASCE/SEI 37-02, Design Loads on Structures During Construction, American Society of Civil Engineers, Reston, Virginia, 2002.

5.

ASCE/SEI 37-14, Design Loads on Structures

Table 2. Environmental Load Factors Load Description

Load factor Arbitrary point(Cmax) in-time load factor (CAPT) 1.0 0.3 1.2 --

W T

Wind load Thermal load

S

Snow load

1.6

0.5

E

Earthquake load

1.0

--

R

Rain load

1.6

--

I

Ice load

1.6

--

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Volume 46 Number 1 March 2016 9

During Construction, American Society of Civil Engineers, Reston, Virginia, 2015.

6.

ROSOWSKY, D.V. 1996. Load Combinations and Load Factors for Construction. In ASCE Journal of Performance of Constructed Facilities, November 1996, Vol. 10, No. 4, pp. 175-181.

7.

ASCE/SEI 7-10, Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers, Reston, Virginia, 2005.

8.

SUBRIZI, C., FISHER, A. & DEERKOSKI, J. 2004. Introducing ASCE/SEI 37-02 Design

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Loads on Structures During Construction. In STRUCTURE Magazine, pp.26-28, March 2004

Acknowledgements The Chair and Subcommittee Chairs of the ASCE37 Standard Committee who led the development and maintenance of the document, and the revisions for the ASCE 37-14 edition, are: Robert T. Ratay (Chair), Rubin Zallen (Chapter 1), John Duntemann (Chapter 2), Chris Subrizi (Chapter 3), John Deerkoski and Alan Fisher (Chapter 4), Vincent Tirolo (Chapter 5), Donald Dusenberry and James Soules (Chapter 6).

The Bridge and Structural Engineer

SLIPFORM SYSTEM FOR CONSTRUCTION OF HIGHRISE HOLLOW CONCRETE STRUCTURES

Vijay M. DHARAP Advisor (Technical) Gammon India Limited, Mumbai, India dharapvijay@yahoo.com

S. Abhilash KUMAR Manager, Construction Systems, Gammon India Limited, Mumbai, India abhilash.kumar@gammonindia.com

Mr. V.M. Dharap, BE Civil (1960), joined M/s.

Gammon India Limited in 1969, and retired on 31st December 2015. During this period, he worked on development and designs of temporary structures and construction systems for infrastructures projects along with other responsibilities under various capacities.

Mr. S. Abhilash Kumar is a graduate in Civil Engineering from Mangalore university. He has over 16 years of experience in M/s. Gammon India Limited and worked extensively on planning and designing of construction systems for various infrastructure projects.

Summary Slipforms have now become an absolute necessity for construction of high rise concrete structures in order to complete the projects at a fast speed and time bound manner. This paper describes the components of the Slipform, permissible tolerances and various requirements to achieve the desired results etc. in fair details.

Keywords: Yoke frames, walers, form panels, working platform, jack rods, slipform jacks & pump units.

1. Introduction In the construction of concrete structures, formwork/ falsework forms one of the major components of construction cost, and on which also depend the quality, speed and economy of the construction.

Specialized formwork systems and construction techniques are usually developed considering these factors. There are specialized formwork systems/ The Bridge and Structural Engineer

construction techniques for different types of concrete structures such as travelling formwork for long span bridges, moulds for pre-casting of RCC beams and box girders, launching trusses for erection of pre-cast members etc. Slipform is one such technique. Unlike standard fixed form panel system, the Slipform process raises the forms vertically or horizontally in continuous operation while placing the concrete.

The system is extensively used for the construction of high rise structures with the shortest possible time and with minimum manpower and falsework. Lately the system is also introduced for the construction of horizontal structures like canals, tunnel linings, highway medians, crash barriers etc. However in this paper we are dealing with the techniques of high rise hollow structures under various heads.

2. History Origin and history of the Slipform remains something of a mystery, but it is generally accepted that it first appeared in 1885, when a person in Texas by name Volume 46 Number 1 March 2016  11

Carrico used this principle for building a small concrete shaft. No further development appeared in this field until 1903, when the Americans used a screw jack to propel the formwork. This was the first Slipform system. During 1940s, a Swedish manufacturer developed the now standard hydraulic equipment and it enabled men such as one Mr. Jesperson to produce records in 1960s when he constructed a chimney of 4.5m in diameter and 32.4m high in just nine days time.

3.

Slipform technique

Slipform means continuously moving forms, moving at such a speed that the concrete when exposed has already achieved enough strength to support the vertical pressure from the wet concrete in the forms as well as to withstand lateral pressure caused by wind, inclination of walls etc. The word continuous is not strictly correct because the Slipform is moved by hydraulic jacks pushing the forms about 25mm to 40mm at a time every 5 to 10 minutes depending upon the designed sliding speed. The Slipform consists of a band of formwork assembled as per the shape of the structure, and continuously moved while placing the concrete. Fixing of reinforcement, embedded parts, block outs etc. also is being carried out continuously during the movement of the forms.

4.

Fig. 2: Yoke frame for straight shaft

Fig. 3: Cross section of Slipform for tapered shaft

Major components of Slipform

Although the principles of Slipforming remain same for the construction of vertical shaft with constant wall thickness and tapered shaft with varying wall thickness, a number of changes are done in some of the components while designing the system. This is done mainly to achieve the desired geometry in case of tapered structures where the diameter, circumference and wall thickness of the shell go on varying with height.

Fig. 4: Yoke frame for tapered shaft

The Slip form system mainly consists of; 4.1 Yoke Frames Fig. 1: Cross section of Slipform for straight shaft

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In the case of straight shaft (Fig. 1 & 2), the yoke frame consists of one horizontal yoke beam and two The Bridge and Structural Engineer

vertical yoke legs. The yoke frames are spaced at 1.2 to 2.4 m centers along the periphery of the structure.

They support walers and the formwork and take care of the lateral load from the formwork. The yoke frames also transmit the lifting forces from the jacks to the walers. The working platform and suspended scaffold is also supported by yoke frames. Mild steel rolled hollow rectangular sections are commonly used for manufacturing yoke legs or alternatively they are fabricated out of smaller rolled sections. Sometimes if the thickness of straight shaft is reduced after some height, suitable provision is kept in the yoke frame to slide one of the yoke legs horizontally in order to reduce the thickness. The working platform can also be provided on the top of the yoke legs as in the case of tapered shaft Slipform.

For tapered shaft (Fig. 3 & 4) there are two yoke beams instead of one. They are not rigidly connected with yoke legs so as to enable adjustment in inclination and wall thickness of the shell. Lifting jacks are mounted on the lower yoke beam and are designed to cater for the lifting load and also allow passing the jack rod through the upper and lower yoke beams.

For the construction of tapered shafts, additional components are provided in the yoke fame to adjust the geometry as below.

Radius screw is fitted with the horizontal beam of working platform and connected at the top of inside yoke leg to effect the desired change in the radius.



Horizontal turn buckle is fitted with inside and outside walers for circumferential adjustments.



Wall thickness screw is fitted to the top yoke beam from inside and reaction is taken from the yoke leg for the change in wall thickness.

case of timber boarding, it is required to plane the surface. If plywood is used, it should be installed with grains vertical. The form panels for Slipform are not made very rigid as in the case of conventional methods. A provision is kept for self adjustment during slipping operation. Steel shutter plates of 400 to 600mm width also can be used since no diameter variation is required.

In case of tapered structures, form panels are of plain mild steel sheets of 3 to 4mm thickness and are fitted on walers by means of clamps at one end and the other end overlaps the next form panel about 50 to 100mm and slides horizontally in order to increase or reduce the circumference. Form plates are passed through bending rollers to get the required curvature.

The form panels are of 1.0 to 1.20 m height and 2.3 to 2.5m in width.

The opposite faces of the form panels are kept about 6mm to 8 mm wider at the bottom than at the top in order to minimize the drag caused by the friction while lifting operation, and to reduce the possibility of concrete adhering to the form face.

4.3 The Walers beams The form panels are mounted through angle cleats or a system of adjustable rollers over the walers. These walers give lateral support to form plates and transfer the load to the yoke frame. Also it transmits the lifting forces from the yokes to the form system. Suitable structural steel angle/Rectangular hollow sections are generally used as walers. In the case of straight shaft, walers are bent to the desired shape. For tapered shaft those are fitted with horizontal turnbuckle for the circumferential adjustment.



Inclination screw is fitted at the top of outer yoke leg for the variation in the slope of the wall and adjustments are done against the horizontal beam of working platform.



4.2 Sheathing or Form Panels : In the case of straight shaft, the form panels can be made of 32 to 40 mm timber boarding or 16 to 20 mm thick plywood or 3 to 4mm thick steel sheets.

The panels should be such that the friction between concrete and the panels should be minimum. In the The Bridge and Structural Engineer

4.4 Working Platform In case of tapered structures, working platforms are provided above the yoke frames (Fig.3). It supports the concrete and material hoists and provides a platform for the concreting all around the structure.

It is also used for stacking reinforcement and inserts required in one or maximum two shifts. These working platforms consist of main wing beams (trusses) and spider beams with timber boarding on top. Passenger lift is also attached with the truss or beams. However in straight shaft structures working platform are generally kept at the same level of yoke frames (Fig.1).

Volume 46 Number 1 March 2016 13

4.5 Suspended Scaffolding (Fig.5) The scaffolding suspended under the forms allows finishers to have access to the concrete surfaces getting freshly exposed progressively.

Fig. 5: Suspended scaffolding

4.6 Lifting Jacks (Fig.6) Although there are three types of jacks namely mechanical screw jack, hydraulic and pneumatic jacks, hydraulic jacks are more economical and preferred.

The jacks provide the forces required to pull the forms upwards as the concrete is being placed, and the reaction for the jacks is drawn from the jack rods. In other words, the jack climbs over the jack rods pulling the Slipform alongwith it. One or two jacks and as many jack rods are used per yoke frame depending on the wall thickness and design of yoke frame. Enough jacks must be used to lift the forms without excessive stresses on the jacks, yoke beams and form panels. If the jacks are over loaded, the upward movement of the sections of the form may not be uniform which can cause distortion in the concrete structure.

The latest sophisticated hydraulic jacks are centrally holed, and having the lower and upper grips integrated into its body. The lifting operation takes place in a particular sequence. When the hydraulic pressure is applied, the piston and upper ball grip start moving downwards. After a small downward movement, the balls bite into the jack rod and grip it preventing any further downward movement. As a reaction, the rest of the jack and yoke frame connected to it are lifted upwards, through a height slightly less than the stroke of the piston.

After a complete stroke the hydraulic pressure is released, and the piston is forced back into its upper position. This action releases the upper ball grip which moves up the jack while the lower grip bites into the rod preventing the jack and the yoke from sliding downward.

If the wall thickness is more than 600 mm, two jacks with two jack rods are placed along the thickness.

This however depends upon the design of the yoke frame members and the capacity of the jack rods.

4.7 Pump Units All the jacks are required to be operated simultaneously and hence are interconnected to a centrally located pump and the oil pressure in the system is uniform.

This assures uniform upward movements. However, any jack in the system can be operated individually or taken out of operation, if it is desired to bring a section of the forms to uniform level.

The pump is electrical, and is generally designed to operate manually even up to about 80 jacks simultaneously.

4.8 Jack Rods (Fig.7)

Fig. 6: Slipform jacks 12t, 6t & 3t

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Jack rods are generally made of 25 and 32 mm The Bridge and Structural Engineer

diameter steel rounds for 3 Ton and 6 Ton capacity jacks respectively. Steel of little higher tensile strength and hardness compared to that of ordinary mild steel is preferred. It should also have more uniform roundness.

The jack rods are manufactured in 3 to 4 meter length, to facilitate easy handling and avoid bending of the bars by free standing. They are threaded at either end to facilitate extension by means of studs. The studs are made of higher tensile steel. In most cases the jack rods are positioned centrally in the wall but there are occasions when they are required to be kept eccentric.

In such cases adequate cover must be ensured.

4.9 Tube Sleeves (Fig. 7) The jack rods can be withdrawn on completion of slipping through a height of about 40 to 50 m. A tube sleeve trailing with the Slipform creates a void around the jack rod facilitating extraction of rods. The tubular sleeve is attached with the horizontal yoke beam and the jack rod passes through this tubular sleeve. The tubes are about one meter long. Sometimes the sleeves are tapered on the external face to offer minimum resistance during lifting.

4.11 Screws and turnbuckles In case of tapered shaft, yoke frame is fitted with radius screws, wall thickness screws, horizontal turn buckles and inclination screws. All the four are operated at regular interval to achieve the desired dimensions of the structure at a particular elevation.

5. Planning and construction aspects of Slipform system 5.1 Planning Slipforming is continuous and must be executed as if a factory process. Planning and special detailing are necessary as there is little flexibility for change once the process of continuous concreting starts.

All resources should be maintained surplus, around 25% more than required at a particular point of time. Standby plant and equipment are necessary as the slipping should not be interrupted. Labour requirement shall be calculated considering the peak requirement and 5% extra labour need to be maintained all the time. Materials like aggregate, cement, sand and reinforcement should be stored at least for 15 days at a time or depending on the planned break in Slipforming. Reinforcement should be bent and stacked in advance with proper identification. Pockets and other embedded parts should be made ready in advance. Safety harnesses like nets, belts, helmets, lightning arrester etc. to be organised in advance. Uninterrupted power and water supply should be ensured along with 24hr canteen facility.

5.2 Construction 5.2.1 Slipform Program

Fig. 7: Jack rod, Tube sleeve & drain shoe

4.10 Drain Shoes (Fig. 7) At the starting point, the jack rods are erected in drain shoes which get embedded in concrete. The tube sleeve is just fitted over the drain shoe, and the joint is sealed, so that no grout leaks in the drain shoe. The drain shoe has a small tube at the base which drains out water collected in the hole formed in the concrete wall by the sliding tube sleeve.

The Bridge and Structural Engineer

It is required to be prepared for the construction of tapered shaft structure. Since the variations in dimensions mentioned earlier are required to be carried out without stoppage of Slipform operation, a definite program of operation for every 50 cm or 100cm height of the concrete shaft is worked out.

The timing and extent of each operation of radius & wall thickness screws, horizontal turn buckles and inclination screws are worked out with respect to the height of slipping.

Volume 46 Number 1 March 2016  15

plummets and laser instruments are used.

Fig. 8: Slipform assembly

5.2.2 Slipform Assembly (Fig. 8) To facilitate assembly of forms a 50 mm ledge on either side of the wall for resting the form panels is advisable. Kickers at the commencement level should be avoided. It is difficult to construct a kicker absolutely perfect and consequently initial adjustment of the forms to the correct taper and setting out becomes extremely difficult.

When tendency of the structure to go out of plumb in a particular direction is noticed, the stroke of the jacks is so adjusted that the forms on that side are raised comparatively higher than opposite side jacks. The verticality should be checked every 6 to 8 hours. It also observed that very tall chimney deflect to some extent if only one side is heated up throughout the day. This factor is also required to be considered while checking the verticality.

c)

Twist or Rotation in Plan

The entire Slipform load and the frictional resistance between concrete surface and the sheathing are taken by the slender jack rods. In short, it is lifted over some sticks which do not have adequate lateral rigidity at the load level.

In the case of cylindrical tapered and straight shaft, a small horizontal force can deflect the jack rods laterally, and if not controlled in time it goes on aggravating very fast. For checking this spiraling effect of the Slipform some marks are made on the form panels and adjacent concrete surface and these marks should be observed every 15/20 minutes. For correcting the twist the yoke frame is required to be pulled by some means in the opposite direction. This is done either by stretching screws, or providing some anchor rod and max pull arrangement.

d)

Acceptable Tolerances in construction by Slipform system as per various specifications

5.2.3 Various controls during Slipforming and Tolerances a)

Level Control

For control of level of the Slipform during jacking operation, simple water level network using colored water in 12 to 16 mm diameter plastic pipes is quite satisfactory. Marks indicating correct level are fixed on the yoke leg and the plastic pipe is fixed along the yoke leg.

All these vertical plastic pipes are connected by tees with a horizontal circular pipe ring. Colored water is filled in the tubes, without allowing any air bubbles. If the level mark is above the water level, it means the form is too high. The Slipform jacks are provided with screws for adjustment of the stroke, and the level of the yoke frame is adjusted gradually over a longer period.

b)

Verticality

i) ACI Standard 347 – 1978 Variation in wall - 10 mm; + 25 mm thickness Variation from design + 25 mm or + 12.5 diameter mm per 3 m dia whichever is larger, but in no case more than + 75 mm Variation in verticality 25 mm per 15 m height subject to a maximum of 75 mm

The simplest and cheapest means of checking the verticality is heavy plumb bobs weighing 10 to 15 kgs. The plumb bob is kept suspended from working platform with a piano wire wound over a pulley attached to the platform. Only problem is that the plumb bob swings if subjected to wind pressure and care is required to be taken in that respect. For more precise control, the optical

ii)

16  Volume 46

Number 1 March 2016

East German Code TGL 12860 Normal tolerances for structures of over 100 m height: Deviation from verticality Âą 205 mm Heights + 60 mm Dimensions of components + 60 mm (Cross section / Plan dimensions)

The Bridge and Structural Engineer

iii) NTPC Specifications Deviation of shell from plumb 1 in 1000 Variation of shell from true circular + 75 mm cross section and the specified diameter Shell thickness - 5 mm; + 25 mm

5.2.4 Reinforcement Apart from its normal function in the permanent concrete structure, the reinforcement helps during Slipforming in two ways. One is to hold the concrete from lifting during the process of Slipforming and the second is to give adequate strength to concrete in order to withstand lateral loads from jack rods. In view of these functions, the reinforcement should be in double layers i.e. on both the faces of the wall.

Large diameter bars are very heavy to handle and small diameters can be very flimsy. Diameter between 10 and 25 are recommended for reinforcement bars.

Vertical bars should not be longer than 4.5 meters and horizontal bars not more than 6 meters. If longer vertical bars are used, it becomes difficult to hold them in position and may get bent due to wind force.

Spacing of 150 to 450 mm for vertical bars and 150 to 300 mm for horizontal bars is recommended.

strong column of reinforcement bars. Alternatively, a temporary concrete column 0.25 m x wall thickness can be cast around the jack rod. These columns are required to be demolished immediately after the Slipform has moved above the opening by about a meter height, and well before the concrete in the column has attained strength to make the demolition difficult.

5.2.6 Concrete Although very sophisticated and well designed Slipform equipment is provided, the success of slipforming depends on the concrete that is being placed in the forms. Highest control on mixing and supply of concrete is demanded by this system of construction. Considerable experimental works have been carried out to assess the concrete pressure on forms and friction exerted during the process of sliding. The concrete should preferably be mixed at site, adjacent to structure to be slipformed. a)

Concrete Mix Design and Setting time

For Slipforming,concrete should be of minimum M-20 grade. No practical upper limit for the strength is specified. The speed of sliding should be such that the exposed concrete is stiff enough to withstand the pressure of concrete freshly laid inside the forms. Another requirement is that it should also be plastic enough to ensure that the cracks do not develop when the forms are lifted up. Thus the setting time of concrete plays an important role. The setting time is influenced by composition of cement, water content and ambient temperature of the area of work. According to American specifications ASTM-C403-70, the setting time is measured by recording penetration resistance of a standard needle in the laboratory. The penetration resistance of 1.75 to 7.00 kg / sq. cm is considered to be ideal for slipforming operation.

It is desirable for concrete to set at 7 to 30oC. When the temperature is low, ingredients can be heated and those can be cooled when the temperature is high.

b)

Cement and Aggregates

Ordinary Portland cement is preferable under normal conditions and rapid hardening Portland cement is recommended in winter conditions

To ensure proper cover for the reinforcement, cover spacers are fitted at the top of the sheathing every 1 to 1.5 m centers. Walls to be constructed using Slipform should have a minimum thickness of 150 mm.

5.2.5 Openings, pockets & inserts During Slipforming openings and pockets can be formed in the concrete by inserting timber frames or blocks in the Slipform. In Slipforming no projections beyond the face of the forms are possible. Great care is required while fixing the block out or timber frames; otherwise these may interfere with the sliding form and distort the same. Smaller openings up to 0.6 x 0.6 m can be formed by inserting clay bricks and card board boxes or such easily removable material.

For larger openings adequately braced timber or adjustable steel forms are common.

If a jack rod is passing through an opening of more than 0.6 m height, the jack rod is required to be supported laterally. This can be done by providing lateral supporting clamps or welding some reinforcing bars with adjacent reinforcement to form an adequately The Bridge and Structural Engineer

Volume 46 Number 1 March 2016  17

where the temperatures are very low. Natural rounded or crushed aggregates may be used.

Rounded aggregate is preferable to the crushed aggregate as it will reduce the harshness of the mix, causing less drag on the forms, sand acts as a lubricant between the wall surface and the sheathing and consequently give easier slide and better surface finish.

Under normal conditions admixtures are not required for Slipforming, however may be required considering the setting time, sliding speed and time required to place, reinforcement density etc. The concrete mix shall have a slump of 75 to 100 mm whilst the first 0.9 m height is being placed in the forms. During normal sliding, 25 to 50 mm slump at the time of placement is recommended. The use of high slump concrete during initial filling of the forms is required to allow easy compaction of concrete even when heavily reinforced and to ensure least possible use of vibrators so as to avoid damage to the forms. Use of high slump concrete during normal sliding is not recommended.

The increased water content may reduce the concrete strength; excessive grout water may leak through form and spoil the surface finish.

5.2.7 Filling of Forms At the starting position of the Slipform, 3 to 5 cm thick layer of cement and sand grout is placed and then the concrete is poured in layers of about 20 cm.

This is to be matched with the normal sliding speed to be achieved. When the fourth layer is completed the slipping operation is started. During normal sliding, the level of concrete in the forms is kept within 30 cm from the top.

5.2.8 Compaction During normal sliding, concrete should be vibrated by using 40 mm size needle vibrators, and the needle should be lowered in the concrete by thickness of freshly placed layer plus about 40 mm.

5.2.9 Curing of Exposed Concrete During normal conditions a perforated hose is fixed to the underside of the hanging scaffold. Where there is scarcity of water, moisture retaining chemical agents can be applied to the concrete surface.

5.2.10 Form Pressures and Friction The pressure exerted by fresh concrete in the forms 18 Volume 46

Number 1 March 2016

is important, firstly for safe design of the forms themselves, and secondly for the degree of frictional resistance developed.

Pressure and friction are inter-related and depend on a number of factors such as; Form surface



Initial setting time of concrete



Sliding speed



Type of compaction



Degree of workability of concrete



Taper in the forms



Within the vibrated layers, full hydrostatic pressure is developed. Below this depth the pressure rises to a maximum at about 2/3 of the depth of the form in actual contact with the concrete. At the point of separation the pressure reduces to zero.

5.2.11 Sliding speed The sliding speed is determined by; The rate of setting and hardening of the freshly placed concrete.



The rate at which concrete can be supplied and



The rate at which reinforcement steel, block outs and inserts can be fixed.



With ordinary Portland cement average sliding speed can be from 15 cm to 30 cm per hour. The speed in tropical climate should not be less than 15 cm an hour.

5.2.12 Hoisting of concrete The capacity of hoist for the concrete should be atleast 25% higher than the actual requirement based on the designed sliding speed. The concrete can be hoisted by means of suitable tower cranes, climbing cranes or conventional concrete hoists. The top pulley of the hoist is sometimes fixed over the truss platform of the Slipform or it can betaken up through a separate hoist staging. Pump concreting may not be feasible and economical because the quantity of concrete is not much to pump at a particular rate of slipping. Also discontinuous pumping is not advisable as it may damage the pump.

5.2.13 Stoppages If the Slipform has to be stopped for bad weather, plant breakdown etc., the lifting of the forms should be continued till the time the freshly laid concrete The Bridge and Structural Engineer

is adequately set and there is no bond developed between the concrete and the sheathing. This stage is generally achieved when the shuttering is lifted by about 70 cms above the top of the last laid concrete.

Sometimes stoppages are required to be planned in order to give rest to the staff and workers.

5.2.14 Electricity, illumination and communication Where the power breakdown or shut offs are quite frequent, diesel equipment is preferable. Alternatively, suitable standby power generators are required. As the work is proceeding 24 hours a day, good illumination is a must. A constant dialogue is required between the people working at top and the bottom level. Very effective telephone system is absolutely essential.

level when the Slipforming is in progress. If it is absolutely required, then suitable precautions and safety measures must be taken to ensure safety of the workers.

7. Advantages and disadvantages of Slip forming Advantages Much faster construction and time saving.



No construction joints creating monolithic and water tight structure.



Temporary scaffoldings and platforms are reduced or eliminated.



No requirement of separate material handling equipment.



5.2.15 Organisation and quality control The Organisation chart should be prepared to cover the requirement of proper personnel at ground and top levels. Responsibilities should be fixed and the activity charts should be maintained rigorously. There should be separate personnel to ensure quality control at both the levels of execution. There are instances that due to nonperformance of the equipment and due to bad planning, the slipformed concrete wall came out as defective and had to be dismantled over 1 to 2 meters in height.

5.2.16 Economy and breakeven height

Accuracy and high quality surface finish.



Disadvantages Initial cost is very high



Day and night shift of skilled labour required to be organised.



Planning is required for continuous supply of concrete, reinforcement and other items.



Reserve plan must be kept on standby in case of a break down.



8.

Troubleshooting during operation

Even if the slipform equipment is available, it may not always be economical. The equipment may need some alternations to suit a particular structure.

This involves additional cost. It takes about three to four weeks for assembly of the slipform equipment and dismantling if from the top level. From general experience the break even height may be about 50 meter for shells of about 8 to 10 meters in diameter.

Prior to opting for the Slipform system, economics should be worked out for individual structures and suitable decision taken.

Slipform operations are not straightforward. Blockouts, fixing of embedded parts, intermediate projections etc will add to the complexity of concrete placement and continuous operation of Slipform system. Extreme care and constant monitoring is required from start till end of the operation to avoid flaws in the concrete structure. Twisting of Slipform in plan, deviation in verticality and dragging of concrete are the three major problems required to be taken care off constantly.

6.

9.

Safety aspects

General safety harnesses like belts, helmets, shoes etc should be mandatory for those who work on the Slipform system. Entire working platform alongwith suspended platform are required to be covered all around and underneath from the point of view of safety of workers and to take care of falling objects.

There should not be any work going on at lower The Bridge and Structural Engineer

Some projects by Gammon

9.1 Coal storage Silos at Bokaro steel project (Fig.9) It was constructed in 1970-1971 by straight shaft Slipform system. The working platforms were provided for the material stacking and movement of workers. Concreting was done by a tower crane.

Group of 6 silos were constructed simultaneously.

Volume 46 Number 1 March 2016 19

Fig. 11: Blending Silo for M/s Raghuram Cements

10. Conclusion Fig. 9: Coal Storage Silos at Bokaro Steel Project

9.2 Singrauli RCC Chimneys for NTPC (Fig. 10) Constructed in 1980, this is the first tapered multi-flue chimney in India using state of art Slipform system which is being used today for the construction of tapered shaft. The chimney was having 21m diameter at base and is 220m tall. Top working platform was provided for the hoisting of concrete, material and manpower. Yoke legs are fitted with all adjustment screws and turnbuckles for the adjustment in dimension of the tapered shaft.

Fig. 10: Singrauli RCC Chimneys for NTPC

9.3 Blending silo for M/s. Raghuram Cements (Fig. 11) Constructed in 2008, the silo was of 22.7m outer diameter and 50.3m height. The design of the structure was done such a way that no construction joint allowed on the RCC shell. Straight shaft Slip form system was adopted for construction. There was no working platform covering entire area. Concrete and materials were hoisted by tower crane and access tower was provided for the manpower movement.

A circular plate of 20mm thick was provided at the center, on which the wire ropes/mild steel rods were connected with the yoke frame radially to control and achieve uniform slipping operation.

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Slipform equipment is very sophisticated and much costlier than the conventional shuttering. Over the years, Slipform technique has become regular in construction of high rise hollow structures and is found to be used by many contractors successfully. However adequate care need to be taken during the planning and construction stage in order to achieve good results, particularly with respect to the quality of concrete, surface finish, achieving verticality and dimensional tolerances etc. It also needs personnel having greater skills. Naturally, any small loss of time will immediately reflect on the economy of using this system.

11. Acknowledgment Both the authors have worked with M/s. Gammon India Limited for a long period. All the above information was collected while working on various projects involved with the organization. There was time when as many as 14 RCC chimneys with 14 sets of Slipform systems were operational at one stage on Gammon’s project sites across India. It was a tremendous task for the management to organize, co-ordinate and maintain the equipment as well as skilled manpower considering the operation of Slipform system is a continuous activity. So far Gammon has constructed RCC chimney of maximum diameter 36.7m and height 270.5m. It must also be acknowledged that all the know-how, equipment and training particularly for the tapered shaft was received from M/s. Inter form of Sweden since 1978.

12. References 1.

2.

3.

M. K. Hurd “Formwork for concrete- ACI SP. 4 - Formwork for concrete. 6th edition.

Good concrete guide-6: “Slipforming for vertical structures”.

R. G. Batterham “Slipform concrete”- The construction press 1982.

The Bridge and Structural Engineer

The right climbing system for every highrise project Thorsten KIRCHWEGER Product Manager Doka GmbH Amstetten, Austria thorsten.kirchweger@doka.com

Summary Selection of the appropriate climbing system will result in crucial improvements to highrise construction workflow. However, not all systems are alike. Investing in a higher-quality climbing system makes sense if it leads to savings of manpower, cost and construction time.

Keywords: highrise, building core, construction method, cycle time, climbing system, climbing formwork, jump form.

Introduction Contemporary architecture is dominated by ever higher buildings and ever more complex geometries. The success of such construction projects depends in large part on successful optimisation of the construction process. In the field of highrise construction, the decision for the appropriate climbing system has a huge impact on time and cost of construction. As a result, diligent operations scheduling is of crucial importance: in order to find the optimal formwork solution, factors such as cycle time, construction method, type of reinforcement and site equipment must be taken into account as early as during the planning phase.

Not all highrises are alike Highrises not only differ in terms of their outside appearance or architecture but mainly in terms of structural design, building materials and construction methods as well. However, many have common features, such as one or more cores built with insitu concrete for developing systems that ensure The Bridge and Structural Engineer

Thorsten Kirchweger: Product Manager for Climbing Systems for Doka. Previously, he was Group Leader and Project Leader in Applications Engineering at Doka.

Kirchweger has a degree in Construction Engineering from Technical University Vienna and Supply Chain Management from University of Applied Sciences Steyr, Austria.

accessibility. For this reason in most cases it makes sense to use a climbing system here.

The building industry is increasingly shaped by minimising cost and time of building. For this reason it is beneficial to include the formwork supplier as early as possible in the operations scheduling. Even the specifications should take into account current options of formwork technology. It is also extremely important to identify problematic building zones in advance as well. They not only consist of changing wall cross-sections, different wall inclinations or intermediate storeys with varying heights. They may also be installations weighing several tons that need to be considered. Anything that is not considered in advance will frequently result in subsequent added costs and risks caused by time-consuming improvisations after the fact that often impact safety too.

The market offers many climbing systems that differ in terms of technical function and price. It makes sense to invest in a higher-quality climbing system if it improves construction processes and results in savings of manpower, cost and construction time.

Observing cycle times when producing a storey plays an important part in staying on schedule.

Highrise cores are frequently built in a four- to fiveday cycle.

The following pie chart (Fig. 1) shows how the different activities are typically arranged when building a highrise core. In addition to forming work, a large percentage of the hours worked is used on reinforcement and mounting parts installation.

Volume 46 Number 1 March 2016  21

Typical example core

Fig.1: Selecting the appropriate climbing system may affect scope and distribution of jobs in a way that is material to project success.

Not all climbing formwork systems are alike The term "climbing formwork“ identifies the combination of shaping wall formwork with a loadtransferring primary working platform in form of a climbing scaffold or a climbing platform. Anchor parts with load capacity predefined by the manufacturer allow for safely suspending the climbing system on the preceding casting section at any height. Minimum concrete strength must be observed diligently because the climbing formwork is always attached to the most recent wall section.

It is important to carefully check each suspension point to make sure the concrete can absorb the forces introduced - possibly by way of additional reinforcement that might be required. Usually rising and suspended platforms for reinforcing, pouring, operating the climbing system, reworking the concrete and dismantling the suspension points are installed above and below the main working platform.

Climbing formwork is lifted up to the next casting section either by crane or independent of a crane by way of hydraulic cylinders, with and without being guided on the structure. Depending on type of building, climbing systems can also be used at the edge of the slab: for producing façade walls or columns, vertically transporting formwork material, or in the form of a fully enclosed screen system to protect the site crew from falling and weather.

formwork is that it can be adapted to allow for customization with any ground plan in terms of panel size, fresh concrete pressure and number of form-tie points. On the other hand there are framed formwork systems consisting of standard panels in various sizes. They are assembled in accordance with the kit principle and adapted to the shape of the structural element to be created out of concrete.

Mainly when building shafts a well thought-out formwork design may result in saving hours of work due to the often large number of similar casting sections and repetitive operations. Here “thinking of stripping while making plans for forming” may turn out to be a crucial advantage. Especially on inside corner areas it is vital to ensure easy separation of formwork from concrete and to create the most spacious stripping distance possible for efficient working conditions. At the same time it is beneficial to keep the number of form-tie points to a minimum.

Tie rod systems that can be operated from one side may result in significant time savings.

In general it is important to use durable formwork sheets when producing a large number of casting sections. Generally these are high-quality multi-ply formwork sheets coated with phenolic resin or plastic.

Formwork sheets made of steel are used as well.

Changing sheets is a time-consuming operation best avoided or deliberately scheduled in the construction workflow.

In addition to its own weight and that of the formwork, the climbing scaffold must also transfer live and wind loads into the casting section already completed. For this reason, securely anchoring the climbing scaffold is of enormous importance. The climbing system can be lifted as soon as the section poured last has achieved sufficient strength.

Crane-dependent climbing

Climbing systems function as kit solutions

When using a crane for lifting, it will lift the climbing scaffold and formwork to the next section as one unit.

Crane and load capacity must be planned accordingly.

Here a distinction is made between systems that are "guided on the building" and those that are "not guided on the building".

The climbing scaffold can be combined with largearea formwork and with framed formwork systems as well. The distinguishing feature of large-area

During lifting, climbing formwork not guided on the building are completely detached from the structure and suspended freely from the crane. Even at low wind

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The Bridge and Structural Engineer

speeds the area exposed to and resisting wind may lead to problems. The process of lifting individual units creates temporary fall hazard locations that must be secured accordingly. Systems that require cranes for lifting are normally used for buildings up to 20 casting sections (Fig. 2).

building. The process of lifting individual units by means of a crane creates temporary fall hazard locations that must be secured accordingly.

Crane-independent climbing Crane-independent climbing systems guided on the building avoid some of the open fall hazard locations because several climbing units are lifted simultaneously. The preferred way of moving these climbing systems is through hydraulics, using portable hydraulic cylinders and hydraulic units. A single hydraulic unit can supply power for several hydraulic cylinders at once. When crane capacity is available, some types are quickly lifted as well by means of a crane (Fig. 3).

Fig.2: The risk of downtimes caused by wind and limitations of crane capacity must be taken into account when using crane-dependent systems not guided on the building.

The advantage of climbing systems guided on the building is that they remain connected to the building during the lifting process as well. The aspect of safety while lifting climbing systems must be considered as early as during formwork planning. Average wind speed rises proportionally to height above ground. In order to reduce the risk of downtimes, systems that can be lifted even at higher wind speeds are used here.

All-hydraulic drives ensure speed

Currently the limit is at 72 km/h wind speed. Steel profiles secured in climbing shoes attached to the structure ensure that the system is guided on the

The principal difference to simple crane-independent climbing systems guided on the building is the allhydraulic equipment of climbing units. They allow

The Bridge and Structural Engineer

Fig.3: Crane-independent climbing systems guided on the building allow for consideration of downtimes due to wind and weather as well as compensation of crane downtime through use of a mobile hydraulic unit.

Volume 46 Number 1 March 2016  23

for safely climbing large platform gangs such as all platforms on the outside of a core in a single lifting procedure without open fall hazard locations. Such systems cannot be lifted via crane.

The hydraulic lifting process requires two important steps: In the first step the climbing profiles in the climbing shoes anchored on the building are raised by hydraulic cylinders up to the next section. In the second step the climbing scaffolds are pushed upward along the climbing profiles by the same hydraulic cylinders.

This type of climbing formwork is extremely versatile and also allows for climbing inclines, radii and bends.

In addition to highrise cores, these systems are also used with piers and pylons. Systems with 5 and 10 tons lifting capacity per climbing unit are established in the market (Fig. 4).

Fig.4: Crane-independent climbing systems with allhydraulic drive as exemplified by the “core formed ahead” construction method largely uncouple the construction workflow from wind, weather and crane capacity.

the entire site equipment consisting of formwork, reinforcement steel for daily work, material container and concrete placing boom for a building core. Longstroke hydraulic cylinders raise the platform in a single lift to the next casting section without a crane.

The formwork is suspended from a girder grille like a curtain for easy forming and stripping. The larger the area of formwork that can be positioned below the pouring and reinforcement platform the more economical the system. Structural and customer requirements, especially installation of reinforcement or mounting parts, play an important role in this regard (Fig. 5).

Fig.5: Automatic climbing platform systems uncouple the construction workflow in highrise cores from wind, weather and crane capacity as much as possible.

Platform systems with spacious work area

Everything must be in synch

Platform systems are formwork machines geared especially to building highrise cores. The primary component is an enclosed forming and work platform for safe working conditions and protection from weather even at lofty heights. It can accommodate

The method of construction is greatly influenced by the building‘s structural design with corresponding reinforcement layout. Here a distinction is made between the "core formed ahead" and the "slab and walls cast in one pour" construction methods.

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The Bridge and Structural Engineer

Most times subcontractors carry out reinforcement work by the piece. It is important to gear the climbing system to the requirements and in doing so influence the workflow positively. Vertical scaffold systems start off with simple pouring platforms on the formwork. Disadvantage: Once the formwork is stripped, these platforms can no longer be used for installing the reinforcement. In contrast, pouring and reinforcement platforms that are independent of the formwork allow for optimal reinforcement installation even during the stripping process. In this way forming work is separated from reinforcement work, thereby allowing for simultaneous work on several levels. To accommodate taller reinforcement bars in advance, several rising reinforcement-platforms can be arranged vertically. In the event of thicker walls and increased degree of reinforcement, planning for reinforcement work to be carried out from two sides makes sense as well (Fig. 6).

Another important consideration are confounding factors resulting from changed building geometries and related modifications to the formwork and replacement of worn formwork sheets. Work for producing staircases / stair landings must be included too. For this reason it is important to have the foresight to address these issues during formwork planning.

As mentioned initially, a highrise does not consist solely of a core. It also includes façade and floor-slab through to the installation of the façade panels. It is important to consider the synergy here as well.

Conclusion Depending on the ideas of the customer, there are many different requirements for climbing formwork. Not every climbing system is suitable for every building. Likewise the building height does not immediately determine the best system.

Therefore, when developing a formwork concept it is very important to consider the various customer requirements as well as framework conditions related to construction operations from the very beginning.

With each and every climbing project the following steps are strongly recommended: close cooperation with the formwork supplier, utilising his experience and expertise, and an overall economic concept in terms of engineering, construction workflow and budget to be provided as early as during the project development stage (Fig. 7).

Fig.6: Crane-independent climbing system with all-hydraulic drive and pouring platform on formwork, reinforcement and pouring platform and rising reinforcement platforms.

The higher the building the less economical the concrete installation by way of crane and bucket.

As the building height increases so do lifting and sinking times and also the time the crane is tied up. Installation capacity can be increased by using concrete pumps with various types of placement systems and large booms for efficient installation of concrete. Combining the concrete placement system with an automatic climbing system also provides the opportunity for lifting the system without a crane separately or together with the remaining automatic climbing formwork, as required.

The Bridge and Structural Engineer

Fig. 7: Climbing technology at the edge of the building and for the core during the Omkar Worli construction project in Mumbai, India.

Volume 46 Number 1 March 2016  25

Construction Design of Signature Bridge in Delhi Mario DE MIRANDA Civil Engineer Studio de Miranda Associati Milano, ITALIA info@demiranda.it www.demiranda.it

Summary This article describes the construction and construction engineering of the cable-stayed bridge on the Yamuna River, in the district of Wazirabad, in the city of Delhi, India, carried out by DMA, de Miranda Associati Consulting Engineers, Milan, Italy. Construction is in an advanced stage and this paper briefly describes the main construction issues.

Mario de Miranda is a bridge designer. His work, experience, and research are mainly related to the design and construction of cable stayed and suspension bridges, wind engineering and the history of construction. He obtained his Civil Engineering degree from Politecnico di Milano, Italy, in 1979. He is partner and director of Studio de Miranda Associati - Consulting Engineers.

He has been involved with many major projects, most of them as lead designer, including large cable supported bridges in Italy, Denmark, Algeria, Brazil, Dominican Republic, India, Iraq. Since 2006, he is an Invited Professor of Structural Design at IUAV Venice University. He is the author of more than 60 papers and chapters of books on bridge design as well as of patents of construction methods.

DTTDC Delhi Tourism and Transport Development Corporation, and was developed by a consortium made up of the firms Schlaich – Bergerman und Partners and Construma Consultancy.

The bridge, which is currently under construction, has a main span of 251 metres with steel-concrete deck; . Its layout is shown in Fig. 1.

Keywords: Cable-Stayed Bridge, Steel, Concrete, Cable, Construction,

1. Introduction The subject is a cable-stayed bridge with a main span of 251 metres and breadth of 36 metres, supported by cables that converge at the top of a single steel tower that is 140 metres tall.

Fig. 1: General assembly of the completed bridge

Due to its great width, the construction of the deck, with its composite steel-concrete structure, required some problem-solving.

The 36 m wide deck structure, with three longitudinal beams and transverse girders, is being erected on temporary piers by means of a goliath crane.

Due to its configuration, height, and weight of 7000 tonnes, the construction of the tower also posed some interesting problems that will be described later in this article.

The tower is 150 m high from the deck level, has two main legs inclined in two directions and a top main body with a variable cross section.

2.

Bridge Description

The final design of bridge was supplied to the Contractor, a JV made up of Gammon India, Tensacciai and Construtora Cidade, and the Owner

26  Volume 46

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Its weight is around 7000 t and the method for erecting this structure is a real challenge.

Stay cables, in parallel strands, are anchored to the side longitudinal girders and the two forward boxes of the main body.

The Bridge and Structural Engineer

DMA, which participated in the tender as a consultant for the JV, was in charge of checking the erection analysis carried out by the designer, and of the entire construction engineering design.

It developed the Construction Engineering, which includes the Construction Method Concepts, the Detailed Construction Method Statement, the Design of Auxiliary Structures, Rigging Plans and related equipment, as well as the step- by- step analysis of the erection phases in order to control the bridge geometry and strength during construction.

3.

Construction Design

Starting from the final design, the bridge can be constructed based on a system of detailed construction design called Construction Engineering, or CE, which is the complex activity aimed to define and design the entire construction process, as well as the construction structures and equipment needed to build the bridge.

The importance of Construction Engineering increases proportionally with the size and complexity of bridge.

While the Final Design assumes that the bridge is a completed single structure, the Construction Engineering must take into account the evolution of bridge construction, and the numerous intermediate partial structures that arise, grow and evolve during construction.

The number of drawings required by CE is much larger than the number of drawings that define the final structure, and the designing work, for large structures, is also greater. Fig. 2 summarizes the CE work, highlighting the requirements, tasks and responses.

Signature Bridge, because of its large size and of the unusual shape of its tower, required a challenging CE and many interesting problems, illustrated below, also had to be solved.

4.

Construction Method

Fig. 2: Construction Engineering Flow Chart

by supporting them on temporary towers and by means of a goliath crane;

-

assembling of the tower panels in segments;

-

lifting them and installing the panels on special steel frames,; as later described;

-

lifting segments by means of a crawler crane and placing them over the already erected structure;

-

erecting a special structure able to support and brace the inclined legs during their construction;

-

proceeding up to the end of the erection of the tower;

-

install the stay-cables and applying the first tensioning;

-

dismantling the temporary structures.

4.1 Concept The erection method includes, the following steps: -

fabrication of tower panels and deck girders, their pre-assembly and transportation (Fig. 4);

-

erection of deck girders and precast slab panels

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Fig. 3a and 3b illustrate the main phases.

Volume 46 Number 1 March 2016  27

Fig. 3a: Construction Method – Deck and base of pylon

28 Volume 46

Number 1 March 2016

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Fig. 3b: Construction Method - Cables and top of pylon

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Volume 46 Number 1 March 2016  29

The connection between the Main Body and Legs is created using flanged joints, machined at the workshiop, with a total length of 35 m.

Problems The main design problems to be solved in order to erect the pylon were essentially: how to stabilize an inclined structure, hinged at its base, during construction;



how to recover structure deformation during erection;



Fig. 4: Main Body segments during trial-assembly at fabrication workshop

how to install large, heavy box girder segments that had to be placed, one above the other, in a position with double inclination;



4.2 Challenges There were essentially two main difficulties in the construction of this bridge: building the composite deck, where the width of 36 m and length of 575 m meant solving problems related to alignments, temperature, temporary restraints, and earth quake effects;



how to manage the temperature effect, together with the tight tolerance of a bolted structure.



Solutions The main solutions to these problems were as follows: The longitudinal stabilization of the inclined legs during the first erection phases was done by means of a temporary clamping of the leg bases, realized by installing a set of tie-down cables; Fig. 5.



erecting the steel pylon, which is inclined in two directions, and weighs 7000 t and, which has to be installed at height of 160 m.



This last issue will be described in some detail in the following pages.

The stabilization of the double inclined legs was done by designing and installing a supporting spatial macro structure consisting of the following substructures:



4.3 Pylon construction method Description The pylon is composed of two legs, box girders, inclined backwards and inwards and connected at a level of +63 m by a Main Body, that is a vertical shaft with variable cross section, which hosts the top anchorages for the stay cables.

The legs have a rectangular box girder with a constant width of 2.50 m and height varying from 7.20 to 9.60 m.

The Main Body, still a box girder, has a maximum width, at its base, of 20 m and a minimum width at the top of 13 m.

The two legs are hinged at the base so they would be unstable during erection, unless some sort of device was provided.

The pylon was divided into segments with, weights varying from 40 to 250 t;. The joints between segments were flanged bolted joints, with machined flanges.

30 Volume 46 Number 1 March 2016

- a cross bracing system, progressively connecting the inclined legs, which gave transverse stability to the legs, contrasted the inward deflection and, by means of horizontal jacks, allowed to recover the horizontal displacements in order to preserve the leg design geometry, up to the connection with the main body; Fig. 5.

- a couple of inclined, large diameter pipes provided longitudinal stabilization for the intermediate phases.

- the vertical support of the Main Body, and contribution to longitudinal stabilization, was provided by a couple of large diameter subvertical pipes; with a set of vertical jacks at the top, in order to recover the vertical and horizontal displacements of the cantilever legs in the last erection phases; (see phase 5 in Fig. 3a).

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and designing the following system (Fig. 6-7-8):

- segments were assembled horizontally, then moved over a special frame, made of three layers.

- after assembling, the bottom frame was tilted longitudinally in order to get the proper longitudinal inclination; then it was attached.

- the top frame was then tilted transversally, in order to achieve the proper transversal inclination; then it was propped.

- lifting lugs were installed on the segments, using the of flange joint holes.

- slings of proportionate length were finally installed. The position of the lifting lugs and the length of the slings were designed so that upon lifting the lifting hook would be positioned on a vertical axis passing for the Centre of Gravity of segment. In this manner the segment would travel, from take-off to landing on the preceding segment, always in the same three-dimensional position, which is the 3D final position. A set of centering devices helped the final positioning.

Fig. 5: First level of transverse bracing system

The correct positioning, with double inclination, of the leg segments was achieved by conceiving

ď Ź

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Volume 46 Number 1 March 2016  31

Fig. 6: Sequence of assembling a segment of one leg, inclining it in two directions and lifting it

Fig. 7: Lifting the segment with the same 3D orientation it will have at final matching

32  Volume 46 Number 1 March 2016

Fig. 8; Segment lifting

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Fig. 9: Placing the 450 t base element of the long pylon

Temperature changes, mainly, during the day, due to direct sunlight, modified the real/actual

ď Ź

geometry of the structure, continuously changing the position of working points and apparently making, it almost impossible to install the pipe elements in their theoretical position. In order to fix the problem, we decided to consider temperature change as an opportunity, instead of an adversary. So, we decided to monitor the structural movement over time, detecting the hours in which the joint distance was larger than theoretical, and set these hours for installing the elements, fixing them only at one end, and leaving the other sliding. Then, during the hours in which that distance tended to close, the second end bolts were installed, and tightened only at the time in which the theoretical geometry was achieved.

Fig. 10: Installing the bracing elements taking advantage of temperature changes, and recovering elastic deflections

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Volume 46 Number 1 March 2016  33

Work Progress At the time these notes were written the bridge is about 90% erected, and it is scheduled for completion for the end of this year.

construction engineering analysis from DMA, in Italy; and Swapnil Navalkar from Gammon, in China, who followed fabrication and trial assembly and then came to Delhi to work at the jobsite with Ozi Noel from Cidade to follow the erection, Mathias Widmeier and Uwe Burkhardt from Sbp to check workshop drawings, and under the management of Ramchandra Prakash, Venkatramana Heggade, and Mohan Jatkar, from Gammon. Figures 12 to 15 document the work progress.

Fig. 11: Installing horizontal active bracing between pylon legs

Fig. 13: Installing a 140 t double -inclined leg segment at 60 m

Current Conclusions Bridge construction is always a difficult and challenging task.

Fig. 12: Erection of the second level of the transverse bracing system

Large dimensions, inclined high structure, and heavy weights to be lifted bring additional problems.

The construction work was developed by many engineers in different countries, including Luca Marinini and Luigi Origone who worked on

Nevertheless, a detailed and integrated study construction method, lifting plans, and of the construction structure, along with the constantly

34  Volume 46 Number 1 March 2016

The Bridge and Structural Engineer

checking the structural behaviour, which is proper Construction Engineering, make it possible to overcome even large problems and allow even the most complex and difficult constructions.

Data Block Owner: DTTDC - Delhi Tourism and Transportation Development Corporation.

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Designer for Owner: SBP - Berlin with Construma Delhi.

Contractor: Gammon India - Construtora Cidade, Brazil - Tensacciai, Italy.

Consultant for Contractor and Construction Engineering: DMA - Studio de Miranda Associati Milan - Italy.

Volume 46 Number 1 March 2016  35

Construction of 120m Span Arch Bridge using Cantilever Form Traveller Alok PANDAY Managing Director Elegant Consulting Engineers Ghaziabad, India elegant_alok@hotmail.com

Summary Though bridges are primarily meant to carry the traffic, the picturesque view of hilly surrounding of the bridge over river Parvati in the state of Himachal Pradesh inspired to explore the possibility of adding further “elegance” to the site through bridge aesthetics.

As arch bridges are known to be a true counterpart of hilly surroundings, the same was proposed at the site to enhance the scenic appearance of the surroundings.

While proposing the bridge, one of the key concerns was substantial flow in the river almost throughout the year. Continuous flow in the river refused to accept the use of ground supported staging and formwork for construction of the bridge. It was therefore proposed to use cantilever steel form traveller for the construction of the bridge. The paper primarily discusses about the sequence and methodology of construction the bridge using cantilever form traveller supported over stay cables. The bridge has probably become longest concrete arch bridge of the country.

Keywords: arch bridge; cantilever form traveller; steel pylon; stay cables.

1. Introduction: The bridge over river Parvati near Kullu (HP), which has become a landmark structure of the country, is a reinforced concrete arch bridge having a span length of 120m between springing points of the arch ribs (Fig.1 to 3). Total width of the bridge at deck level is 15.2m which accommodates 7.5m wide carriageway to carry two lanes of the traffic and 1.5m wide footpaths on 36 Volume 46 Number 1 March 2016

Alok Panday, post graduated (structures), IIT Roorkee, is having 22 years of professional experience. He is member of some of the codal committees & guest faculty at IAHE. He has delivered over 75 lectures to train engineers of various countries.

either side of the carriageway (placed outside the arch ribs). BBR DINA hangers (consisting of 75 nos. high tensile 7mm diameter steel wires enclosed in HDPE pipe) suspended from the arch ribs support the cross beams at deck level which finally support the deck slab. Where arch ribs are below the deck level, cross beams have been supported over bracing connecting the arch ribs or piers at the ends.

Fig. 1: Arch bridge over river Parvati near Kullu, HP

Due to continuous flow in the river, it was not feasible to construct the bridge over ground supported staging and formwork. It was therefore proposed to construct the arch ribs over cantilever steel form traveller with the help of about 36m high temporary steel pylon and BBR stay cables. Each arch rib was divided into twenty segments and a closing pour at the crown (Fig.4). The staring stub i.e. first segment (near springing point) on either side was concreted over ground supported staging and remaining segments over steel form traveller supported over previously The Bridge and Structural Engineer

cast segments/temporary front stay cables from steel pylon. Cross beams supporting deck slab were cast over the formwork supported over BBR DINA steel hangers of the bridge suspended from the arch ribs.

The sequence and methodology of construction along with typical details of temporary structures & stay cables are presented in the following sections.

2.

Sequence & methodology of construction

Construction of the bridge was primarily done in the steps given below. Typical details of the temporary structures and stay cables are presented in the following section.

Casting of the well foundation, piers & pier cap on either side of the bridge;



Casting of the open foundations and piers of the left viaduct (147m long, consisting of seven continuous spans of voided deck slab) on Bhuntar side and right viaduct (105m long, consisting of five continuous spans of voided deck slab) on Ramshila side;



Casting of voided deck slab of viaduct on either side except in the end spans near arch bridge;



Casting of starting stub i.e. first segment over ground supported staging, erection of lower part of temporary steel pylon and installation of back stay bottom cables on either side of the bridge (Fig.5);



Fig. 2: Arch bridge over river Parvati near Kullu, HP

Fig. 5: Erection of pylons, installation of stays and casting of starting stub & stage-1 segments, Fig. 3: Typical elevation and section of the bridge

Installation of first front stay cable (SC1) and erection of form traveller (front frame, supported over previously cast segment & stay cable) on Bhuntar side i.e. towards grid “P7” (Fig.5);



Concreting of next (stage-1) segment over form traveller (Fig.5);



Erection of complete form traveller (front & rear frames) supported over previously cast (stage-1) segment and concreting of next (stage-2) segment over the form traveller (Fig.6);



Fig. 4: Half elevation of bridge showing arch segments

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Volume 46 Number 1 March 2016 37

Concreting of arch segments on Ramshila side i.e. towards grid “P8” following the above steps;



Casting of the closing pour over the form traveller (Fig.9) once segments on either side of closing pour have been concreted;



Bracings connecting arch ribs were also concreted along with various segments of the arch ribs;



Concreting of the cross beams over formwork supported over BBR DINA hangers (Fig.10);



Concreting of the deck slab over formwork supported over cross beams (Fig.10);



Fig. 6: Concreting of stage-2 segment over form traveller

Repeating the above steps till concreting of stage-5 segment and installation of fifth front satay i.e. SC5 (Fig.7 & 8);



Typical details of the temporary structures and stay cables are given in the following sections.



Fig. 7: Concreting of further segments over form traveller

Erection of upper part of steel pylon, installation of back stay top cables, installation of further front stay cables and concreting of further segments till stage-9 segment i.e. segment prior to closing pour (Fig.8);



Fig. 8: Further erection of pylon, installation of stay cables and casting of segments

38 Volume 46 Number 1 March 2016

Fig. 9: Concreting of the closing pour over form traveller

Fig. 10: Formwork supported over DINA hangers for casting the cross beams

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3. Typical details of temporary structures and stay cables Typical details of steel pylons which support front and back stay cables are shown in Fig. 11. Pylons were anchored to the pier cap using BBRV short tendon (Fig.12). Typical section of column, tie beam and strut beam of the pylon are shown in Fig.13. Bracings of the pylon were primarily made of a combination of two nos. ISA 100x100x6 angle sections and 8mm/16mm thick plates as required.

Fig. 12: Anchoring steel pylon with pier cap using BBRV short tendons

Fig. 13: Typical section of column, tie beam & strut beam of steel pylon

Typical details of cantilever form traveller are shown in Fig.14 & 15. Top and bottom chords of the traveller were made of a combination of ISMB300 and 8mm/16mm thick plates as required. Vertical and inclined members were primarily made of ISMB200.

Fig. 11: Typical details of temporary steel pylons Fig. 14: Model view of the cantilever form traveller

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Volume 46 Number 1 March 2016  39

using cantilever form traveller is not so common.

With better understanding of the subject, upgraded experience and availability of the software capable of giving accurate & precise results, it is now possible to have long span arch bridges and explore possibility of different methods of construction depending upon the site conditions. The methodology of construction of arch bridge discussed in this paper may be helpful as a reference when going for long spans and where construction of bridge is not feasible over ground supported staging & formwork.

Fig. 15: Elevation of cantilever form traveller

Bottom and top back stay cables consisted of 57 BBRV 7mm diameter cables and 80 BBRV 7mm diameter cables respectively. Front stay cables consisted of 42 BBRV 7mm diameter cables (SC1, SC2 & SC3), 52 BBRV 7mm diameter cables (SC4 & SC6) and 82 BBRV 7mm diameter cables (SC5, SC7, SC8 & SC9).

4. Conclusions Though arch bridges have been constructed since ages, construction of long span arch bridges specifically

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5. Credits Owner:

Ministry of Road Transport & Highways, New Delhi and Himachal Pradesh PWD, Himachal Pradesh, India

Structural Consultant: M/s Tandon Consultants Pvt. Ltd., New Delhi, India Construction Engineer: M/s BBR (India) Pvt. Ltd. Contractor:

M/s V.K. Sood Engineers & Contractors, Chandigarh, India

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TEMPORARY WORKS PAVES WAY TO PERMANENT PROFIT Raja Rajan. K Sr. Design Engineer, AFCONS Infrastructure Ltd, Mumbai, India. raja.ranjan@afcons.com

Summary AFCONS has its own business units like Marine & Industrial, Transportation, Rails & Metro and Hydro & Tunnel which involves its own enabling works in order to successfully complete its some of the landmark projects. Temporary works are among the key factors in determining the success of a construction project in terms of speed, quality and cost of the project. Excellent co-ordination between temporary structure and permanent structure may perceive through operational excellence which ultimately yields sizable profit to company. Nowadays due to heavy competition in bidding, contractor has to reduce his profit margin in order to win the bid.

Even though saving money is the top priority of a construction company, especially adhering to the limited constraints of a tight budget, it is vital that quality of the temporary works not to be sacrificed. In this paper the author attempts to bring out the impact of enabling works in ease of construction and also in cost saving in line with time, quality and safety.

Keywords: Temporary works; profit;cost impact; projects; Infra-structure; contractor; enabling works and co-ordination.

1. Introduction 1.1Infra-Structure in India Given the fact that strong infrastructure facilities form the backbone of a nation’s economy, the Indian government began to shift its focus on infrastructure development. According to twelfth five year plan, Indian government plans to invest around 56 lakhs crore on infrastructure project by the central & state government which also includes the PPP (Public Private Partnership) investments. But in recent The Bridge and Structural Engineer

Raja Rajan, born 1987, received his Masters in Geotechnical Engineering from Anna University Chennai.. Having one year of site experience (marine) and 4 years of design experience in enabling works of bridges and metro projects.

weeks, there has been a spate of reports about delays or reversals in approvals for various projects.

Changes in rules (regarding forest use, environment protection, land acquisition, tribal habitat and so on), or the way these are interpreted, can further stall projects. Several high profile infrastructure projects have come under a cloud – airports, expressways, rail links, highways, thermal power, coal mining, and hydro-electric generation. For infrastructure companies, such situations, if they drag on, can turn an attractive opportunity into a nightmare. Already, there are reports of specialized construction packages being awarded to Chinese and other foreign players.

Infrastructure companies have to evaluate the emerging situation and find ways to compete and win in an uncertain environment. This will bring more global competition into India, especially as contract sizes keep growing. All players need to study these trends, continuously upgrade/refine their offerings, define the verticals, customer segments and packages that form their addressable market, and identify where they are best positioned to compete.

2. Temporary works Temporary works are among the key factors in determining the success of a construction project in terms of speed, quality and cost of the project. Though all competitors in construction industry going to do same work, it is the temporary works which makes a company to stand unique and helps in for completion of project in smart and fastest way.

2.1 Pile cap construction – Change in method of construction In IInd Bhairab railway bridge project, 2.5m diameter pile has to be casted and 6 numbers of pile forms Volume 46 Number 1 March 2016 41

a pile cap having dimension of 15.4m X 10.4m X 3.75m, which consumes approximately 600cum of concrete that leads to a dead load of 1560T only for single pile cap. The bridge alignment was crossing river Megna in which the maximum water level in monsoon season will be touching the soffit level of proposed pile cap. Since the dead load of pile cap is too heavy, formwork of the same will also be very high and number of pile cap is only 9 in numbers, so probably the invested cost in friction clamps and staging material may not be cost effective. Adding to that water level will be touching the soffit of pile cap, so fixing and removing heavy friction clamp and laying all soffit staging material will be a challenging task in monsoon period. So all the above factors leads to think in a different way so that formwork cost also to be effective and at the same time work should not hampered in monsoon period. Ultimately the idea of change in construction method evolves out in order to work in monsoon and also showing a great savings in temporary works. The following case study may clearly explain the impact of method of construction on temporary works.

Initially as per client’s drawings/methods, it was stated that entire pile cap depth of 3.75m to be constructed in a single pour and the same was shown as single stage construction in fig1a which ultimately leads to heavy soffit formwork and friction clamps. Later in design department, a proposal was made considering the above facts that pile cap will be done in stage wise i.e. construction of pile cap will be in stage wise such that first 1m depth of pile cap will be constructed which will be acting as a soffit for next 2.75m depth pile cap as shown in fig1b.

Approval from client: - Since the methodology of construction is deviating from client method, it is the responsible of the contractor to get approval for new proposed method by convincing the client in design aspects and as well as in timely completion of the project. Permanent design check were carried out using software such as MIDAS civil & STAAD pro and concluded that due to stage wise construction some additional moments, interface shear and differential shrinkage were encountered and the same was catered by providing extra reinforcement.

Continuous rigorous follow up with design consultantSTUP & client with sufficient design document leads to approval of the proposed method.

Stage wise construction: - For stage wise construction 175thk precast sacrificial panel were casted so that the precast panel will act as soffit. Friction clamps were fixed with pile and above the clamp, main girders were spanning over which the sacrificial precast panel were laid to act as soffit shutter. Side formwork were erected and connected with tie rods (fig2a).

Fig. 2a: Soffit form work for Stage 1

Fig. 1a: Single stage construction

Fig. 1b: Multi stage construction

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Fig 2b: Stage 1 completed which acts as soffit for stage 2

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Table 1: Rate comparison of all 8 pile caps in IInd Bhairab Railway project, Bangladesh Parameters considered

Cost of Soffit formwork

Method 1 Method 2 One stage Two stage construction construction 34.3 lakhs

10.3 lakhs

Cost of side formwork

11.6 lakhs

11.6 lakhs

Salvage Value (resale of formwork)

-16.7 lakhs

-6.8 lakhs

Cost of Friction clamps

13.65 lakhs

1.2 lakhs

-

15.6 lakhs

Handling cost & Misc.

37.3 lakhs

15.3 lakhs

Cost of crane & other equipments

26 lakhs

26 lakhs

106.1 lakhs

73.2 lakhs

Cost of Extra Reinforcement (additional)

TOTAL COST

First 1m concrete was casted with extra reinforcements to cater the additional moments, shear and shrinkage due to stage wise construction. After 14 days, second stage of concreting started; meanwhile tying of reinforcement took place in order to reduce the time cycle. Now the bottom 1m slab will act as soffit for the remaining 2.75m thick pile cap, which ultimately saves a huge amount in soffit formwork and friction clamps.

curvature, minimum & maximum span length, maximum super elevation, span weight, segment weight & physical dimensions etc. AFCONS has used many launchers like Bridgecon LG, Afcons LG, NRS LG, SPIC LG etc in various projects.

But in Barapullah project, the superstructure design and geometry was very complicated such that the available launchers with AFCONS have gone ruled out. Since it was connecting the Barapullah Phase I lane in many places, our project location/stretches were scattered in different areas. The above critical requirement leads to transport of launcher from one location to other location as per construction schedule, so assembling and dismantling of launcher should be as quick as possible or else we are forced to deploy more number of launchers if project schedule is not in line with construction schedule. The superstructure type and geometry configuration of Barapullah project for choosing launcher has been tabled in 1.2 Table 2: Barapullah project span details & parameters for choosing launcher.

Parameters

Value

Type of super structure

Precast box segment – 3span/2 span continuous

Launching stages

Stage 1 – L + L/5 Stage 2 – L Stage 3 – L-L/5

Minimum Height of Pier

3m

Maximum Height of Pier

13m

Minimum Radius of Curvature

222m

Above table clearly shows that by choosing the Method 2, construction cost can be saved nearly 31% which will be a direct saving to contractor. Though we constructed the same pile cap as instructed by client, just by changing the methodology of construction leads to savings of approximately 33 lakhs in construction cost.

Maximum Super elevation

4%

Maximum Gradient

5%

Minimum & Maximum Span length

19m & 37m

Type of Bearings

POT/PTFE Bearings

Number of stretches

Ramp A, B, F & G. Structure H, J (Left & Right) – Total 7 stretches

2.2 Ground supported staging for erecting precast Box segments

Maximum Segment Weight

45T

Location of Stretches

Fully in Nallah portion

Savings in Construction cost: - So as a contractor, management may be eager to analyse the cost savings part due to adoption of different methodology.

Table 1.2 shows the cost comparison between 2 methodologies.

Success of an elevated viaduct project mainly lies in selection of launcher for erecting precast box segment. Selection of launcher also depends upon type of superstructure, geometry of alignment, location of alignment, maximum gradient, minimum & maximum height of pier, minimum radius of The Bridge and Structural Engineer

Considering all the parameters which were tabled above, a new system called Ground Supported Staging - GSS was developed in order to suit all launching criteria and geometry complications. GSS system had been designed such as matching all the criteria which was dictated by the project.

Volume 46 Number 1 March 2016 43

The below figures (Fig 3a & 3b) shows the ground supported staging before and after segment erection.

Since the entire stretch of the project falls in nallah portion, expected safe bearing capacity was not encountered. In order to overcome that in certain places steel liners were given to ensure that erection

load is safely transferred to soil through friction. For segment feeding a crane is needed along with the system, but once the segment is placed over trolley then system is engineered such a way that entire geometry control can take place with help of jacks given for all movements.

Fig. 3b: GSS after segment erection Fig. 3a: GSS before segment erection

Segment can be moved longitudinally, transversally and also vertically in order to suit the geometry

profile of the span. Apart from above some of the main advantages of the system are tabled below

Table 3: Comparison of Ground Supported staging with Bridgecon Launcher S.No.

Parameters

Ground Supported Staging

Bridgecon launcher

1

Assembling & Dismantling of launcher

Since it was made up of many small components, assembling and dismantling of GSS is very easy and less time consuming.

Service crane of 30T will do for erection of GSS.

Since wt. of 1 Bridgecon module itself weighs around 36T, needs a big crane and elaborate arrangement for assembling and dismantling of launcher which consumes months together.

2

Different pier heights

GSS Towers were made in modules of 2m, 1m & 0.5m, so accordingly combination of different modules will make the desired pier height which ranges from 3m to 15m.

It can be used in different heights but restricted to maximum gradient of 2% only.

3

Transportation of launcher

Since project is in many stretches (different locations), transportation of GSS from one location to other was very easy with help of service crane itself.

It is always advisable to use in continuous stretches only since erection and dismantling takes lot of time.

4

Span geometry

The geometry profile of span consists of maximum gradient of 5%, maximum superelevation 4%, minimum radius of curvature 150m were considered while designing the GSS launcher.

In this launcher, maximum gradient of 2%, maximum super elevation of 4%, minimum radius of curvature 302m were considered.

5

Launcher weight

The main advantage of this system, the weight of launcher is only 80T which is only 25% weight of overhead launchers

Weight of 1 Bridgecon launcher is 310T

6

Load on Permanent structure

While erection load is transported through tower legs directly over pile cap

Erection and launcher load transferred to Pier cap, sometime exceed the design load of pier.

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The Bridge and Structural Engineer

If Overhead launcher would have been deployed, minimum 3 numbers of launchers required for the entire project and that too with very complex design. Since the project

has deployed Ground Supported Staging as main launcher, the project has gained nearly 450T of structural steel which leads to savings of 2 corers directly in fabrication of launcher only.

2.3 Temporary Pre-tensioning frame In elevated viaduct construction, precast box segment is erected using launchers then alignment is cross checked with respect to curvature, gradient and super-elevation. Once alignment is set, then segments are separated and a gap of 200-300mm is created between segments. Glue is applied on face of both segments. Using HT rods which is present in temporary PT frame, segments gets locked such that applied glue should squeeze out on all sides of segment. Normally 25-30% of Permanent PT force shall be applied by temporary PT frames.

The conventional Temporary PT beams (Fig 1a) which AFCONS has used in past decades is of like beam approximately 2.5m in length which weighs around 530kg and for one precast box segment 4 nos of beam will be required which comes to total weight of 2T per segment. The main parameter for deciding temporary PT beams are the cross sectional area of the segment, length of the segment, live end(jacking point) or dead end(locking point) and the temporary force to be applied.

In Barapullah project, superstructure is of 3span/2span continuous precast box segment.

Unfortunately all 35 modules in the project are unique having different span length. Segment length varies from minimum of 1.7m length to maximum of 3.14m length which comes to a total of 1037nos of segment in the whole project. Due to unique span configuration and also due to some odd span length, 27 different length of segment to be casted in order to complete all modules of the project. Due to variation in segment lengths, some 21 different types conventional temporary PT beams has to be fabricated which resulted in extra tonnage and also big chaos while handling the temporary PT beams.

In order to avoid the confusion and also in motto to reduce the tonnage, a new bracket type system (Fig. 1b) has been developed.

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Fig. 4a: Temporary PT beam – Conventional type

Fig. 4b: Temporary PT beam – Bracket type

The main advantage of this bracket type system is applicable to all modules irrespective of span lengths and segment lengths, which weighs around only 140 kg and that makes handling very easy so that there is no need of any special cranes for lifting, all the PT brackets has been lifted manually and transported to adjacent span in small wheel bogie. Comparison between conventional PT beam vs PT bracket has been made in below table 4.

Table 4: PT beam vs PT bracket Properties

PT beam

PT bracket

Weight of 1 PT beam/bracket

530 kg

140 kg

No. of beams in one segment

4nos

8nos

Weight of PT beam for 1 segment

2.12T

1.12T

Weight of PT beam for 28m span

19.1T

10.1T

For lifting and handling

Crane required

Manual handling

Volume 46 Number 1 March 2016 45

The above table clearly states the difference in cost saving and also easiness of handling temporary PT brackets. Normally in project number of Temporary PT sets are decided based on number of launchers deployed in project. Accordingly in Barapullah project, 2 sets of PT brackets fabricated for 2 launchers and adding to that one set of PT bracket fabricated and deployed in casting yard. Because of this PT bracket system site has straight away saved nearly 30T of steel material and also reduction in utilization of service cranes for handling the temporary PT brackets.

Net savings to site by adopting PT bracket system @ 75,000/T of steel which includes material cost & fabrication cost, comes to a direct savings in total of 22.5lakhs adding to that less utilization of service crane.

2.4 Re-Use of Available I-girder Formwork In Barapullah Phase II project, in addition to precast box segment certain spans were comprised of pretensioned I-girders. It was found that the physical dimension of the proposed I-girder in PWD project was almost similar to that of I-girder in JUHP project.

And fortunately all the I-girders of JUHP project were casted and formwork system was completely idle. So a thought process had given to use the same I-girder shutter which was already used in Udampur project for casting of I-girders, but with minimum modification since there was difference of 150mm of height in both I-girders. Table 2 shows the comparison of physical dimensional properties of both I-girders.

Based on the dimensional details of both I-girders it was noticed that web portion has to be cut by 200mm and the flange portion to be extended by 50mm so that the same JUHP I-girder formwork system is applicable for PWD project. In order to bypass the modification work, even the design consultant of PWD project were approached to increase the height of I-girder by 150mm so that same shutter shall be used. But due to addition in permanent quantity and also difficulty in matching the RL of viaduct, the proposal was denied by the design consultant. Hence it was finally decided that the existing formwork shall be transported all along from Udampur to New Delhi and necessary modifications to be carried out to suit the requirement. Fig.2 shows the formwork in Udampur site and the other one is after modification, currently using in PWD site.

As per project planning, 4 sets of formwork were required to complete the I-girder casting, so all 4 sets of formwork of JUHP project were transported.

Since the modification works involves high level skill, qualified fabricator has been chosen to finish the work, in order to meet the quality output. Two proposals namely if site would have gone for new fabrication and re-use of existing JUHP formwork, cost comparisons has been made to analyse the financial part of both proposals.

Table 5: Comparison of physical dimensions of both projects I-girder Parameters

3564 – PWD 2615 – JUHP

Total Depth of Girder

1500 mm

1650 mm

Width of base

820 mm

820 mm

Web thickness

300 mm

300 mm

Height of web portion

955 mm

1155 mm

Height of flange portion

150 mm

100 mm

Total nos of girders

370 nos

340 nos

46 Volume 46

Number 1 March 2016

Fig. 5a: I-girder @ JUHP site

The Bridge and Structural Engineer

contractor may propose to the client for change of structure which may directly benefit client and also the contractor.

In Barapullah project Phase II, in Ramp A, the radius of curvature is 90m which has precast box segment as super-structure. It had been technically defended with client and also with design consultant that erection of superstructure would be very difficult in such complex geometry profile, after which it leads to change in super-structure as I-girder. But as contractor, the following advantages were ensured Designing of launcher for such complex geometry got eliminated.



Fig. 5b: I-girder after modification @ New Delhi site

Table 6: Comparison of physical dimensions of both projects I-girder Weight of 1 set of formwork

7.25 T

Total number of sets required

4 nos

Total weight of formwork

29 T

New Fabrication Material + Fabrication cost (@ 1,00,000/Ton)

Total Cost

= 29 * 1,00,000 =Rs. 29,00,000/-

=Rs. 29,00,000/-

Re-use of JUHP formwork Material taken from JUHP site (scrap value @ 25,000/Ton)

= 29 * 25,000 =7,25,000/-

Modification cost

=5,00,000/-

Transportation cost

= 50,000/-

Total Cost

=12,75,000/-

Based on the above values it was very clear that there was huge savings by re-using the available formwork, net savings to site was approximately 16 lakhs and for AFCONS it was approximately 23 lakhs.

2.5 Changes in permanent structure to reduce the construction cost There is always a myth lies among the contractor that for an item rate project, material quantity is directly proportional to profit percentage, but the same may not be applicable in all cases. In some work, the rate of construction cost is much higher than permanent work due to complexity in structure. In that case

The Bridge and Structural Engineer

Erection time of I-girder was very less when compared to erection time of precast box segment, so it leads to early completion of that particular loop.



Construction cost of I-girder is very less compared to construction cost of precast box segment.



Though the permanent quantity got reduced due to change in super-structure but considerable profit had been ensured by less equipment utilization, early completion and also eases of construction.



The profit cost is not only directly linked to quantity but also to time which leads to save in equipment and resources.

3.

Role of Other Departments in Temporary Works

Though the enabling works is the product of the design department, it success lies with the co-ordination of other departments and perfect execution as per drawings. Some of the departments which are very closely associated with enabling works are Planning, Quantity Survey, CPE, Fabrication, Purchase & Store and last but not the least Execution department. But to co-ordinate between these departments, role of co-ordination engineer will play a very vital role which was centrally focused in below fig.4. Let us see the role of other departments in making success of enabling works, which indirectly has a impact on profit of the project.

Volume 46 Number 1 March 2016 47

availability to be made well in advance for further fabrication. Sometimes work will get delay due to non-availability of materials.

Fabricator: - Fabricator should strictly follow the fabrication details as mentioned in the drawing. If fabrication cannot be carried out as mentioned in drawing, he should immediately contact the designer.

Small fabrication errors may lead to big mishap in site.

Fig6.of Role of Other departmentsin insuccess success ofofenabling works Fig. 6: Role other departments enabling works

Planning: - Planning department usually raises the request for any type of enabling works so that permanent structure shall be built in safe and engineered way. It will make the designer job more easy if planning department raises the request well in advance, added to that a preliminary scheme in which site wishes to execute, available materials, some basic information like soil bore log, SBC of soil, if any hindrance in site can be plotted in Auto cad to give a very clear picture before the design can be carried out so that all firsthand information will be available with designer. Once the design/drawing is released, planning engineer should go through the drawing and check whether it was as desired by the site team because of that revisions of drawings can be limited which ultimately saves the time. Time is the most important key player for a contractor to decide his profit margin.

Execution team: - Site execution team should thoroughly read the drawings and come back if the proposed scheme is not workable or any better scheme will give more productivity and less in time cycle. Once the site execution team is fully satisfied with the proposed scheme then the drawing shall be sent to other departments for further proceedings.

Quantity Survey: - Role of QS engineer is to take quantity estimation from the drawings and the same to be immediately conveyed to Purchase department and to EIC. QS shall always check whether the quantity is within the budget limit or exceeding and the same to be intimated to EIC. Purchase & Store: - As per drawings the required material should be intended and the material 48 Volume 46

Number 1 March 2016

CPE: - CPE department should study the drawings/ scheme and check for any special requirement needed to take over work. If so, suitable arrangements to be made and equipment planning to well planned in order to take maximum utilization of the equipment.

Co-ordination department: - In order to coordinate between all the above departments, role of co-ordination engineer plays a very vital role. He should take responsibility of getting clearance from all departments and the advantage of making such coordination are listed below: Designer shall have all basic inputs and clear idea of site requirements



Re-work or revisions of drawings will be limited which will save adequate time and money



Since all the departments are involved, re-work due to material non-availability may not happen



Cost incurred due to re-work drawings; reapproval from third party etc. shall be reduced.



4. Inference/Conclusion The foregoing sections discussed about Indian Infrastructural scenario, permanent works, temporary works, role of various departments in temporary works and formwork strategy. Some of the conclusion were derived and listed below Method of construction has its own impact on cost of temporary works. In Bangladesh project, just by changing the methodology of pile cap construction, 30% of construction cost has been reduced.



For elevated bridge projects, selection of launcher plays a vital role in terms of timely completion of project, safety and profit ratio in project. Of course in Barapullah project Phase II, proposal of Ground supported staging has proven in reduction



The Bridge and Structural Engineer

of 50% material cost of conventional launcher and also producing equal competitive time cycle in erection of segments when compared to conventional launchers.

•

By re-using the available I-girder formwork of JUHP in PWD project, with some extra fabrication leads to cost saving of approximately 30 lakhs to the company.

Proposal of Bracket type Temporary PT frame for carrying out temporary pre-stressing in precast box segment after erection has proven that there was 50% reduction in material cost when compared to conventional temporary PT beam system. Since temporary PT bracket was less in weight, there was no need of service crane utilization and all brackets were handled manually which saves in more time also for early completion of span erection.



Thought the temporary work is the product of Design department, its success lies only if there is full co-ordination between other service departments.



Role of co-ordination engineer plays a key role for success of temporary works. The schemes/ drawings has to be co-ordinated between other departments like planning, Quantity survey, execution team, Purchase, Fabrication, CPE department to get clearance and to ensure that the execution has been followed as the same way it was dictated in the scheme/drawing.



As per construction industry norms nearly 10% of project cost has been invested in formwork and staging materials. So the aim of a contractor should be recovering maximum profit from the

formwork material and try to make maximum utilization of the same.

Even though saving money is the top priority of a construction company, especially adhering to the limited constraints of a tight budget, it is vital that quality of the temporary works not to be sacrificed.



Thus by providing reliable, efficient and high quality temporary works will result in increasing the profit margin of the company and at the same time which will meet safety, time, quality and various requirements of the project.



5. Acknowledgement Author thanks specially Er. Vivek Abhyankar (Sr. Manager, Design, AFCONS) for his continuous valuable guidance and for teaching practical approach to site related problems. Also thank Shri. S.B. Joshi (consultant), who taught about launching techniques and complications during erection. I would like to thank Er. M.D. Karnik (JGM, Head-Design, AFCONS) who gave full freedom to work extensively on the project. Last but not least Barapullah Site Team, New Delhi especially Er. Ragavendar (Site planning) for sharing all the site related problems and data in order to come up with this paper.

6. Reference 1.

Rosignoli, M., Bridge Launching, Thomas Telford Publishing, 2002, 352 pp.

2.

Project information of 3564-Barapullah Project Phase II and 6265-Bhairab Railway bridge project, Bangladesh.



The Bridge and Structural Engineer

Volume 46 Number 1 March 2016 49

Enabling works for India’s first Double decker bridge “Santacruz Chembur Link road”- A case study Rakesh Kumar MEHTA Dy. General Manager (Tech.), Gammon India Ltd, Mumbai, India rakesh.mehta@gammonindia.com

Summary To construct the first double decker bridge was never going to be an easy task and that too when the bridge was to be built in a very congested area of Mumbai and partly crossing the Railway tracks, it became even more challenging. In this paper, we present the different enabling works involved in the construction and the different challenges that were met and overcome through effective planning and designing of enabling works.

Keywords: Enabling works, Double Decker Bridge, Rail over Bridge, Steel Plate Girders, Box Girder, I – Girder, Temporary structures.

1. Introduction

Fig. 1: General Layout

The Bridge is constructed in the vicinity of congested Mumbai area, for connecting the city’s west region to east region, for time saving & providing comfortable transport facility for people of Mumbai.

50 Volume 46 Number 1 March 2016

Rakesh Mehta, born 1972 received his Master degree in Structural Engineering from University of Roorkee. He has 18 years of experience in Design & construction methodology for Transportation system like bridges, flyover, ROB & marine jetties.

The Santacruz – Chembur Link Road (SCLR) is 6.45 km long and 45.7 meters wide arterial road (Refer Fig.1). The SCLR has three flyovers/bridges on its route, namely, CST Road flyover, the 560 meter long Kurla-Kalina flyover above LBS Marg, and the double-decker Bridge (combined length of 1.525 km) crossing over the Central and Harbour Line railway tracks at Kurla and Tilak Nagar. The double-decker bridge has two arms (Total length equal to 0.877Km) – one for Lokmanya Tilak Terminus and the other one for Kurla Dairy.

The 1096 meter long Amar Mahal junction flyover was also planned, to connect the double decker bridge of SCLR project with the Eastern Express Highway (EEH).

The six lane road was constructed as a part of the World Bank funded-Mumbai Metropolitan Urban Transport (MUTP) at a cost of Rs.454 Crore (Total estimate).

But the World Bank withdrew the funding at midway due to repeated delays in completing the project, and consequently, the second phase had to be financed

by Mumbai Metropolitan Region Development Authority (MMRDA) with its own fund. Louis Berger Group Inc. served as project management consultants for the entire project. The SCLR project was executed in two phases, Phase 1 – Connecting the Mithi River to Amar Mahal junction of EEH (3.45 Km) & Phase 2 – Connecting the Mithi River to WEH (3 Km). The Phase 1 was further divided in three Sections and section-II of phase-1 was awarded to Gammon India Ltd. General layout of Section-II of phase-1 is shown in Fig-2 and details of SCLR section-2 is given in Table-1. Typical cross section and longitudinal views The Bridge and Structural Engineer

are given in Fig-3 and Photo-1.

Fig. 2: General Layout of SCLR Section II, Phase 1

Stretch

Length (Km) Description

2) Viaduct portion

0.99

Gazi Nagar to Tilak Nagar

3) Ramp portion

0.19

At Tilak Nagar

B) Secondary Arm

0.877

CH. 338.5 CH. 1215

1) Ramp portion

0.15

Kurla Dairy

2) Viaduct portion

0.6

Kurla Dairy to LTT

3) Ramp portion

0.13

LTT

2.

Salient Features and Scope of Works

Salient features for section-II of Phase-1 of SCLR project are as follows: a)

Length of the SCLR Section II Bridge = 2.4 Km

b)

Clear carriageway width is 11m at the main arm, and 7.5m, at double decker portion & LTT arm.

c)

Types of Foundation used were, pile foundation of 1200 mm dia. and open foundation at abutment location.

d)

Type of substructure is RCC.

e)

Type of superstructure is cast-in-situ PSC Box girder for second level and first level (except double decker portion). Span length is 21 m minimum & 49 m maximum, between center to center of pier, and box depth is 2.3m.

f)

Type of super structure is PSC I-girders, of depth 2.35m, at first level of double decker bridge portion. Minimum and maximum span lengths are 15.7m & 31.8m, respectively, between c/c of pier.

g)

Strip Seal Type Expansion Joint has been used, with a varying movement of 50 to 80mm.

h)

POT/PTFE bearings have been used for supporting the girders.

i)

83 mm thick (3 mm thick water proof membrane + 50mm thick DBM + 30mm thick BC with PMB) wearing coat is provided above the deck of superstructure.

Fig. 3: Typical Cross Section of Bridge

Photo 1: Typical Cross Section & Long. View of Bridge

Table 1: Details of SCLR Section II Stretch

Length (Km) Description

A) Main Arm

1.525

CH. 1250 CH. 2775

j)

Super structure of ROB is Composite steel plate girder with RCC Deck slab.

1) Ramp portion

0.35

At Gazi Nagar

k)

Main span length at Kurla ROB (Main center

The Bridge and Structural Engineer

Volume 46 Number 1 March 2016  51

line) is 50.9m and 40.5m at Tilak Nagar ROB (Harbour Line) Brief scope of works,quantities of material used as well span arrangement are given in Table-2, 3 & 4 Table 2: Scope of works Description

Grade of Nos. Concrete/Steel

1.2m dia. Bored Cast-in-situ Pile

M35 & M40

1420

Pile cap

M35 & M40

166

Piers

M35,M40 & M45

181

Cast-In-situ PSC Box Girders

M40 & M45

102

Cast-In-situ PSC I Girders

M40 & M45

198

Steel Plate Girder for ROB portion

Fe 410 WB as Per IS 2062-Grade-B

80

Reinforcement Steel

Fe 500 with CPCC treatment

Description

Span Length

Type of Super Structure

Remarks

P6-P7

40.5m

Steel Plate Girder

ROB at KurlaOver Kurla Railway Shed

P7-P8

31 m

Steel Plate Girder

Adjacent of ROB

P8-P9

33 m

PSC I Girder

P9 to P16

31 m

PSC Box Girder

For First & Second Level deck

P16-P17

26.275 m

PSC Box Girder

For First & Second Level deck

P17-P18

28.953 m

PSC I Girder – First level PSC Box Girder – Second Level

P18-P19

21.881 m

PSC I Girder – First level PSC Box Girder – Second Level

P19-P20

18.757

PSC I Girder – First level

For Double Decker Portion

P20-P21

31.318 m

PSC I Girder – First level

For Double Decker Portion

P19-P21

48.053 m

PSC Box Girder –Second Level

For Double Decker Portion

P21-P22

27.979 m

PSC I Girder – First level PSC Box Girder – Second Level

P22-P23

31 m

PSC I Girder – First level PSC Box Girder – Second Level

P23 to P27

31 m

PSC Box Girder

For First & Second Level deck

P27-P28

35 m

PSC Box Girder

For First & Second Level deck

P28 to P32

31 m

PSC Box Girder

For First & Second Level deck

P32-A2

31 m

PSC Box Girder

For First & Second Level deck

Table 3: Quantities of Material used Description

Unit

Quantities

Concrete

Cum

96990

Reinforcement Steel

MT

11620

Total HT Steel (Prestressing Steel)

MT

545.79

Structural Steel for Steel Plate Girder

MT

2800

Structural Steel for Liner

MT

1362

Table 4: Span Arrangements Description

Span Length

Type of Super Structure

Remarks

A) Main Arm-Viaduct Portion

B) Secondary Arm-Viaduct Portion

A1-P1, P1-P2 & P3-P4

31 m

PSC I Girder

P3-P4

31 m

Steel Plate Girder

Adjacent of ROB

P4-P5

50.9m

Steel Plate Girder

ROB at KurlaOver Main Line

P5-P6

18.3m

Steel Plate Girder

ROB at KurlaOver Kurla Railway Shed

52 Volume 46 Number 1 March 2016

P33-P34

20.58

PSC I Girder

P34P35,P35-P36

22.8 m

PSC I Girder

P36P37,P37-P38

22.8 m

PSC Box Girder

P38-P40

40.5

Steel Plate Girder

For Double Decker Portion

ROB at Tilak Nagar

The Bridge and Structural Engineer

Description

Span Length

Type of Super Structure

P40-P42,P42P43,P43P44,P44P45,P45-A3

31 m

PSC Box Girder

P46-P47

14.383 m

PSC I Girder

P47-P48

22.43 m

PSC I Girder

P48-P49

30.72 m

PSC Box Girder

P49-P51

38 m

PSC Box Girder

P52-P53,P53P54,P54-A4

31 m

PSC Box Girder

3.

Remarks

For Double Decker Portion

Type of structures

Photo 3: A-Frame Rig.

3.1 Foundation

3.2 Pier & Pier Cap

All the foundations are pile foundations except at abutment A1 location. Foundation of A1 is open foundation. The total no. of piles is 1420 nos. of 1200 mm dia. bored cast-in-situ piles. Founding level of each pile is 3D in soft/weathered rock and 1.25D in hard rock, where, D is diameter of pile. Depth of pile varies from 5m to 15m.All the pile foundations were done with help of Hydraulic Rotary Rig (MAIT HR-180) (Refer Photo-2). This rig was not used at P5A Foundation because of its vibration effects, as it was close to the railway tracks. The P5A foundation was of total 24 nos. of pile which was very critical from construction point of view. To protect the embankment of railway tracks and from safety point of view, we erected sheet piles around 26 nos. at a distance of 3.218m from the central line of the railway track within one night. The piling of P5A was done with the help of A-Frame rig (Refer Photo-3) within the time frame of 3 – 4 months.

The normal pier is rectangular shaped, of 3.0m x2.2m with embossing of a flower, for aesthetic appearance of pier. The pier was cast with FRP shuttering for proper embossing of flower on face of pier. The pier cap of the bridge portion is flared shape, which adds to the beauty of the structure (trophy type shape).

The pier cap was constructed with the help of trestles as the supporting arrangement. The pier cap at the junction location was very congested as the pier cap for the upper deck level was cast before the piercap of first deck level. Therefore, it took more time for supporting arrangement, fixing of the reinforcement and shuttering arrangement for casting the first level pier cap (Refer Photo-4).

Photo 2: Hydraulic Rotary Rig.

Photo 4: Single Pier Cap Arrangement.

The Bridge and Structural Engineer

Volume 46 Number 1 March 2016  53

Photo 5: Common Pier Cap Arrangement.

3.3 Superstructure The Superstructure of the main arm and secondary arm of bridge and for first level of double decker portion (at Kurla terminal junction), is cast in-situ box girder. Cast in-situ I-girders were used, where carriageway varies from 11m to 7.5m. For ROB at Kurla & Tilak Nagar, superstructure consists of Prefabricated Steel Plate Girders. There are two carriageways. Total Deck width for ROB portion is 16m for each carriageway.

PSC Box Girder – A total of 102 nos. of box girder were constructed out of which 58 nos. were constructed at first level & 44nos. at the second level of double decker portion (At Kurla terminal).

The span length of the box girder varies from 21m to 49m & width of the Box girder varies from 8.6m to 10m with a constant height of 2.3m (Refer Fig. 4).

Fig 4: Cross Section of Typical PSC Box Girder

54 Volume 46 Number 1 March 2016

Fig 5: Cross Section of Typical PSC I Girder

The concreting of the box girder was done in two stages. In the first stage, soffit along with web was cast & in the second stage, deck slab casting was carried out. 8 nos. of 19 K12 cables were stressed by the hydraulic jacks after concrete had achieved M30 strength or after 7 days, whichever is more.

During casting, PSC box girders were supported on trestles resting on ground.

PSC I-Girder –The total of 198 nos. of I-girder were constructed out of which 140nos. was constructed at the first level for double decker portion. Normal span length of I girder was 31m & 33m for main arms of double decker portion but it varies from 15.5m to 31.8m, for I-girders at first level of double decker portion (at Kurla terminal junction). Depth of I girders is 2.35 m, constant for all spans (Refer Fig-5).4 nos. of 19K12 cables were stressed in each PSC I girder. For span 15.5m, only 2 cables of 19K12 were stressed, and for span 31.8m, 4cables of 19K12 were stressed. During casting, PSC I Girders were supported on trestles resting on ground. The construction of I–girders was difficult at first level of double decker portion (at Kurla terminal) due to girders length varying in each span. Also the gap between two girders in longitudinal direction is only 150mm. As a result, prestressing for the girder that would be cast first was possible but the adjacent next span girder which would be cast later could not be prestressed because of the narrow 150 mm gap. As a solution to the problem, the girders were cast at some distance away from their position in the transverse direction (in between two already cast next span girders), The Bridge and Structural Engineer

where prestressing was possible and then they were side shifted to their desired position. This method was used for some spans, but as it was taking a lot of time, one end prestressing of the girders was introduced for the later spans.

Steel Plate Girder – For ROB portion, steel plate girders were proposed, due to weight of steel girders being very less in comparison to weight of PSC I girder. Due to weight of steel plate girder being less, it became easy for its erection on its location, without disturbing the running rail traffic.

The steel plate girders were fabricated as a built up I-section with top, bottom & web plates along with stiffeners, bracings, splices, etc. All the members were fabricated under skilled supervision & amended as per the railway regulatory codes.

Weight of one steel plate girder is 32 MT & depth is 1.8 m for span 40.5m and weight of girder is 68 MT & depth is 2.2m for span 50.9m. All steel plate girders were painted with five coats (DFT200 Microns) of Epoxy, after sand blasting. Once the fabrication was complete, the members were transported to the site & assembled at the suitable location before launching of the girders to its location.

4.

Major Works

4.1. Double Decker Bridge portion The main attraction of the entire project is the double decker portion of the bridge. The double decker portion consists of upper deck (Second level) & lower deck (First level). The upper deck of the flyover connects the Western Express Highway (WEH) to Eastern Express Highway (EEH) & the lower deck has two arms one to the Kurla terminus and the other to the Kurla dairy. The upper deck is made of Box girders while the lower deck consists of I-Girders at the junction.

For casting the PSC box girders & PSC I- girders, barricading of the full area was not possible, due to presence of a pathway from Tilak Nagar Station (Harbour Line) to Lokmanya Tilak Terminus & due to a 10m & 12m nalla, present on two sides of the location. Therefore, resource deployment became very critical due to less space availability, with proper pre-planning becoming a necessity.

The casting sequence was finalized as the casting The Bridge and Structural Engineer

of lower level I girders from Kurla terminus side were to be cast first followed by the upper level of Box girder from Kurla terminus side. Thereafter the upper level adjacent box girder were to be cast before casting the lower level I-girder on the Kurla dairy side.

Span length for upper level PSC Box girder between P19-P21 is 48.053m, which passes over the lower level PSC I girders. Span length for lower level PSC I girders varies in each span, ranging from 18.757m to 28.953m (Refer Fig. no-6).The casting of I-girder was not an easy task due to variations in longitudinal & transverse direction of I-girder for each span. So to minimize the time cycle we prepared reinforcement cage at ground level and lifted it with crane to its location. Once the casting was done we dismantled the entire supporting arrangement & re-erected it at other location for casting the other I girders. One of the critical span P33 – P34 was entirely over the nalla and length of each PSC I girder varied from 19.5m to 21.5m.

Using conventional supporting arrangement for casting these I girders was not possible. For casting of I girders for this span, we used an inverted truss, which was resting on transverse structural beams on both sides of nalla. Above this inverted truss, staging pipe was erected for casting the I girders in span P33-P34 (Refer Photo-6). After casting one I-girder, the entire inverted truss is side shifted, along with staging pipe over transverse structural beam to next I girder location. Another critical activity was the casting of the Box girder for span P19-P21 at junction location of double decker portion.

Span length of PSC box girder was 48.053m and supporting height was 18m. Many supporting arrangement schemes were prepared but finally from safety point of view and pathway under neath, we cast the box girder over inverted truss between P19- P20. For the remaining length between P20- P21, trestle supporting arrangements were provided (Refer Photo-7).

Once the supporting arrangement was done, fixing of the outer side shutter panels & reinforcement was started, and the box girder was cast in this supporting arrangement. After 14 days from casting of the concrete, stressing of the cables was carried out.

Volume 46 Number 1 March 2016  55

4.2 ROB at Tilak Nagar (Harbour Line of the Central Railways)

Fig. 6: Plan view at Kurla terminal location (Double decker)

Photo 6: Supporting arrangement for casting of I Girder over Nalla Span P33-P34

Photo 7: Supporting arrangement for casting of Second Level PSC Box girder for span P19-P21

56  Volume 46 Number 1 March 2016

Secondary arm towards Kurla dairy passes over the Harbour railway line of Central railway near Tilak Nagar station. There are only two rail linesUp line & Down line, and their center to center distance is 4.5m (Approx.). In tender stage, client had proposed a 50m PSC box girder for each carriageway without taking approval from Central Railway authority. After awarding this project, Railways rejected the scheme for casting in-situ PSC box girder of 50m span. Then this ROB span was reduced to 40.5m and a PSC I girder was proposed in 2004. There were 5 girders in each carriageway. After changing to PSC I girder, from PSC box girder, we had submitted the plan of casting the PSC I girder on its location over the trestle supporting arrangement. Again Railways rejected the scheme for safety reasons. Then, the casting of PSC I girder on adjacent span and rolling it in longitudinal direction on trestle supporting arrangement, was proposed. After reaching at bearing location, PSC I girders would be lowered on its location by hydraulic jacks. Weight of one PSC I girder was 120 MT. This scheme was again rejected by Railways, in year 2010. Finally using steel plate girders instead of PSC I girders was proposed, due to ease in erection of steel plate girder in comparison of PSC I girders. Finally in year 2012, the scheme for launching of the steel plate girders was approved by Railway authorities.

General Arrangement of ROB is given in Fig-7.

Fig. 7: General Arrangement for ROB at Tilak Nagar

The Bridge and Structural Engineer

4.2.1. Erection Method for steel Plate girders The steel plate girders were assembled adjacent to railway span (near the P38 pier). Before erecting steel girder on its location, a trial of lifting the steel plate girders & its movement was carried out at night time between 1 AM to 3 AM by crane, in the presence of the concerned authorities. The steel plate girder was lifted by 300T capacity Kobelco 7300 crane with help of spreader beam. (Refer Photo-8). Weight of steel plate girder with spreader beam was 42t. The maximum working radius for crane was 22m with boom height was 38m. The arrangement of steel stool was made on the pedestals of the pier for properly locking the steel plate girder, when the first steel plate girder was erected on its location. Once the first assembled girder was placed over the steel stool with proper alignment the girder was locked in position with the locking arrangement for safety purpose.

Afterwards, the spreader beam was removed from erected steel plate girder.

railway tracks near Kurla local station. At initial stage, designer proposed a 60 m span for each carriageway, for 2 spans P4-P5 & P5-P6. One span of 60 m passes over main line of central line, which has 4 railway tracks for fast and slow trains, Up & Dn lines, along with 3 railway tracks for local maintenance shed.

Another span of 60m passes over the existing Kurla shed.

Fig. 8: General Arrangement for ROB at Kurla

Photo 8: Erection of Steel Plate Girder by Crane

After completion of erection of two girders, a safety net and permanent bracings were attached to the steel girders. This procedure was carried out for all the remaining girders. Launching of 5 nos. steel plate girders for one carriageway was finished in 5 hours of traffic & power Mega Block. Deck slab was then cast by taking support from bottom flanges of steel plate, between two steel plate girders. The cantilever portion of deck slab was cast by bracket attached with vertical stiffener of steel plate girders.

4.3 ROB at Kurla (Main Line of the Central Railways) The main arms of bridge, crosses over the central The Bridge and Structural Engineer

Type of superstructure proposed, was cast-in-situ PSC box girder in each carriageway. But it was not possible to cast the in-situ Box girder above the running railway track, where local train passes in every 5 minutes from 3.30 AM to 1 AM. Railway authority rejected cast-in-situ box girder proposal in year 2003 and proposed the new span arrangement of 35.4mx35.8mx40.5m (P4-P5,P5-P6 & P6-P7) with precast PSC I girder superstructure and introduced the pier P5 between the slow rail track & fast rail track, where center to center distance of rail track is 9.5m.For erection of PSC I girders, we proposed the launching truss. In this proposal PSC I girders were to be cast behind the ROB span on overhead casting bed, and casted PSC I beams were to be erected by 90 m length launching truss between the two bearing location, and then side shifted to its location. In year 2010, Railway authority rejected this scheme on basis of safety of rail traffic and as the no. of power & traffic blocks required were more than 4 hours for each block. Railway authorities then proposed steel plate girder in place of PSC I girders. Now construction of P5 foundation between the running slow & fast rail track was most crucial & difficult part of the ROB. For construction of P5 foundation between rail tracks, in year 2011, Volume 46 Number 1 March 2016  57

Railway authority approved the scheme with 3 hours traffic & power block on alternate days and 4 hours traffic & power block on every Sunday, in night time between 12.30 AM to 3.30 AM. But as per this type of traffic & power block given by Railway authority, construction of P5 foundation would take 2-3 years. For avoiding further delay in project due to construction of P5 foundation, in year 2012, Railway authorities proposed to shift this foundation, outside the railway tracks and name this foundation P5A. Span arrangement between P4-P5 was changed from 35.8 to 50.9m (P4-P5A), P5-P6 from 33.8m to 18.3m, keeping the remaining span length, same, for P6-P7 i.e. 40.5m. This was the 9th General arrangement drawing of ROB, which was finally approved by railway authorities on June 2012. Final approved GAD & cross section of ROB is given in Fig-8.

Assembled Steel Plate girder for Span P4-P5A P6 P5

Photo 9: View showing position of the assembled girder on Deck of P6-P7

4.3.1 Erection Method for steel Plate girders Erection of steel plate girder in span P4-P5A (Span length-50.9m) was very critical due to weight of one steel girder being 70MT and same had to be erected in 2 hours traffic & power block, as required

by Railway authority, for not disturbing the traffic of local trains.

All the 14 nos. of steel plate girders, were assembled above the deck of Span P6-P7 (Refer Photo-9). The span length was 40.5m but our girder’s length was 50m. The extra 15m erection bed behind the span P6-P7 was made, for proper assembling of the steel girders on span P6-P7.

Erection of steel plate girders in span P6-P7 was done similar to harbour line, by crane, in 2 days of 5 hours of traffic & power blocks. For deck slab

58  Volume 46 Number 1 March 2016

casting, plate of 12 mm thickness, was provided between the steel plate girders to act as shuttering during casting of deck slab.

We had planned to erect the combined 2 steel plate girders, with all permanent cross bracing and end diaphragm along with top shuttering plate for deck slab, in 2 hours of traffic and power block. Combined weight of two girders including bracings was around 160MT. For this purpose, an 18.04 m temporary launching truss (Weight-15 Mt) between P5-P6 and two temporary launching trusses of span 35m (Weight-34 Mt) and 15.88m (Weight-13 Mt) over span P4-P5A were used.

Temporary launching trusses of span 35m and 15.88 m, resting on temporary trestle of 2m x 2m, were erected between the two tracks, where spacing between two tracks was 9.5m.

This temporary trestle and launching truss were erected by 250t single crane from P4 and P5 side, in three separate traffic and power blocks of 1hour each. After placing the temporary launching truss, the combined girder made of two steel plates, was moved in longitudinal direction, from span P6-P7 to span P4-P5 over trolley. These trolleys were motorized and speed was 5m/minute. After reaching the desired location on span P4-P5, these assembled girders were lifted by 1 m with the help of two cranes (250t capacity) on either side and placed over its bearing location or temporary support location. This entire operation was finished in 1.5 hours of traffic and power blocks. Similarly, all the steel plate girders between span P5-P6, were erected. Erection of 14 nos. of steel girders was finished in seven traffic and power blocks of 1.5 hours, each (Refer Fig-9 & Photo-10). After finishing the entire erection operation, temporary launching truss and trestle were de-erected from its location by crane on each side in separate two traffic and power blocks of 1.5 hours, each.

Afterwards, each steel plate girders were moved transversely by jacks, taking the support from pedestal and placed on its final locations (Refer Photo-11). The deck slab was cast over already welded deck plates over steel girders, without power and traffic blocks.

The Bridge and Structural Engineer

Fig. 9: Stage wise Launching Scheme for Steel Plates Girders between P4-P5A

The Bridge and Structural Engineer

Volume 46 Number 1 March 2016  59

as barriers & roadblocks during the execution of the project, consuming significant amount of time and hitting the project to the ground. The phase-1 of section –II of SCLR project was awarded to Gammon in May 2004. The Contract period was 24 months and its contract value was 79.91 crores. Out of the total land for Phase-1 of section-II of SCLR project, 46% land belongs to Railways, 26% to MHADA & balance 28% to MMRDA. Hence, acquiring the permissions from these various authorities consumed significant time.

Photo 10: Launching activities during Traffic and Power Blocks

Photo 11: Completed view of Kurla ROB

5. Major Roadblocks & Challenges in Project Schedule The SCLR was proposed in 2002 but the issues related to rehabilitations and land acquisitions acted 60  Volume 46

Number 1 March 2016

During the 24 months contract period, only 23% work front area was available for construction and only 18% working drawings were issued by client, for the total scope of work. Again, project duration was extended by 12 month (Up to May 2007) for same contract value but again only 39% work front area was available for construction, along with changes in the system for ROB span from 50m Box-Girder to PSC I beams, and addition of one more pier at ROB Kurla. Again, the project duration was extended by 24 months (Up to May 2009) with revised contract value of 156.19 crore, with the addition of 0.23 Km LTT arms and 0.13 Km ramp portion in scope of works, but only 64% work front area was available for construction. Only after completion of this extended period (up to May 2009), it was possible to hand over the 100% area for construction activities. Again, the contract period was extended up to Dec, 2014 with revised contract value of 214.96 crore. In this revised contract value, the superstructure system of ROB from PSC I beams, was changed to composite steel girders i.e. converting the 52 nos. of PSC I beam to composite steel girders in railway traffic area and 28 nos. at adjacent of railway traffic area for fulfilling the requirements of Railways for easy erection and fast construction. Also the no. of PSC I girders were increased from 24 nos. to 196 nos. at Kurla terminal junction location.

Apart from this, there were many changes in the alignment of project. The Base line Socio-Economic Survey (BSES) was finalized in Dec, 2014. According to this revised BSES, a total 3167 structures were affected wherein 2575 were residential, 540 commercial, 33 residential cum commercial and 19 community/religious structures. Nearly 3500 people as well as 350 MHADA tenements were displaced

by SCLR, which have been rehabilitated. Acquiring The Bridge and Structural Engineer

permissions from these authorities had consumed significant time.

A major delay also occurred in getting clearance from Central Railway (CR) to construct a 50.9m bridge over central line at Kurla (ROB Kurla). Despite receiving the request in 2007, CR took 5 years and asked for four changes in design before finally approving for construction in July 2012.

Some of the critical issues are summarized below: a.

Land acquisition was a critical issue, which affected the entire project schedule. The land acquisition of around 1092 sq. m in phase-1 & approx. 40000 sq. m in phase-2 was required.

b.

Finance- as the World Bank withdrew its funding midway; therefore Phase-2 of the project was funded by MMRDA.

c.

Alignment Changes, as per the revised Base line Socio-Economic Survey (BSES).

d.

Shifting of Utility services.

e.

Delay due to approvals for GAD and Erection scheme for superstructure from the railways authority for ROB at Kurla & Tilak Nagar.

f.

Variation in planning due to presence of multiple authorities in the same project (Railways, MHADA & MMRDA).

g.

Casting of 198 nos. in-situ PSC I-girders of various lengths at Kurla Terminal Junction.

h.

Casting of 48 m span Box-girder for double decker portion.

i.

Unavailability of GFC drawings as per schedule.

adopting the right scheme for the given site conditions.

The enabling works should be designed with practical considerations by foreseeing the different challenges and by being always prepared to suitably modify the construction system to take care of any last minute constraints on site.

Another important learning from this experience was that when you have multiple agencies involved in the project, better co-ordination and understanding between the various agencies will play a major role in the timely completion of the project. It would be advisable to prepare and approve the general arrangement (GAD) and the technical design from all the involved agencies before the start of the construction. Railways too can standardize the superstructure system vis-à-vis the span length and construction aspects so that time spent for approval of erection method can be reduced.

After overcoming all the hindrances, SCLR was ready & opened to public traffic on 18.04.2014. Earlier it used to take around 1 to 1.5 hours to cover the distance between Santacruz-Chembur, but now it takes only 30 minutes. The flyover also provides better connectivity between WEH to EEH, along with driving comfort & less stoppage. The first double decker bridge of India has been termed as an “Engineering Marvel” by the National Geographic Society.

6. Conclusion The SCLR is a perfect example of a mega project that involves extreme engineering. Such projects require extensive study of various construction schemes and

The Bridge and Structural Engineer

Photo 12: Night View of the SCLR

Volume 46 Number 1 March 2016 61

LAUNCHING SYSTEMS FOR PRECAST SEGMENTAL BRIDGES Vinay GUPTA Chief Executive Officer Tandon Consultants Pvt. Ltd. 17, Link Rd, Jangpura Extn.

New Delhi-14 vinay.gupta@tcpl.com

Summary Till the recent past India was averse to providing precast segmental bridges, primarily because some of the older precast segmental bridges had shown minor to major distresses, for some reasons or the other.

However, an awakening came in late nineties and engineers decided to try this technology once again, with necessary modifications. Today, a majority of bridge construction employs precast segmental technology. Even an Indian code of practice has been published in the year 2005. Precast segmental bridges require launching systems, for assembling the segments before epoxy gluing and prestressing.

Various types of over-head and under-slung launching systems have been devised by constructors and specialized agencies. In general, overhead system works faster. Speeds as high as 2 ½ days per superstructure span has become possible to achieve through precast segmental technology. Spliced girder system is another form of precast-segmental technology. Such construction requires a matching speed of precasting of segments in the casting yard and also transportation and erection.

Keywords: Segmental, Precast, Launching Girder, Erection, Transportation

1. Introduction India has witnessed a large growth in the field of construction, with construction sector comprising 40% to 50% of India’s capital expenditure on the projects in various sectors. While the growth has been equally high in the field of real estate and infrastructure projects, a much larger growth has been witnessed in the field of segmental bridge construction. This is due 62 Volume 46

Number 1 March 2016

Vinay Gupta, born 1963 received his civil engineering degree from the BITS, Pilani. He is the CEO of Tandon Consultants Pvt Ltd. He has been involved in planning, designing and coordination of various structural engineering projects. He is the recipient of several awards.

to the distinct advantage of speed and aesthetics that this technology provides.

There are various types of segmental bridges, to name a few: i)

Precast segmental superstructure, simply supported or continuous, internally prestressed or externally prestressed, epoxy jointed or dry jointed.

ii) Balanced cantilever construction using precast segments iii) Spliced girder superstructure constructed using concrete stitch or epoxy joint, etc.

As a matter of information, until year 2005, Indian codes did not cover design and construction of segmental superstructures. Now, a new document IRC: SPs: 65-2005 prepared by the author under the aegis of the IRC code committee, has been published.

This document covers design and construction aspects of segmental bridges.

In totality there are many forms of segmental construction. However, the most popularly known form of segmental construction is precast segmental superstructure, constructed by span-by span method of construction. In this technique, precast box girder segments, aggregating a total length equal to approximately one span at a time are assembled and prestressed. Thereafter segments of similar total length are assembled for each subsequent span.

The assembled length can either be between two consecutive piers, each time or 1 ¼ span then ¾ span + ¼ span then ¾ span + ¼ and so on. At each stage, prestressing has to be carried out, in order to make the The Bridge and Structural Engineer

constructed structure self supporting. It may be noted that precast segmental superstructure, so constructed, has to necessarily be prestressed, as untensioned reinforcement can not continue through the joints of precast segments.

Assembling of precast segments is facilitated through either under slung assembly truss or over head assembly truss.

A. Underslung Assembly Truss

the assembly truss for the traffic movement during construction is available. But, it entails a larger barricading width. It is worthwhile to mention here that the cantilever slab would require extra bottom reinforcement in order to be able to carry the segment weight.

This type of Underslung Launching Truss system is suited to sharp plan curvatures, where long straight launching truss can not negotiate the curves, due to the transverse offset, that is created between the arc of the bridge centre line and chord line of the launching truss. In this system, short span straight segments of steel girders/trusses of 6m to 8m are placed over steel trestles resting over temporary spread footings at ground level. These straight girder segments negotiate the curvatures with kinks at their junctions. Over these girders, a set of jacks and trolley for maneuvering the segments longitudinally, transversely and vertically, including the movement for dry matching is provided.

Ref figs. 1 & 2 for depiction of this system.

Fig. 1: Under Slung Launching Truss with Strainght Segments

Fig. 3: Self Launching Type under Slung Launching Truss

Fig. 2: Supporting System of Precast Segments

Under slung assembly system of assembling and prestressing the segments has been used in several important bridges and flyovers. In this arrangement the assembly truss is located below the segments, wherein the segments may either be supported through the flange (cantilevering deck slab) or through the soffit slab. Former being more often employed, has the advantage that larger vertical clearance below The Bridge and Structural Engineer

Fig. 4: Handling of Segments on under Slung Launching Truss

This type of underslung system is slow but, it makes it feasible to construct segmental superstructures in Volume 46 Number 1 March 2016  63

as sharp as 70m radius of plan curvatures. In this system, the precast segments can either be fed from the forward end, which takes more time to slide the segments back or from sides, if space is available, entailing a faster construction. In another system of feeding of segments, over head Goliath Crane is provided, which makes it faster to move the segments.

A more versatile and faster system is the one as shown in figs. 3 & 4, which uses a self launching type launching girder. (approximately 2 ¼ span length) as used for Delhi-Noida bridge, wherin13 spans of 42.5m each, making a continuous superstructure of approximately 550 m were constructed. Here, the segments were fed through a 64 wheel trailor plying over the previously cast deck. These are picked up by a cantilevering portal to place it on trolleys to rest over the underslung launching girder. This type of system is faster but it is suited to straight or near straight spans only.

Another interesting system of underslung launching girder uses mid span articulation to negotiate the plan curvatures, as depicted in figs. 5 & 6. This system has been successfully used for 26 km long LRT System 2 in Kuala Lumpur, Malaysia over 10 years ago, wherein Dry Jointed Precast Segmental Superstructure using External Prestressing was used.

B. Over Head Assembly Truss This system of launching involves assembly truss (launching girder) that rests on either pier, precast segment over pier or separate temporary supports taken from ground. In most cases the launching girder is made self launching type and it is about 2¼ span long. 22 km long line 3C of DMRC has used ‘C’ shaped segments. Fig. 7 Depicts lifting system of such type of segments. In this case the launching girder rests on the pier cap using a specially fabricated steel frame, placed over the pier cap.

Fig. 5: Articulated Under Slung Launching Girder Fig. 7: Over Head Launching of ‘C’ Shaped Precast Segments

Fig. 6: Handling of Segments: LRT Kuala Lumpur

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Figs. 8 & 9 depict the over head launching system employed for 8 span continuous superstructure of 10 km long Bangalore-Hosur Elevated Expressway (a BOT Project). In this case, the 250t, 80m long overhead launching girder (LG) rests on specially designed and fabricated steel frames that rest over temporary steel brackets attached to the respective piers. During hauling, the LG rests on three supports.

Thereafter, the middle supporting frame is removed and replaced by a precast segment. This pier segment is moved over double span launching girder and placed over the middle pier. Subsequently, the pier segment is temporarily nailed down to the pier cap The Bridge and Structural Engineer

than span length are cast, in order to restrict the length and weight of the segments to be handled. These girder segments are placed on permanent piers and temporary steel trestles for assembling through either concrete stitch or epoxy jointing. These segments are then post tensioned to make them a full span or multi span unit, as the case may be. Subsequent to removal of temporary trestles, deck slab and diaphragms are cast. Alternatively, post-tensioning is carried out after casting of deck slab and diaphragm, in which case the temporary trestles are removed later. See fig 10 for Spliced Girder system.

and then launching girder rested on the pier segment including temporary nailing down.

Fig. 8: Over Head Launching of Bangalore – Hosur Expressway

Fig. 10: Spliced Girder Superstructure

Conclusions

Fig. 9: Over Head Launching of Bangalore – Hosur Expressway

C. Spliced Girder System In this system of segmental construction, precast segments of concrete girder (RCC or PSC), smaller

The Bridge and Structural Engineer

A careful planning of erection technique for launching of segmental bridges can lead to desired speed and economics. Speed of construction is of paramount importance because the infrastructure facility is always a prerequisite to development of an area. More so, in the BOT projects, the concessionaire has a commercial stake, wherein he has to start collecting toll as soon as possible. Use of precast concrete makes the structure amenable to better aesthetic appeal, due to better finish and adaptability to innovative designs.

Volume 46 Number 1 March 2016 65

SEISMIC ANALYSIS OF WELL FOUNDATION BY FORCED AND DISPLACEMENT METHOD

RNP SINGH Research Scholar Dept of Civil Engg, NIT Hamirpur rnpsgs@yahoo.co.in RNP Singh, born 1947, received his civil engineering degree from BCE, Patna and Masters in Structures from IIT Delhi. He worked in CWC, GOI for 35 years and retired in 2007. His area of research involves Seismic Design of Bridges.

Hemant Kumar VINAYAK Assistant Professor Dept. of Civil Engg., NIT Hamirpur hemant.vinayak@gmail.com Hemant Kumar Vinayak, born 1975, received his civil engineering degree from PTU, Jalandhar.

He was a research scholar at IIT Roorkee before becoming Assistant Professor at NIT Hamirpur.

His area of research is on Damage detection and Retrofitting of Structures.

Summary

1. Introduction

Seismic analysis of bridge pier with well foundation requires consideration of soil-structure interactions.

This paper presents the design forces generated for bridge piers of varying heights and constant diameter for medium soil in different seismic zones by analytical methods. The results have shown that the difference in base shear demand between Force Based and Direct Displacement Based Methods decreases with the increase in pier slenderness ratio. Similar trend was observed in the base shear difference between Capacity Spectrum and Direct Displacement Based Methods. The variation pattern revealed that the base shear difference derived from analytical methods was minimal for a particular range of pier heights. The diameter can be obtained corresponding to any pier height such that the base shear values obtained by different Methods are quite closer.

Well foundations are commonly used in India for highway and railway bridges across rivers and streams. In other countries like United States, Japan, Thailand, Portugal and Taiwan, similar type called caisson foundations are used. The ability to carry safely the heavy vertical loads, horizontal forces, moments arising due to earthquakes, hydro-dynamic pressures etc. makes the well foundation a popular choice. Bridges are important infrastructures and life line of transportation network and their safety during earthquakes is vital for their role in postearthquakes for rescue and relief operations. Well foundations are considered quite safe against earthquake motions because of their large crosssection and high rigidity [1]. However, they cannot be considered immune to seismic loading and many bridges supported on well/ caisson foundations have suffered damages [2][3][4].

Key words: Bridge pier, well foundation, SoilStructure Interaction, Force Based Design, Direct Displacement Based Design and Capacity Spectrum Method.

66  Volume 46

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The stability and sinking of well foundations depend broadly on the grip length, diameter and steining thickness which need to be sized adequately as this The Bridge and Structural Engineer

aspect affects the base shear demand of the bridge pier [5]. The scour depth caused by constrictions of water way, changes in the flow pattern around the bridge pier, generation of eddies and vortex system need to be properly estimated [6][7], since it governs fixing of grip and overall length, diameter and steining thickness of the well [8][5]. There are certain measures like rip-rap, collars and slots [9][10] to control scour around bridge piers which could be made use of, if necessary. The soil-structure interaction plays an important role and affects the response significantly, especially in case of well foundations [11].

Soil-structure interaction effect is considered in two steps: kinematic interaction and inertial interaction.

The excavation and insertion of well into the soil changes the motion and the rigid base experiences horizontal displacement and a rocking component.

The rigid body motion results in acceleration varying over the height of structure. The response is called the kinematic response. The accelerations generated in kinematic interactions result in inertia forces in the structure, which in turn produce over turning moments and transverse shear. These forces and moments cause deformation in the soil and change the motion at the base. This part of analysis is called inertial interaction. Kinematic and inertial processes go on simultaneously. A complete analysis involves consideration of both kinematic and inertial interactions [12][13].

In case of caisson/well foundations the lateral resistance comes from the lateral soil reactions, vertical shear traction at the periphery and shear traction at the base [14]. Several simple analytical models have also been developed representing the soil by linear and rotational springs. The pier well system is modelled as a lumped mass system with springs applied at the centre of embedded part of the well [15][16][17][18]. An approach for seismic analysis using two mass system (super structure and well at the surface) with two degrees of freedom have been developed [12][19]. Winkler model has attracted many investigators for the study of seismic responses of bridge piers supported on well/caisson foundations [13][20]. In general, the Winkler model uses four types of springs with dashpots: distributed lateral springs and dashpots at circumference of the well, distributed rotational springs and dashpots at circumference of well, shear translational spring The Bridge and Structural Engineer

and dashpot at the base and rotational spring with dashpot at the base of well [20]. Varun et.al have used such model with linear springs [13] while Gerolynos and Gazetas have used both type of springs linear and non-linear [14][20]. During strong earthquake motions significant nonlinearity in soil around the well and interface nonlinearity (gapping, sliding and uplifting) occur. These influence the response considerably. The soil non-linearity and interface non-linearity have been accounted for in various studies using FEM formulations [1][11][21] [22]. Winkler model was adopted in this paper for taking into account the effect of soil-well-structure interaction.

2.

Seismic Design of single Bridge Pier

The work is carried out on a single bridge pier supported on well foundation (Fig.1) considering soil-well- structure interaction. The objective of this paper is to understand the variation pattern in the design output i.e. base shear and displacement with respect to different seismic design methods i.e. Force Based Design (FBD), Capacity Spectrum Method (CSM) and Direct Displacement Based Design (DDBD) and changes in bridge pier height (6m, 9m, 12m, 15m, 18m). The cross-section of the bridge pier is considered constant i.e. 1.8m. The well is modelled as beam element with each element of length 1 m and well pier intersecting element of 0.5m. The pier is also modelled as a beam element with each element of length 0.5m. Although the height of the pier depends upon the site condition but as far as possible the value of slenderness ratio of the piers are kept below 12.0 so that if bridge pier fails, the failure is governed by shear and not flexure [23]. The seismic inertial mass at the top of pier determined from the weight of super structure, weighted live load on the span was calculated as 4277 kN. The foundation consists of a 25m deep well with 6.5m external and 4.5m internal diameter.

The grip length below the scour is 17.5m. The reinforcement in bridge pier, well steining and well cap are based on code provisions [5]. The concrete grade M-40 has been used in the pier and M-20 in the well. Reinforcement of grade Fe-415 has been used in all components. Modulus of elasticity for M-40, M-20 and Fe-415 are 3.16x1010N/m2, 2.2x1010N/m2 and 2x1011 N/m2 respectively.

Volume 46 Number 1 March 2016  67

horizontal spring constants were determined at each node. The horizontal spring constants (kh) varied from 1.8x103kN/m to 91.8x103kN/m; 2.116x103kN/m to 107.7x103kN/m and 2.67x103kN/m to 136x103kN/m for seismic zones III, IV and V. The vertical and rotational springs applied at the bottom of well had the values 7.25×105kN/m and 1.918×106kN/m respectively.

2.1.

(a) Well Foundation

(b) Analytical Model

Fig.1: Bridge pier on well foundation.

Assuming the well to be supported on harder strata having Standard Penetration Test (N) values greater than 30; the modulus of subgrade Kuc value for cohesion less soil for 30 cm x 30 cm plate can be adopted as 8 kg/cm3 [24]. The corrected modulus of subgrade for 6.5 m diameter well works out to kc=2.19x104kN/m3. From kc vertical and rotational spring constants at the base of well were determined as kv =7.25x105kN/m and kθ = 1.918x106kN-m/radian.

For calculation of horizontal spring constants acting on the well circumference the horizontal modulus of subgrade reaction (ηh) was adopted as 4x103kN/m3 for medium soil under submerged condition [25]. The dynamic active (ka) and passive (kp) earth pressure coefficients were calculated as ka=0.464, 0.544, 0.688 and kp = 1.772, 1.592, 1.283 for seismic zones III, IV and V [26]. Assuming shape factor as 0.9 for circular cross section of well [8] the total horizontal modulus values were calculated as 10.8x103kN/m2, 12.7x103kN/m2 and 16x103kN/m2 for seismic zones III, IV and V. The winker model requires application of horizontal soil springs over the grip length of the well below the scour level and vertical and rotational springs at the bottom of the well. Accordingly, the grip length of 17.5m was divided into 21 segments; top 14 of 1 m length and lower 3.5 of 0.5m length.

Assuming triangular variation of soil pressure the 68 Volume 46

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Force Based Design Method

The Force Based Design Method (FBD) assumes elastic behaviour of the structure and idealisation as single degree freedom system. The procedure involves calculation of elastic stiffness of members considering their support conditions. The natural time period of the structure is obtained from the given mass and calculated stiffness. Based on the natural time period, spectral acceleration (Sa/g) is determined for the specified soil type from the response spectrum at the specified damping ratio. Then, the design base shear is computed as

(1)

where, W is the weight on top of the bridge pier, Z is probability of occurrence of earthquake as zone factor, I is importance factor and R is response reduction factor for transforming structural elastic behaviour into inelastic. In case the displacements are not within the specified limits, the analysis is repeated with revised member dimensions until the drift criteria are satisfied. The Indian code [27] for seismic analysis has adopted Force Based Design Method that has been considered in this study. The empirical parameters adopted are: Earthquake response spectrum with damping ξ= 5 %, Z=0.36, 0.24, 0.16 for Zones-V, IV and III respectively, I = 1.5 and R = 4. The horizontal soil springs at the circumference of the well, vertical and rotational springs applied at the base of the well take into account the soil-well interaction effects.

2.2. Direct Displacement Based Design Direct Displacement Based Design (DDBD) [28] is based on achieving required performance defined in terms of damage level. This method assumes an equivalent single degree of freedom system with energy dissipation in terms of equivalent viscous damping and inelastic behaviour of the structure. The design procedure uses spectral displacement at the natural time period of 4 sec, called as corner period The Bridge and Structural Engineer

displacement (Δc). Yield curvature (φy) and yield displacement (Δy) for the bridge pier were determined using yield strain (єy) of steel and strain penetration length (Lsp). The design displacement (∆d) is calculated based on displacement ductility (µ) assumed as 4 and limiting rotation (θd) at the base of pier taken as 0.035 radians. Having calculated design displacement, ductility (µ), equivalent viscous damping (ξeq), damping modifier (Rξ) and the maximum spectral displacement demand at equivalent damping are calculated. For the design displacement less than the spectral displacement demand, the effective time period (Te) is calculated as (4×∆d⁄Δc,ξ)

(2)

When the design displacement (∆d) is more than the spectral demand (Δc,ξ), an iterative procedure is adopted to find the design displacement. The procedure starts with an assumed value of design displacement, say corner period displacement (Δc), calculation of revised ductility, equivalent viscous damping; damping modifier and then revised design displacement is calculated. This procedure is repeated till convergence. The converged value is taken as final design displacement and effective time period is taken as 4 sec. The effective stiffness (Ke) is calculated from the given mass (m) on the bridge pier and effective time period. The base shear (Vb) is taken as the product of stiffness and design displacement and the calculated base shear is for the fixed base.

The base shear computed requires modification for the soil-well interaction effects. To incorporate this displacement at the pier top (Δf) due to foundation rotation is required to be calculated. For this it is necessary to find the point where rotation takes place in the well. Accordingly, the deformed shapes in the analysis by forced based method were considered. A typical deformed shape is shown in Fig.2. The analysis of deformed shapes showed the point of rotation from the bottom of the well in terms of fraction of embedded length as 0.276, 0.272 and 0.286 for Zone III, IV and V with an average value of 0.278. This implies that the point of rotation lies at 0.278D from the bottom of well; where D is the depth of embedment. For the considered embedded length the point of rotation lies at 4.865m from the bottom of well. Assuming well to be rigid, considering equilibrium of all forces (spring forces and base shear at the top of pier) yields following relationships between angle of rotation of The Bridge and Structural Engineer

the well (θ) and base shear at the pier top shown in equations 3,4 and 5 for Zone III, IV and V. (3) (4) (5)

Fig. 2: Deformed shape of well pier

The displacement at the pier top can be obtained as

Δf = θ×(L+h–4.865) (6) where, L=length of the well and h=height of the pier.

Having calculated (Δf), computation of base shear for Well foundation is similar to that of fixed base with following changes: The design displacement is calculated as Δd = Δy + Δf limited to ɵdh And

(7)

(8)

Then structural damping is calculated as ξe = 0.05 + (µ – 1)/ µπ

(9)

Considering hysteretic and radiation damping of the soil (taken 5%), the equivalent viscous damping is calculated as (10) With the above changes followed in both the cases: ∆d<∆c,ξ and ∆d>∆c,ξ; Δd, ke, Te and Vb for the well foundation are determined.

2.3. Capacity Spectrum Method Capacity Spectrum Method (CSM) [29] assumes inelastic behaviour of the structure and idealized as a single degree of freedom (SDOF) system. Reduced secant stiffness and increased damping proportional to hysteretic energy are used to estimate the response spectra of non-linear system which represents the inelastic seismic demand. The seismic demand curve was generated based upon the site location Volume 46 Number 1 March 2016 69

and the foundation condition using design response spectrum on acceleration displacement response spectrum format. The pushover curve was generated by applying step wise incremental load on the top of the bridge pier until failure. The force displacement relationship obtained was based on considered Nonlinear M-φ Plastic Hinge relation of cross-section, Plastic hinge length, Takeda Hysteretic model, material stress strain relationship and steel yield stress. The performance level of the structure is the point of intersection of seismic demand and capacity curves plotted on acceleration displacement response format. From the capacity spectrum method, base shear, yield displacement, design displacement, ductility, effective time period and equivalent viscous damping are obtained. The horizontal soil springs at the circumference of the well, vertical and rotational springs applied at the base of the well take into account the soil-well interaction effects.

3.

Observations drawn from Fig.3 are: The values of base shear obtained by different methods differ because of difference in their approaches and assumptions. The Forced Based Design calculation of base shear is based on the fundamental structural time period, spectral amplification, zone factor and response reduction factor. The approach of Direct Displacement Based Design is based on corner time period displacement, equivalent viscous damping due to hinge formation, yield curvature. The capacity spectrum method is dependent on sectional moment curvature relation, response spectrum, effective damping, and estimated displacement demand.



The seismic design forces depend on pier height based on their different method of approach. In case of FBD and CSM, base shear is calculated based on natural time period of structure which depend upon stiffness which in turn is a function of pier height. The base shear calculated with DDBD approach depends on effective stiffness which in turn depends on effective time period that is design displacement dependent. Further, design displacement is yield displacement dependent which depends on the height of the pier.



Design Computations

The analysis using FBD and CSM was carried out using Structural analysis program (SAP2000) [30] and DDBD through computational algorithm. For FBD and CSM the response spectrum given in code [27] with 5% damping ratio was considered for seismic zones-III, IV and V for pier heights (6m, 9m, 12m, 15m, 18m). The moment curvature relation for nonlinearity of hinge was derived from the section designer incorporated in SAP2000.

4.

In general, the values of base shear obtained by FBD and CSM decrease with increase in pier height. The decrease in base shear is because of increase in flexibility.



Discussion of Results

The Base Shear and the displacement at the pier top are important parameters for seismic design of bridges.

Accordingly, the results of base shear obtained by Force Based Design (FBD), Direct Displacement Based Design (DDBD) and Capacity Spectrum methods (CSM) for different pier heights (6m, 9m, 12m, 15m, 18m) have been presented and discussed.

The base shear versus pier height for seismic zones III, IV and V are shown in Fig.3.

The values of base shear obtained by CSM are higher than those obtained by FBD; but the difference in base shear decreases with increase in pier height.



The values of base shear obtained by DDBD increase with increase in height of piers in ZoneIII. This is because the design displacements are more than the corner period displacement at equivalent damping. Therefore, the effective time period remains 4 sec, while, the design displacements increase with increase in pier height resulting in increase in values of base shear.



(a) (b) (c) Fig. 3: Base shear versus pier height for Medium soil in (a) Z-III (b) Z-IV (c) Z-V

70 Volume 46 Number 1 March 2016

The values of base shear obtained by DDBD for Zone-IV and V decrease from 6m to 9m and then increase with increase in pier height. For



The Bridge and Structural Engineer

smaller heights the design displacements are less than corner period displacement at equivalent damping. Hence, their effective time periods are less than 4 sec and in increasing order. This results in decreasing trend in base shear.

Base shear disparity versus pier height is plotted to understand its variation pattern. The base shear disparity between FBD and DDBD and between CSM and DDBD versus pier height for seismic zones-III, IV and V are shown in Fig. 4.

(a)

(b)

(c)

Fig. 4: Base shear disparity versus pier height for Medium soil in (a) Z-III (b) Z-IV (c) Z-V

The variation pattern shows that the difference in base shear is minimal in the range of Pier height between 14m to 15m. This infers that for slenderness ratio around 8.0 the base shear values by FBD, CSM and DDBD are comparable. Therefore, slenderness ratio of 8.0 can form the basis for selecting diameter of a bridge pier. However, practical need should be kept in view. The displacement at the top of the pier versus pier height has been plotted and shown in Fig. 5 for seismic zones-III, IV and V.

(a)

(b)

(c)

Fig. 5: Top Displacement versus pier height for Medium soil in (a) Z-III (b) Z-IV (c) Z-V

very high compared to other considered methods because of difference in approach and assumptions.

5. Conclusions The capacity spectrum method and direct displacement design method give an insight to the behaviour of the bridge pier through various parameters such as yield displacement, ductility and equivalent viscous damping. The DDBD approach sets the target displacement based on the ductility and drift limit whereas CSM define the displacement as the intersection point of capacity and the demand on the pier cross-section. FBD divides the calculated value of base shear by a response reduction factor to account for inelastic structural behaviour. Thus, the methods have difference in approach and assumptions and hence, the base shear values obtained by them are different.

The values obtained by FBD and CSM decrease with increase in pier height; but the base shear values by DDBD have a general trend to decrease first and then to increase with increase in pier height. The values of base shear obtained by CSM are higher than those

by FBD and the difference between them decreases with increase in pier height. The base shear disparities i.e. the difference in base shear values between FBD and DDBD and between CSM and DDBD were found to be minimal for a particular range of pier height.

Therefore, a diameter could be obtained for a given height such that the base shear values determined are closer for the designed pier for better performance during earthquakes. However, the practical need should not be lost sight off. Incase, the design shear values by all methods used are closer, better seismic performance of the structure is expected.

References 1.

MONDAL G., PRASHANT A., and JAIN S. K., “Simplified Seismic Analysis of Soil-WellPier System for Bridges”, Soil Dynamics and Earthquake Engineering, Vol. 32, No. 1, 2012, pp. 42–55.

2.

PRIESTLEY M. J. N., SINGH J. P., LESLIET. Y., and ROLLINSK. M., “Bridges” Earthquake Spectra, Vol. 7, No. s2. 1991, pp. 59–91.

3.

ΑNASTASOPOULOS N., GEROLYMOS N. and GAZETAS G., “Possible Causes of the Collapse of an Approach Span of

The observations are: The displacements at the pier top increase with increase in height due to decrease in stiffness of the pier.



The displacements and the base shear obtained

by FBD and CSM are quite closer, since same response spectrum has been considered in both the methods.



The displacements obtained by DDBD are



The Bridge and Structural Engineer

Volume 46 Number 1 March 2016 71

the Nishinomiya-ko Bridge : Kobe 1995,” Proceedings of 4th Hellenic Conference on Geotechnical and Geoenvironmental Engineering, Athens, Greece, 2001, pp. 83–90.

4.

EDWARD S C., “Thailand Lifelines after the December 2004 Great Sumatra Earthquake and Indian Ocean Tsunami”, Earthquake spectra, Vol. 22, No. s3, 2006 pp. 641–659.

5.

The Indian Roads Congress., “Standard Specification and Code of Practice for Road Bridges, Section-VII Foundations and Substructure”, IRC: 78, New Delhi 2000.

6.

7.

8.

9.

GARDE R. J. and. KOTHYARI U. C., “Scour around bridge piers,” Proceedings of Indian National Science Academy, Vol.64, No.4, 1998, pp. 569–580.

KWAK K. S. and BRIAUD J. L., “Case study: An analysis of pier scour using the SRICOS method”, KSCE Journal of Civil Engineering, Vol.6, No.3, 2002, pp.243-253.

The Indian Roads Congress, “Recommendation for Estimating the Resistance of Soil below the Maximum Scour Level in the Design of Well Foundations of Bridges.,” IRC: 45, New Delhi,1972.

NEGMA. M. MOUSTAFAG. M., ABDALLAY M. and FATHY A. A., “Control of Local Scour Around Bridge Piers Using Current Deflector,” Thirteenth International Water Technology Conference, Hurghada, Egypt, 2009, pp. 1711– 1722.

10. BEG M. and BEG S., “Scour Reduction around Bridge Piers : A Review”, International Journal of Engineering Inventions., Vol. 2, No. 7, 2013, pp. 7–15.

11. MONDAL G., PRASHANT A., and JAIN S. K., “Significance of interface nonlinearity on the seismic response of a well-pier system in cohesionless soil”, Earthquake Spectra, Vol. 28, No. 3, 2012, pp. 1117–1145.

12. TSIGGINOS C., GEROLYMOS N., ASSIMAKI D., and GAZETAS G., “Seismic response of bridge pier on rigid caisson foundation in soil stratum”, Earthquake Engineering and Engineering Vibrations, Vol. 7, No. 1, 2008, pp.

33–43.

72 Volume 46 Number 1 March 2016

13. VARUN, ASSIMAKI D., and GAZETAS G., “A simplified model for lateral response of large diameter caisson foundations - Linear elastic formulation”, Soil Dynamics and Earthquake Engineering, Vol. 29, 2009, pp. 268-291.

14. GEROLYMOS N. and GAZETAS G., “Winkler Model for lateral Response of Rigid Caisson Foundations in Linear Soil”, Soil Dynamics and Earthquake Engineering, Vol. 26, No. 5, 2006 pp. 347–361.

15. BEREDUGO Y. O., and NOVAK M., “Coupled Horizontal and Rocking Vibration of Embedded Footings”, Canadian Geotechnical Journal, Vol.9, No.4, 1972, pp.477–497.

16. PARMELEE R. A. and KUDDER R. J., “Seismic Soil-Structure Interaction of Embedded Buildings”, Fifth World Conference on Earthquake Engineering, Rome, Italy, 1974, Vol. 2, pp. 1941–1950.

17. GAZETAS G., “Formulas and Charts for Impedances of Surface and Embedded Foundations”, Journal of Geotechnical Engineering, Vol. 117, No. 9, 1992, pp. 1363– 1381.

18. WOLF J., Soil-Structure Interaction Analysis in Time Domain. Prentice Hall, Eaglewood Cliffs, New Jersey, 1998.

19. CHOWDHURY I., SINGH J. P. and TILAK R., “Seismic Response of Well Foundation with Dynamic Soil Structure Interaction”, Fifteenth World Conference on Earthquake Engineering, 2012.

20. GEROLYMOS N. and GAZETAS G., “Development of Winkler Model for Static and Dynamic Response of Caisson Foundations with Soil and Interface Nonlinearities”, Soil Dynamics and. Earthquake Engineering, Vol. 26, No.5, 2006, pp. 363–376.

21. MONDAL G. and JAIN S. K., “Effect of Nonlinearity in Pier and Well Foundation on Seismic Response of Bridges”, Proceedings Fourteenth World Conference on Earthquake Engineering, Beijing, China 2008.

22. GEROLYMOS N. and GAZETAS G., “Static and Dynamic Response of Massive Caisson Foundations with Soil and Interface The Bridge and Structural Engineer

Nonlinearities - Validation and Results,” Soil Dynamics and Earthquake Engineering, Vol. 26, No. 5, 2006, pp. 377–394.

23. The Indian Roads Congress, “Code of Practice for Concrete Road Bridges”, IRC : 112, New Delhi, 2011.

24. Bureau of Indian Standards, “Code of Practice for Design and Construction of Raft Foundations”, IS:2950 (Part-I), New Delhi 1981 .

25. Bureau of Indian Standards, “Design and Construction of Pile Foundations-Code of Practice-Concrete Piles-Driven Cast In-situ Concrete Piles”, IS:2911 (Part-I) Section 1, New Delhi 2010.

26. The Indian Roads Congress, “Standard Speciications and Code of Practice for Road

The Bridge and Structural Engineer

Bridges, Section-II Loads and Stresses”, IRC: 6, New Delhi, 2014.

27. Bureau of Indian Standards, “Criteria for Earthquake Resistant Design of Structures, General Provisions and Buildings”, IS:1893 (Part 1), New Delhi, India. 2002.

28. PRIESTLEY M. J. N., CALVI G. M., and KOWALSKY M. J., “Displacement Based Seismic Design of Structures”, IUSS press, Pravia, Italy, 2007.

29. Applied Technology Council., “Seismic Evaluation and Retrofit of Concrete Buildings”, ATC 40, Redwood City California, 1996.

30. Computers and Structures., Structural Analysis Programme 10.0.5, SAP2000, Inc., Berkeley CA, www.csiberkeley.com.

Volume 46 Number 1 March 2016 73

STEEL FIBRE REINFORCED HIGH PERFORMANCE CONCRETE EXTERIOR BEAM COLUMN SLAB JOINTS UNDER REVERSE CYCLIC LOADING

Ganesan N. Professor of Civil Engineering, NIT Calicut, India. ganesan@nitc.ac.in

Indira P.V. Professor of Civil Engineering, NIT Calicut, India. indira@nitc.ac.in

Nidhi M. Ph.D Scholar, Civil Engineering, NIT Calicut, India. nidhi.srijith2012@gmail. com

Dr. N. Ganesan is a Professor of Civil Engineering at the National Institute of Technology, Calicut, India. He received his M.E and Ph.D degree from I.I.Sc, Bangalore. He is a fellow of The Institution of Engineers, India and IFIC consultant. He was a visiting professor at the Asian Institute of Technology, Bangkok and King Khalid University, Kingdom of Saudi Arabia. He had visited University of Dundee, Scotland, Queens University, Belfast, National University of Singapore, University of Stuttgart, Germany and University of Michigan, USA.

Dr. P.V. Indira is a Professor of Civil Engineering at the National Institute of Technology, Calicut.

She received her M.Tech from IIT Madras and Ph.D degree from University of Calicut. She is a member of The Institution of Engineers, India.

Nidhi M received her B.Tech (Civil Engineering) from Calicut University, Kerala and M.Tech (Structural Engineering) from College of Engineering Trivandrum, Kerala. At present she is a Ph.D scholar in NIT Calicut, Kerala state.

Abstract:

obtained and the results are presented.

Behaviour of steel fibre reinforced high performance concrete (SFRHPC) beam column slab joints was investigated. High performance concrete (HPC) of M60 grade was designed based on guidelines suggested by Aitcin. The variable considered was the volume fraction of crimped steel fibres i.e., 0%, 0.5% and 1.0% in the joint region. The specimens were subjected to reverse cyclic loading and performance based parameters such as strength, stiffness degradation and energy dissipation capacity were

Keywords: Beam column slab joints, high performance concrete, reverse cyclic loading, stiffness degradation, energy dissipation capacity

74â&#x20AC;&#x192; Volume 46 Number 1 March 2016

1. Introduction Reinforced concrete (RC) beam column joints in frames, bridges etc., when subjected large reversals of loading results in major distress in the joint region and hence entail special attention. Identifying the importance of RC beam column joints under cyclic The Bridge and Structural Engineer

loading, several experimental investigations have been carried out in the past [1-5]. However, most of these tests were conducted on isolated subassemblages and did not consider the effect of slab. However, slab is cast monolithically with the beam and the slab reinforcement within the effective width of the slab acts along with the flexural reinforcement of the beam and this imparts additional strength to the beam.

This may lead to a strong beam weak column criteria leading to column failure which is undesirable.

Formerly few studies have been carried out to study the effect of slab in normal strength beam column joints [6-10].

Nowadays, HPC is extensively used for the construction of high rise buildings, long span bridges, off-shore structures and earthquake defiant structures etc. owing to its dense microstructure. This guarantee durable, lighter and thinner sections resulting in costeffective structures. Large number of investigations are available on high strength concrete (HSC) [11,12] fibre reinforced HSC [13], high performance concrete (HPC) [14] and fibre reinforced HPC [3,15]. In this experimental investigation, the effect of steel fibres on the strength and overall behaviour of exterior HPC beam column slab joints are studied.

and steel fibres used are given in Table 1 and Table 2 respectively. The photograph of crimped steel fibre used in this study is shown in Fig. 1.

Table 1: Properties of silica fume Specific gravity SiO2 Moisture content Retained on 45 microns sieve Bulk Density

2.10 90.36% 0.60% 0.40% 640 kg/ m3

Table 2: Properties of steel fibre Type Length Diameter Aspect ratio Ultimate tensile strength

Crimped steel fibre 30 mm 0.45 mm 66 800 MPa

2. Experimental Programme The experimental investigation consisted of casting and testing of three number of 1/3rd scaled down exterior beam-column-slab joints under reverse cyclic loading. The variable considered was the volume fraction of crimped steel fibres i.e., 0%, 0.5% and 1.0% in the joint region.

2.1 Materials The materials used in this study are as follows (i) Portland Pozzolana Cement conforming to IS 1489 (Part 1):1991[16] crushed stone aggregate passing through 4.75 mm IS sieve conforming to grading zone II of IS: 383-1970 (reaffirmed 2002) [17] with fineness modulus 2.92 and specific gravity 2.39 and crushed stone with a maximum size 12.5 mm with specific gravity 2.78 were used for this investigation.

Silica fume supplied by Elkem Micro Silica were used as mineral admixtures. A naphthalene based superplasticizer (Conplast 430) was used to obtain the required workability. High Yield Strength Deformed bars (HYSD) of Fe 415 grade was used as steel reinforcement. The properties of silica fume The Bridge and Structural Engineer

Fig. 1: Crimped steel fibres

2.2 Mix proportions for HPC ACI 211.1-91[18] guidelines which was further modified by AĂŻtcin [19] was followed for designing M60 grade HPC mix. Part of cement was replaced by micro filler silica fume. The dosage of superplasticizer was adjusted to maintain the workability. The details of mix proportions are given in Table 3.

Table 3: HPC mix proportions (kg/m3) PPC

Silica fume

Fine aggregate

507

44

48

Coarse Water Superplasticizer aggregate 585

55

22

Volume 46 Number 1 March 2016â&#x20AC;&#x192; 75

2.3 Details of specimens The mechanical properties of the reinforcements are as given in Table 4 . The overall dimension and reinforcement detailing of exterior beam-columnslab-joint specimen is shown in Fig. 2 and the details of the specimen are given in Table 5.

3 in order to simulate actual construction practice.

The specimens were cured for 28 days by using wet jute sacks which were wetted periodically to ensure continuous curing.

Table 4: Mechanical Properties of Steel Reinforcement Diameter of bar (mm)

Yield Strength (N/mm2)

Ultimate Strength (N/mm2)

Modulus of Elasticity (N/ mm2)

12

419

580

2.28x105

10

426

570

2.32x105

6

431

660

2.44x105

Fig. 3: Casting of specimen

2.5 Testing

Fig. 2: Reinforcement detailing of beam-column-slab-joint

Table : 5 Details of specimens Sl No.

Specimen Designation

Specimen

Volume fraction of fibres (%)

1.

B1

HPC beam-column-slabjoint

0.0

2.

B2

SFRHPC exterior beamcolumn- slab-joint with 0.5% steel fibre

0.5

3.

B3

SFRHPC exterior beamcolumn- slab-joint with 1.0 % steel fibre

1.0

2.4 Casting of specimens The moulds for the specimens were fabricated using half-inch thick marine plywood. The reinforcement cage was placed in the mould correctly in position.

Materials were batched by weight and mixed in the concrete mixer. Compaction of concrete within the mould was done using needle vibrator. The specimens were cast in the upright position as shown in Fig. 76â&#x20AC;&#x192; Volume 46 Number 1 March 2016

The test setup consisted of a steel loading frame with a capacity 300 kN. The specimens were tested in an upright position in the loading frame after 28 days of curing. The top support of the column was a hinged support, which was simulated by a steel ball placed between two steel plates provided with spherical grooves. The bottom of the column was firmly resting on top of the I-beam fixed to the test floor. An axial compressive load of 25% of the axial capacity of the column was applied on the column by means of a hydraulic jack so that the specimen was just firmly supported in position without toppling. A hydraulic jack of 500 kN capacity which was connected to a 50 kN load cell through a plunger was used to apply the loads. The load was transferred to the tip of the beam through the arrangement of two channel sections and two rods. The speciÂŹmens were loaded up to 2 kN then unloaded to zero, and then reloaded to 2 kN in the negative direction and again unloaded to zero, which was continued till the failure of the specimen.

Fig. 4 shows the loading sequence. The schematic diagram of the test setup is shown in Fig. 5 and the photograph of test arrangement in Fig 6.

The Bridge and Structural Engineer

Fig. 4: Loading history

later stages of loading the cracks propagated from beam to the slab. Moreover, horizontal cracks parallel to the longitudinal reinforcement of the beam were observed on the top portion of the slab which deviated from the initial portion and branched out upon further loading. As the volume fraction of fibres increased from 0 to 0.5 % and 1.0 %, the load carrying capacity of the joint improved. This may be attributed to the fact that the crimped steel fibres intercepts the crack and prevents its further propagation. The cracks have to take a meandering path and hence more energy is dissipated during this process.

(a) HPC exterior beam column slab joint (B1)

Fig. 5: Schematic diagram of the test set up

(b) SFRHPC exterior beam column slab joint with 0.5% steel fibre (B2)

Fig. 6: Photograph of the test set up

3.

Results and discussions

3.1 Overall Behaviour Figs. 7(a)-(c) shows the crack pattern observed in the specimens B1, B2 and B3 respectively. The first crack occurred in the soffit of the beam for all the specimens.

The initial cracks propagated further during the successive loading cycles, leading to the formation of additional cracks in the beam portion. During the The Bridge and Structural Engineer

(c) SFRHPC exterior beam column slab joint with 1.0 % steel fibre (B3) Fig.7: Crack patterns of specimens

Volume 46 Number 1 March 2016â&#x20AC;&#x192; 77

3.2 Load displacement behaviour The seismic performance of a structure can be understood from the load-displacement hysteresis loop. The load displacement plots of three exterior beam column slab joints B1, B2 and B3 are given in Figs. 8 (a)-(c). The envelope load displacement graph was plotted for each specimen by joining the peak load and displacement points at each cycle of loading and is shown in Fig. 9. The load corresponding to the point at which the envelope curve deviated from linearity is noted as the first crack load [4]. Table 6 shows the first crack load, ultimate load and displacement at ultimate load of the specimens.

Table : 6 Experimental results Specimen First Crack Ultimate DisYield disLoad (kN) Load placement placement (kN) at Ultimate (mm) Load (mm)

Absolute displacement ductility factor

B1

1

8.20

22.00

17.35

6.20

B2

11.50

29.00

22.00

6.80

1.15

B3

13.60

35.00

26.50

7.40

1.28

(b) SFRHPC exterior beam column slab joint with 0.5% steel fibre (B2)

(c) SFRHPC exterior beam column slab joint with 1.0 % steel fibre (B3) Fig. 8: Typical load displacement plots of specimens B1, B2 and B3

(a) HPC exterior beam column slab joint (B1)

Fig. 9: Load versus displacement envelope of specimens

78â&#x20AC;&#x192; Volume 46 Number 1 March 2016

The Bridge and Structural Engineer

3.3 Stiffness Degradation Due to repeated reversals of loadings RCC beamcolumn-joints shows stiffness degradation which is caused due to cracking and loss of bond. The secant stiffness gives a measure of stiffness degradation and is calculated by drawing a line between the maximum positive displacement point in one half of the cycle and the maximum negative displacement point in the other half of the cycle [4, 21]. The stiffness degradation plots for the beam column slab joint specimens is shown in Fig. 10. It may be noted from the figure that as loading cycle increases, there is reduction in stiffness. The HPC specimen has lower initial secant stiffness than the SFRHPC specimens with 0.5% and 1.0 % steel fibre. Also, as the number of cycles increases, the stiffness decreases, however, the SFRHPC specimens showed less stiffness degradation. This behaviour may be attributed to the following reason: as the number of cycles increase, microcracks develop and the steel fibres, which are distributed at random, intercept these cracks and bridge across these cracks. This controls further propagation of cracks and results in higher energy demand for debonding and pullout of steel fibres in the vicinity of cracks. Due to this, the stiffness of specimens with steel fibres will not undergo much reduction. The initial stiffness is increased by 12% and 39% respectively for the SFRHPC specimen with 0.5% and 1.0 % steel fibres when compared to that of HPC specimen.

is numerically equal to the area under the loaddisplacement curve [20, 21]. The sum of the area under the hysteresis loops in different load cycles gives the total energy dissipated by the specimen.

The cumulative energy dissipation capacity of the specimens is given in Fig. 11. The cumulative energy dissipated is higher by 1.35 and 1.54 times for SFRHPC specimen with 0.5% and 1.0 % steel fibre respectively when compared to HPC specimen.

Fig. 11: Comparison of cumulative energy dissipation capacity

4. Conclusions This investigation leads to the following conclusion: 1.

The first crack load of SFRHPC specimen with 0.5% and 1.0 % steel fibre is 40% and 66% higher than the HPC specimen.

2.

HPC beam-column-slab-joints exhibited less stiffness degradation compared to SFRHPC joints. The initial stiffness is increased by 12% and 39% respectively for the SFRHPC specimen with 0.5% and 1.0 % steel fibres when compared to that of HPC specimen

3.

When compared to the HPC specimen, the cumulative energy dissipated is higher by 1.35 and 1.54 times for SFRHPC specimen with 0.5% and 1.0 % steel fibre respectively.

References Fig. 10: Comparison of stiffness degradation of squat shear walls

1.

ABBAS A.A., MOHSIN S.M.S., and COTSOVOS D.M., “Seismic Response of Steel Fibre Reinforced Concrete Beam–Column Joints”, Engineering Structure, Vol. 59, 2014, pp. 261-283.

2.

GANESAN N., BHARATI RAJ, and SHASHIKALA A.P., “Behavior of SelfConsolidating Rubberized Concrete Beam-

3.4 Energy Dissipation Capacity The ductility and energy dissipation capacity of a structure when subjected to reverse cyclic loading are interrelated. The energy dissipation capacity of a structure is defined as the work done in deforming a structure up to the limit of useful deflection, which The Bridge and Structural Engineer

Volume 46 Number 1 March 2016 79

Column Joints”, ACI Materials Journal, Vol. 110, No. 64, 2013, pp. 697-704.

3.

4.

5.

6.

GANESAN N., INDIRA P.V., and RUBY A., “Steel Fibre Reinforced High Performance Concrete Beam-Column Joints Subjected to Cyclic Loading”, ISET J Earthq Technol, Vol. 44, 2007, pp. 445-456.

GANESAN N., INDIRA P.V., and SABEENA M.V., “Behaviour of Hybrid Fibre Reinforced Concrete Beam-Column Joints under Reverse Cyclic Loads”, Materials and Design, Vol. 54, 2014, pp. 686-693 HANSON N.W., and CONNER H.W., “Seismic resistance of reinforced concrete beam-column joints”, Proceedings ASCE, Vol. 93, 1967, pp.

533-560.

CANBOLAT B.B., and WIGHT J.K., “Experimental Investigation on Seismic Behaviour of Eccentric Reinforced Concrete Beam-Column-Slab Connections”, ACI Structural Journal, Vol. 105, No. 2, 2008, pp.

154-162.

7.

DURRANI A.J., and WIGHT J.K., “Earthquake Resistance of Connections including Slabs”, ACI Structural Journal, Vol. 85, No. 5, 1987, pp. 400-406.

8.

EHSANI M., and WIGHT J.K., “Effect of Transverse Beams and Slab on Beam-toColumn Connections”, ACI Journal, Vol. 82, No. 2, 1985, pp. 188-195.

9.

PANTAZOPOULOU S., and FRENCH C.W., (2001), “Slab Participation in Practical Earthquake Design of Reinforced Concrete Frames”, ACI Structural Journal, Vol. 98, No. 4, 2001, pp. 1-11.

10. SHIN M. and LAFAVE J.M., “Reinforced Concrete Edge Beam–Column–Slab Connections Subjected to Earthquake Loading”, Magazine of Concrete Research, Vol. 55, No. 6, 2004, pp. 273-291.

11. SHAH S.A.A., RIBAKOV Y., “Experimental and Analytical Study of Flat-Plate Floor Confinement”, Materials and Design, Vol. 26, 2005, pp. 655-669.

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12. ISKHAKOV I., RIBAKOV Y., and SHAH A., “Experimental and Theoretical Investigation of Column Flat Slab Joint Ductility”, Materials and Design, Vol. 30, 2009, pp. 3158-3164 13. HOLSCHEMACHER K., MUELLER T., and RIBAKOV Y., “Effect of Steel Fibres on Mechanical Properties of High Strength Concrete” Materials and Design, Vol.31, 2010, pp. 2604-2615.

14. ELAHI A., BASHEER P.A.M., NANUKUTTAN S.V., and KHAN Q.U.Z., “Mechanical and Durability Properties of High Performance Concrete Containing Supplementary Cementitious Materials”, Construction and Building Materials, Vol. 24, 2010, pp. 292–299.

15. GANESAN N., INDIRA P.V., and SABEENA M.V., “Tension Stiffening and Cracking of Hybrid Fiber-Reinforced Concrete” ACI Materials Journal, 2013, Vol.110, No. 66, pp.

715-722.

16. IS 1489 (Part I): 1991, Portland pozzolona cement specifications, Part I, Fly ash based, Bureau of Indian Standards, New Delhi.

17. IS 383: 1970 (reaffirmed 2002), Specification for coarse and fine aggregates from natural sources for concrete, Bureau of Indian Standards, New Delhi.

18. ACI 211.1-91 (reapproved2009), “Standard practice for selecting proportions for normal, heavyweight, and mass concrete”, American Concrete Institute, Farmington Hill, Michigan, 19. AITCIN P.C., High Performance Concrete, London: U.K., E & FN Spon; 1998.

20. PAULAY T., and PRIESTLEY M.J.N., “Seismic Design of Reinforced Concrete and Masonry Buildings”, John Wiley & Sons, NewYork, 1992.

21. GANESAN N., INDIRA P.V., and SEENA P., “High Performance Cement Concrete Squat Shear Walls under Reverse Cyclic Loading”, The Bridge and Structural Engineer- International association of bridge and structural engineer (IABSE), Vol.44, No.1, 2014, pp.100-107.

The Bridge and Structural Engineer

Seismic Behaviour of Concrete Barrel Shell Structures under Static & Dynamic loads

Raana PATHAK PhD Research Scholar Shri G.S. Institute of Technology & Science Indore, MP, INDIA raanapathak@rediffmail.com

Rakesh KHARE Professor Shri G.S. Institute of Technology & Science Indore, MP, INDIA rakeshkhare@hotmail.com

Raana Pathak received her Bachelor degree in Civil Engineering in 2002 and Masters degree in Structures in 2006 from SGSITS, Indore. Then registered herself for PhD at RGPV Bhopal. She is presently working as Assistant professor at SGSITS, Indore since 2007.

Rakesh Khare received his Bachelor degree in Civil Engineering in 1985 and Masters degree in 1987 from Bhopal University. He joined SGSITS in 1988 and did his PhD in 1996 from DAVV Indore. He is presently working as professor at SGSITS, Indore.

Summary

1. Introduction

This study deals with seismic behaviour of reinforced concrete single barrel shell structures under static and dynamic loads. IS: 2210-1988, Criteria for Design of RC Shell Structures and Folded plates, suggests to design shell structures for seismic loads in accordance with IS: 1893-2002, Criteria for earthquake resistant structure, however lack in detail specifications for shell structures to be adopted. Therefore, from this point of view, a methodology needs to be proposed for understanding the behaviour of shell structures under seismic loads. Linear static and dynamic analyses are performed on the basis of IS: 1893-2002 using SAP-2000 software. The Equivalent Static method is performed for 67 load combinations and the Response spectrum method is performed for 155 load combinations. The results show that the single barrel shell structure considered here with designed lateral force resisting system behaves well under seismic loading.

This study deals with seismic behaviour of reinforced concrete single barrel shell structures under static and dynamic loads. Shells and spatial structures are adopted for construction of large span structures in which a large space is realized without columns as the structural components [1]. In those cases, the structures are expected to resist against various design loads mainly through their extremely strong capability which can be acquired through in-plane or membrane stress resultants and this is just the reason by which they themselves stand for external loads without columns as their structural components in the large span structures. In civil engineering construction, singly curved cylindrical shells are commonly used as roofing units. However, they are frequently subjected to dynamic loadings in their service life and hence, the knowledge of their dynamic behaviour is important from the standpoint of analysis and design [2].

Keywords: Shell structure, Seismic behaviour, linear static and linear dynamic analysis.

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It is well known that shells structures gain their strength by virtue of the three dimensional development of their surfaces, with a resulting ability to carry external Volume 46 Number 1 March 2016â&#x20AC;&#x192; 81

loads primarily through in-plane stresses rather bending. The internal force and stress distribution in shell structures is in general, spatial. Then a careful study must be performed to catch the real behaviour of such structures under lateral forces when bending will be a non-negligible effect.

IS: 2210-1988, Criteria for Design of Reinforced Concrete Shell Structures and Folded plates [3], suggests to design the shell structures for seismic loads in accordance with IS: 1893-2002, Criteria for earthquake resistant structure [4], however lack in guidelines and specifications for seismic analysis and design of shell structures to be adopted. IS: 2210-1988 suggests the use of ASCE Manual of Engineering Practice No. 31, Design of Cylindrical Concrete Shell Roofs [5], for dead and live loads. However, ASCE Manual also lack in guidelines and specifications for seismic analysis and design of shell structures [6] [7] [8]. Therefore, from this point of view, a methodology needs to be proposed for understanding the behaviour of shell structures under seismic loads.

Linear static and dynamic analyses are performed on the basis of IS: 1893-2002 using SAP-2000 software [9]. So, a three-dimensional finite element model for seismic analysis is then required. A linear static and linear dynamic analysis is performed on the basis of IS: 1893-2002 code using SAP-2000 software. The Equivalent Static method is performed for 67 load combinations and the Response spectrum method is performed for 155 load combinations.

2. Methodology 2.1 Geometrical Characteristics of the Shell Structure

No. 7.

8.

9.

10.

11.

12.

Description Column Size Beam Size Shell reinforcement Diaphragm thickness Radius of Shell Thickness of Shell

Parameter 0.5 m x 0.5 m 0.5 m x 1.0 m 10d @ 200 c/c on both-faces.

0.50 m 20 m 0.15 m

Table 1 gives the details of parameters considered for single barrel shell structure. Figure 1 (a) shows the meshing view for single barrel shell structure.

The radius of shell is 20 m. The thickness of shell is 0.15 m. The semi-central angle is kept 30° to keep radius and chord width same. All columns are 0.6 m x 0.6 m in size and 6 m in height. Shell surface and diaphragms are discritized as area elements. The edge beams are modelled as area elements for a true representation of connectivity with shell element.

Columns are modelled as frame elements [8].

2.2 Finite Element Model The Finite Element model includes the shell structure and its supporting structure. The number of shell area elements is 720 and the shell is discritized in to 1m x 2m element [9]. The shell element is idealized as an assemblage of thin constant thickness element with each element subdivided into three numbers of layers. The layered shell allows any number of layers to be defined in the thickness direction, each with an independent location, thickness, behaviour, and material [10]. Material behaviour is considered to be linear. Three-dimensional finite element modelling of the single barrel shell structure is performed using SAP 2000 program.

A long single barrel shell is used in this study to cover an area of 36 m x 20 m. The cylindrical shell is supported on rigid diaphragm at edges in Y-direction and edge beams in X-direction. A live load of 0.75 kN/m2 is applied on the structure.

Table 1: Details of parameters for Barrel Shell Roof No. 1.

2.

3.

4.

5.

6.

Description Span in X direction Span in Y direction Live load Grade of Concrete Type of Steel Column Height

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Parameter 36 m 20 m 0.75 kN/m2 M-25 HYSD bars 6.0 m

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(a)

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2.3 Free Vibration Analysis

(b)

The free vibration analysis of single barrel shell structure is performed to get a first important insight into structural dynamic properties [11] [12] [13].

The modal characteristics of the single barrel shell structure are presented in the X, Y and Z directions in Table 2 for first 10 modes. The prominent modes in the X, Y and Z directions are Mode 1, 2 and 5 respectively. Figure 1 (b) shows deformed shape of first mode, Figure 2 (a) & (b) shows deformed shape of second mode and fifth mode for single barrel shell structure respectively and Figure 3 (a) & (b) shows the variation of frequencies and periods with regards to modes respectively.

Fig.1: (a) & (b) Meshing view and First Mode Shape of Single Barrel Shell Structure respectively

(a)

(a)

(b) Fig. 3: Variation of frequencies and periods with regards to modes (b) Fig.2: (a) & (b) Second Mode Shape and Fifth Mode Shape of Single Barrel Shell Structure respectively

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Table 2: Modal Characteristics of Single Barrel Shell Structure Mode

Period (s)

Frequency (Hz)

Modal Participating Mass Ratio X

Y

Z

X

Y

Z

1

1.0859

0.920925

0

0.9553

2.12E-11

3.6E-11

-39.2475

0.0002

2

1.5223

0.656885

0.9996

2.91E-20

6.49E-17

40.1475

6.85E-09

-3.2E-07

3

1.6453

0.607782

8.96E-10

0

0

0.0012

3.15E-11

-1.5E-09

4

2.6454

0.378014

0

0.0387

6.35E-12

1.31E-09

7.9009

-0.0001

5

2.8022

0.35686

0

1.52E-13

0.3757

-1.3E-09

0.00002

24.6112

6

4.2819

0.233544

4.09E-19

3.58E-14

0.1294

-2.6E-08

7.6E-06

14.4447

7

4.6525

0.214938

8.02E-11

7.8E-18

4.49E-16

-0.0004

1.12E-07

8.51E-07

8

5.0292

0.198839

1.39E-06

3.54E-18

3.12E-15

-0.0474

7.55E-08

2.24E-06

9

5.4538

0.183358

4.17E-19

1.85E-12

0.00815

2.59E-08

0.00005

3.624629

10

5.6912

0.17571

0.0001

3.51E-17

1.1E-15

0.4015

2.38E-07

1.33E-06

2.4. Linear Static Procedure (LSP) An effort has been made to apply the equivalent linear static methods permitted in IS: 1893-2002, Criteria for earthquake resistant structure, on Single Barrel Shell Structure. The design spectrum used is of medium soil as per IS 1893 Part I (2002), and the structure is considered in Zone-V [14]. The response due to earthquake force (EL) is the maximum of the following three cases if load is applied in x and y directions: ± ELx ± 0.3 ELy ± ELy ± 0.3 ELx ±

Mass Participation Factor

x and y are two orthogonal directions .

As per IS: 1893-2002(Part-1), the following load combinations shall be accounted for: 1.5 (DL+IL) 1.2 (DL+IL± EL) 1.5 (DL±EL) 0.9 DL ± 1.5 EL The Equivalent Static method is performed through 67 possible load cases.

forces in structures. The analysis consists of a three dimensional mode shapes and natural frequencies of vibration calculation. These are the undamped free vibration response of the structure. In this method ten numbers of modes are considered for the structural response calculation. It is assumed that all the maximum modal values are statistically independent.

The design spectrum used is of medium soil as per IS 1893 Part I (2002), and the structure is considered in Zone-V. Three consecutive modal spectrum analyses are performed in the three principal directions x, y and z.

As per IS: 1893-2002 (Part-1), when responses from the three earthquake components may be combined using the assumption that when the maximum response from one component occurs, the responses from the other two components are 30 percent of their maximum. All possible combinations of the three components (ELx, ELy and ELz) including variations in sign (plus or minus) are considered. Additionally, the response due to the combined effect of the three components is obtained on the basis of ‘square root of the sum of the square (SRSS)’. Thus, the response due to earthquake force (EL) is the maximum of the following four cases: ± ELx ± 0.3 ELy ± 0.3 ELz

2.5 Linear Dynamic Procedure (LDP)

± ELy ± 0.3 ELx ± 0.3 ELz

The type of linear dynamic analysis performed is the response spectrum analysis. This method is used for the prediction of displacements and element

± ELz ± 0.3 ELx ± 0.3 ELy

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±

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x and y are two orthogonal directions and z is vertical direction.

As per IS: 1893-2002(Part-1), the following load combinations shall be accounted for: 1.5 (DL+IL)

Table 4: Absolute Maximum Membrane Forces and Bending Moments in Shell Elements

1.2 (DL+IL± EL) 1.5 (DL±EL)

Parameters

0.9 DL ± 1.5 EL The spectrum combination is performed through 155 possible load cases.

3.

Results and Discussion

To understand the behaviour of shell structure parameters like displacements, membrane forces, membrane stresses, nodal reactions, base shear and shell layer stresses are determined for shell elements.

Absolute Maximum values in shell elements are reported for these parameters.

Table 3: Absolute Maximum Displacement in Shell Elements Parameters

Linear Static Linear Dynamic Analysis Analysis

Horizontal Displacement in XDirection, Ux (m)

0.00657

Horizontal Displacement in Y-Direction, Uy (m)

0.01530

Vertical Displacement in Z-Direction, Uz (m)

0.03422

0.00676

0.01533

0.03422

The absolute maximum values of nodal displacements for linear static and linear dynamic analysis cases are tabulated in Table 03. The maximum absolute horizontal displacements are equal to 0.00676 m in X-direction and 0.01533 m in Y-direction. The maximum absolute vertical displacement is equal to 0.03422 m.

The internal membrane (in-plane) forces consists of two membrane normal resultant forces F11, F22 and a membrane in-plane shear force F12 per unit length.

The bending forces field consists of two bending moments M11, M22 per unit length, a twisting Moment M12 of the shell cross-sections per unit length, and two transverse out of plane shear forces

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V13, V23 per unit length. The X, Y and Z directions are denoted as 1, 2 and 3 in element resultants as per SAP 2000. The absolute maximum values of the Membrane Forces per unit length for linear static and linear dynamic analysis cases are tabulated Table 4.

Linear Static Linear Dynamic Analysis Analysis

Membrane Force in X-direction, F11 (kN/m)

1527.24

1527.24

Membrane Force in Y-direction, F22 (kN/m)

1182.16

1177.93

In Plane Shear Force, F12 (kN/m)

544.03

544.03

Out of Plane Shear Force in X-direction, V13 (kN/m)

13.1942

13.2164

Out of Plane Shear Force in Y-direction, V23 (kN/m)

50.5798

50.5798

Bending Moment in X-Direction, M11 (kN-m/m)

8.2329

8.2329

Bending Moment in Y-Direction, M22 (kN-m/m)

63.23

64.35

Twisting Moment, M12 (kN-m/m)

68.19

69.11

The basic shell element stresses are identified as S11, S22, S12, S13, and S23. S11 and S22 denotes the membrane direct stress in X and Y direction respectively. S12 denotes the membrane shear stress.

S13 and S23 denotes the plate transverse shear stress in X and Y direction respectively. The absolute maximum membrane stresses are tabulated in Table 5.

Table 5: Absolute Maximum Membrane Stresses in Shell Elements Parameters Membrane Direct Stress in X-direction, S11 (kN/m2)

Linear Static Linear Dynamic Analysis Analysis 6104.48

6104.48

Volume 46 Number 1 March 2016 85

Membrane Direct Stress in Y-direction, S22 (kN/m2)

7377.24

7377.24

Membrane Shear Stress, S12 (kN/m2)

2605.56

2605.56

Absolute maximum values of horizontal base reaction and bending moment in X & Y-direction and vertical base reaction and bending moment in Z-direction are tabulated in Table 7.

Plate Transverse Shear Stress in X-direction, S13 (kN/ m2)

488.85

505.31

Table 7: Absolute Maximum Base Shear at the base of Barrel Shell Structure

Plate Transverse Shear Stress in Y-direction, S23 (kN/ m2)

514.45

Parameters 530.38

The force load is used to apply concentrated forces and moments at the joints. Values may be specified in a fixed coordinate system or the joint local coordinate system. All forces and moments at a joint are transformed to the joint local coordinate system and added together. Forces and moments applied along restrained degrees of freedom add to the corresponding reaction, but do not otherwise affect the structure. Absolute maximum values of horizontal reaction nodal force and bending moment in X and Y-direction, vertical reaction nodal force and bending moment in Z-direction are tabulated in Table 6.

Table 6: Absolute maximum Nodal Reactions in Shell elements Parameters Horizontal Reaction Nodal Force in X-direction, fx (kN) Horizontal Reaction Nodal Force in Y-direction, fy (kN) Vertical Reaction Nodal Force in Z-direction, fz (kN) Horizontal Reaction Nodal BM in X-direction, mx (kN-m) Horizontal Reaction Nodal BM in Y-direction, my (kN-m) Vertical Reaction Nodal BM in Z-direction, mz (kN-m)

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Linear Static Linear Dynamic Analysis Analysis 783.502 783.502

Linear Static Linear Dynamic Analysis Analysis

Horizontal Reaction Nodal Force in X-direction, Fx (kN)

640.575

662.942

Horizontal Reaction Nodal Force in Y-direction, Fy (kN)

456.915

440.084

Vertical Reaction Nodal Force in Z-direction, Fz (kN)

12668.329

12668.329

Horizontal Reaction Nodal BM in X-direction, Mx (kN-m)

730.533

498.8872

Horizontal Reaction Nodal BM in Y-direction, My (kN-m)

1024.176

852.9876

Vertical Reaction Nodal BM in Z-direction, Mz (kN-m)

0.047

0.4739

1002.422

1002.421

Absolute maximum values of Shell Layer Stresses for critical load combination are determined for the concrete & steel layers and are tabulated in Table 8.

483.405

483.405

Table 8: Absolute Maximum Shell Layer Stresses for critical load combination

77.076

78.28

54.0686

55.9986

Shell Layer Stresses

27.6118

Number 1 March 2016

28.6003

Parameter Concrete layer

Top bar in x direction

Top bar in y direction

Bottom bar in x direction

Bottom bar in y direction

39610.16

0

38781.32

0

S11

5618.87

S22

4413.56

0

31669.64

0

34432.74

S12

2192.84

7291.61

7291.61

9886.78

9886.78

S13

263.27

0

0

0

0

S23

351.2

0

0

0

0

Variation of membrane stresses in centre line shell elements are plotted with regards to the distance from the centre point of the plan. Figure 4 shows the The Bridge and Structural Engineer

variation of membrane direct stress in X-direction, S11 and variation of membrane direct stress in Y-direction, S22. Figure 5 shows the variation of membrane shear stress, S12 and plate transverse shear stress in X-direction, S13. Figure 6 shows the variation of plate transverse shear stress in Y-direction, S23.

These plots give an idea of the variation of membrane stresses as the distance varies from 0 to 10 m.

Membrane direct stresses, membrane shear stress and plate transverse shear stresses increase as distance increases towards edge beams.

Fig. 5: Variation of Membrane Shear Stress and Plate transverse Shear Stress in X-direction

Fig. 6: Variation of Plate transverse Shear Stress in Y-direction

The contour plots for membrane forces and membrane stresses presented in Figure 7 to Figure 13. The contour plots are for the maximum values.

Fig. 4: Variation of Membrane Direct Stress in X-direction and Y-direction

Fig.7: Membrane in-plane Force in X-direction and Y-direction, F11and F22

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Fig. 8: In-Plane Shear Force, F12 and Bending Moment in X-direction, M11

Fig. 10: Out of Plane Shear Force in X-direction and Y-direction, V13 V23

Fig. 9: Bending Moment in Y-direction, M22 and Twisting Moment, M12

Fig. 11: Membrane Direct Stress in X-direction and Y-direction, S11 and S22

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95.53 %, in Y-direction is 99.96% and in Z-direction is 37.57 %. The mass participation in Z-direction is least as the mass of structure is also less in that direction.

The permissible vertical deflection as per IS-456:2000 [15], is 0.08 m (span/250). The maximum absolute horizontal displacements are equal to 0.00676 m in X-direction and 0.01533 m in Y-direction. The maximum absolute vertical displacement is equal to 0.03422 m. It is evident that Z-direction is the weakest one, while X-direction is the strongest because of lateral force resisting system. The vertical deflection is within the permissible limit.

The out-of –plane shear forces are negligible in comparison with membrane forces. However, inplane shear force cannot be negligible. The bending and twisting moment are very low. This confirms the membrane resisting mechanism in shell structures. The Z-direction is more flexible than X and Y-direction.

Fig. 12: Membrane Shear Stress, S12 & Transverse Shear Stress in X-direction, S13

The absolute maximum membrane stress is 7377.24 kN/m2. The maximum stress in concrete layer is 5618.87 kN/m2 and 39610.16 kN/m2 in steel layer.

The permissible stresses in concrete and steel as per IS-456:2000 are 11150 kN/m² (0.446*fck) and 361050 kN/m² (0.87*fy). The stresses in concrete and steel layers are within the permissible limit.

The results show that the single barrel shell structure considered here with designed lateral force resisting system behaves well under seismic loading. In general, it is observed that the single barrel shell structures can carry the external seismic actions exclusively by membrane mechanism.

Fig. 13: Plate Transverse Shear Stress in Y-direction, S23

4. Conclusions The linear static and dynamic analyses of Single barrel shell structure are done with proper finite element model in software SAP 2000. It is relatively a simpler way to explore the seismic behaviour of structures and an attempt has been made here for Single barrel shell structures. A three dimensional finite element analysis is performed to assess the seismic performance of the structure subjected to earthquake actions.

The prominent modes in the X, Y and Z directions are Mode 1, 2 and 5 respectively. The modal analysis results show that mass participation in X-direction is

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5. References 1.

BELMOUDEN Y., LESTUZZI P., SELLAMI S. , “A Modular Shell System for Housing”, Journal of the International Association for Shell and Spatial Structures: IASS, Vol. 48, No.1, 2007

2.

HUA, L.W., SHAN, Y.Q. and YU-JI, T., “Response analysis of national stadium under spatially varying earthquake ground motions”, Journal of international association for shell and spatial structures: IASS, Vol. 40, No.4, 2005

3.

IS 2210-1988, Criteria for Design of Reinforced Concrete Shell Structures and Folded plates, Bureau of Indian Standards, New Delhi, India Volume 46 Number 1 March 2016 89

4.

IS 1893-2002, Indian Standard Criteria of practice for Earthquake Resistant Design of Structures, Bureau of Indian Standards, New Delhi, India

12. CHAN, A. and DAVIS, G., “A simplified finite element model for the impact of thin shells”, Department of aeronautics, Imperial College, London.

5.

ASCE , Manual No. 31, Design of Cylindrical Concrete Shell Roof, ASCE, New York, 1952

6.

VARGHESE P.C., Design of Reinforced Concrete Shell and Folded Plates, First Edition, PHI Learning Private Limited, Delhi.

13. SONG, H.W., HYO, S., BYUN, K.J. AND MAEKAWA, K., “Failure Analysis of Reinforced Concrete Shell Structures using Layered Shell Element with Pressure Node” ASCE Journal, Vol. 21 2002

7.

BANDYOPADHYAY J.N., Thin Shell Structures Classical and Modern Analysis, New Age International Publishers, New Delhi, 1998.

8.

CHANDRASHEKARA K., Analysis of Thin Concrete Shells, Tata McGraw Hill, New Delhi, 1986.

9.

HABIBULLAH, A. and PYLE, S., “Practical Three Dimensional Nonlinear Static Pushover Analysis”, Structure Magazine, winter, 1998.

10. PHILLIP, G.L., HERMAN, S. and SUBIR, S.K., “Stresses in Column-supported hyperboloidal shells subject to seismic loading”, Earthquake engineering and structural dynamics, Vol. 5, No.3, 1997, pp. 3-14.

11. ZIENKIEWICZ, O. S. and TAYLOR, R. L., The Finite Element Method, McGraw-Hill, New York , 2000.

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14. LUO Y. F. AND YANG M.W., “Static elasto-plastic analysis of long-span rigid spatial structures under vertical earthquake”, Proceedings of the 6th International Conference on Computation of Shell and Spatial Structures, May, 2008, NY, USA. 15. SAMANTA, A. & MUKHOPADHYAY, M., “Free vibration analysis of stiffened shells by the finite element technique”, European Journal of Mechanics and Solids, Vol. 23, 2004.

16. AGRAWAL P., and SHRIKHANDE M., Earthquake Resistant Design of Structures, Prentice Hall India Publication 17. IS-456:2000, Indian Standard Plain and reinforced Concrete-Code of Practice, Bureau of Indian Standards, New Delhi, India

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Ministry of Road Transport & Highways, Government of India Transport Bhavan, Parliament Street New Delhi-110001 (International Competitive Bidding) Notice Inviting Tender No. RW/NH-12037/1325/Retender-Zozila/J&K/2016/NH-I 1.

Dated: 15.03.2016

Ministry of Road Transport & Highways (MoRT&H) invites RFQ Applications and RFP Bids under single stage two cover system (referred to as the "Bidding Process") for selection of the Bidder for award of the Project from the Applicants/Bidders interested in design, engineering, construction, development finance, operation & maintenance of the following project to be executed on Design, Build, Finance, Operate and Transfer (DBFOT) (Annuity) basis for a pre-agreed concession period (the "Concession Period"):

State

NH No.

Name of work

Jammu & NH-1 Construction, Operation and Kashmir (Old Maintenance of Zozila Tunnel NH-1D) including approaches on National Highway No. 1 (SrinagarSonamarg-Gumri Road) in the State of J&K on BOT basis

Length

Total Project Cost (TPC)

14.083 km long Single Rs. Tube bi-directional crore tunnel with parallel egress tunnel

Concession period

9090 22 Years (including construction period of 7 years)

2.

The Detailed RFQ and RFP documents can be viewed/downloaded from official portal of MORTH http://www. morth.nic.in or e-procurement portal of MORTH https://morth.eproc.in from 01.04.2016 up to 29.06.2016 (17:00 Hours). Last date of sale of RFQ and RFP documents is 29.06.2016 (upto 17:00 Hours). Due date for submission of Applications/Bids is on 30.06.2016 up to 11:00 Hrs. Opening of Applications/Bids will be on 30.06.2016, 11:30 Hrs.

3.

To participate in bidding, Bidders have to pay a sum of Rs. 27,30,000/- (Rupees twenty seven lakh thirty thousand only) as the cost of RFQ and RFP process (non-refundable) to "Ministry of Road Transport & Highways"" as Demand Draft Payable to RPAO, New Delhi and Rs. 1,295/- (Rupees one thousand two handred and ninety five only) towards tender processing fee (non-refundable) to "M/s C1 India Pvt. Ltd." on e-tender portal of MORTH https://morth.eproc.in through integrated only payment gateway enabled on E-Tender portal.

4.

Complete bid document can be viewed/submitted at e-tendering portal of MORTH https://morth.eproc.in.

5.

Pre-Bid Meeting will held on 25.04.2016 at 11:30 Hrs.

6.

Amendments/Corrigendum for RFQ and RFP documents, if any, would be hosted on the e-tendering portal of MORTH https://morth.eproc.in.

Address for Communication: Mr. Dheeraj Superintending Engineer (P-1), Room No. 144, Transport Bhawan, Ministry of Road Transport & Highways, No. 1, Parliament Street, New Delhi-110001 Phone: 011-23314328 Fax : 23710358 Emal: dheeraj.rth@nic.in

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Bearings by mageba* storied 12,000 Tons sky bridge at 120 m above ground level between two towers of Atmosphere, a luxury condominium in Kolkata. The ming pool etc. Each bearing designed for 36000 kN load in service conTons and measures about 2.8 m x 2.5 m.

most severe earthquakes

LASTO®LRB Lead Rubber Bearings

LASTO®HDRB High Damping Rubber Bearings

RESTON®PENDULUM Bearings

RESTON®SA Fluid Viscous Damper

RESTON®STU Shock Transmission Unit

India

The Bridge and Structural Engineer

RESTON®PSD Preloaded Spring Damper

www.mageba.in

Volume 46 Number 1 March 2016 93

Office : 01732-224835 (Resi.) : 01732-231953 Mob. : 098120-03121

ESTD.: 1954

E-mail: jkunits1@gmail.com, jkunits1@rediffmail.com

✰✰✰

With Best Compliments From : ✰✰✰ R MO

H T&

R.D

.S. O

AP PR VED O

STEEL AUTO INDUSTRIES (AN ISO 9001:2008 CERTIFIED CO.)

Designer, Manufacturer & Supplier of all types of: Bridge Bearing, Elastomeric Bearings/Pads, Expansion Joints, Sheathing Bollards, Hydraulic Jacks, Sugar Mill Machinery Parts, Steel Casting & Forgings

✰✰✰ Works : 484, V.P.O. Damla Kishanpura, Yamuna Nagar (Haryana) INDIA Website : www.steelautoindustries.com Office : Hotel J.K. Residency, Residency Road, Yamuna Nagar-135 001 Fax : 01732 - 229980

94 Volume 46

Number 1 March 2016

The Bridge and Structural Engineer