B&SE_Volume 45_Number 3_September 2015
The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION FOR BRIDGE & STRUCTURAL ENGINEERING
Aesthetics of Structures
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Volume 45 Number 3 September 2015  i
ii  Volume 45
Number 3 September 2015
The Bridge and Structural Engineer
The Bridge & Structural Engineer ING - IABSE
Indian National Group of the International Association for Bridge and Structural Engineering
Contents :
Volume 45, Number 3 : September 2015
Editorial • From the desk of Chairman, Editorial Board : Mr. Alok Bhowmick
vi
• From the desk of Guest Editor : Mr. V.N. Heggade
viii
Highlights of ING-IABSE Event • Highlights of the Workshop on “Project Preparation and Repair/Rehabilitation of Bridges and Structures” held at Raipur (Chhattisgarh) on 7th & 8th August 2015
xi
1. Elegant Structures Mike Schlaich
1
2. Aesthetics of Shell Structures R. Sundaram
6
3. The Engineer’s Responsibility for Aesthetics Frederick Gottemoeller
17
4. World’s Aesthetic Foot Bridges Dr. Subramanian Narayanan
29
5. Bridge Aesthetics (Case of Science taken to the Level of Art) 42 V.N. Heggade 6. Incorporating Aesthetics in Bridge Design Frederick Gottemoeller
55
Contents
Special Topic : Aesthetics of Structures
7. Living Root Bridges: State of knowledge, Fundamental Research and Future Application 70 Sanjeev Shankar
Research Papers 1. Synthesis for Ultimate Limit State of Induced Deformations (Section 11 of IRC:112) V.N. Heggade
77
Panorama • Office Bearers and Managing Committee Members 2015
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90
Volume 45 Number 3 September 2015 iii
The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING
December 2015 Issue of the Journal will be a Special Issue with focus on GEOTECHNIQUES & FOUNDATION DESIGN FOR STRUCTURES
SALIENT TOPICS TO BE COVERED ARE :
1. Geotechnical Investigations & Interpretations 2. Liquefaction Analysis for Foundation Design 3. Ground Improvement Techniques 4. Foundations in difficult Ground conditions 5. Choice of Foundation System for Buildings and Bridges 6. Any other topic of relevance
The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING
March 2016 Issue of the Journal will be a Special Issue with focus on ENABLING WORKS, FORMWORKS & SACAFFOLDING SYSTEMS–Principles of Design and Construction SALIENT TOPICS TO BE COVERED ARE : 1. Modern Formwork System 2. Enabling & Temporary Works 3. Lifting, Transportation, Handling & Erection 4. Scaffolding Systems 5. Design & Codal Provisions 6. Safety & Precautions 7. Formwork Failures & Case Studies Those interested to contribute Technical Papers on above themes shall submit the abstract by 15th January 2016 and full paper by 31st January 2016 in a prescribed format, at email id : ingiabse@bol.net.in, ingiabse@hotmail.com
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Number 3 September 2015
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
Front Cover : Top Right: Bridge of peace spanning the river Kura in Georgia’s capital city Tbilisi. Top Left: Golden Section for living forms and shapes in nature. Middle Right: A matured living root bridge at Nongriat. Middle Left: Indoor Stadium in Bangalore, an ‘fip’ award winning structure. Bottom Right: Balasone bridge at Darjeeling, a balanced cantilever bridge incorporated in nature. Bottom Left: Stunning Sunniberg bridge in Switzerland, a creation of Christian Menn. • Price: ` 500
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 S S Chakraborty, Former Chairman, CES (I ) Pvt. Ltd., New Delhi B C Roy, Former Senior Executive Director, JACOBS-CES, Gurgaon Published : Quarterly : March, June, September and December Publisher : ING-IABSE C/o Secretary, Indian National Group of the IABSE IDA Building, Ground Floor (Room Nos. 11 and 12) Jamnagar House, Shahjahan Road New Delhi-110011, India Telefax: 91+011+23388132 Phone: 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.
The Bridge and Structural Engineer
Journal of the Indian National Group of the International Association for Bridge & Structural Engineering
September 2015
The Bridge & Structural Engineer, September 2015
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Volume 45 Number 3 September 2015 v
From the Desk of Chairman, Editorial Board
The current practice of structural engineering in India and structural engineer’s nature of involvement in the design of built environment requires a serious re-look. Many structural engineers in the profession gives little importance to the aesthetic quality of the structure they design and there is a growing trend amongst the structural engineering fraternity to believe that the appearance of our built environment and aesthetic qualities of structure are merely a visual considerations, which are ‘cosmetic’ in nature, a luxury rather than real need for the sustainable development of the society. For Building Structures, the role of ensuring aesthetics in design is usually the responsibility of ‘Architects’, who takes over the leadership in coordinating all aspects of planning and technology while being primarily responsible only for the aesthetic quality of a building project and they in turn appoint engineers, who are made responsible to ensure strength, safety and functioning of the building. This unnatural separation of roles between architects and engineers has also created many problems since these two professionals with different approach to the problem, work in water tight compartments with architects focussing more on external means using independent facades vi Volume 45
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for enhancing aesthetic quality of the structure rather than utilising the inherent beauty of the structural form itself, as a means of expression. Many of the built-structures indicates a-priori aesthetics imposed by some architects who do not work closely with the engineers and do not have an inner feeling of the natural forms of structures. Present generation of structural engineers on the other hand focusses only on ensuring strength, safety, economy and serviceability of the structure with no sensitivity for the aesthetic forms. For infrastructure projects (e,g. bridges, flyovers, metro viaducts, various industrial projects …etc.), there is generally no split in the overall creative responsibility between architects and engineers and aesthetic design of structure is still the responsibility of structural engineers. The insensitivity and lack of sensibilities of structural engineers, contractors and clients in dealing with the aesthetic aspects of these infrastructure projects in urban landscape is visible in many of the existing flyovers, metro viaducts and other structures that has mushroomed all over the cities in India. An appreciation of the aesthetics of structures is fundamental to the very idea of what it takes to be a good designer of structures. Time has come for civil engineers to put equal focus The Bridge and Structural Engineer
on aesthetics in addition to efficiency and economy. The academic institutions teaching civil engineering need to place the importance of aesthetics in their educational curriculum. Considering the importance of this topic for Structural Engineers, the editorial board has decided to bring out this special edition of the journal with a focus on the subject of ‘Aesthetics of Structures’. Our Guest Editor for this edition is Mr VN Heggade, who is a well-known personality in the field of structural engineering and deeply associated with several important
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infrastructural projects throughout his career. I am sure the papers published in this journal will further stimulate the structural engineers in focussing their attention towards this neglected area of their responsibility in times to come. Wishing you all happy reading!
ALOK BHOWMICK
Volume 45 Number 3 September 2015 vii
From the Desk of Guest Editor
As a guest editor I am very excited to welcome you all to this September 2015 issue of ING-IABSE journal with the theme Aesthetics of structures. Indeed it has been privilege and honor to be a witness to authors’ Romance with structures in the process of editing. The structures of any era reveal the idiosyncrasies of the time in terms of the degree of sophistication in technology, material sciences, state of the art research and finally financial and mental health of the state at that time. In fact, the structures reveal the state of the nation’s progress and civilization of a particular era. The great Mandirs (Temples), Mahals (Palaces & forts) and Masjids (Mosques) in India , Churches, Cathedrals, Castles and Bridges elsewhere not only give insights to the mental makeup of the rulers but also help us in understanding the degree of religiosity and civilization of the century. It is normally perceived that the aesthetics is an outcome of ornamentation and embellishments and the derivative of higher cost consumption. Structural aesthetics is different from that of building architecture in which (in Structural aesthetics) the visual impact is imparted necessarily from the structural form where either form follows forces or forces are channelized to get required form on which the debate is on universally. In a country like India which is on the path of unprecedented economic growth to be fuelled by missions like ‘Swatch Bharat’, ‘make in India’,‘hundreds of smart cities’‘thousands of kilo meters of project highways’, ‘rural electrification of eighteen thousand villages’ and associated viii Volume 45
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infrastructure, the aesthetics and sustainability to be left behind to our posterity is not only a duty but also becomes a question of ethics and morality to our engineering fraternity. This gains the critical mass as there is a lurking danger of hastily churned out eyesores around especially in the wake of ambitious infrastructure development program government likely to embark upon in the near future. Inarguably, no engineer wants his structures to be unpleasant. But still aesthetics that is invariably a result of creativity remains irrelevant as most of the times engineers’ creativity is directed only to achieve economy and safety by the specifications. There is an urgent need for the policy makers to create an environment to nurture and nourish the aesthetic orientation apart from economy and safety by emphasizing on aesthetics and sustainability in contractual and codal stipulations. Within the general theme of Aesthetics of Structures, the issue covers the following topics: Architecture and Aesthetics in general & state of the art, Aesthetics of Structures other than Bridges,Aesthetics of Bridges, and Aesthetics of shell Structures and Aesthetics attributes and quantification. While there are six papers on the general theme including from world’ srenowned experts on the subject like Mr Gottemoeller and Prof Mike Schlaich, two research papers are complementing the general theme in the tradition of ING-IABSE journal. Prof (Dr) Mike Schlaich in the lead paper while elaborating elegance aspects of aesthetics in the structures created in the space by engineers, architects and sculptors, emphasises that engineer’s The Bridge and Structural Engineer
task is cut out over their counterparts in learning to what he calls dance with chains to produce elegant structures which he claims in the conclusion is necessary to stimulate elegant life. We are lucky to have two papers from the author Mr Frederick Gottemoeller of famous book Bridgescape on bridge aesthetics. The papers together are a complete compendium on conceptualisation and the art of designing contemporary bridges. In his own words, the bulk of the first paper is about structural art and inspired by the works of Prof David Billington who coined the word structural art for engineers’ aesthetic. The author identifies three leading ideals of structural art: efficiency, economy and elegance which are measured respectively by scientific, social and symbolic dimensions. Illustrating the works of Robert Maillart whose Salignatatobel bridge was formally recognised as a work of art by New York’s museum of modern art in 1949 (incidentally this bridge is referred by four authors in this issue alone), the author demonstrates that design and development of the form by the engineer alone is the reason for visual impact where analysis is just a servant of design, not the source of it. In the second paper Mr Gottemoeller explains the importance of conceptual engineering by ten determinants of appearance in the form of building blocks to improve the aesthetics of everyday structures. Readers are provided with an excellent treatise on aesthetic foot bridges around the world by Dr N Subramanian. The designs of the pedestrian bridges are breeding ground for experimentation where bio mimicry, structures in motions etc. are tried due to light weight nature. In particular context to bio mimicry, the award winning research paper in Geneva IABSE symposium by architect Sanjeev Shankar which has been reproduced in this issue is quite enlightening. The architect strongly infers that living root bridges offer an exemplary model for sustainability based infrastructure solutions and
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also imply that the study of bio mimicry can help engineers handle traditional issues and also may address emerging issues like aesthetics. The period between 1920s to the early 1960s, can be considered the golden age of concrete shell construction. The various shell structural form were the natural choice of connoisseurs of aesthetics as the form could rhythmically blend with the nature. Subsequently, concrete shells began to receive less attention. Fewer technical papers were published on their design methods and construction techniques, and the number of signature structures built declined noticeably. But to Mr R Sundaram, a recipient of ‘Eduardo Torroza Medal’ from IASS, shell structures are like ‘frozen music’. In his words, one can actually detect and feel the subtle music in the form of beauty and what better material one can find which can create the ecstasy in concrete. His passions for shells are manifested by some of the outstanding structures near and around Bengaluru that are illustrated in his paper. Finally, in my paper I have given the efforts of our ancient aestheticians to capture aesthetics in the form of mathematical relationship on the basis of formations in nature. However, if aesthetics is confined to rules, standardization, regulation, norms and some equations, it will become stereotype and will not remain aesthetics anymore due to monotony. Though there can be no definite regulations for satisfying aesthetics as the adage goes ‘Beauty lies in beholders’ eyes’, the beholders can be saved from witnessing mediocrities by observing certain quantifiable attributes as explained in the paper. Wish you all a very happy reading. V.N. HEGGADE
Volume 45 Number 3 September 2015 ix
Brief Profile of Mr. V.N. Heggade
Mr.V.N.Heggade
passed out with distinction in Bachelor of Engineering (BE, Civil) from
National Institute Of Engineering (Mysore University) in 1984 and did his Post Graduate Diploma in Construction Management (PDCM) from NICMAR (National Institute Of Construction Management & Research ) thereafter completed his Masters in Administrative Management (MAM) from Jamnalal Bajaj Institute of Management Studies ( Bombay University). Mr. Heggade is presently Senior Vice President (Special Bridges) and Head of EDMS (Engineering Design Management) of Gammon India Ltd. During his long professional career, spanning for 31years he is responsible for the designs and construction of all types of bridges in concrete and steel including cantilever and cable supported bridges, hyperbolic Natural Draught Cooling Towers (NDCTs), concrete and timber Induced Draught Cooling Towers ( IDCTs), single and multi-flue brick & steel liner chimneys, marine structures like jetties & ports, hydraulic structures like bridge cum aqueducts, sea and river intakes and sub marine tunnels etc. The versatility and ability to improvise in design, execution of special structures and publications on them have not only won him personally four National Awards and an International Prize from Indian Roads Congress (IRC), Indian Concrete Institute (ICI), National Design Research Forum of Institution Of Engineers ( NDRF of IE ) and IABSE ( Switzerland ), almost all civil engineering professional bodies of the country, but also his company has won several awards for the various outstanding structures. He has facilitated the growth of industry-academia interaction by giving guidance to post graduates for their dissertations in addition to being an invited faculty for professional training institutes. He has been very active in furthering the cause of standardization in the country by being a member of various IRC and BIS code making committees and abroad of fib commissions. He was one of the key members in getting the fourth FIB Congress to Mumbai in 2014 and also responsible for the very successful completion of the same. Recently in 2015 he has been elected a ‘Fellow’ of Indian National Academy of Engineering (INAE). While the papers and presentations aggregating to more than ninety in national and international forums and memberships to various professional bodies are the testimony of his keenness in dissemination of knowledge, he is also a great ambassador of Indian civil engineering fraternity across the borders, representing Indian delegation of FIB and IABSE in various international seminars, symposiums and congresses.
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HIGHLIGHTS OF THE WORKSHOP ON “PROJECT PREPARATION AND REPAIR/ REHABILITATION OF BRIDGES AND STRUCTURES” HELD AT RAIPUR (CHHATTISGARH) ON 7TH & 8TH AUGUST 2015 The Indian National Group of IABSE in co-operation with Govt of Chhattisgarh, PWD had successfully organised two day Workshop on “Project Preparation and Repair/ Rehabilitation of Bridges and Structures” at Raipur on 7th and 8th August 2015. The Workshop was well attended by more than 200 delegates from various Govt Departments as well as other private and public organizations. The aim of the workshop was to provide a detailed understanding of the various aspects of good project preparation for bridges and structures etc to the Engineers of State PWD and Consultants. The Workshop was inaugurated by Shri Rajesh Munat, Hon’ble Minister of Public Works Department, Govt of Chhattishgarh by lighting the traditional lamp in the presence of S/Shri DO Tawade, Chairman, INGIABSE, RK Pandey, Secretary, ING-IABSE and AK
Banerjee, Chairman Scientific Committee as well as other dignitaries. During his inaugural address, Shri Rajesh Munat expressed that the deliberations of the Workshop will be highly educative with guiding parameter to meet any challenges in the matter of repair and rehabilitation of bridges by the practicing engineers and participants. Shri Anil Rai, Secretary, PWD extended warm welcome to the participants of the Workshop. Shri DO Tawade and Shri RK Pandey delivered their addresses during the Inauguration. Shri DK Pradhan, Engineer-in-Chief proposed Vote of Thanks. The Workshop on “Project Preparation and Repair/ Rehabilitation of Bridges and Structures” was addressed by the following eminent experts covering the following Sessions:
7th August 2015
Session 1 – Project Preparation of Bridges & Structures 1
Shri AK Banerjee
– Overview of Feasibility Study & DPR
2
Shri Ravi Sundaram
– Geo-technical Investigation for Bridges
3
Shri Alok Bhowmick
– Design of Foundation & Substructure
4
Shri Vinay Gupta
– Design of Superstructure
5
Shri Jitendra Rathore
– Bearings & Expansion Joints
6
Shri Somnath Biswas
– Reinforced Earth Walls
8th August 2015
Session 2 – Repair and Rehabilitation of Bridges & Flyovers 7
Shri AK Banerjee
– Overview of Inspection, Investigation and Repair / Rehabilitation
8
Dr Lakshmy Parameswaran
– Condition Survey and Detailed Investigation
9
Shri PY Manjure
– Rehabilitation of Bridges & Other Structures – The Challenging Discipline
Session 3 – New Materials/ Repair Techniques & Case Studies 10
Dr NR Bose
– New Materials and Repair Techniques
11
Shri Jitendra Rathore
– Case Studies of Repair/Rehabilitation of Bearings, Expansion Joints and Bridge Structure
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The Valedictory Session was held on 8th August 2015 (afternoon). Shri RK Pandey, Secretary, ING-IABSE gave the Valedictory Address. 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 KK Pipri, Convener of
the Workshop proposed Vote of Thanks. A cultural programme was organized in the evening of 7th August 2015 for the participants who rejoiced the evening. The Workshop was a great success.
A view of the Dais during the Inaugural Function
Shri DO Tawade, Chairman, ING-IABSE Delivering his address
Shri RK Pandey, Secretary, ING-IABSE Delivering his address
Shri Rajesh Munat, Hon’ble Minister of Public Works Department, Chhattishgarh Delivering his address during Inaugural Function
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The Bridge and Structural Engineer
Elegant Structures Mike Schlaich
Mike Schlaich, is Professor for Structural Engineering chairing the Department of Conceptual and Structural Design at Berlin Institute of Technology (TU Berlin).
Civil Engineer schlaich bergermann partner and Berlin Institute of Technology, Germany m.schlaich@sbp.de
Summary Good structures are an important part of our quality of life, they contribute to what in German is called “Baukultur”, the culture of building. It is the responsibility of structural and civil engineers to dope buildings and our built technical infrastructurebridges, towers, roofs - with good, i.e. quality structures to make a positive contribution to the culture of building and to satisfy ourselves. We engineers talk about structural elegance, but is elegance really an ingredient for a quality structure? Keywords: elegance; light weight structures; holistic quality; culture of building; conceptual and structural design.
1. Introduction There is not much written about elegant structures and it could come to mind that this is because elegance is not an issue to be worried about when engineering structures. As soon as we identify elegance as a part of beauty we have arrived in the field of aesthetics, i.e. how matters move our senses, and the aesthetic quality of our structures is clearly of importance. The intent of this paper is the, admittedly personal, definition of structural elegance, to show that it is clearly an ingredient to good structures and what we engineers must do to achieve them.
2.
What is elegance?
Like many other terms “elegance” has changed its meaning over time. The word stems from the Latin verb eligere = select, which later appeared in the French noun élégance. We use it today when we want The Bridge and Structural Engineer
He is also the Managing Director of schlaich bergermann partner, Consulting Structural Engineers, with offices in Stuttgart, Berlin, New York, São Paulo, Shanghai and Paris.
to describe something of selected beauty. It is more than beauty-only. We relate, everyone subjectively, elegance to - beauty plus selected taste, like a stylish fashion model or a famous actress. -
beauty plus lightness, transparency and movement like a graceful ballet dancer.
-
beauty plus streamlined shapes like a noble sports car.
- beauty also in the sense of sensual purism of being reduced to the bare minimum like a black and white nude photograph. Very importantly, elegance appears effortless [1]. We find that something is elegant when we feel but do not see all the work that was needed to achieve it. Sometimes elegance is mistaken for superficial luxury. Then the word loses its allure, consumerism has had its day. Following the above definitions, are both actresses shown below beautiful? Are both elegant? Looking at furniture, the lounge chair by Ray and Charles Eames is most beautiful (and very comfortable) but many would agree that Barcelona Chair by Ludwig Mies van der Rohe is more elegant. I am sure that aesthetics are looked at quite differently in different cultures. What does elegance mean in different languages, how is it translated? I am told that in Japanese and Chinese the word for elegance is the same 優雅. It is just pronounced differently, “yuga” in Japanese “you ya” in Chinese. In Arab it is yet completely different: Eleganz = ( ةقانأAnaka). Does this affect the way we define and design elegant Volume 45 Number 3 September 2015 1
structures? Such thoughts require further and deeper analysis than possible here.
3.
Is elegance desirable?
What are the ideals of good structures? When we study milestone structures we find that engineers and architects try to follow similar principles.
Fig. 1: Marilyn Monroe
The Roman architect Vitruv, perhaps the most cited writer in this context and certainly one of the first ones to write about structural design, coined the terms firmitas, utilitas and venustas as the basics of good structures as early as 25 B.C. First, they must stand up (firmitas), secondly they must be useful in the sense of durability and robustness (utilitas) and finally they should be pleasing (venustas)[2]. Volkwin Marg, a contemporary German architect, defines the culture of building as the synthesis of two sides of a coin - technology and art - which, he says, can only be achieved when architects and engineers creatively work together. He reaches back to the Platonic trias: truth, goodness and beauty. Intellectual
Fig. 2: Audrey Hepburn
Fig. 3: Lounge Chair by Ray and Charles Eames
Fig. 4: Barcelona Chair by Ludwig Mies van der Rohe
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truthfulness where structure and form coincide, goodness in the sense of our buildings´ contribution to society and its individuals and finally beauty in the aesthetic sense which starts to shine when goodness and truthfulness are successfully merged [3]. In the context of this paper lightweight structures seem especially interesting and the German engineer Jörg Schlaich identifies them as ecological, social and cultural. They are ecological in the true sense of sustainability as they minimise the use of our resources and as they are easy to assemble and to recycle. They are social because they require the employment of a proportionally high number of skilled designers and well-trained workers. Finally, they “can make a significant contribution to enrich the architectural spectrum”. Refined lightness triggers positive emotions and we like the beauty of lightweight structures because we understand them as nothing is hiding the flow of the forces. They are an “integral part of the culture of building” [4]. David Billington, an American engineer, in the 1980s coined the term structural art, the art of structural engineering parallel to architectural art. He defines the ideals of structural art as efficiency, economy and
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elegance. He notes that engineers are no scientists as they rather invent than discover. They invent good bridges, towers, long-span roofs and highrise buildings by successfully merging minimized use of material at minimal cost with conscious aesthetic decisions [5]. The Japanese architect, Tadao Ando does not list a trias when he writes about elegance and the aesthetics of simplicity as part of the Japanese way of life. According to him, “Wabi Sabi”, modest and weathered, inspires elegance in architecture by minimising and minimising again until only utility and beauty are left. The Wabi Sabi house is the result of “modest living, learning, being pleased with a life that does without anything superfluous and living the moment” [6].
the sculptor who can freely choose which way to go. For us engineers this is even more so. Numerous restrictions by codes and standards provide us with the excuse to give up dancing all together, to only follow part of the principles that define a good structure. We seem to be so absorbed by dealing with the chains, by arranging them, by making them bearable and by not trying to break them that we forget that, yes, dancing is still possible that it is actually a must, a responsibility. If we learn how to dance in chains, there is a good chance that elegance will appear. If we holistically approach our work, we will be rewarded with good structure that contribute to the culture of building. The principles of good structures, that are presented above, all include elements of beauty and elegance and clearly show that we may not work without bearing them in mind. There is evidence. In all fields of engineering and architecture elegant structures have appeared and we see and feel that elegance does not appear alone but rather in a package with the other principals. Four examples of elegant structures, a house, a roof, a tower and a bridge:
Fig. 5: The principles for good structures
Looking only at the few writers cited above it is interesting to note that only one of them, the engineer Billington, uses the term elegance. What is surprising at first is also that sustainability is not explicitly mentioned. However, as soon as we look closer we detect that sustainable building, i.e. resource efficiency and environmental responsibility throughout the life-cycle of a structure, is an inherent feature of the principles above. Engineers, architects and sculptors all create three dimensional structures and, therefore, they have to follow the above principles alike. The difference between them is the importance they give to each of the principles. Of course, also the sculptor has to make sure his work stands up but no code requires a 100-years design life for his work. He can concentrate on moving the senses. The prototype of the architect´s building is the one-family house and there firmitas is usually easy to achieve. Social issues become more important. Volkwin Marg calls architecture a “dance in chains” because so many boundary conditions make “dancing” much more difficult than it is for the artist,
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Fig. 6: L. Mies v. d. Rohe, Farnsworth House, USA
Fig. 7: F. Candela, Bacardi factory, Mexico
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achieve this, how we call the ideals and principles we want to follow does not really matter. We can follow any of the above ways. We do not have to become dogmatic in our efforts to design good structures. What is important, however, is that in addition to the principles we understand the design of a structure as a conscious act, an act of conceiving the solution by carefully considering the local context, the boundary conditions to our design that can be of topographicalphysical, technical-fabricational or political-cultural nature. It is interesting to note, that often good structures show a readable flow of forces, perhaps because they are easy to understand and because we like what we understand. Often elegant structures are light-weight structures.
Fig. 8: V. Shukhov, Shabolovka Tower, Russia
It is important to create public awareness for good design of structures and much should still be done in this field: – competitions: design competitions for buildings should ask for teams that include engineers and there should be more design competitions for our infrastructure especially for bridges. – advisory boards: in many cities around the globe there are advisory boards who assist politicians in taking the right decisions on new buildings. These boards should include engineers. – discussions and guidelines: architects criticize and discuss each others´ work much more than engineers do. In the community of engineers we need more discussions about the design quality of our work. The results of such exchange could be helpful guidelines and state-of-the-art reports on good design.
Fig. 9: R. Maillart, Salginatobel Bridge Switzerland
The books listed in the appendix show numerous other examples but by their nature they can only show static images. We are conditioned by the media we have at hand. The new trend of electronic books also allows to show the elegance of movable structures [7]. Will this affect the way we will design?
4.
How do we achieve elegance?
When our structures are of holistic quality, then they can also become elegant. Which way we follow to 4 Volume 45
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– education: perhaps most important are our students. Conceptual and structural design can be taught at university level. Ten years ago “Conceptual and Structural Design” was introduced to the curriculum of the engineers at the Berlin Institute of Technology [8] and the author can confirm that it is a successful concept. In Berlin, however, still only one third of the civil engineering students are female and none of the professors, which is certainly not enough. The author is convinced that we will see more elegant structure when these numbers increase. The Bridge and Structural Engineer
Conceptual and Structural design of structures is a creative act based on sound theoretical knowledge and the principles described above. If the result appears to be achieved effortless we have come to an elegant structure. This is not easy to do and it requires experience. Many of the great engineers achieved their greatest successes only when they were between forty and sixty years old. There is hope still for many of us.
3. MARG V., “Architektur ist - natürlich nicht unpolitisch”, Prestel, 2008 (in german).
5. Summary
7. SCHLAICH BERGERMANN PARTNER, “movable structures”, www. www.moveables.sbp.de, 2014.
In addition to “firmitas” and “utilitas” structures need to be beautiful to become holistically good, to become a “Gesamtkunstwerk”. Good structures stimulate good life, they can add to our quality of life. Elegance appears when the challenging task of fusing the principles of good structures seems to be achieved without much effort. If the response to a challenge appears effortless, elegance has appeared. Good life is not easy, it is a challenge but we want to live it elegantly. The claim is that elegant structures stimulate elegant life.
Literature 1.
BOTTON A., “The Architecture of Happiness”, Hamish Hamilton Ltd., 2006.
2.
VITRUV: De Architectura Libri Decem, Marix, 2012 (latin - german).
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4. SCHLAICH J., “leicht weit - light structures”, Prestel, 2005 (german - english). 5. BILLINGTON D.P., “The Tower and the Bridge”, Princeton University Press, 1995. 6.
ANDO T., “Der Geist des Wabi Sabi”, in lettre 105, lettre international, summer 2014. UND i-book,
8. SCHLAICH M., “Challenges in Education”, Conceptual and Structural Design, IABSE Symposium Budapest, Hungary, 2006.
Credits / Copyrights Fig. 1 Actress Marilyn Monroe, Credits: Laura Loveday, public domain. https://www.flickr.com/photos/ likeabalalaika/4510483444/in/photostream/ Fig. 2 Actress Audrey Hepburn;Author: Bud Fraker, public domain. http://upload.wikimedia.org/wikipedia/ commons/c/c8/AudreyHepburn_leggings.jpg
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Aesthetics of Shell Structures R. SUNDARAM SM [M.I.T., USA], President – Structural Engineers World Congress [SEWC] Inc. Worldwide, President - Structural Engineers World Congress – India. Registered Architect & Practising Architect and Structural Engineer, Member of the Council of Architecture, India Chairman & Managing Director Sundaram Architects Pvt. Ltd. Bangalore – 560 001 India edp@sundaramarchitects.com Sundaram’s contributions include large concrete hypar shells, large span RCC and steel folded plate roofs, inverted umbrella, cylindrical shells, pracast prestressed folded plates, segmental bridges etc. He has been responsible for the design of several major projects including Industrial projects, IT campuses, Bio-Tech facilities, Shopping malls, Sports stadia, Educational campuses, Chemical plants, Auditoriums, Convention centres, Hospitals, Housing, Townships, Road transportation net works like Flyovers, Subways. Recipient of a number of prestigious National & International Awards, which includes the prestigious “EDUARDO TORROJA MEDAL“ by the International Association for Shell and Spatial Structures [IASS] based in Madrid, [The first Indian to receive this prestigious International award] The International Award “SEWC Roland Sharpe Medal”. “Life-Time Honorary Membership” by the Prestressed & Precast Concrete Society, in
Singapore in August 2010. Prestigious Award - conferred on him by the Construction Industry Development Council, New Delhi – the 5th CIDC Vishwakarma Award namely the “ACHIVEMENT AWARD FOR INDUSTRY DOYEN” for the year 2013 etc.
Summary This article highlights the developments in the design and construction of aesthetically pleasing concrete shell structures in India. The author has designed various concrete shell structures including precast and prestressed structures Examples of a few such shell structures are discussed in this article.
1. Introduction Concrete is one of the most wonderful materials and at the same is a material of contradictions. It is highly brittle and yet can be moulded to any shape. What it requires is a little but important help from other elastic materials like steel either in the form of rods/ mesh or fibres. The unlimited capacity and the awe inspiring nature of this unique combination of concrete and steel is a source of inspiration for many who have created some innovative shapes and large structures in different parts of the world. Such structures are immensely pleasing to the eye and of course satisfy the functional requirements. Some of these structures are like “frozen music”. One 6 Volume 45
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can actually detect and feel the subtle music in the form of beauty and what better material one can find which can create that Ecstasy in Concrete.
2.
Lotus shaped structure for Sri Aurobindo Trust, Bangalore [Built in the year 1995 ]
This unique structure conceived and conceptualised by the Author, is designed in two floors. The ground floor houses a hall for prayers and the first floor is a meditation hall. This Complex Trust situated in J.P. Nagar houses a variety of buildings like School complex, Gym, Printing press, Library, Computer centre and the core of all this is the meditation hall. The Meditation hall hexagonal in plan has its sides as 10.3 M and diagonal length of 24.6 M and it covers an area of approximately 3000 Sft. A small raised platform in the middle of the hall holds the relics of Sri Aurobindo. The significance of this unique structure is its roofing system. This is designed as a prismatic folded plate system. A great deal of interactions with the clients and the philosophy of Sri Aurobindo has led the Author to create this unique LOTUS shaped roof. The Bridge and Structural Engineer
The roof built in cast-in-situ RCC with an average thickness of 75 mm [3”] was covered by white Kent tiles. Wedge shaped slits in the roof panels allow natural light that make the hall more appealing from the inside. The triangular shaped openings that are formed due to the roof structure are also glazed which allow a great amount of diffused light. The entire roof structure rests on a drum, 4.0M high and rises up to 10.5 M above the drum. All the six petals [plates] converge to meet a ring beam on the top. The ring beam holding all the plates together also
View just before the dome is being fixed on top
supported a 6.0M dia stainless steel Globe, symbolising oneness.
3.
RCC Groined Vault roof over Food Court at Infosys Campus, Bangalore.
Infosys Technologies Ltd. [ Infosys ] is located about 25/30 K.M. south of Bangalore on the National Highway. Their new Technology Park houses seven Software blocks, Education and Research Centre and two Food Courts. While all other buildings are normal reinforced concrete framed structures, the Food Court has a unique Groined Vault roof accommodating 250 persons under each shell. There are three such shells of 20 m x 20 m. The height of the shell at the central portion is 7.5 m and at the entry 10 to 12.5 m on the four sides. Each shell is separated by 10 m open space which also can be used for dining on occasions.
Prayer Hall/Meditation Hall of Sri Aurobindo Trust, Bangalore.
During construction
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All the three shells are located on an elevated podium of 2.50 m high. Vast podium is housing in the basement, a well equipped gymnasium, kitchen, medical, aerobics, meditation, banking, AHU’s, steam sawana bath, change rooms and toilets and so on. The geometry of the shell is a hyperbolic paraboloid. One eighth of the shell which repeats itself and joined along common parabolic arches resemble trunks of
A View from Swimming Pool
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paraboloid shells of 15 m x 15 m grids with 75 mm shell thickness. The height at the centre is 3.5 m and at the edges 5.5 m to the top of shell. The cluster of shells is aesthetically very pleasing to the eye and provides excellent light and ventilation. The large column free space created by thin unique roofing system is ideal for exhibitions, show rooms etc.
View of the Shell
Construction methodology adopted was insitu concrete [M-25 grade] tubular scaffolding and plywood form work. The rhythmic configuration of the white ceramic clad shells creates a spectacular skyline and lends a certain sense of sanctity to the whole geometry of the building. The structure was designed using computers for various loadings including earth-quake.
Shuttering
View of the shell from outside
Shuttering & after de-shuttering
an elephant. The elevation on the four sides is same and has high parabolic arch of 12.5 m high, 20 m wide opening. While overall shell thickness is 75 mm, the main diagonal arch elements have 200 thick over 3m wide tapered to 75. These are the main arch elements which share the load of the entire shell. The span of this arch element is 28.28 m. The shell emerge from the podium level.
4.
View of the shell from inside
S. K. R. Market, Bangalore
In response to the surrounding urban environment and site conditions, we have tried to create a special form that brings to it a sense of balance and rhythm. The highlight of the whole complex is the roofing system. The roofing structure consists of 21 Hyperbolic 8  Volume 45
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Arial view of the shell
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5.
Jayanagar Shopping Complex, Bangalore – Hyperbolic-Paraboloid Shell in Concrete – Cast in Situ
This shopping complex was built in 1971-73. Consists of cylindrical shell roofs, hyperbolic paraboloid shell roof, folded plate roof. Special mention to be made on hyper shell. This covers a vegetable market. Designed to bring natural light and ventilation. This is square and spans 24 m x 24 m. The folded plate structure has 25 m span and is 75 mm thick.
View of the existing structure
The complex is being demolished and a new complex will be built. Existing and proposed views are as follows:
Another view of the existing structure
Existing structure View of the shell
This shopping complex is built in 1971-73. Consists of cylindrical shell roofs, hyperbolic paraboloid shell roof, folded plate roof. Special mention to be made on hyper shell. This covers a vegetable market. Designed to bring natural light and ventilation. This is square and curves 24 m x 24 m. The folded plate structure has 25 m span and is 75 mm thick.
Existing structure with cylindrical shell roof
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View of the proposed structure
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The vegetable market in Jayanagar Shopping Complex in Bangalore City is provided with hyparbolic paraboloid shell spanning 24 m x 25 m consisting 4 Nos. of hypar of 12 m x 24 m joined together and supported on gable frames. The shell proper is only 75 mm thick and gradually increases to 125 mm near the supporting edges. Due to planning requirements the low nodal points through which the load gets transferred were resting on the beams, hence diagonal ties were introduced to overcome the thrust. The total height available inside is 11 m at high nodal points and 6m at low nodal points. The single unit hypar shell fitted well into the environment and the vegetable market is provided with excellent ventilation and natural light.
6.
of the shell is 3.5 m. The shells are supported on four columns at 6 m and 27.675 m. Stiffening arch is provided between the columns in the front. Two edge beams are also provided. The general thickness of the shell is 75 mm. These shells are analysed for selfweight, live load and earthquake load conditions using the finite element method.
Canteen building for ITC at Saharanpur, near Delhi.
View from inside
Perspective view
Front view of the shells
View of shells
The canteen building has three identical shells. The geometry of each of the shells has been obtained by cutting a parabolic cylindrical shell of width 15.3 m, height 10 m and span 27.675 m along four vertical planes inclined to the axis of the shell. Thus parabolic shapes were obtained on the sides. Minimum width 10  Volume 45
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Aerial view of the shells
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Front view of the Shells
Inside view
7. Inverted Umbrella – for MICO-BOSCH Canteen in Bangalore This consists of cluster of shells of shape of hyperbolic paraboloid in the form of inverted umbrella. Size of each shell is 6.0 m x 6.0 and diameter of the column is 350 mm. The thickness of the shell is 50 mm and edge beam of size 150 mm x 150 mm is provided at the edge of the shell. The spring level is 4.0m and depth of shell itself is 1.6 m. The indirect lighting from the shell provides average illumination level of 120 lux and looks pleasing aesthetically. The gap of 1.0m between adjoining shells is covered with aluminum sheet on top and hit and miss ventilator arrangement on sides provides natural light and ventilation.
Inside view
8.
Meditation Hall, Sringeri, South India
A column free space of 30 m x 30 m has been planned to seat about 1000 people. A 3 m wide corridor around adds to the beauty of this grand structure. The most interesting feature of this structure is the roof, which has been designed, in stepped form with a combination of solids and voids. The solids are covered with pre-cast concrete slabs and the voids with glass to let in light & air. Inverted umbrella shell outside view
Inverted umbrella shell inside view
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Outside view of Meditation Hall
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View of the shell
Inside view of the meditation hall
9. Food Court, Hyderabad.
Infosys
campus
in
A number of Buildings in the campus have been built. 4 Software blocks, Food court, Swimming Pool, Amphi Theatre, Power Block, Chillier block, UGR and ETP. One of the most interesting buildings in the campus is the Food Court it is planned with a dining capacity of 800. This is a unique column free space shell structure of 46 m diameter. The shell structure is divided into 16 units. The entire roof sits on a series of columns, which are 5 m high. The building is designed with flexibility to convert it into an auditorium with a seating capacity of about 1000-1200 people. This food court itself sits on a podium of approximately 4m above ground level. In this podium, services like kitchen, Gymnasium, aerobics, general store room, health club, bank ATM Kiosks and Medical Center etc are provided.
Structural Analysis & Design Details. The Dome consists of 16 segments of Paraboloidal shell, resting on 16 columns raised above podium. The dome is 54 m in diameter at outer edge and 46 m in diameter at column edge. The dome consists of lower ring beam and a top ring beam and shells. The thickness of shell is 75 mm, increases to 150 mm at valley beam location.
10. MICO [Bosch] factory, Bangalore: In an area of 60 Acres on the outskirts of Bangalore a Factory Complex has been built for Bosch. The Complex consists of four production buildings [160 m x 60 m each] linked to other ancillary buildings. Fuel injection equipments and auto ancillaries are the components manufactured here. The designed master plan has three different entries based on the functions namely; the workers entry, administrative entry and material [Raw material and finished product] entry. The raw material stores are in proximity to the material entry and from these stores materials flow into the four hangers. Each production hanger [20 x 20 m grid] has precast concrete roofing system consisting of folded plates [3.3 m x 20 m x 40 mm thick] supported on prestressed Y-girders [gutters]. All precast elements were of M-40 grade and steam cured. The idea behind this roofing system was to create an extremely workable and comfort condition and well lit natural environment for the workers yet maintaining the architectural value and harmony of the building. The facade of the buildings have exposed stone masonry walls with intermittent horizontal and vertical concrete bands. This innovative facade reflects the Indian passion for stone work [ancient temples] and breaks the monotony of industrial building facades. The natural treatment of the facade blends well with the surrounding landscape to form an integral whole. One of the innovative ancillary buildings within the complex is the Canteen. Due to the unique features of the Complex, it is considered to be one of the finest not only in India but also in the rest of the world.
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The Bridge and Structural Engineer
Folded plates inside view – during construction
Folded plates inside view – after construction
Folded plates top view – during construction
View of the structure
View of the structure from outside
View after commissioning the factory
11. Dr. TMA Pai International Convention Centre at Mangalore
the Central Lobby for both right and left wings. A capsule elevator and an escalator is also provided in the entrance lobby.
A multipurpose facility for holding conventions and exhibitions has been designed for Manipal Academy of Higher Education [ MAHE ] at Mangalore, India and constructed. The Auditorium is designed for a capacity of 2000. The auditorium commences from the first floor level. At the ground floor level in the left wing facilities for dining with kitchen etc. are provided and on the left wing Conference rooms are provided. In the first floor an Exhibition hall of 44 mtrs. dia. is provided. The main access is from The Bridge and Structural Engineer
The auditorium is itself a unique structure which is in an octagaonal shape and the roof is a circular shell with a bottom dia. Of 54 mtrs. and top 10 mtrs. This is an RCC structure, the slab has a varying thickness from 75mm to 120 mm with ribs in between. Similar is the roof for exhibition hall but with a bottom dia. Of 44 mtrs. and top 10 mtrs. dia. The Auditorium with a seating capacity of 2000 plus is fully air-conditioned with best acoustic system depicting a cleaner environment. Volume 45 Number 3 September 2015 13
Car parking facility is provided on the surface level as well as in the basement area. The parking on surface can accommodate 96 cars and the basement can accommodate 145 cars. The site is low lying and is 2.5 mtrs. below the main road accessible from the cross road which is almost at the same level. Innovatively, the building is designed in such a way that the basement for parking gets access from cross road so that the Auditorium located above the basement can be accessed from the main road which is 2.8 mtrs. above the basement level. The levels have been carefully looked into and the basement floor is kept at almost the same level as the original ground level, considering the maximum flood level. A lot of ventilation to the basement is provided from two sources - west side of the basement is open to outside since the basement level and the formation ground level outside are more or less same. Also efficiently designed skylights to get natural light and ventilation are provided in the landscaped area.
Inside view
11.1 Geometry of Shell The Auditorium at Mangalore has two multipurpose halls of octagonal shape in plan, The two halls have a doubly curved circular shell roof. Any section cut horizontally is circular in plan; the roof surface is obtained when all concentric circles will move on another doubly curved radial beams. The shell emerges from a stiff tie beam over the columns on the periphery. The total height of the shell is 12.42 m & 12.27 m. The diameters of the shells are 54.876 m & 37.284 m. Generally the thickness of the shell is 75 mm. The radial ribs are supported over columns at the bottom periphery and the central ring beam with skylight dome at top. There are transverse concentric circular ring beams. The geometry is maintained by these radial beams and transverse circular beams.
Another Inside view
11.2 Analysis The elements, which transfer the forces onto the columns participating in the structural behaviours are the top and bottom ring beams, radial beams together with the circular beams located at various predetermined levels. The complete model along with the shell ( plate elements) of average 75 thick is analysed by finite element method using STAAD PRO Software. The shell proper is thickened to 150mm for a required distance at the junctions of beams and also to cantilever portion to meet the structural requirement. 11.3 Design
Outside vide
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The reinforcement in the shell proper is provided in two layers. The bottom tie beam has been designed for moment, axial and torsional forces. The top ring beam is designed for moment, compressive forces and to resist hoop forces. The Bridge and Structural Engineer
11.4 Construction methodology Form work : Entire shell form work was done with multilevel scaffolding system Steps for Concreting : Concreting is of M40 is done from bottom to top First : Lower ring beam concreting was done. The diametrically opposite panels are selected so that no imbalance is created during concreting. Second : Radial beam and transverse circumferential beams were concreted starting from lower end moving upwards. Once the concreting is completed at one level circularly from one end to the other, it is moved to next higher level. Third : Finally top ring beam is concreted. Chiller water was used for concreting since climate was hot. De-shuttering was done 21 days after the last concreting Two diametrically opposite points were selected and deshuttering was done moving in a clock wise direction and at the same time moving down wards towards periphery. Deshuttering was done starting from the centre (top ring) proceeding towards the supports
12. Indoor Stadium in Bangalore Inspired by their predecessors, who have converted rock into architectural masterpieces like Taj Mahal etc., modern architects & engineers in India especially the author has created many architectural masterpieces using the material concrete. The thread of Indian traditions lingers on in our buildings. Painstaking attention to detail has taken the place once held by ornamentation. With this, we try to lend some order to this chaotic urban landscape. The Indoor Stadium is a classic example in this case. The Indoor Stadium of 4000 members capacity is located in the close vicinity of the rich green Cubbon Park in Bangalore. The stadium is designed to house all modern facilities such as Giant Electronic T.V display, screen for any specific projection of the event. The public and the participants/officials movement area is segregated. The public have independent entrances on all the sides and will directly enter the complex from outside. The sportsmen/officials will enter into the stadium through the warm up room/rest room located below the gallery at ground level. They will enter the main The Bridge and Structural Engineer
arena without any hindrance with public movement. Adequate toilets and Kiosks are provided inside the stadium for the use of public. The VVIP’s & VIP’s movements are channelized with separate entry with a lift leading to the VIP seating area. The unique feature of the indoor stadium is the large independent cubicles which can be reserved for the sponsors who can depute their personnel to watch the events at 3rd tier level. A cat walk/M.S space frame is suspended from the roof to suspend the lights and audio/video equipments for uniform spread inside the stadium. The flooring is granolithic to take any standard type of flooring of specific requirements. The Stadium has an elliptical dome consisting of 120 folded plates [precast] of varying cross-section [average 2 m] with the plate thickness of 40 mm and series of inter-connected ribs. The lower end of the dome is supported on the elliptical ring beam at 8m level which in-turn is supported on 24 equally spaced arch columns. The top of the dome is supported on elliptical ring of 16 m x 8 m at 29 m lvl. A small elliptical paraboloid insitu dome of 4 m height and having a series of interconnected stiffeners is resting on the top ring. The folded plate spans about 40m between the two rings. The seating galleries are precast while the other cubicles are insitu. The construction technique adopted is unique and innovative. The folded plates are precast in the casting yard and steam cured for 24 hours. Later the elements are lifted and placed in the stacking yard by specially designed gantry. From the stacking yard the elements are placed on the specially designed trolleys one on either side of the bottom ring which is in-situ. The trolley moves on the elliptical rails to bring the element to the place of erection. The folded plate is then erected using 3 cranes [one outside and two inside the ring ]in position where it rests on the bottom ring and the central staging. The central staging is a structural steel space frame whose functions are to temporarily support the folded plates and to support the form work for the top ring and dome. In the closing bay [four folded plates] the elements are erected by the outer crane and the inner feed derrick tied to the staging replacing the movable cranes. After the completion of folded plate erection the top ring beam/dome are cast-in-situ. The top ring/dome being the keystone for the complete structural system is to be carefully decentered by
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using hydraulic jack system and predetermined releasing sequence consisting of various cycles. Neoprene bearing pads for jacks were employed to facilitate the decentering. The Catwalk [structural steel rigid frame work prefabricated on ground is hung from the folded plates by suspenders attached to the folded plates. The magnificent appearance and geometric purity of this design makes the building stand out in this mediocre setting without being intrusive. Although, it’s huge bulk and unusual design ensure that it is the centre of attention this new stadium blends exceedingly well with its surroundings. The stadium covering a 90 m x 120 m column free space is considered to be one of the most innovative structures in India.
Inside view
FIP Award
IABSE Magazine Cover Page May 1998
13. Conclusion
View of the stadium from outside.
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The development of concrete shell structures has undergone a radical change. Iron, then steel, then Reinforced concrete and finally Prestressed Concrete has opened up new and unforseen possibilities for Form. This has given rise to a new art form namely Structural Art, Parallel to and independant of Architecture. Using the principle of “Force Follows Form” the Author has through his works demonstrated once again the significance of a “natural” shape for a structurally sound and aesthetically pleasing design.
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The Engineer’s Responsibility for Aesthetics Frederick GOTTEMOELLER PE, AIA Principal Bridgescape, LLC fred.gottemoeller@bridgescape.net
Frederick Gottemoeller received bachelor degrees in architecture in 1963 and engineering in 1965 and a masters degree in architecture in 1965, all from Carnegie Mellon University, Pittsburgh. Early in his career he served on a number of multidisciplinary teams designing major transportation projects. During this period he earned licenses as a registered architect and as a professional engineer. He then spent 14 years with the Maryland Department of Transportation, including 5 years as Deputy Administrator of the State Highway Administration. For the last 22 years he has consulted on the aesthetics of approximately 30 major bridges including bridges over the Mississippi, the Missouri, the Ohio, the Niagara and the Colorado, two National Wild and Scenic Rivers in the US and a World Heritage Site in Canada, the Cataraqui River and Rideau Canal. Bridgescape, his book on bridge aesthetics, is a familiar reference for many bridge designers.
It so happens that the work which is likely to be our most durable monument, and to convey some knowledge of us to the most remote posterity, is a work of bare utility; not a shrine, not a fortress, not a palace but a bridge. — Montgomery Schuyler, 1883, writing about John Roebling’s Brooklyn Bridge
Summary This paper presents the often unrecognized aesthetic tradition of engineering, showing how it grows out of the engineers’ dedication to efficiency and economy, and indeed constitutes an art form in its own right. It then discusses some of the reasons why this tradition has been neglected in contemporary engineering, and suggests ways that the neglect can be repaired.
1.
The Aesthetic Tradition in Engineering
People know intuitively that civilization forms around civil works: for water supply, transportation, and shelter. The quality of the public life depends, therefore, on the quality of such civil works as aqueducts, bridges, towers, terminals, and meeting halls: their efficiency of design, their economy of construction, and the appearance of their completed forms. At their best, these civil works function reliably, cost the public as little as possible, and, when sensitively designed, become works of art. The latter goal is widely accepted for the largest, most prominent bridges, but applies as well, perhaps even The Bridge and Structural Engineer
more strongly, to the many everyday bridges that stud our landscapes. Because there are so many of them, these everyday bridges have an even stronger impact on our daily lives than the monumental bridges. The public is becoming ever more aware of their potential, and is demanding an ever higher standard for the appearance of all of the bridges in their communities. As the professionals responsible for bridge design, the public looks to engineers to provide this aesthetic quality. Many contemporary engineers are not aware that early engineers welcomed the responsibility for the appearance of their works and made aesthetics an explicit component of their efforts. 1.1 Aesthetics at the Inception of Engineering The assumption of responsibility for aesthetics began with the British engineer Thomas Telford, who many recognize as the first person to practice what is now considered civil engineering. In 1812 Telford defined bridge aesthetics as the personal expression of structure within the disciplines of efficiency and economy. Efficiency here meant reliable performance with minimum materials. Economy implied construction
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with competitive costs and minimal maintenance expenses. Within these bounds, the engineer finds the means to choose forms and details that express their
Roebling (1806-1869) as the undisputed leaders in their fields during the 19th century. They designed the largest and most technically challenging structures and they were leaders of their professions. Telford was the first president of the first formal engineering society, the Institution of Civil Engineers, and remained president for 14 years until his death. Eiffel directed his own design-construction-fabrication company and created the longest spanning arches and the highest tower of the time; Roebling founded his large scale wire rope manufacturing organization while building the world’s longest spanning bridges (Fig. 2).
Fig. 1: Thomas Telford’s Craigellachie Bridge
In reinforced concrete, Robert Maillart (1872-1940) was recognized for his approach to aesthetics in the early 20th century. Maillart, first in his 1905 Tavanasa Bridge, and later with the 1930 Salginatobel (Fig. 3) and others, imagined a new form for three-hinged arches that included his own invention of the hollow box in reinforced concrete. In the later half of the 20th century the Swiss engineer Christian Menn (b 1927) has demonstrated how a deep understanding of arches, prestressing, and cable-stayed forms can lead to structures worthy of exhibition in art museums, as for example his 1992 bridge at Sunniberg (Fig. 7). In seeking such aesthetic expression the best structural engineers have recognized that structural engineering can be an art form parallel to but independent from architecture.
own vision, as Telford did in his Craigellachie Bridge (Fig. 1). The arch is shaped to be an efficient structural form in cast iron, while the diamond pattern of spandrel bars, at a place in the bridge where structural considerations permit many options, is clearly chosen with an eye to its appearance. Telford was the first of a line of engineers engineers who were conscious of the centrality of aesthetics for structure and were also regarded as the profession’s best technical practitioners. After Telford (1757-1834), we can identify Gustave Eiffel (1832-1923), and John
Fig. 3: Robert Maillert’s Salginotobel Bridge
1.2 Aren’t Bridges “Architecture”?
Fig. 2: John Roebling’s Brooklyn Bridge
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The popular press (as well as the architectural press) tends to classify towers, stadiums, and even bridges as “architecture”, creating an important, but subtle, fallacy. The visible forms of the Eiffel Tower and the Brooklyn Bridge result directly from technological ideas and from the experience and imagination of individual structural engineers. Sometimes the engineers have worked with architects, just as with mechanical or electrical engineers, but the forms have come from structural engineering ideas.
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Structural engineers give form to objects that are of relatively large scale and of single use, and these designers see forms as the means of controlling the forces of nature to be resisted. Architects, on the other hand, give form to objects that are of relatively small scale and of complex human use, and these designers see forms as the means of controlling the spaces to be used by people. The prototypical engineering form - the public bridge - requires no architect. The prototypical architectural form - the private house - requires no engineer. Structural engineers and architects learn from each other and sometimes collaborate fruitfully, especially when, as with tall buildings, large scale goes together with complex use. But the two types of designers act predominately in different spheres, and the results of their efforts deserve to have different names. Engineering historian David Billington has analyzed and described the structural engineer’s approach and given the name “Structural Art” to forms arising solely from structural considerations and the aesthetic sensibilities of an engineer. John Roebling’s Brooklyn Bridge is an example. No architect was involved. To summarize: “Architecture” is what architects do; “Structural Art” is what engineers do.
Even though newer materials gradually became available and better understood, the natural tendency was to imitate the forms that had worked before. Many of the notable structures of the late nineteenth and early twentieth century took this approach. However that approach also requires hiding and ignoring the capabilities of the modern materials of which the newer bridges were actually built. Many communities still see architectural sources as the only proper model for an important bridge, particularly in an area filled with historic buildings (Fig. 5). This approach has the great advantage of familiarity, especially if the bridge is replacing an older bridge built in a traditional architectural style. Residents tend to want a new bridge that looks like the one that they had before. It can be successful if the designers and builders go to the trouble of authentically imitating the source architecture.
2. The Three Sources of Aesthetic Form for Bridges
Fig. 5. Lambeth Bridge, London, 1932
2.1 The Imitation of Architecture The first source of aesthetic form for bridges was the imitation of architectural forms and styles. This began when architectural design and engineering were still considered the same activity and when the materials in use for buildings and bridges were the same, stone and wood. With spans limited by the characteristics of these materials and engineering based on trial and error and rules of thumb, buildings and bridges were similar in size and naturally imitated each other. Historical structures such as the Pont Neuf are early examples.
Unfortunately, in recent years this approach often takes the form of tacking vaguely historical detail on an otherwise modern structure (Fig. 6). The sham is always apparent and doomed to aesthetic failure.
Fig. 6: Vaguely historical architectural detail pasted on a conventional bridge
2.2 The Engineer’s Aesthetic: The Expression of Structure: Structural Art Fig. 4: Pont Neuf, Paris 1797
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The second source of form arose with the availability Volume 45 Number 3 September 2015 19
of iron and steel and the development of engineering theory based on science and mathematics. Suddenly much larger spans were possible than were required for buildings. Plus, they could be combined into structures of unprecedented length. Old architectural ideas based on the scale and proportions of buildings no longer suited these much larger structures. At the same time, the railroads and road agencies charged with building these structures focused on achieving the most functional structure for a minimum cost. This ruled out hiding the presence and capabilities of these new materials.
Association of State Highway and Transportation Officials has recently published a Bridge Aesthetics Sourcebook based on these ideas Given its importance in the field and the fact that the other two sources of form can be defined in reference to it, the bulk of this article will focus on Structural Art. The ideas are based on and inspired by David Billington’s work illuminating the history of structural art in bridge design.
In response leading engineers developed an aesthetic based on expressing the capabilities of these new materials and techniques and on the structural needs of the bridge, seeking to integrate efficiency, economy and elegance. Designers sought the shortest path for bringing loads to the ground and tried to minimize stresses in the structure, The engineers introduced in Section 1, Thomas Telford, John Roebling and Robert Maillert along with Gustave Eiffel, initiated and personified this change. At first the art and architecture establishment vociferously objected to this new aesthetic, most famously in the initial reactions to the Eiffel Tower in Paris. But others quickly saw its value and appeal, as recognized by Montgomery Schuler in the quote that begins this article. In this aesthetic, dimensions are set based on structural needs and not by preconceived notions of shapes with visual appeal. Structural elements are thick where they need to be thick for structural reasons, and thin everywhere else. The options for the two span bridge in the next section illustrate the simplest application of this idea. Many people find this approach appealing because of their intuitive understanding of structure. Most people develop an understanding of structure based on their exposure to the world around them. Trees are thicker at the bottom because the forces of wind and gravity are greatest at the bottom. Tables stand with three or more legs but not with two. And so on. Manmade structures that emulate these characteristics seem natural and attractive. This engineers’ aesthetic, what David Billington termed Structural Art, is now the consensus aesthetic for most bridge engineers worldwide, and has been officially recognized by many bridge building agencies. In the United States the American 20 Volume 45
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Fig. 7: The form of Christian Menn’s Sunniberg Bridge is based on and expresses the structural needs of the bridge.
2.3 The Sculptural Manipulation of Structure In recent years a number of designers have developed an aesthetic based not on expressing structural needs but on violating structural needs. Thus, the works of Santiago Calatrava and others seek not the shortest path for bringing loads to the ground, but the most indirect and convoluted one. Thus, we have Rotterdam’s Erasmus bridge (Fig. 8), where the tower is bent so as to maximize, rather than minimize its bending moment. It looks as if it were already starting to buckle. The Bridge and Structural Engineer
The goal of this approach may be to attract attention by violating expectations, or by inventing what appears to be a new structural type, or perhaps the goal is simply sculptural: to create an appealing shape as arbitrarily defined by some artistic notion. Since structural efficiency is not a criterion, these structures are unavoidably costly to build and problematic to maintain.
of freedom and discipline are held in balance. The disciplines of structural art are efficiency and economy, and its freedom lies in the potential it offers the individual designer for the expression of a personal style motivated by the conscious aesthetic search for engineering elegance. These are the three leading ideals of structural art--efficiency, economy, and elegance.
Notwithstanding their high cost, many local governments pursue these bridges out of a desire to create a unique civic symbol, a “signature” bridge. Since the choice is based essentially on aesthetic taste, it seems more appropriate for the excessive costs to be supported by private funds. If taxpayer funds are involved, one wonders whether the same goals could not be achieved with less cost. After all, Florida’s Sunshine Skyway (Fig. 9) is a splendid symbol of the Tampa Bay area, and it was built very economically. Then the public money would be available for other uses, schools for example
3.2 The Three Dimensions of Structure
The experience in the field of architecture is cautionary: designs based on the search for novelty or the latest design fad can quickly become dated and lose their appeal. Bridges are too prominent and long-lasting to run that risk.
Fig. 8: Erasmus Bridge
3.
The Engineer’s Aesthetic: Structural Art
3.1 Efficiency, Economy and Elegance The engineers’ aesthetic results from the conscious choice of form by engineers who seek the aesthetic expression of structure within the disciplines of efficiency and economy. Their forms are not the unconscious result of the search for economy nor the product of supposedly optimizing calculations, but are made in response to specific aesthetic evaluation by the engineer simultaneously with his structural and economic analyses. These works of structural art provide evidence that the common life flourishes best when the goals The Bridge and Structural Engineer
Structure’s first dimension is a scientific one. Each working structure must perform in accordance with the laws of nature. In this sense, then, technology becomes part of the natural world. Methods of analysis useful to scientists for explaining natural phenomena are often useful to engineers for describing the behavior of their artificial creations. It is this similarity of method that helps to feed the fallacy that engineering is applied science. But scientists seek to discover preexisting form and explain its behavior by inventing formulas, whereas engineers invent forms (or apply forms previously invented by other engineers), using preexisting formulas to check their designs. This scientific dimension is measured by Efficiency. Technological forms live also in the social world. Their forms are shaped by the patterns of politics and economics as well as by the laws of nature. Thus, the second dimension of structure is a social one. In the past completed structures might, in their most elementary forms, be the products of a single person. In the civilized modern world, however, these technological forms, although at their best designed by one person, are the products of a society. The public must support them, either through public taxation or through private commerce. The social dimension of structure is measured by Economy. Technological objects visually dominate our industrial, urban landscape. They are among the most powerful symbols of the modern age. Structures and machines define our environment. The locomotive of the nineteenth century has given way to the automobile and airplane of the twentieth. Large-scale complexes that include structures and machines become major public issues. Power plants, refineries, river works, transportation systems and bridges-all have come to symbolize the promises and problems of industrial civilization. Volume 45 Number 3 September 2015 21
Bridges such as the Golden Gate, the George Washington, and the Sunshine Skyway, Fig. 9, serve that function for our time and carry on the traditions set by the Brooklyn Bridge. Nearly every American knows something about these immense structures, and modern cities repeatedly publicize themselves by visual reference to these works. So it is that the third dimension of technology is symbolic, and it is, of course, this dimension that opens up the possibility for the new engineering to be structural art. Although there can be no measure for a symbolic dimension, we recognize a symbol by its expressive power and its Elegance.
engineer. It eliminates the imaginative half of the design process and forfeits the opportunity for the integration of form and structural requirements that can result in structural art. Design must start with the selection of a structural form. It is a decision that can be made well only by the engineer because it must be based on a knowledge structural forms and how they control forces and movements. Many engineers focus on analysis in the mistaken belief that the form (shape and dimensions) will be determined by the forces as calculated in the analysis. But, in fact, there are a large number of forms that can be shown by the analysis to work equally well. It is the engineer’s option to choose among them, and in so doing to determine the forces by means of the form, not the other way around.
Fig. 9: Florida’s Sunshine Skyway
The designer must think aesthetically for structural form to become structural art. All of the leading structural artists thought about the appearance of their designs. These engineers consciously made aesthetic choices to arrive at their final designs. Their writings about aesthetics show that they did not base design only on the scientific and social criteria of efficiency and economy. Within those two constraints, they found the freedom to invent form. It was precisely the austere discipline of minimizing materials and costs that gave them the license to create new images that could be built and would endure. The ultimate goal is to make every bridge efficient, economical and elegant by giving meaningful visual expression to loads, equilibrium and forces. With this as a goal every bridge will become an asset to its community and environment, even the everyday bridges that are most influential in shaping our communities because they are so numerous.
Fig. 10: Maryland Route 18 over U.S. Route 50
Take the simple example of a two-span continuous girder bridge, using an existing structure in the United States, Maryland Route 18 over U.S. Route 50 (Fig. 10). Here the engineer has a wide range of possibilities such as a girder with parallel flanges, or with various haunches having a wide range of proportions (Fig. 11). The moments will depend on the stiffness at each point, which in turn will depend on the presence or absence of a haunch and its shape. The engineer’s choice of shape and dimensions will determine the moments at each point along the girder. The forces will follow the choice of form (Fig. 12). Within limits, the engineer can direct the forces as he chooses.
3.3 Design versus Analysis Many of today’s engineers see themselves as a type of applied scientist, analyzing structural forms established by others. Seeing oneself as an applied scientist is an unfortunate state of mind for a design 22 Volume 45
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Fig. 11: Another possibility for Maryland Route 18 over U.S. Route 50
The Bridge and Structural Engineer
when the search for economy also results in an improvement in appearance (Fig.14). Whether there is additional cost varies widely depending on region of the country, owner preferences and practices, contractor capabilities, span length, size of project, community aspirations and other project specifics.
Fig. 12: Forces Determined by the Engineer’s Choice of Form
Now, let’s examine which form the engineer should choose. All of them can support the required load. Depending on the specifics of the local contracting industry, many of them will be essentially equal in cost. That leaves the engineer a decision that can only be made on aesthetic grounds. Why not pick the one that the engineer believes looks best? That, in a nutshell, is the process that all of the great engineers have followed. Maillart’s development of the three hinged concrete box arch (Fig. 3), as one example, shows that the engineer cannot choose form as freely as a sculptor, but he is not restricted to the discovery of preexisting forms as the scientist is. The engineer invents form, and Maillart’s career shows that such invention has both a visual and a rational basis. For Maillart, the dimensions were not to be determined by the calculations alone, and even the calculations’ results could be changed by adjusting the form. That is because a designer is at work, rather than an analyst. Analysis is the servant of design, not the source of it. Design, the selection and development of the form, is by far the more important of the two activities. Before there is any analysis, there must be a form to analyze.
4
Why do Contemporary Engineers Neglect Aesthetics?
4.1 Common Objections to Considering Aesthetics It always adds cost. Not true. Simply paying attention to proportions and details can result in an attractive bridge with no increase in cost (Fig.13). Indeed, there are times The Bridge and Structural Engineer
If there is an increased cost, then the relevant question becomes: does the aesthetic improvement justify the additional cost? Few people automatically buy the cheapest car or living room sofa no matter what it looks like. We make decisions every day to spend additional money to get a better quality product. We can make the same kind of judgments about bridges, keeping in mind that the bridges we build today will be prominent features in our communities for the next 80 years or more. If the affected community is involved, as it should be, we can take advantage of their concerns and insights as well.
Fig. 13: Often simply paying attention to proportions and details can result in an attractive bridge with no increase in cost. Canyon Creek Bridge, Anchorage, Alaska.
People can’t agree on what looks better. Not true either. People have agreed for centuries on which paintings look better, which symphonies sound better and which buildings are more attractive. A consensus on which bridges look better and why has existed since at least 1812 as articulated in the writings of Thomas Telford . That consensus has been recognized by artists and others. As one example, Robert Maillert’s Salginatobel Bridge (Fig. 3) was formally recognized as a work of art by New York’s Museum of Modern Art in 1949 and by many others since. That consensus is described in Section 2 and is embodied throughout this article. My client/boss won’t let me. Show your client/boss this article. Volume 45 Number 3 September 2015 23
I don’t know how. “Aesthetics” is a mysterious subject to most engineers, not lending itself to the engineer’s usual tools of analysis, and rarely taught in engineering schools. However, there is no reason that engineers can’t learn about aesthetics and become skilled in its practices. The experience of the engineers discussed above prove that. This article aims to help engineers do so. 4.2 Aesthetics Skills are Lacking My education was blessed by the opportunity to study both engineering and architecture. Looking back and comparing the educational approaches taken by the two professions has been very instructive. It has clarified to me the reasons that many engineers have difficulty dealing with aesthetics. In the engineering school from the very beginning my problem assignments were abstracted bits of an actual structure: calculating forces in a free body diagram or stresses in a beam. By contrast, in the architecture school from the very beginning my problem assignments required looking at a complete and usable building, albeit at first a very simple one. For example, my first problem in architecture was a garden gazebo, basically an open platform with a roof. Simple enough, but I still had to think about where to put it in the garden, how to orient it to the sun, and what shape to give it from among thousands of possibilities. By the third year of architecture I was designing small but complex buildings, such as a clinic with extensive building code and service requirements. In engineering by then we had moved on to dynamics and stresses in more complicated members, but always as applied to beams and columns abstracted for us as mathematical problems, not with actual structural members within an actual structural system. It was only in the last semester of my fourth year of engineering that I was assigned a complete structure with some flexibility to pick my own configuration of members, but even then it was just a typical beam/column/decking bay in a simple building. That year In the architecture curriculum I was designing an elementary school, which required researching the school’s educational program and interviewing teachers and principals. The engineering approach to education creates habits of thought for engineers that become real limitations in trying to deal with complex problems in the public 24 Volume 45
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realm, such as aesthetics. Many engineers see the answer to every problem as the solution of a mathematical equation, for which, of course, there is just one answer. In fact, for most real world problems there are many answers that will satisfy calculation. The goal is to pick the right one based on other factors. A derivative of this habit is that many engineers are too quick to jump to the parts of a problem that lend themselves to mathematical analysis, and are not willing or able to deal with aspects that don’t, such as aesthetics. For some types of engineering these habits of thought might work just fine, for elements that are physically limited and not publically visible. Bridges are not in that category. They are visible structures, part of our daily economic and social fabric. Urban bridges and prominent bridges elsewhere have symbolic importance: they come to stand for a region or culture’s creativity, wealth or ambition. Engineers who cannot respond to these influences fail their society and their places in it. Hopefully this article will help engineers get past these limitations. 4.3 Aesthetics can be left to Architects, Landscape Architects and Artists Gifted engineers working without the assistance of architects, artists or other visual professionals have produced masterpieces. Thus, it is not always desirable and it is certainly not necessary for all bridge design teams to include visual professionals. To meet his professional responsibilities the engineer should seek to develop his aesthetic skills as much as possible. However, for reasons of time or personal inclination, there may be limits. Accordingly, engineers have often sought the advice of other visual professionals – experts in aesthetics who are consulted in the same way as experts in soils, traffic or wind. Many memorable bridges illustrate the potential success of this approach. The Golden Gate Bridge is a famous example. Such collaboration does not relieve the engineer of the responsibility to be knowledgeable about aesthetics. As the leader of the design team, he or she remains responsible for the final result. Many over-decorated and expensive failures have been created when the collaboration was done poorly or when someone other than the engineer took over the lead role. The visual professional’s role should be as aesthetic advisor and critic, making comments and suggestions for the engineer’s consideration. In this role a landscape The Bridge and Structural Engineer
architect, urban designer, architect or artist can have a positive impact, but the engineer must have the last word. If the involvement of aesthetic advisors is to be successful, the engineer must be sure that they understand the basic issues involved in bridge design. Most visual professionals are used to dealing with buildings and their immediate surroundings, but bridges are significantly different than buildings. They are much larger, they are often seen at high speeds, and they typically have few surfaces that are flat and level. The architect/landscape architect needs to take the time to understand these differences, and the engineer needs to insist that he or she does. Effectively working with other visual professionals also requires that the engineer develop sufficient knowledge about aesthetics and sufficient self-confidence to recognize valuable ideas and reject inappropriate ones. Some have observed that the public seems to more readily accept bridges designed by teams that include architects, urban designers or landscape architects than those that do not. Communities seem to feel that more of their goals will be met when such professionals are involved, in part because most people in these professions are skilled at discussing and responding to community concerns. Unfortunately, engineers have a reputation for being insensitive to community wishes, due in part to many engineers’ inability to speak clearly and knowledgeably in this area. Engineers need to develop the vocabulary and knowledge to remain the project’s spokesman to the client and community groups, even concerning aesthetic ideas. Gaining the vocabulary and knowledge to respond to a community’s aesthetic concerns allows an engineer to fulfill the leadership role and retain the community’s confidence. 4.4 Replacing a Historic Bridge/Designing a Bridge in an Historic Place Forecloses Aesthetic Options Some communities see themselves as historic enclaves and view a bridge as a chance to restate local architectural traditions. In those situations a formal historic review process may be in place. The result is often pressure to build a new bridge that looks just like a previous bridge or matches a nearby architectural The Bridge and Structural Engineer
style. These projects are seldom an aesthetic success. Indeed, in the United States such an approach violates the Secretary of Interior Standards for Historic Preservation. Contrary to the all-too-common practice of taking a standard design-bridge and applying conjectural historic decoration and then calling it compatible, the Standards call for the use of contemporary design that clearly differentiates new construction from the old. Nowhere do the Standards say that new work has to mimic the old. To the contrary, they state that “changes that create a false sense of historical development shall not be undertaken.” The overall goal should be to let the historic resources dominate, not the new feature. The approach to replacing an individually historic bridge or a bridge located in historic districts should be no different than any other design – the same principles and guidelines that underlie good aesthetic design everywhere should be used. When historic bridges were built, they were usually examples of then-current technology, and this time-honored practice should still be used to develop pleasing examples of current technology that blend with their setting. Engineers should understand how historic materials and finishes were applied before using them as a treatment on a new bridge. They should be used only when plausible and appropriate for the setting. For instance, form liners imitating stone should be used only where stone is an indigenous material and in a manner that is structurally appropriate, such as for load-bearing abutments. Stone-like finishes are not appropriate, for example, on the cantilevered arms of hammerhead piers, elements that would be impossible to construct in actual stone. 4.5 Owners’ Standard Details prevent Aesthetic Improvement Perhaps the single biggest impediment to improved bridge appearance is the inertia created by inappropriate standard details. Standard details have an important place in bridge design. They may represent the distillation of hard-won functional experience, as in a crash-tested railing. However, many agencies attempt to design their bridges by applying standard details to every situation. Standard pier shapes, parapet profiles, and standard abutments essentially establish the appearance of an average highway overcrossing no matter what else the designer might do. There is Volume 45 Number 3 September 2015 25
some obvious economy in this approach. However, it does not relieve anybody of responsibility for the appearance of the resulting bridges. Typically those tasked with developing standard details are asked to consider only safety, constructability, durability and cost. It should be no surprise that the results do not produce attractive bridges. If they had been asked to consider aesthetics they might have come up with something just as safe/ durable/economical which also looked good. The challenge should be to develop a set of details that are inexpensive but also produce attractive bridges. The major difficulty with comparing the cost of new details with the current standard is that the current standard has years of contractor familiarity behind it. Of course it will be less expensive. But, if we break that mold and make something better, the new standard will soon become as economical as the old one. By the time the third or fourth bridge has been advertised the contractors will have gotten the message and the new standard will fit right into the normal cost distribution. 4.6 Difficulty in Finding a Place for Aesthetics in the Normal Design Process Much bridge design is governed by procedures, protocols, schedules and budgets that assume a “typical” bridge and move immediately into generating plans for a standardized product. These practices assume away the opportunity for improvement, innovation or aesthetic quality that most often results from the Conceptual Engineering phase of design.
5. Conceptual Engineering, the Neglected Phase of Design 5.1 Why is Conceptual Engineering Important? Creative engineering design consists not in applying free visual imagination alone nor in applying rigorous scientific analysis or careful cost analysis alone, but of applying all three together, at the same time. Creative engineering design starts with a vision of what might be. Development of the structural vision requires what many engineers call conceptual engineering. Conceptual engineering is the stage when the basic concept and form of the bridge is determined. Conceptual engineering is the most important 26 Volume 45
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part of design. All that follows, including the aesthetic impression the bridge makes, will depend on the quality of the concept and form selected. Unfortunately, it is a stage that is often ignored or foreclosed by the application of unwarranted assumptions or preconceived beliefs that may not in fact apply. Reasons given for short-changing this stage include “Everybody knows that (steel plate girders, precast concrete girders, cast in place concrete) are the most economical structure for this location, “ or “Let’s use the same design as we did for ______ bridge last year.” Or the selection of form is based largely on precedents and standards established by the bridgebuilding agency. For example, the form of a highway overpass may be predetermined by the client agency to be (steel plate girders, precast concrete girders, cast in place concrete) because that is what the agency is used to or what local contractors are used to or even because the (steel plate girders, precast concrete girders, cast in place concrete) industry is a dominant political force in the locality. Or the decision to forgo conceptual engineering may be simply habit - either the engineer’s or the client’s - often expressed in the phrase “We’ve always done it that way”. The assumption underlying all of the above is that the current bridge cannot benefit from any changes in ideas, practices or materials that might have occurred since previous designs were done. Some will protest conceptual engineering is unnecessary because costs will indeed differentiate and determine the form. However, if only the previously accepted designs are evaluated, how will anyone know if some new concept is less expensive? To compound the problem, engineers often rely too much on unit costs from past projects, ignoring changing conditions or unique aspects of the proposed bridge that might result in different unit costs. Or the engineer might be assigning unwarranted precision to the results of his cost calculations. The cost of the bridge will not be the cost the engineer calculates; it will be whatever cost a contractor is willing to build it for. Rarely do engineer’s estimates get within 5% of the contractor’s bid. Given the engineer’s lack of knowledge about the precise cost, differences of 5% or less might as well be treated as cost - neutral. Perhaps the most insidious reason conceptual engineering is shortchanged is the practice of bridge The Bridge and Structural Engineer
building agencies to budget design separately from construction. This leads to pressure to minimize the cost of design, and the design phase most likely to be cut is conceptual engineering. Such decisions are usually based on the types of unexamined assumptions listed above. Thus, potential savings of hundreds of thousands of dollars in construction are foregone in order to save tens of thousands of dollars on design, the ultimate example of penny/wise – pound/foolish thinking.
Fig. 14: A Conceptual Engineering Study for the Seattle LRT viaduct produced a design that both reduced cost and improved appearance compared to a design based on previous standard bridges.
Accepting these unwarranted assumptions and preconceived beliefs places an unfortunate and unnecessary limitation on the quality of the resulting bridge. It often results in “hammering a square peg into a round hole”, using an inappropriate design originally developed for another site. The resulting suboptimal bridge can create unnecessary construction costs that far outweigh the cost of conceptual engineering. Ignoring conceptual engineering also sacrifices the chance for innovation. By definition, improvements must come from the realm of ideas not tried before. As Captain James B. Eads put it in the preliminary report on his great arch bridge over the Mississippi River at St. Louis: “Must we admit that, because a thing has never been done, it never can be, when our knowledge and judgment assure us that it is entirely practicable?” Unless these unwarranted assumptions and preconceived beliefs are challenged, no design will occur. Instead, there will be a premature assumption of the bridge form, and the engineer will move The Bridge and Structural Engineer
immediately into the analysis of the assumed type. That is why so many engineers mistake analysis for design. Design is more correctly the selection of the concept and form in the first place, which many engineers have not been permitted to do.
6.
The Engineer’s Challenge
No one has the right to build an ugly bridge. Bridge designers must consider visual quality as fundamental a criterion in their work as performance, cost and safety. Engineers can learn what makes bridges visually outstanding and develop their abilities to make their own bridges attractive. They can achieve outstanding visual quality in bridge design without compromising structural integrity or significantly increasing costs. The ideal bridge is structurally straightforward and elegant, providing safe passage and visual delight for drivers, pedestrians and people living or working nearby. It is an asset to its community and its environment. The engineer’s challenge is not just to find the least costly solution. The engineer’s challenge is to bring forth elegance from utility: we should not be content with bridges that just move cars and trucks and trains; they should move our spirits as well.
Acknowledgements As mentioned in Section 2.3, the concepts in this article are based on and inspired by the works of David Billington, formerly Professor of Engineering at Princeton University. Through his descriptions and analyses of the works of outstanding engineers such as Thomas Telford, John Roebling, Christian Menn and particularly Robert Maillert, he has reminded us all of the role that aesthetics has always played in the design of the highest quality bridges. Indeed, Sections 2 and 3 are largely his work, adapted from previous articles that he and I developed together.
References: 1.
Frederick Gottemoeller, 2004. Bridgescape, the Art of Designing Bridges, 2nd Ed. John Wylie & Sons, Inc., New York, NY
2. Billington, D. P. 1983. The Tower and The Bridge - The New Art of Structural Engineering, Basic Books, Inc., New York, NY Volume 45 Number 3 September 2015 27
3.
Billington, D. P. 1989. Robert Maillart And The Art of Reinforced Concrete, The MIT Press, The Massachusetts Institute of Technology, Cambridge, MA
4. Billington, D. P. 2003. The Art of Structural Design, a Swiss Legacy, Princeton University Art Museum, Princeton, NJ 5. Allen, E. and Zalewski, W. 2010. Form and Forces, Designing Efficient, Expressive Structures, John Wylie & Sons, Inc., New York, NY
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6. Leonhardt, F. 1983. Brucken, MIT Press, Cambridge, MA 7.
David Pye, D. 1999. The Nature and Aesthetics of Design, 5th Reprinting, Cambium Press, Bethel, CT
8. Man-Chung Tang, M. C. 2001. 36 Years of Bridges, Tango International, New York, NY 9.
Schlaich, J. and Bergermann, R. 2003. Light Weight Structures, Prestel Publishing, New York, NY
The Bridge and Structural Engineer
World’s Aesthetic Foot bridges Dr. Subramanian NARAYANAN Consulting Engineer Gaithersburg, MD 20878 USA drnsmani@gmail.com
Summary Current day footbridges are often built in the urban environment and hence may require collaboration between the architect and the structural engineer. Many types of structural materials such as steel, concrete, prestressed concrete, masonry, timber and fibre-reinforced plastics, and a number of different forms like simple beam, arch, truss, stress-ribbon, cable stayed, cable supported and a combination of these systems could be used efficiently in order to build aesthetic footbridges. A few earlier aesthetic bridges are listed and a few elegant recent footbridges are described. Serviceability problems encountered in a few footbridges and the methods adopted to overcome are also described. An introduction to the current trend of using biomimicry to develop efficient, economic, aesthetic and sustainable footbridges is also provided. Keywords: Footbridges; Aesthetic design; Stressribbon bridge; cable stayed and cable suspended bridge; biomimicry; economy; vibration; sustainability
1. Introduction Footbridges have a longer history than road or railway bridges. Ancient footbridges comprised of natural materials such as roots of trees, ropes, stones, masonry, and wood. Modern footbridges are built using reinforced concrete, steel, prestressed concrete, and fibre reinforced plastics. Though earlier footbridges were built using beams and arches, current footbridges are built in various configurations like inclined arch, trusses, stress-ribbon, cable stayed, cable suspended and a combination of these forms. In recent decades, The Bridge and Structural Engineer
Dr. N. Subramanian earned his PhD from IIT, Madras in 1978 and has 40 years of professional experience which includes teaching, research, and consultancy in India and abroad. Dr. Subramanian has authored 25 books and more than 225 technical papers, published in international and Indian journals and conferences. He has won the Tamil Nadu Scientist Award, the Lifetime Achievement Award from the Indian Concrete Institute (ICI) and the ACCE(I)-Nagadi best book award for three of his books. He also served as the past vice-president of ICI and ACCE(I). footbridge designers have been able to push the boundaries of what is possible, much further than ever before. This is largely due to growing capabilities in computer visualization and analysis techniques, as well as developments in materials technology and other factors, with the result that creative designers are able to imagine and create more adventurous designs. However, such imaginative and creative designs should obey economic, environmental, social, and other constraints, in order that the built footbridges are safe, economical, durable, aesthetic and sustainable. A bridge or a footbridge leaves an impression, and that impression remains as long as the bridge remains; hence bridge designers should strive to create something that is beautiful. Modern technology and tools provide ample opportunity to create dramatic bridges which not only provide safe passage but also result in creating adventurous structural and artistic expression. However, it is not always appropriate to build extravagant foot bridges, just because it is possible to do so, and in many cases the right solution may be much more modest and gentle. A variety of special characteristics set footbridge design apart from other bridge work. Some of these special characteristics are (Wells and Clash, 2008): 1.
Live load actions are not significant in comparison with dead load actions; however dynamic behaviour must be carefully studied.
2. The light loadings of footbridges, allow structures of extreme delicacy and simplicity to be built and make expressive or experimental designs economically viable. Volume 45 Number 3 September 2015  29
3. Unlike bridges (which are usually conceived, planned and designed by structural engineers), footbridges are built in urban environment and hence may require collaboration between the architect and the structural engineer. The relative input from them varies widely between projects. However, it is possible to build footbridges which are lightweight and have elegance and slenderness. 4.
Many types of structural materials such as steel, concrete, prestressed concrete, masonry, timber and fibre-reinforced plastics, and a number of different forms like simple beam, arch, truss, stress-ribbon, cable stayed, and cable supported systems could be used efficiently.
5. As the user of a footbridge will have a slow speed, it will allow him/her to have a slow and measured interaction with the design of the bridge and its surrounding environment, which may demand the utmost attention to the design of its component parts. As the parts of a footbridge can be touched, the tactile and visual details must be carefully planned and executed. 6.
The aesthetic elements of a footbridge are given below: a)
Transparency and slenderness
b) Form c) Proportion d) Scale e)
Expression of function
f)
Unity and harmony
g)
Visual stability and balance
h)
Rhythm and rhyme
i) Illusion All these factors are discussed in detail in Ref. 4 (Structures Design Manual, 2006) and guidelines for the design of footbridges are provided in Schlaich et al., 2005. The inter-relationship between the principal elements is illustrated in Fig. 1.
Construction technique can have a significant impact on form.
In this paper the approaches to aesthetic design is considered first, which is followed by a short description of some of the earlier aesthetic footbridges. A few modern footbridges are then listed with some details. One should not aim to construct aesthetic footbridges at the expense of economy and the built structure should serve the purpose, for which it was built, effectively. A few aesthetic footbridges that had serviceability problem of vibration are explained along with the remedial measures. The current trend is to build footbridges based on biomimicry- which will result in these looking differently and mimic natural things but also will be safe, efficient, economic, and sustainable.
2.
noise barriers, long term appearance, maintenance and operational requirements (Subramanian, 1987; Keil, 2013 and Subramanian, 2014).
Approaches to Aesthetic Design
Aesthetic design involves the consideration of a number of key elements, such as landscape and environmental aspects, approaches and access, materials and their modes of assembly, functional and structural considerations, details, texture, scale, colour, form, lighting and shading, ornamental features, drainage, 30  Volume 45
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Transparency Slenderness Form
Utility Harmony
Texture, Colour Light and shade Illusion Lighting Highlight
Expression of function Visual stability Balance
Proportion
Rhyme Rhythm
Scale
Fig. 1: Aesthetic Concepts and Considerations (Structures Design Manual, 2006)
3.
Aesthetic Footbridges during 1934-2000
Traditionally, the aesthetic aspects in bridge design were given secondary importance and the primary aim was to develop technical solutions; only in the early twentieth century it was given its proper prominence. Although safety is an important criterion, other considerations such as environmental impact, usability, appearance and economy all need to be balanced together. Robert Maillart ‘s (1872-1940) small pedestrian bridges are excellent early examples of his contribution to finding forms for concrete (reinforced with iron or The Bridge and Structural Engineer
steel) that are appropriate to the material. One such example is the Tösssteg footbridge in WinterthurWülflingen built 1934 at Zürich, Switzerland (see Fig. 2). This slender elegant 38 m polygonal arch bridge (rise-to-span ratio = 1: 10.84) had a stiff deck girder that also formed a base for the iron railings (Baus and Schlaich, 2008). The arch slab and the cross walls are each 140 mm thick and the stiffening girder is 540 mm thick. Due to a slight reverse curvature at both ends, the transition to the shore is especially elegant. Fritz Leonhardt, one of the most experienced experts on reinforced concrete and bridges, first designed the aesthetic footbridge at Enzsteg in Vaihingen, Germany, during 1962. Many of the later footbridges were either stress ribbon bridges or cable stayed bridges.
Fig. 2: The Tösssteg footbridge, Zürich, Switzerland (http:// commons.wikimedia.org/)
3.1 Stress Ribbon Footbridges Stress ribbon structure represents the simplest structural form in which the suspension cables are embedded in the deck and follows a catenary arc between supports. Such structures can either be cast in-situ or formed of precast units. In the case of precast structures, the deck is assembled from precast segments that are suspended on bearing cables and shifted along them to their final position. Prestressing is applied after casting the joints between the segments to ensure sufficient rigidity of the structures. The first concrete stress ribbon bridge for pedestrians was built in Bircherweid, Switzerland, in the mid 1960s by Rene Walther (stress ribbon bridges are not the cheapest option as large foundations are required for anchoring the tension forces developed in the structure). Other notable stress ribbon bridge is in Geneva, Lignon-Loex, Switzerland, built in 1971. Jiří Stráský, one of the experts in stress ribbon bridges, also designed a multi-span stress ribbon bridge near Prague (1985) and the Maidstone Footbridge in UK (2001), with a change of direction at mid-span The Bridge and Structural Engineer
(Stráský, 2005). Schlaich Bergermann and Partner designed several stress ribbon bridges and the notable ones are the bridge at Enzauen Park, Pforzheim, Germany (1991) with a sag of 800 mm only on a span of 67.7 m, and a multiple span stressed ribbon North Bridge in Rostock, Germany (2003). The 87.43 m span stressed ribbon pedestrian bridge over the Rogue River, Grants Pass, Oregon, USA, designed by OBEC Consulting Engineers, Gary Rayor & Jiří Stráský in the year 2000 is shown in Fig. 3. Another notable stress-ribbon bridge is the Punt da Suransuns, Viamala, Switzerland (1997) designed by Conzett, Bronzini, Gartmann AG.
Fig. 3: Stressed Ribbon pedestrian bridge over the Rogue River, Grants Pass, Oregon, USA (Source: http:// en.wikipedia.org/wiki/Stressed_ribbon_bridge)
3.2 Cable-stayed or Cable-suspended Footbridges In the cable-stayed/cable-suspended bridge, the towers are the primary load-bearing structures which transmit the bridge loads to the ground. [It is of interest to note that the Venetian inventor Fausto Veranzio (1551-1617) was the first to design cable stayed bridges- he was also the first to design modern suspended bridge]. There are two major classes of cable-stayed bridges: harp, fan (see Fig. 4). In the harp or parallel design, the cables are nearly parallel so that the height of their attachment to the tower is proportional to the distance from the tower to their mounting on the deck. In the fan design, the cables all connect to or pass over the top of the towers. The fan design is structurally superior with minimum moment applied to the towers but for practical reasons the modified (semi) fan is preferred especially where many cables are necessary. In the modified fan arrangement the cables terminate near to the top of the tower but are spaced from each other sufficiently to allow better termination, improved environmental Volume 45 Number 3 September 2015 31
protection, and good access to individual cables for maintenance.
Fig. 4: Types of cable arrangements in cable stayed bridge
Fritz Leonhardt built the first cable-stayed bridge with a harp arrangement in 1952 in the Düsseldorf family of bridges. Ingenieurbüro Leonhardt und Andrä, Stuttgart designed more than 140 cable-stayed bridges, which included the Schillersteg at Stuttgart-main span 68.6 m (1961), Kehl-Strasbourg bridge -185 m main span Germany/France(2004), Passerelle des Deux Rives in Strasbourg (2004). They also designed concrete arch type footbridges (at Waiblingen (1978,1980), steel asymmetric arch Bridge crossing the River Rhine (229 m main span), and the 63 m Kocher bridge at Hagenbach, Germany. Prof. Leonhardt attempted to create light and slender structures, so that they look aesthetic. His designs strived hard to reduce the depth of deck slab as small as possible and to make the footbridge look elegant. The structural system of the cable-stayed bridge is well suited to this desire; by decreasing the distance between cable supports, the deck can be made more slender as the bending moments are reduced. Prof. Leonhardt considered the fan arrangement to be the most “natural and technically effective” cable arrangement, and adopted it for the Neckar Footbridge at the Collini Centre in Mannheim, Germany (1973) and Footbridge in Rosenstein Park, Stuttgart, Germany (1977) (Baus and Schlaich, 2008) Prof. Jörg Schlaich, who first worked with Leonhardt und Andrä and designed the 78.1 m span selfanchored suspension bridge with inclined suspenders at Rosenstein Park, Baden-Württemberg, Germany (1977). He later established his own company, Schlaich und Bergermann in 1980, and designed a number of aesthetic cable supported bridges. Their 32 Volume 45
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designs include: Bridge at Max Eyth Lake near Stuttgart, Germany, 1989 (with a span of 114 m, the curved deck of this footbridge is only 300 mm deep), the 70 m span Berching Footbridge, over Main Danube canal, Bavaria, Germany (1991), the 105 m span Glacis Footbridge at Minden, Germany (1995), the 73.72 m span movable suspension Innenhafen Footbridge at Duisburg, Germany (In order to let boats pass underneath, the cables can be pulled up while the pylons incline away from the deck and the deck curves sharply upwards), the 350 m long Weinberg bridge, Rathenow, Germany, 2014 (Angled steel arches support the S-curved superstructure. The hangers are not located as usual along the outer edge of the circular edge beam, but rather on radial cantilevers that almost reach the arch planes), and the 160 m span Passerelle de la Paix, at Lyon, France (Footbridge of Peace, 2014). More details about these footbridges may be found in the works of Baus and Schlaich (2008), Idelberger (2011), Keil (2013), and www.sbp.de.
4.
Modern Bridges
In the second half of the 20th century, bridge builders chased one record after another. They attempted long spans, curved bridges [examples: Pasarela del Malecon in Murcia, Spain (1996), designed by Javier Manterola, the doubly curved West Park Bridge in Bochum, Germany (2003), designed by Schlaich Bergermann & Partners and Liberty Bridge at Falls Park on the Reedy, Greenville, South Carolina (2004), designed by architects Rosales + Partners of Boston and Schlaich Bergermann & Partners], combination of different structural systems (such as an edge supported circular girder bridge suspended from a spatial arch), innovative designs with the use of computer software, movable bridges [examples: Kiel-Hörn Bridge, Kiel, Germany (1997) designed by Schlaich Bergermann and Partner (architect: von Gerkan, Marg and Partner), plastic movable footbridge at Fredrikstad, Norway (2006) designed by COWI A/S, and Twin Sails bridge (2012)- a double leaved bascule bridge in Poole, Dorset, England- designed by Wilkinson Eyre Architects and Gifford UK (Ramboll)] and the use of materials like fibre reinforced plastics [examples of FRP footbridges include those at Aberfeldy, Scotland (1992)- cable stayed and has the longest main span (63 m), Pontresina in Swiss Alps(1995), Kolding, Denmark (1997), Lleida, Spain (2001), Winterthur, The Bridge and Structural Engineer
Switzerland (2001), and ApATeCh arched footbridge, Moscow, (2008)]. A few of these innovative and aesthetic bridges are described in the next section. In addition to these footbridges, a number of aesthetic footbridges were constructed by COWI A/S, and Buro Happold. Details of other aesthetic bridges may be found in Dundas (2009), www.bridgemeister.com, and www.steelconstruction.info. 4.1 Recent Footbridges Several outstanding and aesthetic footbridges have been built in the recent past, with different configurations and technology. Some of these footbridges are discussed below. 4.1.1 Helix Bridge, Singapore (2010) Previously known as Double Helix Bridge, this twisting bridge is modeled after the DNA structure; The Land Transport Authority claims it is a world first in architectural and engineering bridge design. Linking the Marina Bay and Marina Center in Singapore, the 280 m long Helix Bridge symbolizes life and continuity with its intertwining steel frame (see Fig.5). Made of a special stainless steel, this bridge was assembled over two years with great precision. Canopies (made of fritted-glass and perforated steel
viewing platforms sited at strategic locations which provide stunning views of the Singapore skyline and events taking place within Marina Bay. At night, the bridge is illuminated by a series of lights that highlight the double-helix structure, thereby creating a special visual experience for the visitors. The design consortium is an international team comprising Australian architects the Cox Group and engineers Arup, and Singapore based Architects 61. More details of this bridge may be found in http:// en.wikipedia.org/wiki/The_Helix_Bridge 4.1.2 Langkawi Sky Bridge, Malaysia(2005) Extending across Malaysia’s Mount Gunung Mat Chinchang on Pulau Langkawi, the 125 m long Langkawi Sky Bridge is one of the world’s highest, at 700 m above sea level, and is accessible by cable car. It is a curved pedestrian cable-stayed bridge in Malaysia, completed in 2005 (see Fig.6). It was constructed by Langkawi Development Authority
Fig. 6: Langkawi Sky Bridge, Malaysia (http://en.wikipedia. org/wiki/Langkawi_Sky_Bridge)
4.1.3 Gateshead Millennium Bridge, England(2002)
Fig. 5: Two views of the Helix Bridge, Singapore (Source: http://www.archdaily.com & http://en.wikipedia.org/wiki/ The_Helix_Bridge)
mesh) are incorporated along parts of the inner spiral to provide shade for pedestrians. The bridge has four The Bridge and Structural Engineer
The 126 m long Gateshead Millennium Bridge is a pedestrian and cyclist tilt bridge and loops over Gateshead and Newcastle, England, spanning the River Tyne (see Fig. 7). This award-winning structure was conceived and designed by architects Wilkinson Eyre and structural engineers Gifford. The bridge was lifted into place in one piece by the Asian Hercules II, one of the world’s largest floating cranes, on 20 November 2000. Six 450 mm diameter hydraulic rams (three on each side, each powered by a 55 kW electric motor) rotate the bridge back on large bearings to allow small ships and boats (up to 25 m tall) to pass underneath. The bridge takes about 4.5 minutes to rotate through the full 40° from closed Volume 45 Number 3 September 2015 33
to open, depending on wind speed. Its appearance during this maneuvering has made it nicknamed as the “Blinking Eye Bridge”. The construction of the bridge won the architects Wilkinson Eyre the 2002 Royal Institute of British Architects (RIBA) Stirling Prize and won Gifford the 2003 IStructE Supreme Award. In 2005, the bridge received the Outstanding Structure Award from International Association for Bridge and Structural Engineering (IABSE).
Fig.8: Two views of the Rolling Bridge, London (Source: http://www.toxel.com/tech/2008/09/21/incredible-rollingbridge-in-london/)
4.1.5 Henderson Waves Bridge, Singapore(2005)
Fig. 7: The Gateshead Millennium Bridge, England(Source: http://en.wikipedia.org/wiki/Gateshead_Millennium_Bridge)
4.1.4 The Rolling Bridge, London (2004) Like a modern drawbridge, London’s 12 m long Rolling Bridge unfurls to connect workers and residents to the two sides of the Grand Union Canal without obstructing boats. At present, this curling bridge is the only one of its type in the world (see Fig. 8). The Rolling Bridge was conceived by British architects Thomas Heatherwick Studio, designed by SKM Anthony Hunt with Packman Lucas, and built by Littlehampton Welding Ltd. The Hydraulic design and development was done by Primary Fluid Power Ltd in the North West.
The rolling, steel-ribbed Henderson Waves is Singapore’s tallest pedestrian bridge and connects two of the city-state’s parks. The total length of the bridge is 284 m, and is considered the highest footbridge in Singapore. The bridge is designed from a single form comprising seven steel undulating curves composed of ribs which in turn, are raised above and below the deck (see Fig. 9). Under each curve undulating shaped shell, above the deck, the seats are located, protecting the visitor who can easily observe the surrounding landscape. Its width is 8 m and rises 36 m above Henderson Road highway. This pedestrian and cycle bridge was designed by IJP Corporation and RSP Architects, Planners & Engineers, and the structural engineers were Adams Kara Taylor of Consulting Civil and structural engineers.
Fig. 9: Henderson Waves Bridge, Singapore (Source: http:// en.wikiarquitectura.com/index.php/Henderson_Wave_ Bridge)
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4.1.6 Te Rewa Rewa Bridge, New Zealand (2010) Managing to simultaneously represent a breaking wave and a whale skeleton, the award-winning Te Rewa Rewa Bridge is built across the Waiwhakaiho River at New Plymouth in New Zealand (see Fig. 10). The 68.8 m span Te Rewa Rewa Bridge is a pedestrian and cycleway bridge and designed and constructed by a consortium of Whitaker Civil Engineering, Novare Design Ltd, Apex Consultants Ltd (now Spiire) and Fitzroy Engineering. It is made of three steel tubes; two beneath the deck and the remaining one, together with 19 ribs, forming a distinctive arch. It uses 85 t of fabrication steel, 62 t of reinforcing steel and 550 m3 of concrete for its construction.
Michele De Lucchi, the lighting design was created by French lighting designer Philippe Martinaud.
Fig. 11: Two views of the Bridge of Peace, Georgia (Source: http://en.wikipedia.org/wiki/The_Bridge_of_ Peace_%28Georgia%29)
4.1.8 Slinky Springs to Fame, Oberhausen, Germany (2011) The 406 m long bridge “Slinky Springs to Fame”, which spans the Rhine-Herne Canal, is a pedestrian bridge near Oberhausen in Germany. The helical architectural sculpture designed by German artist Tobias Rehberger is part of the “Emcherkunst.2010” project (see Fig. 12). This stressed ribbon bridge was designed by Schlaich Bergermann & Partner. Fig. 10: Two views of the Te Rewa Rewa Bridge, New Zealand (Source: http://en.wikipedia.org/wiki/Te_Rewa_ Rewa_Bridge)
4.1.7 Bridge of Peace, Georgia (2010) The 150 m long Bridge of Peace spans the Kura River in Georgia’s capital city of Tbilisi. It is shaped like a marine animal and has a curvy steel and glass canopy top which shimmers with an interactive light display at night, generated by thousands of white LEDs (see Fig. 11). The bridge was designed by the Italian architect The Bridge and Structural Engineer
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Fig. 13: The Python Bridge, Amsterdam (Source: http:// nl.wikipedia.org/wiki/Pythonbrug)
4.1.10 Kurilpa Bridge, Australia (2009)
Fig. 12: Slinky Springs to Fame Bridge, Oberhausen, Germany (Source: http://www.stylepark.com/)
A colorful ribbon wrapped in a light, swinging spiral connects the two existing parks. The support structure for the tensioned ribbon bridge was reduced to a bare minimum to create the structure’s airy appearance. Two steel ribbons made of high strength steel connect to the inclined supports across the canal. The resulting tension force is transferred into strong abutments through the outer vertical tension rods. The walkway consists of pre-cast concrete plates, which are bolted to the stress ribbon, to which the railing and spiral are attached. The bouncy plastic surface of the walkway combines with the alternating colors of the concrete and the surface to intensify the dynamic experience while walking on the bridge. (www.sbp.de). Railings consisting of steel posts and cable nets effectively dampen the oscillation of this vibrant structure. Rehberger’s bridge design resembles the toy Slinky, a pre-compressed helical spring, invented by the American Richard James in the early 1940s. Hence, it has been named “Slinky Springs to Fame”. This bridge received several awards including the StahlInnovationspreis 2012, and ECCS Award for steel bridges 2012. 4.1.9 Python Bridge, Amsterdam (2001) This dipping Borneo-Sporenburg pedestrian bridge is one of three that connects Amsterdam with Borneo Island. Its unusual snake like shape lends it the name “Python Bridge” (see Fig. 13). This bright red bridge is about 90 m long and designed by Adriaan Geuze of the architectural firm West 8. Built in 2001 it won the International Footbridge Award in 2002. 36 Volume 45
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Brisbane,
Queensland,
Costing around $63 million, Australia’s 470 m long (with a main span of 128 m) Kurilpa Bridge is the world’s largest solar-powered footbridge and links Kurilpa Point in South Brisbane to Tank Street in the Brisbane central business district. In 2011, the bridge was judged World Transport Building of the Year at the World Architecture Festival.
Fig. 14: Kurilpa Bridge, Brisbane, Queensland (Source: http://en.wikipedia.org/wiki/Kurilpa_Bridge)
Baulderstone Queensland Pty Ltd constructed the bridge and the company’s design team included Cox Rayner Architects and Arup Engineers. Kurilpa Bridge is the world’s largest hybrid tensegrity bridge (see Fig.14). Only the horizontal spars conform to tensegrity principles. The Kurilpa Bridge is a multiple-mast, cable-stay structure based on principles of tensegrity producing a synergy between balanced tension and compression components to create a light structure which is incredibly strong. The bridge is lit with a sophisticated LED lighting system which can be programmed to produce an array of different lighting effects. Depending on lighting configurations, 75%-100% of the power required is provided by solar energy. All electrical work was done by Stowe Australia. The Bridge and Structural Engineer
4.1.11 Aesthetic bridges by Engineer turned Architect Santiago Calatrava The Sundial Bridge (2004) is a cantilever spar cablestayed bridge, similar to Calatrava’s earlier design of the Puente del Alamillo in Seville, Spain (1992), and Puente de la Mujer (Spanish for “Women’s Bridge”), Buenos Aires, Argentina (2001). Calatrava designed a similar bridge, The Bridge of Strings, Jerusalem, Israel, which was opened in 2008. This type of bridge does not balance the forces by using a symmetrical arrangement of cable forces on each side of its support tower; instead, it uses a cantilever tower, set at a 42-degree angle and loaded by cable stays on only one side (see Fig. 15). This design requires that the spar resist bending and torsional forces and that its foundation resists overturning. While this leads to a less structurally efficient structure, the architectural expression is found to be dramatic. The bridge is 210 m in length and crosses the river without touching the water, a design criterion that helps protect the salmon spawning grounds beneath the bridge. The cable stays are not centered on the walkway but instead divide the bridge into a major and minor path.
Volantin Bridge (also called as the Zubizuri) shown in Fig. 16, which is a tied arch footbridge across the Nervion River in Bilbao, Spain. The bridge’s unusual design consists of a curved walkway which is supported by steel suspension cables from an overhead arch (the inclined arch dominates most of Calatrava’s bridges). The inclined parabolic arch spans over 75 m and creates a stable spatial structure together with its hanger cables. The slenderness of the arch indicates that its form is not random, but is the result of a complicated form-finding procedure to minimize bending moments in the arch (Baus and Schlaich, 2008). As is usual in Calatrava’s works, the structure of the bridge is painted white and the bridge deck consists of translucent glass bricks.
Fig. 16: Campo Volantin or Zubizuri footbridge, in Bilbao, Spain, Source: http://en.wikipedia.org/wiki/Zubizuri)
4.1.12 BP Pedestrian Bridge, Chicago (2004) The BP Pedestrian Bridge (2004) is a girder footbridge situated in the Millennium Park, Chicago, Illinois, United States (see Fig. 17). Designed by Pritzker Prize-winning architect Frank Gehry, and named for energy firm BP, which donated money for its construction, it is the first Gehry-designed bridge. BP Bridge has a curving form, similar to that of a snake. Fig. 15: Sundial Bridge at Turtle Bay, Redding, California, USA (Source: http://en.wikipedia.org/wiki/Sundial_Bridge_ at_Turtle_Bay)
It has to be noted that a “side-spar cable-stayed bridge” is different from “cantilever spar cablestayed bridge” - it has only one tower and is supported only on one side. One bridge built on this principle is the 197 m long Esplanade Riel pedestrian bridge in Winnipeg, Manitoba, Canada (2004) designed by Colin Douglas Stewart of Wardrop Engineering and the architect Étienne Gaboury-it is the only bridge with a restaurant(at the center of the bridge) in North America. Another unconventional but aesthetic footbridge designed by Santiago Calatrava in 1997 is the Campo The Bridge and Structural Engineer
Fig. 17: BP Pedestrian Bridge, Chicago (Source: en.wikipedia.org/wiki/BP_Pedestrian_Bridge)
Designed to bear a heavy load without structural problems caused by its own weight, it has won awards for its use of sheet metal. The bridge is known for its aesthetics, and Gehry’s style is seen in its biomorphic Volume 45 Number 3 September 2015 37
allusions and extensive sculptural use of stainless steel plates to express abstraction (en.wikipedia.org). The pedestrian bridge serves as a noise barrier for traffic sounds from Columbus Drive. BP Bridge uses a concealed box girder design with a concrete base, and its deck is covered by hardwood floor boards. It is designed without handrails, using stainless steel parapets instead. The total length is 285 m, with a five percent slope on its inclined surfaces that makes it barrier free and accessible.
5.
Issues Related to Aesthetic Bridges
Many designers are of the view that aesthetic bridges will result in uneconomical structures. But, any bridge design that is regarded as structural art, is found to have a very good balance on economy, efficiency, and elegance (Hu et al., 2013). Sometimes, giving more importance to aesthetics alone has resulted in serviceability problems. These aspects are discussed below briefly. 5.1 Economy It has to be noted that aesthetic bridge design should also be reasonably economical and should serve the intended purpose (Subramanian, Nov. 2014). The BP bridge, even though it received favorable reviews for its design and aesthetics, is closed in winter because ice cannot be safely removed from its wooden walkway! Similarly, many of Calatrava’s bridges are very expensive or resulted in cost overruns. For example, the Sundial Bridge was completed in 2004, three years later than originally planned; at a cost of $23.5 million (original budget was only $3 million). The high cost is not primarily due to their newness, but rather due to the irrationality of their forms (Hu et al., 2014). The Campo Volantin Bridge has also been accused of impracticality: due to the glass bricks set into its floor, it often became slippery during the wet climate.
dynamic vibrations, and reopened only after the installation of damping devices. In the Millennium Bridge (2000), designed by Ove Arup and partners, (architects: Foster and Partners), to improve the view, the bridge’s suspension design had the supporting cables below the deck level, giving it a very shallow profile (it is 330 m long and has a central span of 144 m). The inclination of the hangers made the bridge susceptible to lateral oscillations and resulted in synchronous lateral excitation, when people walked over. This kind of phenomenon could occur on any bridge with a lateral frequency below about 1.3 Hz loaded with a sufficient number of pedestrians (Dallard et al., 2001). After an extensive analysis, the problem was fixed by the retrofitting of 37 fluidviscous dampers (energy dissipating) to control horizontal movement and 52 tuned mass dampers (inertial) to control vertical movement. It has to be noted that visco-elastic dampers require relatively large deflections to be effective, whereas tuned mass dampers are effective for some frequencies only and require a rather large mass, typically 1 to 5 percent of the total bridge mass. In some recent footbridges with unconventional designs, such dampers are included in the original scheme itself. For example, the 84.12 m span Bagley Street Pedestrian Bridge, Michigan, USA, (2010), designed by HNTB Corporation, has a unique asymmetric design with asymmetry in two major planes. A single 47.2 m tall inclined and tapering concrete and steel pylon supports the main span via ten forestays set in a fan arrangement. Five tuned mass dampers limit any vibrations due to wind or pedestrian traffic. [In this connection, it is interesting to note that the oscillating 137 m span Capilano suspension bridge, Vancouver, British Columbia (originally built in 1889 and completely rebuilt in 1956) is a tourist attraction].
5.2 Avoiding Vibration
6. Bio-Inspired Strategy for Developing Innovative Bridges
It has to be noted that while considering aesthetics proper care should also be taken to keep the vibration of the footbridge under control. The 106 m span Passerelle Léopold-Sédar-Senghor in Paris, France (1999) and the 325 m long Millennium Bridge in London (2000), which has a main span of 144 m, were closed shortly after their inauguration due to
Bio-inspired design is perhaps the oldest methodology of design with several examples from the architectural history (Hu et al., 2013). In fact, all basic types of modern bridges (beam, arch and suspension) have their ancient prototypes in nature. During the last century, architects and engineers realized to learn and inspired by structures in nature and utilized those
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ideas in the design and construction of man-made structures. For example, the tree is a classic prototype in bio-inspired research. For example, Schlaich Bergermann und partner used structural principles of tree which provide multiple load paths to maintain a uniform load distribution in the Nesenbach Valley Highway Bridge, Vaihingen, Germany, (1999) and Hessenring Footbridge, Hesse, Germany, (2002)- See Fig. 18 (It has to be noted that they also designed the roof of Stuttgart airport based on similar principles of a tree)
Fig. 18: Hessenring Footbridge, Germany (Source: http:// www.sbp.de/en)
have been derived from the shape of an earth-worm or snake [It has to be noted that the BP bridge in Chicago (Fig.17) also has a curved layout]. These designs show a similarity between natural and man-made structural forms, but the efficiency and economy of the design may be questionable. The double Helix Bridge (Fig. 5) was inspired from the shape of the DNA while the curvilinear steel “ribs” of the Henderson Road Bridge (Fig. 9) was inspired from natural waves. However, simply copying the geometric shape from nature may lead to designs which are difficult to construct and have high cost. For example, the shape of Chunhua Footbridge at Shenzhen, China, was designed in the shape of a flower, but is not costeffective [see Fig. 20(a)]. Similarly, the Peace Bridge at Calgary, Canada (2012) designed by Santiago Calatrava and Hans Wilsdrof Bridge in Geneva, Switzerland (2012) designed by Amsler, Bombelli & Associates and architects Brodbeck & Roulet might have been inspired by fishbone structure [see Fig. 20(b)].
The shape of the Hacking Ferry Bridge, Lancashire, U.K., designed by Flint & Neill Partnership and architects Wilkinson Eyre has a three-way deck (45 m on each side), is shown in Fig. 19(b)- this not only provides sufficient structural stability but also necessary clearance, is inspired by the shape of star fish. The Webb Bridge at Melbourne, Australia, shown in Fig. 19(d), has a curved layout, which might
Fig. 20: (a) The Chunhua footbridge in Shenzhen, China (Source: www.arch2o.com) and (b) Hans Wilsdorf Bridge in Geneva (Source: http://nemetschek-scia.com)
Fig. 19: Biological Vs structural shape in bridge design (a) Shape of starfish, (b) Hacking Ferry Bridge, (c) shape of earthworm, (d) Webb Bridge [Source: Hu et al., 2013]
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The twin inclined steel arches of the 32 m Butterfly Bridge (1997) in Bedford, U.K. designed by Wilkinson Eyre Architects was inspired from butterfly wings. Like his predecessor Spanish architect Antonio Gaudi, many bridges designed by Calatrava were inspired from the structural forms of plants and animals. For example, the main girder of the Campo Volantin Bridge (Fig. 16) was inspired from the spine structure while the tower of the Bridge of Strings (Fig. 15) was
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created with inspiration from our legs. It has been found that the study of biomimicry can help engineers handle traditional issues (efficiency, economy and elegance) and may also address emerging issues (sustainability and energy use). A multidisciplinary collaboration approach may help engineers build more sustainable and smart structural systems for bridges in the 21st century (Waggoner and Kestner, 2010; Hu et al., 2013).
7.
Summary and Conclusions
The design of a pedestrian bridge is often claimed to be an experimental regime in the field of design art (Hu et al., 2014). In fact, the best footbridge designs came from inventive engineers, architects or artists who, based on their disciplines, integrated economy, efficiency, and elegance. The understandings of structural principles as well as the efficient use of construction materials are two necessary qualities an engineer must consider in order to develop structural art. Several engineers had two common misconceptions about the design of footbridges: A structure that is efficient will automatically be elegant, and a beautiful structure is always expensive. Many examples described here have shown that achieving an aesthetic goal is possible within the limits of structural feasibility, efficiency, and economy. Developments in computer visualization and analysis techniques, as well as research in materials technology and construction techniques, have resulted in the creation of modern footbridges which are creative, adventurous and have stunning elegance. Engineers while creating aesthetic designs should not forget to satisfy the basic principles of structural design: safety, stability, serviceability, economy, durability, sustainability, and constructability. The current practice of using biomimicry to arrive at the configuration of footbridges may lead to stunning footbridges which will satisfy all the basic principles of structural design.
8. Acknowledgements All the figures and much data about footbridges are taken from the Net. The author wishes to acknowledge the different sources for the same.
9. References 1. BAUS, U., and SCHLAICH, M., Footbridges: 40 Volume 45
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Construction, Design, History, Verlag AG, Basel, 2008, 255 pp. 2.
Birkhauser
DALLARD, P., FITZPATRICK, A. J. , FLINT, A., LE BOURVA, S. , LOW, A. , RIDSDILL SMITH, R. M., and WILLFORD, M., The London Millennium Footbridge, The Structural Engineer, Vol. 79, No. 22, Nov. 2001, pp. 17-33.
3. DENNIS, R., Footbridges- A Manual for Construction at Community and District Level, RATP No. 11, International Labour Office Geneva, Department for International Development, UK and I.T. Transport Ltd, 2004,185 pp. (http://www.ilo.org/public/ english/employment/recon/eiip/download/ratp/ ratp11.pdf) 4. DUNDAS, G., “Examples of Recent Aesthetic Landmark Footbridges in Western Australia”, 7th Austroads Bridge Conference, Auckland, New Zealand, 26-29 May 2009. http://www.cmnzl. co.nz/assets/sm/3576/61/0062-E14Dundas.pdf 5.
HU, N., FENG, P., and DAI, G.-L., “Structural art: Past, Present and Future”, Engineering Structures, Vol. 79, 2014, pp. 407-416.
6.
HU, N., FENG, P., and DAI, G., “The Gift from Nature: Bio-Inspired Strategy for Developing Innovative Bridges”, Journal of Bionic Engineering, Vol. 10, 2013, pp.405-414.
7.
IDELBERGER, K., The World of Footbridges, Wilhelm Ernst & Sohn Verlag für Architektur und Technische Wissenschaften GmbH, Berlin (Germany), 2011
8.
KEIL, A. Pedestrian Bridges: Ramps, Walkways, Structures, Walter De Gruyter, Berlin, 2013, 112pp.
9.
SCHLAICH, M., BROWNLIE, K., CONZETT, J., SOBRINO, J., STRASKY, J., and TAKENOUCHI, K., Guidelines for the Design of Footbridges, fib Bulletin 32, International Federation for Structural Concrete (FIB), Lausanne, Nov. 2005, 150 pp.
10. STRÁSKÝ, J., Stress Ribbon and Cablesupported Pedestrian Bridges, Thomas Telford , London, 2005 11. Structures Design Manual for Highways and Railways, Third Edition, Highways Department,
The Bridge and Structural Engineer
The Govt. of Hong Kong, Aug. 2006, 265 pp. 12. SUBRAMANIAN, N., “Aesthetics of Nonhabitat Structures”, The Bridge and Structural Engineer, Journal of ING/IABSE, Vol. 17, No.4, Dec. 1987, pp.75-100. 13. SUBRAMANIAN, N., “Can Architecture be Absurd?”, The Master Builder, Vol.16, No. 11, Nov. 2014, pp. 1-7. 14. SUBRAMANIAN. N., “Structural EngineeringAn Art or Science-Part 2?”, Structural Engineering, Quarterly Journal of Indian Society of Structural Engineers, Vo. 16, No.1, Jan-Mar. 2014, pp.3-11
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15. WAGGONER, M.C., and KESTNER, D., “Biomimicry and Structural Design: Past, Present, and Future”, ASCE Structures Congress 2010, pp. 2852-2863 16. WELLS, M., and CLASH, P., “Footbridges”, ICE Manual of Bridge Engineering, Institution of Civil Engineers, London, 2008, pp.459-484 17. en.wikipedia.org/wiki/Moveable_bridge 18. Schlaich-Bergermann Partner- www.sbp.de/en 19. www.bridgemeister.com 20. www.steelconstruction.info/Bridges#Case_ studies
Volume 45 Number 3 September 2015 41
BRIDGE AESTHETICS (Case of science taken to the level of art)
V.N. HEGGADE Sr. Vice President & Member Board of Management Gammon India Limited, Mumbai venkat.heggade@gammonindia.com
V.N. Heggade presently is Sr Vice President & Member, Board of Management of Gammon India Limited. He has more than 31 years of experience of Designing and Constructing Bridges, Energy structures like Chimneys & Cooling towers, Marine structures and Hydraulic structures etc. He is a first engineer to receive ‘IABSE-Prize’ (International Association Of Bridge & Structural Engineers, Switzerland) from developing countries in addition to National awards like Pt Jawaharlal Nehru Centenary award from IRC; Pre stressed concrete design award from Institution of Engineers, and ICI awards for best publications. He has more than 90 papers to his credit and is a member of various IRC (Indian Roads Congress) and BIS (Bureau of Indian Standards) committees. He is also a member of Indian Member Committee of Federation Internationale Du Beton, IMC fib. He has been an invited and a keynote speaker in National and International Seminars, Symposiums and Congresses. He has a passion for tall and long structures and he is an ardent advocate of sustainability and aesthetics in construction.
Summary
1. Introduction
Bridges being subjected aesthetic treatment is a recent phenomenon of perhaps since a century. There has been a fascinating debate across as to whether bridge aesthetics is an art or a science. There has been evidence of aesthetics of artifacts and art being subjected to mathematicisation in the form of Golden section rules in which the art and art forms are related an irrational ratio called ‘ɸ’ whose value is 1.618. In Indian context before Christ era (BC), the structures especially temples were built on the principles of Vastupurushamandala (Divine Square) and the art particularly music short and long syllable conformed to Fibonacci series whose limiting ratio is 1.618. Apart from this, there also have been views that in case of bridges, the mere principle of ‘Form Follows Forces’ is adequate for aesthetic elegance.
In buildings, structure is invariably hidden by finishes, claddings and other ornamentations not exposing the structural design while the bridges being devoid of such embellishments expose the structural design nakedly to beholders. It is obvious to the observers that architects are at work in buildings, camaflouging flow of forces where in bridges structural designer shapes the flow of forces in to form. The architectural approach is often to integrate the buildings into the ambience, local culture, etc. despite the demerits of the building’s structural form whereas the engineering approach to bridge design is quite often to consider a bridge as an abstract structural form independent of its ambience.
The paper discusses, the various issues including controversial ones as above relating to bridge aesthetics finally concluding that it is our moral and ethical obligation to our posterity to leave behind the memorable bridges as our predecessors left us with memorable mandirs, mahals, masjids, churches, cathedrals and castles. Key Words: Aesthetics, Creativity, Idiosyncrasy, Form Following Forces. Mathematicisation, Golden section rules.
Fig. 1: Root bridges of India
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The Architecture is arrangement of abstract and visual forms while constructing artifacts for practical, aesthetic and symbolic purposes that exist in space and which are experienced by walking through it. Architects address Functions, Forms and Structures, without necessarily giving meaningful expressions to loads, equilibrium and forces. The Aesthetics is a perception and the experience of human sensibilities as a response to overall culmination of visual form. In the literature, there is no evidence to the fact that bridges being considered for the aesthetic treatment till the middle of 18th century. Till the time of the inception of engineering establishments including military engineering establishment in Paris around 1750, bridges were considered to be structures spanning and providing passage over road, waterway or gorges and they were synonymous with either vaulting or hanging wooden passage on tensile fibers. Even now such bridges provide passages in India, popularly known as Root bridges (Fig. 1). In a sense the concept of bridge being functional and yet to be beautiful is a recent recognition of last one and half centuries. Since then the story of bridge building has become the yard stick for the progression in civilization of Nations.
our past by beautiful mandirs, (Temples) masjids (Mosques) and mahals (Palaces), our posterity should remember us by the bridges, we create. It is unthinkable to propose an argument that any engineer wants his bridge to be unpleasant and ugly. But still aesthetics that is invariably a result of creativity remains mysterious as most of the times engineers’ creativity is channelised only to achieve economy and adequacy by the specifications and codal stipulations. There is an urgent need for the rulers to create an environment to nurture and nourish the aesthetic idiosyncrasies apart from economy and mediocrity by removing impediments in contractual and codal stipulations
2.
Mathematicisation Of Aesthetics
The theory of Building Architecture and the Aesthetics associated with has been evolving since ancient times, has been subject of discussions and numerous principles and guidelines are available in manuscripts for connoisseurs. These include well known rules of ‘Golden Section’ of Greece and various subsequent attempts to produce geometric formulations in Greek for living forms and shapes.
Fig. 3: Golden rectangle, triangle, pentagon, spiral, etc. Fig. 2: Represent mind of rulers at that time.
The structures of a particular era reveal the idiosyncrasies1 (Fig. 2) of the rulers and technologists, the degree of sophistication in technology and material sciences i.e. state of the art research and finally financial health of the state at that time. The bridge building being such a serious business, which stands as a testimony of the mental state of engineers of a particular time, to the future generation, it is imperative for us to make our posterity believe that we engineering fraternity possessed healthy, aesthetically pleasant, creative minds. In India, as we reminisce The Bridge and Structural Engineer
The Golden ratio is a special number found by dividing a line into two parts so that the longer part divided by the smaller part is also equal to the whole length divided by the longer part.” What this is saying in an equation is a/b= (a+b)/a= 1.61803398874989… (Etc.). This is also referred to be as φ phi, and it is an irrational number. The ratio is represented as shown in the Fig 3. They are also known as Golden mean, Golden number, divine proportion, divine section and Golden proportion. This irrational ratio ‘φ’ (Fig 3) is a part in some or the other way in rectangle, triangle, pentagram, spiral. etc, to make them ‘divine’ section. Volume 45 Number 3 September 2015 43
An important sequence is introduced when we are talking about the golden ratio. This sequence is called the Fibonacci sequence: 0,1,1,2,3,5,8,13… Each term is the sum in the two previous terms. The more you go to the right of the sequence the ratio of two terms right next to each other it will get closer to the Golden Ratio.
Thus the golden section satisfies the relationships φ2 = φ + 1 = 2.618, φ3 = φ2 + φ = 4.236 and so on. Thus it has a mathematical threshold of equipartition, succession and continuous proportion which can give rhythm to any art and physical form.
Fig. 4 : Golden section seem to be all around in nature
When there is a mathematical elegance in the nature all around and the human psyche is used to this rhythm of this mathematical ratio, it is quite natural for humans to imbibe this very ratio in arts and artefacts (Fig 6) for aesthetic appeal. If the manmade artefacts are made to follow golden section rule in some or the other form, they can be incorporated in to nature with harmony.
This ratio is incredible as it has certain algebraic and geometric properties and is a transcendent number similar to ‘π’ (ratio of perimeter to diameter of a circle). The proportions are divisible infinitely where each subdivision retains its original proportion and is harmonically related not only to whole but to all subdivisions. For example, when a series of golden rectangles are assembled on each other and their outside corners are connected by a smooth curve as depicted in Fig 3, the culmination is a golden spiral. Luca Pacoli friend of Leonardo da Vinci called this as ‘divine proportion’ and Kepler called the ratio 1.618 as ‘one of the two jewels of geometry’ and expressed it as a positive root of x2 = x+1.
Golden ratio seem to be everywhere in the nature (Fig 4). This cannot only be seen in nature but it can be seen in everything around us. The petals, leaves, pine cones, shells and even space seem to be mysteriously conforming to Golden section rule as such our ancient European aestheticians tried to attribute even aesthetic features of human being as those features conforming to Golden section rule. These are quite obvious in some of the classical art works (Fig 5) like An Old man, The Vitruvian Man (The Man in Action), MonaRisa by Leonardo Da Vinci and Sacrament of the Last Supper, by Salvador Dali.
Fig. 6: Golden section in pyramids, temple & churches
Fig. 5: Golden section in paintings of Da Vinci and Salvador Dali
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The Ahmes Papyrus of Egypt gives an account of the building of the Great Pyramid of Giaz in 4700 B.C. with proportions according to a “sacred ratio”. The Greek sculptor Phidias sculpted many things including the bands of sculpture that run above the columns of the Parthenon. Even from the time of the Greeks, a rectangle whose sides are in the “golden proportion” has been known since it occurs naturally in some of the proportions of the Five Platonic. This rectangle is supposed to appear in many of the proportions of The Bridge and Structural Engineer
that famous ancient Greek temple in the Acropolis in Athens, Greece. The Medieval builders of churches and cathedrals approached the design of their buildings in much the same way as the Greeks. They tried to connect geometry and art. Inside as well as outside, their buildings were intricate construction based on the golden section. There is no evidence in the literature that golden section rules were consciously applied to the design of bridges. However, some of the elegant arch bridges seem to be satisfying the divine proportions.
Fig. 7: Left : Salginatobel Bridge φ 4 = 6.85, Right: Coronation bridge φ2 = 2.618
It is interesting to note that the span to rise ratio of Maillart’s famous arch bridges varied from 4.9 to 10.7 and were very close to golden section, like Stauffacher Bridge with span/rise ratio 10.7 (φ5 = 11.09), Bridge at Zuoz with span/rise ratio 10.6 (φ5 = 11.09) Schrahbach Bridge with span/rise ratio 7.2 (φ4 = 6.85), Hombach Bridge with span by rise ratio 7.0 (φ4 = 6.85) Salginatobel Bridge (Fig 7) with span by rise ratio 6.92 (φ4 = 6.85), Schwamback Bridge with span by rise ratio 6.23 (φ4 = 6.85) and Luterstalden Bridge span/rise ratio of 4.9 (φ3 = 4.236). The coronation bridge (Fig 7) at west Bengal over river Teesta despite having span to rise ratio of 2.06 which is very low for an arch bridge seem to be deriving its aesthetic appeal by golden section rule φ2 = 2.618.
houses. The testimony of the same is found in sixty chapters of Sanskrit manuscript Kamikagaria. This explains the types of architecture including Testing and Preparation of soil and Site Selection etc. In fact Manasara written in barbarous Sanskrit between 5th and 7th century AD is fairly comparable to Vitruvius of Roman architecture. The Salva Tantra and Kama Sutra of Vatsayana enumerate 64 arts including Taksanam (Carpentry), Vastuvidya (Architecture), Dhantuvidya (Metal making), Adarajnanam (Mining) and Chalitaka yogah (Illusionary art). It is interesting to note that the Greek and Gothic principles considered sculpture and painting as independent part of aesthetics while Indian aestheticians considered the same as a part of science and philosophy of fine art among drama, dance and music etc. 20th century Chambers Dictionary explains the word ‘aesthetics’ as principles of taste and art: the philosophy of fine art and gives reference to Greek word aisthetikas meaning perceptive. The Hindu philosophy was among the first to relate the human figure as the basis of a system of proportion, which was years later demonstrated by Leonardo da Vinci and by Le Corbusier in Modular system of measurement. In Hindu philosophy the form of the purasha (human) body was made to suit the abstract idea of the square, as the supreme geometric form.
Fig. 9 : Vastupurashamandala transformed into architectural plans, superstructure depicted emotions
Fig. 8 : Left : Modulur man, Right : Vastupurashamandala
In India during Rig Vedic age, the architectural concepts were highly developed pertaining to Mandirs (Temples), Mahals (Palaces & Forts) and The Bridge and Structural Engineer
The basic form of the Vastupurashamandala (Fig 8) is the square and square is the important and ideal geometric form in Hindu philosophy, which represents the earth. All the necessary forms like the triangle, hexagon, octagon and circle, etc. can be derived from the square. The four sides of the square represent the four cardinal directions. The square also Volume 45 Number 3 September 2015 45
symbolizes the order, the completeness of endless life and the perfectness of life and death. Similarly, the circle represents the universe and is considered as the perfect shape, without any beginning and end, suggesting timelessness and infinity, a typically heavenly feature. The Vastupurashamandala, having all the geometrical, astronomical and human properties was the basis of plan for Hindu temples. The basic shape acquired by the temple plan is the outer most ring of square of the mandala forms the thickness of walls of main shrine. The central 4 squares acquire the place of the main deity and the inner ring of 12 squares form the walls of the garbhagriha (shrine) and the next 16 to 28 forms the pradkshina patha (holy circling path). These simple divisions of square with many permutations and combinations became the base for the complex structures of the temple; in the form of orthogonal and
3.
Art Versus Science of Bridge Asthetics
There has been a fascinating debate for some time now as to whether bridge aesthetics is an art or science. It has been argued that Roebling’s Brooklyn, Maillart’s Salginatobel and Christian Menn’s Sunniberg bridges (Fig. 11) are classical art and that too ‘structural art’as coined by David Billington in bridge engineering. These bridges when conceived and built were “revolutionary”, “ground-breaking”, and “visionary” and indeed challenged commonly held views at that point of time. The inherent characteristic of art is to challenge the existing ideas in meaningful ways. When the time tested ways are challenged in a meaning full ways, the human sensibilities are emoted and lingers much beyond wearing off instant ‘awe’ value for the experience to be termed as artistic.
Fig. 10 : Fibonacci Series from Pingala’s Mount Meru
stellate plans of the temple. Therefore the large squares of mandala were divided into thousand squares thus virtually forming a graph paper (Fig. 9) for the architect to facilitate him to add a unit at one side and setting back on the other. The superstructure consisting of plinths, columns, walls, ceilings and crowns depicted emotional poses and events. It is quite obvious that ancient aestheticians considered fine arts including music, drama and dance as part of aesthetics but not necessarily the structures like temples. As a historical background, if one goes to Pingala’s Chandahśāstra in which while classifying poetic meters of long and short syllables, Pingala ( BC 200) presents the Mount Meru which is also known as the Pascal’s triangle (Fig. 10, left side). The shallow diagonals of the Mount Meru sum to the Fibonacci series, whose limiting ratio is the golden mean (Fig 10, right side). Thus there is historical evidence that golden section rules were in built in music and other art of India, much before the Fibonacci series were recognised. 46 Volume 45
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Fig. 11 : Roebling’s Brooklyn, Maillart’s Salginotobel & Menn’s Sunniberg
The aesthetic appeal of these bridges are also attributed to the principle called ‘Form Follows Forces’ which is a variation of ‘Form Follows Functions’ of famous architect Louis Henry Sullivan who was an architect of skyscrapers. Sullivan’s idea of ‘Form Follows Functions’ was from architectural point of view where the utilities having identical functions should be consistent in tall multistory buildings. In case of bridges ‘Form Follows Forces’ means the structural dimensioning of members just to cater for internal forces where the force flow is reflected in appearance or the form itself. Here we are dealing with statics, equilibrium, flexure, mechanical properties of materials etc., which is a scientific process. Science is a method of doing things. It “is the organized, systematic enterprise that gathers knowledge about the world and condenses the knowledge into testable The Bridge and Structural Engineer
laws and principles” There are five ‘diagnostic features’. The first is the repeatability of research results, preferably by independent investigators. The second is a reporting of research as simply and elegantly as possible. Third, scientific findings are subject to universally accepted and unambiguous scales of measurement. Fourth, scientific research stimulates new learning and new knowledge. And finally, science is consistent. Research results can be connected and proved consilient with one another. Thus, there seem to be merit in both the arguments that bridge aesthetics is an art as well as science. While the artistic and scientific activities are different, there seem to be some commonalities in both the activities such as:
Both are creative process and have the element of synthetic thinking and generation of ideas in the process.
‘Visual thinking’ & ‘visualizing imagined worlds’ are the essential part of art as well as science.
Both share sensitivity to aesthetics, although their criteria for ‘beauty’ may be quite different.
and not influenced by personal feelings or opinions in considering and representing facts. It is very objective being completely detached and impartial. Gold’s representation of the ‘four hats of creation’ (redrawn in Fig 12) is very useful in understanding the bridge aesthetics vis-à-vis science and art. The upper half represents the ‘search for truth’ whereas lower half represents ‘problem solving’. Left half represents the strength of drawing skills, sketching and imagining visual world on the basis of strong observation of nature. The right half represents the strength in mathematical ability. As we can see in the Fig12, Salginatobel Bridge follows the principle of ‘Form Follows Forces’ which gives the efficiency and economy of the bridge. The design and construction of any bridge including engineering has to be a scientific process whether bad or good which is a truth (Reality). But the other truth is that the design and engineering, efficiency of the structure by ‘Form Follows Forces’ alone can’t render the artistic elegance to the bridge. There has to some qualitative and subjective attributes to ‘take the science to the level art’.
Artists as well as scientists are generally averse to social interactions; they prefer to toil in their laboratories or studios. The labour and inspiration of science as well as art depends largely on nature and natural world.
It is not surprising that the notable figures like Leonardo da Vinci, Galileo, and Michelangelo who contributed during Renaissance period were artists as well as scientists. Throughout the Renaissance, art and science continued to develop and interact. In particular, the seventeenth century represented a time and place where scientific inquiry became so pervasive that science and art were inseparable. Art as well as science is a creative process culminating in truth (Reality) and the process involves idea generation and idea validation. In artistic settings, the first step is a value in itself and validation is not that essential. In contrast to Science, Art (like Beauty) is in the eye of the beholder and it is accepted that works of art will receive subjective interpretation. Scientific creativity has to be in a system of domain consisting of rules and procedures like mathematics, theorems, and laws (For example Hooke’s law) etc. The Bridge and Structural Engineer
Fig. 12 : ‘Four hats of creation’ by r Gold (redrawn)
4.
Bridge Aesthetics In India
Though there are enough examples of monumental structures like Tajmahal, Temples, Palaces, Forts, Churches and Mosques in India, there is no evidence of subjecting bridges to aesthetic treatments consciously in India. Prior to independence in1947, may be hundreds of bridges were built in timber and stone with a very small spans merely for the purpose of crossing the rivers. Bridge building activities increased seriously only after the independence, though sporadically British built some long span railway bridges in structural steel here and there. Even after the independence, if at all some long span Volume 45 Number 3 September 2015 47
bridges are looking elegant and aesthetically pleasing, it is only because they are designed to structural efficiency and economy, accidentally (not by intent) conforming to the principle of ‘Form Follows Forces’. Few of the aesthetically appealing bridges are analysed below for their qualitative aesthetic attributes. 4.1 Arch bridges Most of the long span bridges constructed in India up to 1950’s was of arch types, either of spandrel type arch, semi-through arch or tied arch (bow-string girders). This is author’s strong intuition that the arch bridges are most sustainable bridges as majority of the structural components in arch are axial members where the flexure is minimum. Among them the Coronation Bridge, an open spandrel arch, which is constructed in 1941 across Teesta River, Northern Bengal, deserves the special recognition. The arch span of 81.71 m with the unusual central rise of 39.63 m was constructed by suspended shuttering staying from temporary tower at the location adjacent to springing point. This durable, elegant structure has visual appeal because of its shape and also containment in the river valley with high bluff. The visual impact is accentuated by rise to span ratio conforming to golden section rule, apart from blending with the environment. The visual success can also be attributed to the fact that the arch element, spandrel columns and deck beams are dimensioned to the principle of Form Follow Forces. The main columns at the springing location enhance the containment effect. The entire structure has an artistic elegance.
45.12 m span each. The bowstrings are realized by vertical mild steel hangers. The visual impact is achieved by continuous slender tie-chord from abutment to abutment and also a smooth integration of side spans with the abutments. The key to good appearance in the bowstring girder bridge is the graceful overall shape, the minimum variety of members, simple and attractive connection details, judicious choice of materials such as concrete for arch to take compression, mild steel for hangers to take tensions and masonry pier which is predominantly subjected to vertical force. Sometimes, it is not possible to support the deck by spandrel, as in the case of Mand bridge constructed in 1946, which has a main span of 50.0 m supporting the deck at around mid rise level by hanging stringers, that can be classified as ‘semi through’ or ‘half through’ arch bridge. The latest in the family is the true arch bridge in India on NH-21 across river Beas at Ramshilla. The national highway leading to the most popular hill station Manali in Himachal Pradesh passes through congested Kullu town. The Ramshilla Bridge has a span to rise ratio of 5.7 for the arch span of 100 m. Perhaps, the aesthetic appeal of the bridge could have been accentuated by avoiding the arch being skewed to the direction of the flow of the river as well as by bringing the span to rise ratio closer to golden section rule φ4 = 6.85. 4.2 Integral & submersible bridges During 1930’s to 50’s, multi framed submersible bridges were constructed in India and functionally warranted very slender aerodynamically shaped deck as well as pier sections. These days the similar portal framed structures are being adopted for flyovers and is now called integral bridges. The Indrāvati Bridge in Orissa (Fig14) constructed in
Fig. 13 : Coronation, Ramshilla, Mand & Alwaye
The Alwaye Bridge of 1941, which is constructed across Periyar in kerala, has three tied arches with 48 Volume 45
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Fig. 14 : Top : Indrani bridge, Bottom : Krishna bridge
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1942 is idealized with piers and deck rigidly connected on continuous frames. Though the idealization requires shorter spans, the horizontal clearance is larger than the vertical clearance from aesthetic consideration. The span-by-span construction was introduced in India in 1970 for Krishna Bridge (Fig14) in Karnataka. The 540 m long submersible bridge having 18 spans of 30 m each with six spans continuity for live and superimposed loading actions was called semicontinuous bridge at that time. The superstructure was of 3-cell trapezoidal box section on Teflon bearing over solid elliptical piers. The pre cast box segments were match cast in casting yard (vertically), transported to the location and laid in position, glued by epoxy mortar. The entire span being supported by staging and temporary bearing was pre stressed and the span was made self sufficient for dead load. The continuity pier unit over the permanent bearing was cast-in-situ and the pre stressing was carried out progressively from the front end of construction. The aerodynamic shape of the deck, continuity in the lines of deck slab, the matching of thickness of pier elements to that of deck slab elements, the flaring up of pier at the junction of pier top and deck slab to reflect the stress concentration can be attributed to the visual appeal of these submersible integral bridges. 4.3 PSC box girder bridges & flyovers Since the experiment of span by span construction using precast segmental technology for Krishna Bridge at Deodurg in 1970, many bridges & flyovers have been constructed across the country. Among them (Fig 15), Punjagutta flyover at Hyderabad, JJ hospital flyover in Mumbai, Hebbal flyover at Bengaluru & Lajpatnagar flyover at Delhi are recognised for their aesthetic appeal. Two and half Km long J.J. hospital flyover has aesthetic rendering by its geometry, superstructure shape including parapet & railing, pier shape, etc. The geometry of the flyover is just matching with the existing road surface. The fish-belly central spine of the superstructure is flanked on either side by ribs .While the central fish-belly spine represents the strength, the side arm ribs reflect the characteristics of the stress flow and are not hidden. The geometry of the roadway being serpentine in plan, the selection The Bridge and Structural Engineer
and the construction type of the above superstructure offers an overriding simplicity.
Fig. 15 : Box girder PSC bridges & flyovers
The height of the piers is judiciously proportioned and, though the pier is of significantly different heights, all are accommodated within the same family of shapes. The fluted piers are flared up at top to accommodate the bearings. There is a continuity of the outer lines of the piers with that of the curve of the fish-belly and the flaring up of the piers eliminates the pier cap. The pier cap neither belongs to super structure nor to substructure and harmonizing of the same with the both is a Herculean task as such avoided. Especially, where the height of the piers varies from obligatory spans to abutment, it is a challenge to choose a pier shape to accommodate them into same family. The aesthetic appeal of JJ hospital flyover is enhanced by texturing (Fig15, right top) of piers and superstructure. Texture is found on the surface of all objects and is closely related to form. Texture helps define form through subtle surface variations and shadings. It can be used to soften or reduce imposing scale, add visual interest, and to introduce human scale to large objects such as piers, abutments, and retaining walls. Distance and motion alters the perception of texture. When viewed from a distance or at high speeds, fine textures blend into a single tone and appear flat. 4.4 Girder slab bridges Pre cast girder slab construction in urban environment for the flyovers to suit the fast track construction is most conducive. To make this kind of economical construction aesthetically acceptable is a challenge in itself. Invariably, the flyovers in urban area have larger obligatory spans compared to adjacent approach spans Volume 45 Number 3 September 2015  49
and in the river bridges the navigational spans decide the span lengths for slab girder system construction.
integrated with the longitudinal girders thereby establishing continuity on top of pier being supported by bearings. As can be seen from Fig. 17 (Top left), the continuity established by girder integrated by cross diaphragms renders an appearance of longer superstructure, taller pier and lighter deck. In the flyover, especially for the wide decks, the selection of pier shapes plays a vital role in the visual impression. It is always a challenge to accommodate same family of piers for varying height giving slender appearance. The common attributes of good-looking piers are:
Fig. 16 : Aesthetics of slab superstructure
In the design of the slab girder system, the aesthetic goals are achieved by slenderness, continuity in lines and apparent lightness by shaping the various structural elements akin to flow of forces. The aesthetic appeal of Vashi-CMLR flyovers (Fig 16, top left) in Mumbai is achieved by judicious proportioning of various structural elements. It is a myth that by hiding the bearings either at the location of abutments or at the location of piers, the visual appeal is augmented. As can be seen from the photograph, if the ears were avoided on the pier cap (with an intention of hiding the bearings), the exposure of the bearings on the slightly elevated pedestals would have made the superstructure look lighter, thinner and continuous thereby further enhancing the aesthetics. What people perceive is not always what is there. Our vision is susceptible to manipulation and illusion (Fig. 16, bottom left). Designers can use illusion to improve the appearance of an element. For example, placing a series of vertical grooves on a column will make it appear thinner. By not providing the ears to hide the bearings, the continuous line would not have been broken and rendered the illusion of deck being slimmer and longer. However, the parapet and the end girder with the overhang larger than the depth of the end girder, causing the shadow on the girder are visually prominent features of this flyover.
(a) The pier caps are as small as functionally possible or otherwise eliminated. (b) Shape is in harmony with girders and parapet. (c) The bearings are not hidden but made conspicuous and deeper not wider, to distinguish between substructure and superstructure rendering the appearance of lightness and slenderness to superstructure. (d) Multiple columns piers are avoided and the patterns are simple and large. (e) The grooves, curves and flutes make the piers look thinner. (f) For the haunched/curved belly superstructure, piers are flared up at top, highlighting the strength. The abutment joins the bridge to the roadway in bridges and brings the bridge from higher elevation to the ground level in case of flyovers. The selection of the height of the abutment in relation to the pier heights (Fig. 16 bottom right) decides the visual impact of the overall bridge. Aesthetic appearance is enhanced by provision of shorter abutments compared to the pier heights both in bridges and flyovers. In fact, though
Though the length of the obligatory span is more than the approach spans, it is imperative to keep the depth of superstructure same throughout or continue the lines by gradually varying depth to make the structure look unified, longer and thinner. In some cases, even for flyovers, the pier caps can be eliminated by provision of the cross diaphragm 50  Volume 45
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Fig. 17 : Continuity of ‘Line’ & Balance
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fact, though people insist for hiding the bearings supported on abutment shaft, it doesn’t help in making the superstructure look longer. When the abutment shaft is distinct from return walls, by reducing the thickness of the shaft to half of the girder depth, the bridge looks slimmer. Choosing a color scheme and landscaping for bridges and flyovers has not yet gained momentum in India. The judicious choice of color scheme to merge with the surroundings can be seen in recently constructed New Mattancherry Bridge (Fig 16, top right) at Cochin. It can be observed that the colors are used to distinguish the structural elements and the variety in colors is minimal. Normally the brighter colors like red, blue, green and orange are preferred to lighter colors. Sometimes the colors can be picked to create contrast against background to make the structure very conspicuous. The colors are never used to obscure the functionality of an element but can be used to emphasize the shape. Colours are perceived differently at different times of the day and at different times of the year because of the changes in light conditions created by changes in sun position and atmospheric conditions Another important feature of the Mattancherry Bridge is the landscaping of the approach protection. The elegance of the bridge can be further enhanced by plantation of greeneries on the bank protection. Visual balance (Fig. 17 top right & bottom) which is the perceived equilibrium of design elements around an axis or focal point is very important for aesthetic rendering. Rather than a physical balance, it may refer to equilibrium of abstract elements of design, such as masses, visual weights or texture.
Fig. 18 : Cast in situ balanced cantilever construction
Barak Bridge at Silchar (Fig: 18, top left), built in 1961 was first of this kind constructed by cantilever castin-situ segmental construction method in India. The foundation meant for originally envisaged suspension bridge was utilized. The bridge has a clear span of 122.0 m with a mid-span pendulum hinge. The twin piers, monolithic with the spans are slender. The slenderness of the main piers and the high stiffness of the approach piers accentuate the functionality reflecting the force flows. The elimination of the pier caps for the main spans brings harmony between superstructure and substructure while the provision of crest vertical curve renders slightly an appearance of arch. There after many bridges like Zuari at Goa, Bassien Creek Bridge, Gourang Setu, Balason Bridge at Darjeeling and so many others were constructed with this principle. The 290 m long Balson Bridge at Darjeeling (Fig. 18, bottom left) is one such bridge with the continuous system having central span of 130 m and two shore spans. Situated among the scenic surrounding, Balason is one of the most aesthetically beautiful bridges. The elegance of the bridge is enhanced by the piers, which are unusually slender, perfectly blends with the ambience.
4.5 Cantilever construction For rivers and strait crossings, also to bridge the gaps of the ravines and gorges and creeks, long span bridges are called for to overcome the foundation problems and to provide navigational clearance, etc. The picturesque surrounding of these locations naturally provides an excellent back ground for long span bridges. The Bridge and Structural Engineer
Fig. 19: Top : Free cantilever cast in situ, Bottom : Precast segmental
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Lubha Bridge of 1961 was the first continuous bridge constructed by cantilever Construction method, having central span of 130.0 m flanked by adjoining 21.0 m anchor spans progressed into rock mass and counterweighted by roller bearing at the top against the rock mass. The Jadukata Bridge (Fig. 19, top left) with the central span of 140.0 m, the longest span in the country when conceived and constructed, was necessitated as the river flowing in the deep gorge with the fissured zones at the banks neither allowed the conception of arch to take the thrust nor the provision of piers in between. The central span being constructed by cantilever in-situ segmental method has adjoining spans of 36.5 m progressed into the tunnels and counterweighted by concrete mass filled inside the adjoining spans. After having gained experience in cast-in-situ segmental cantilever construction for long span bridges, the next evolutionary step was to introduce pre cast segmental cantilever construction for the bridges with many spans. The Buxar Bridge (Fig. 19, bottom right) across Ganges in 1977 was the first bridge in India to adopt this technology. This bridge had 10 spans of 101 m and was followed by Narmada Bridge at Zadeshwar with 13 spans of 96.0 m. 5575 m long Ganga Bridge at Patna (Fig. 19, bottom left) with 45 numbers of 121.05 m span made up of 3.0 m segments match cast by short line method at casting yard is the longest river bridge constructed in the country using pre cast segmental construction method.
mid span is long enough with the parabolic curve akin to the moment diagram.
Reduction in depth from root towards midspan is not formed with straight line as the sharp break makes the haunch look short. Also when the bearings are provided on top of the pier cap, the same is placed on pedestals and higher, making the deck look lighter. Near the abutments, the ground merges with the roadway and the height of the abutment is much lesser than that of piers. At the mid length of the bridge crest vertical curve is provided to give an appearance of arch.
4.6 Cable supported bridges Whenever the signature bridges are envisaged, it is quite common to think of suspension or cable stay bridges. The Akkar Bridge (Fig: 20, top left) over river Rangeet in Sikkim was the first concrete cablestayed bridge constructed in India. The continuous deck of 158.0 m on either side of 57.5 m tall pylon is suspended freely from the pylon which has two concrete box legs on either side of 7.5 m wide carriageway being connected at top by cross tie between cable anchor heads.
Some aspects of transparency of these cantilever bridges reveal some common aesthetic attributes.
The span length to vertical clearance from low water level to soffit are as large as possible, yielding the maximum frame area under the span to view the scenic landscape or view through the bridge. The shape of the structural elements perfectly reflects the stress levels and emphasize on functionality, perhaps following the principle of ‘Form Follows Forces’. The lines are continuous without break and either the pier caps are eliminated or just enough to accommodate bearings, harmonizing the superstructure with substructure. The depth of the girder at the root is generally larger and the gradual reduction in depth towards
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Fig. 20 : Cable stay bridges of India
Each and every structural element of the cable stayed bridges such as cables, deck system, pylon and merging of the deck with abutment is lighter, slender, and simple and expresses the functionality and force level in a pronounced manner, which are obviously the reasons of aesthetic appeal epitomized for this family of bridges. Therefore it is averred that ‘there must be an inherent beauty in cable stayed bridges that despite the best efforts, it is difficult to make cable stay bridges ugly’. The Bridge and Structural Engineer
to ship or a plane and once again testimony of aestheticians’ quest for incorporating the structures in to nature. The cable stay bridges by its inherent nature follows the principles of ‘Form Follows Forces’ but also provides opportunity to apply the principles of golden section rules involving golden rectangle, triangle, spiral and phi.
Fig. 21 : Bridges in motion
852.96 m long Second Hoogly Bridge or Vidyasagar Setu (Fig: 20, top right) at Kolkata with cable stay spans of 457.20 m, supported on two identical pylons with adjacent stayed spans of 183.0 m provides a clear navigational height of 34.0 m under HFL conditions. In fact, when it was conceived it was the longest span cable Stay Bridge in the world. Analogous to any cable supported bridges, the identical pylons, minimum variety in shape and size of structural elements etc are the hallmarks of its aesthetic appeal. Logically it is inconceivable to imagine a cable-supported bridge not to be elegant. The recent Bandra Worli cable stay bridge in Mumbai designed by S Srinivasan (Fig. 20, bottom left) is a gift to the city where the main pylons symbolically greet the guests in a traditional Indian pose “Namaste”. Srinivasan has not only enhanced the aesthetic appeal of this bridge with his trademark texturing but also harmonised approach span deck with cable stay span decks by adopting the same cross section. The Signature Bridge at Delhi (Fig. 20, bottom right) which is under construction created by Schlaich (Jorg & Mike) is one of its kind in the world and a bridge in motion. Santiago Calatrava, an architect cum sculptor cum engineer is a master of structures in motion (Fig. 21). These bridges appear to be floating or sailing akin
The inventor of extradosed bridge, a variation of cable supported bridge, Christian Menn has demonstrated that the bridge design could be a structural art through his breath taking Sunniberg Bridge. Even in India many extradosed bridges are constructed in the recent
Fig. 23 : Extradosed principle opened up numerous aesthetic options
past like, Indraprastha, Moolchand and Siddapura bridges to name a few. In Indian extradosed bridges a special attention to aesthetics are found to be wanting (Fig. 22). This variation of cable supported bridges provides numerous opportunities (Fig. 23) to the designer to enhance the aesthetics of bridges where designer can adjust the height of pylons to suit golden section rules, can shape & incline the pylons to express the local symbolisms, can sway outwards to give an impression of welcoming arms, etc.
5. Conclusions The above illustrations explain numerous common characteristics for bridges to be good looking, such as: 1.
Most of them are first time in the country and hence bold expressions in concrete.
2. Invariably, the aesthetics are complimented by creative and innovative process. 3. The structural elements are simpler and less in variety, viz for the same function, elements has same size and shape. Fig. 22 : Extradosed bridges of India
The Bridge and Structural Engineer
4.
The elements are made to look slender, longer, and lighter and unified in concept. Volume 45 Number 3 September 2015 53
5. The lines are continuous without any abrupt jumps. 6. The structural elements performing different functions are emphasized in its functionality without hiding, for example, hiding bearings make the superstructure look thicker. 7.
The structural elements are shaped to reflect the force flow in them following the principles ‘Form Follows Forces’ .
8. There is a certain pattern or a relationship between the following elements or as a whole which may be accidentally following golden section rules incorporating the bridge in to nature and surroundings :
a. Height of the pier to span length.
b. Width of the pier to span length.
c. Overhang of the slab to girder depth
d. Height of the abutments to pier height
e. Depth of the girder to span length
f. Height of the pylon above formation level to span length in case of cable supported bridges.
g. Height of the crown from foundation top level to span length in case of arch bridges.
9. A slight mid-length vertical curve giving an appearance of arch, which is always pleasant. Bridge Aesthetics is neither the external ornamentations, embellishments nor the building architecture and can be stated with confidence that the aesthetics and creativity have to compliment each other in the art and science of Bridge engineering. Though there can be no definite regulations for satisfying aesthetics as the adage goes ‘Beauty lies in beholders eyes’, the beholders can be saved from witnessing mediocrities by observing certain minimum criteria as laid down in the illustrations above. The bridges of an era reveal the idiosyncrasies of the time in terms of the degree of sophistication in technology, material sciences, state of the art research and finally financial health of the state at that time. In fact, the bridge building reveals the state of the nation’s progress and civilization of a particular era. The great Mandirs (Temples), Mahals (Palaces 54 Volume 45
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& forts) and Masjids (Mosques) in India, Churches, Cathedrals and Castles elsewhere not only give insights to the mental makeup of the rulers but also help us in understanding the degree of religiosity and civilization of the century. Inarguably no engineer predilects his creation to be ugly. Still, in the recent past we witness accelerated growth of fast conceived, hastily churned out in masses, so called fast tracked eyesores particularly in Indian context all around. Do we need our posterity to remember us by these artifacts?
References 1. 2. 3.
4.
5.
6. 7. 8.
9.
10.
11.
Fritz Leonhardt, Bridges-Aesthetics and Design, Publication DVA, 1982. Golden Section in Art and Architecture, (http:// www.camosun.bc.ca/~jbritton/goldslide/). J.H. Cartwright, D.L. Gonzales, O. Pero, and D. Stanzial, “Aesthetics, dynamics, and musical scales: a golden connection.” J. New Music Research 31, 51-68, 2002. Kak, S. “Space and Cosmology in Hindu Temple.” Vaastu Kaushal: International Symposium on Science and Technology in Ancient Indian Monuments. New Delhi, November 16-17, 2002.http://www.ece.lsu.edu/ kak/Time 2.pdf. Michell, G. 1988. The Hindu Temple: An Introduction to its Meaning and Forms. Chicago and London: The University of Chicago Press. Sullivan, Louis. Kindergarten Chats. New York: Wittenborn, Schultz, Inc., 1947 Billington, David P. The Tower and the Bridge. New York: Basic Books, 1983. R. Gold. The Plenitude: Creativity, Innovation, and Making Stuff. MIT Press, Cambridge, Mass., 2007. Andrew J Tapping, The Salginatobel bridge, Bridge Engineering 2 Conference 2007 04 May 2007, University of Bath, Bath, UK Gottemoeller, Frederick. Bridgescape: The Art of Designing Bridges. New York: John Wiley & Sons, 1998. V N Heggade “Bridge aesthetics-Some issues”, 3rd International fib Congress 2010, Think Globally & Build Locally, May 29-June 02, 2010, Washington. D.C.
The Bridge and Structural Engineer
Incorporating Aesthetics in Bridge Design
Frederick GOTTEMOELLER PE, AIA Principal Bridgescape, LLC fred.gottemoeller@bridgescape.net
Frederick Gottemoeller received bachelor degrees in architecture in 1963 and engineering in 1965 and a masters degree in architecture in 1965, all from Carnegie Mellon University, Pittsburgh. Early in his career he served on a number of multidisciplinary teams designing major transportation projects. During this period he earned licenses as a registered architect and as a professional engineer. He then spent 14 years with the Maryland Department of Transportation, including 5 years as Deputy Administrator of the State Highway Administration. For the last 22 years he has consulted on the aesthetics of approximately 30 major bridges including bridges over the Mississippi, the Missouri, the Ohio, the Niagara and the Colorado, two National Wild and Scenic Rivers in the US and a World Heritage Site in Canada, the Cataraqui River and Rideau Canal. Bridgescape, his book on bridge aesthetics, is a familiar reference for many bridge designers.
Summary Building on the ideas presented in the previous paper, The Engineer’s Responsibility for Aesthetics, this paper presents a practical approach to achieving aesthetic quality in bridge design, using the Conceptual Engineering Study as the foundation. The paper then presents in priority order the ten building blocks of aesthetic quality, and ends with a Case Study illustrating the application of these ideas.
1.
Engineering Aesthetics
If civil works are to become works of art, engineers can’t just worry about the structure and leave the appearance to someone else. If a decision affects the size, shape, color or surface texture of a visible part of the bridge, it affects how people will feel about the bridge. The shapes and sizes of the structural members themselves dominate people’s impressions of a bridge. They are the largest elements of the bridge, therefore the first elements people see as they approach and the most strongly remembered. It is impossible to correct the appearance of a poorly proportioned or detailed structure by the application of “aesthetic treatments” involving color, texture or ornamentation, though many have tried. Since they control the shapes and sizes of the structural components, engineers are ultimately responsible for the appearance of their structures. Thus, to meet their obligations as professionals, engineers must respond to the public’s concern about aesthetic quality. For the same reason engineers would not build a bridge that is unsafe, they should not build one that is ugly. All The Bridge and Structural Engineer
engineers are accustomed to dealing with issues of performance, efficiency and cost. Now, they must also deal with issues of appearance. In fact, this is something that the most accomplished engineers have always done. 1.1 Basic Building Blocks: The Ten Determinants of Appearance How people react to an object depends on what they see and the order in which they see it. This means the largest parts of the bridge – the superstructure, piers and abutments – have the greatest impact. Surface characteristics (color/texture) come next, then details. This underlies the idea of a hierarchy of aesthetic design. With this hierarchy in mind, design decisions should be approached in the following order of importance. 1.
Horizontal and Vertical Geometry
2.
Superstructure Type
3.
Pier/Support Placement and Span Arrangements
4.
Abutment Placement and Height
5. Superstructure Shape overhangs and railings) 6.
Pier Shape
7.
Abutment Shape
(including
parapets,
8. Color 9.
Texture, Ornamentation and Details
10. Lighting, Signing and Landscaping It is the last five elements that are usually considered the “aesthetic” elements, but they are the least important in determining the final result. The
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aesthetic impact of the first five elements must be considered from the very beginning, or the resulting bridge will be a disappointment. The following three sections summarize practical ideas for developing an aesthetically successful bridge. The last section is a case study illustrating the successful application of these ideas to a medium sized urban bridge.
2. The Foundation: Engineering Study
the
Conceptual
Conceptual Engineering should be the stage when all of the plausible options, and some not so plausible, are considered. Thus the engineer’s first job is to question all limiting assumptions and beliefs. From that questioning will come the open mind that is necessary to develop a vision of what each structure can be at its best. Unless such questioning is the starting point, it is unlikely that the most promising ideas will ever appear.
2.1 Understanding the Goals and the Site Owner Requirements These requirements begin, of course, with the transportation goals that must be met. These include the widths and design speeds of the roadways being carried or traversed, what types of traffic will the bridge be expected to carry or traverse, and whether that includes pedestrians and/or transit. Among other things, these requirements will determine clearance envelopes the bridge must provide.
Before a designer can start on the bridge itself, he or she must understand what the bridge is expected to accomplish, functionally as part of a transportation system and socially, visually and symbolically as part of a living community and environment. The designer must have an idea of all of the criteria that the structure must meet and all of the concerns that will act on the structure. All of these factors are summarized in a Design Intention, a concise statement of what the goals of the project are. In recent years, many transportation agencies have recognized that this is a broad task, requiring the recognition of many often competing interests. In the United States this process has been given the name Context Sensitive Design. Then multiple options are developed addressing the goals. At this stage it is important to include affected communities in generating the options included and to consider unconventional possibilities. The options are then examined at a rough level of precision, with consideration of the design intention, various materials, size and forms for the major members, constructability, project cost, life cycle economics and appearance. The most promising ideas are then taken to greater levels of refinement. Solutions will emerge that fit the requirements of the site and that are roughly equivalent in terms of structural efficiency and economics. The form of the bridge can then be selected based on which of these solution best appeals to the aesthetic sensibilities of the designer, the owner and the public. 56  Volume 45
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Fig. 1: Community uses under a bridge may be as important as transportation uses. 17th Street Causeway, Ft. Lauderdale, Florida.
The owner may have conducted or be bound by a previous feasibility study, Environmental Assessment, Environmental Impact Study or other document, or there may be a formal project purpose and need statement that defines what the intended result of the project is. Other owner requirements will include design standards and policies, including in many cases existing aesthetic design guidelines. Finally, the owner may have established cost limitations that have to be considered. The Bridge and Structural Engineer
Community and Requirements
Other
Stakeholder
Potential stakeholders include communities, elected officials, businesses, public review agencies and the people that will live with the bridge after it is constructed. They may have requirements, including non-transportation requirements that must be considered. All concerned parties should be involved from the very beginning, before putting pencil to paper. The process will run more smoothly, the final result will address the most strongly held desires of the community and it will meet with their approval.
and the context within in which it will be judged. A rural site will have a background of natural features; an urban site will have a background of adjacent buildings and bridges with their own architectural features.
Fig. 4: Genesee Mountain Interchange, I-70, Colorado. As motorists travel west from Denver on I-70 this bridge frames their first view of the Rocky Mountain Peaks along the Continental Divide.
Fig. 2: Nearby land uses must be considered. Clearwater Memorial Causeway, Clearwater, Florida.
The Site The obvious concerns are the physical features. Bridges over canyons or deep cuts will require a structural type that may be inappropriate for a highway crossing. Rivers have a certain width that must be crossed. Geology may favor a certain type of foundation or substructure layout.
Fig. 3: Rock foundations permit arch bridges. Christian Menn’s Reichenau Bridge, Switzerland. In this type of site the visual relationship of the bridge form to the sides of the canyon/valley will likely define the aesthetic impact
Aesthetically, the site establishes the visual field or background against which the bridge will be seen The Bridge and Structural Engineer
How all of this looks will be affected by the daily movement of the sun and the change of seasons. The viewpoints and areas from which the bridge will be seen and by whom need to be understood and, in many case prioritized. It is not always possible to make a bridge look good from all angles. If the bridge is part of a larger project, an interchange or corridor, where multiple structures will be seen at the same time, the relationships between them need to be considered. The best way to understand the visual field is to go to the site at different times of day, at night and in as many different seasons as possible, and take lots of photos. For both aesthetic and technical reasons, there is no substitute for first-hand familiarity with the bridge site.
Fig. 5: Albuquerque’s Big I interchange has a theme covering pier shapes, MSE walls, standard details and colors, the latter developed with community input, which reduces the visual cacophony that results when bridges with different forms and details are seen together.
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2.2 Developing a Design Intention A Design Intention is usually defined by a written list of all of the factors that will influence the design of the bridge in their order of importance. The designer should solicit comments from all involved parties, make appropriate revisions, and then get it approved by the owner. This will be the basis of all future design work. This step may have already been taken as part of an Environmental Impact Statement or planning study, which often result in a “purpose and need statement” or similar document. However, such statements need to be carefully reviewed to insure that they fully incorporate all of the bridge design issues and that no important component is missing. 2.3 Developing and Evaluating Multiple Options Communities and review agencies will have opinions about what types of bridges are appropriate. Testing their ideas in the Conceptual Engineering phase will avoid the need to go back and look at their options later when they object that their ideas are not being considered. It will also encourage their support of the final decision. It may even result in the adoption of a superior but previously unconsidered bridge type. It is important to make sure all involved stakeholders know all of the implications of the alternatives, including comparative costs. Knowing all of the facts, they will be more likely to support the final decision. Finally, it is critical to test promising options with three dimensional views taken from the important viewpoints. Even seasoned design professionals have
a hard time anticipating all of the visual implications of a design from two dimensional engineering drawings. For non-professionals it is almost impossible. Showing three dimensional views of a planned bridge gives all participants a common image of each option on which to base their opinions. If everybody is picturing the same bridge in their minds’ eye, it Is much easier to come to a consensus. With the current availability of economical, computer generated digital images there is no longer any excuse for avoiding this step. Once the options have been developed, analyzed and presented they can be evaluated based on Efficiency, Economy and Elegance. Only by applying all three criteria to multiple alternatives can the process narrow down to the concept that best satisfies meets all of the requirements. 2.4 Summarize the Conceptual Engineering Study and Proceed to Design In order to have a basis for subsequent design a formal report is needed to record the results of the Conceptual Engineering Study, the commitments made to stakeholders and all the reasons that underlie them. In the United States this report is often referred to as the Type, Size and Location report.
3.
The Five Most Important Building Blocks
The best way to develop the aesthetics of a bridge is to start with the most important elements first. Get them right, and the lesser elements will be easy to fit in, insuring that the final result will be a bridge to be proud of. 3.1 Horizontal and Vertical Geometry
Fig. 6: A photo simulation showing how a proposed bridge will affect an existing recreational lake and nearby commercial strip. Sail-like features at the abutments mark the beginning of the bridge and the entrance to the communities on either side. Proposed Ken Burns Bridge over Lake Quinsigamond, Worchester, Massachusetts.
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Before there is a concept for a bridge, the roadway geometry creates a ribbon in space that in itself can be either attractive or unattractive. The geometry establishes the basic lines of the structure, to which all else must react. A graceful geometry will go a long way toward fostering a successful bridge, while an awkward or kinked geometry will be very difficult to overcome. The structural engineer must work interactively with the project’s highway engineers during development of the project geometry. A proactive approach is highly recommended since it is extremely difficult to change the project geometry during later stages. The flaws that often appear are horizontal and vertical curves that are too short or The Bridge and Structural Engineer
that are not coordinated with each other. Both flaws give the bridge a kinked appearance. As a general rule curves on a high speed roadways should be on the order of 1000’ in length. Shorter bridges or low speed bridges look best when the curve is at least as long as the bridge. For similar reasons horizontal and vertical curves should be coordinated. Either they should not overlap or they should overlap completely, i.e., they should be coterminous.
bicycle or recreational trails the underside of the bridge will be seen as a ceiling due to the slow speed and close proximity of the observers. Its appearance will be important to how the aesthetic quality of the bridge is perceived.
This is a topic that particularly benefits from computerized 3D studies, especially if the geometry can be overlaid on the topography through photos or digital terrain models. 3.2 Superstructure Type The superstructure type refers to the structural system used to support the bridge. It can be an arch, girder, rigid frame, truss or cable-supported type structure. Because of their size and prominence, the most memorable aspect of the structure will be provided by its structural members. The most important principles to keep in mind are:
Generally, thinner structures with longer spans are more visually transparent and pleasing than deeper structures or structures with shorter spans. See Fig. 4. The bridge will be more memorable if the superstructure is shaped to respond to the forces on it, so that the bridge visually demonstrates how it works. For example, haunched girders demonstrate the concentration of forces and moments over the piers. They also reduce the midspan structure depth and provide a more visually interesting opening beneath the structure. The use of different structure types over the length of a bridge should be avoided as it usually interrupts the visual line created by the superstructure and is contrary to developing a sense of unity and integrity. If different structural types are unavoidable then a common parapet profile or other feature needs to be found to tie them together. It is preferable to change girder depth gradually by tapering or not change depths at all for the entire bridge length and not change girder depths based on the length of each individual span. For bridges over civic spaces and pedestrian/
The Bridge and Structural Engineer
Fig. 7: The haunch gives this girder a more interesting and attractive shape that also tells a story about the flow of moments and forces in the structure. The stiffener is utilitarian but its placement and curvature make it ornamental as well, so that it reinforces the story told by the haunch. I-81, Virginia.
3.3 Pier Placement and Span Arrangements Most bridges are linear frameworks of relatively slender columns and girders. A bridge viewed from its side will appear as a transparent silhouette, A bridge viewed looking along its length will appear to be a collection of massive structural forms. Pier placement will largely determine how attractive these views are. The success of the visual relationship between the structure and its surrounding topography will depend heavily on the apparent logic of the pier placement. For example, a pier placed at the deepest point in a valley will seem unnecessarily tall. A pier placed in the water near the shore will seem less logical than one placed on the shore.
Fig. 8: The substructure for this high level crossing with slender piers is virtually transparent. Meadows Parkway over Plum Creek, Castle Rock, Colorado.
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Pier placement establishes not only the points at which the structure contacts the topography but also the size and shape of the openings framed by the piers and superstructure. It is desirable to keep constant the height/span ratio of these openings. 3.4 Abutment Placement and Height The abutment is the location where a bridge reaches the ground and the transparency of the structure transitions to the opaque mass of the adjoining roadway or topography. Abutments may become visually massive structures or practically disappear, depending on their height and the nature of the grading at the bridge ends. Abutment placement is visually more important on shorter bridges than on longer bridges, since an observer is more likely to view a short bridge in its entirety. Shorter abutments placed farther up on the slope widen the opening below the bridge and allow a more inclusive view of the landscape beyond (Fig. 10). Taller abutments placed closer to an undercrossing roadway more strongly frame the opening and create a gateway effect (Fig. 11). Passage through the bridge seems more of an event. The abutment placement also influences the attractiveness of the space below the bridge for pedestrians. The abutment needs to be set back far enough to allow for a decent sidewalk width and shaped to avoid niches and offsets that might become hiding places or maintenance headaches.
Fig. 10: This full-height abutment frames the landscape beyond the bridge. Meadows Parkway Railroad Overpass, Castle Rock, Colorado.
3.5 Superstructure Shape (including parapets, overhangs and railings) The superstructure elements such as deck overhangs, parapets and railings establish and enhance the form of the structural members. The shapes of these elements and the shadows they cast will strongly influence the aesthetic interest of the structure. For example, the overhang dimension between the edge of the bridge deck and the girder fascia is a key dimension. A wide overhang will create a deep shadow on the fascia girder. When used in conjunction with a thin deck slab line and a relatively transparent barrier, the bridge is perceived as being slender and lighter. On the other hand, a narrow overhang will put the face of the parapet closer to the face of the fascia girder, making them look like one surface and making the superstructure seem thicker and heavier.
Fig. 11: This pedestrian fence uses standard chain link fencing, but the arched top edge, carefully designed details and distinctive color improve the appearance of the bridge, as does the shadow line produced by the deck overhang, all without a significant increase in cost. Note also the integration of the slanted pier legs with the pier cap. I-235 Reconstruction, Des Moines, Iowa. Fig. 9: These minimum-height abutments essentially disappear behind the trees, maximizing the opening under the bridge and the view through to the area beyond. It is also a good example of the values to be gained by thinness and simplicity. I-95 over Pulaski Highway, Baltimore, Maryland.
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Railings and parapets are among the most visually prominent elements of a bridge. They are located at the highest point, are usually visible from a distance, and are the bridge components that are closest in proximity to drivers and pedestrians. From a cost The Bridge and Structural Engineer
perspective, modifications to railings and parapets are often less expensive than modifications to girders or other bridge components. Thus improvements to the railings and parapets can be a cost-effective way to improve the appearance of a bridge.
4.
The Other Five Building Blocks
4.1 Pier Shape The pier shape refers to the form and details of the piers. From many viewpoints, particularly those at oblique angles to the structure, the shapes of the piers will be among the most prominent element of the bridge. The majority of piers for many bridges are structural frames consisting of circular or rectangular columns with a cap beam that supports the superstructure girders. They look like an assembly of different parts rather than a unified form. Improving their appearance requires integrating the parts by, for example, aligning exterior columns with the outside end of the cap (Fig. 11). This eliminates the cap cantilevers, integrates the columns with the cap and thus simplifies the overall appearance of the pier A major improvement can be obtained by integrating the pier cap within the plane of the superstructure. This type of cap is commonly used for concrete box girder bridges, and is an important reason for their visual appeal. It can also be used on other bridge types, such as steel plate girders. With this design the pier cap is invisible. The pier appears much simpler because the transverse lines of the cap are eliminated. (See Fig. 9) This change is particularly helpful on skewed bridges, where the length of a dropped pier cap makes it a sizable and distracting element. 4.2 Abutment Shape As we saw in the section on abutment placement, abutments may become visually massive structures or practically disappear. Abutment shapes are typically more important visually on shorter bridges than on longer bridges, since an observer is more likely to view a short bridge in its entirety. Much depends on the height of the abutment together with the grading around it. Mid height and full height abutments create large surfaces that strongly influence how the bridge is perceived. The aesthetic treatment of these The Bridge and Structural Engineer
surfaces becomes important. For structures involving pedestrians, either on the bridge or below it, the provisions made for them at the ends of the bridge can be among the most memorable aspects of the structure. Abutments may also have an important symbolic function, since these are the points where travelers begin and end their passage over a bridge. The abutment shape and/or elements placed on it can also be used to emphasize the bridge as a gateway to communities, parks or other significant places. (See Fig. 10) These elements need to be visually consistent with the bridge itself and large enough to have an effect when seen at the distances from which the bridge is usually observed. This is particularly necessary for elements that will be seen from a multi-lane high speed roadway. The sail-like elements in Fig. 7 are 50 feet high and 15 feet wide, dimensions necessary in order for them to be noticed at all. 4.3 Color Color has a long history of application on bridges due to its strong visual impact at a low cost. Color, or lack thereof, will influence the effect of all the decisions that have gone before. It provides an economical vehicle to add an additional level of interest. The colors of uncoated structural materials as well as coated elements and details also need to be considered. Since bridges are almost always relatively small elements within the visual field of which they are a part, it is necessary to select color in relation to the surroundings. This can be done by means of colored photographs taken at various times of the day and at various seasons, or, better yet, by actually going to the site. There are several plausible strategies, such as: ď Ź
ď Ź
Integrate the bridge into the surrounding landscape by selecting colors similar to nearby vegetation, rock formations, etc. Many designers select shades of green, red or brown with this in mind Create a strong identity for the bridge by visually contrasting it with its surroundings. This may be particularly appropriate in the case of sites with little vegetation where the bridge can be viewed from a distance. The Golden Gate is a famous Volume 45 Number 3 September 2015  61
example of this strategy.
Identify the bridge with a geographic region or culture through the use of colors that will form this association. For example, the American state of New Mexico has a tradition of coloring bridge surfaces to relate to its distinctive Native American culture.
Selection of a strategy should be an outgrowth of the Design Intention.
Above all, don’t use false arches or other fake structural elements as cosmetic “make up” to disguise an inappropriate or uninteresting design. Aside from requiring additional costs to construct and maintain, adding false structure will rarely improve a design and is often viewed as extraneous clutter. There is a reason why this technique has earned the description “putting lipstick on a pig”.
It is foolhardy to select a color for something as large as a bridge or retaining wall by looking at small color samples in the office. At the very least, take the samples out to the site. Better yet, require the contractor to provide large (at least 4’ x 8’) sample panels on site on which candidate colors can be tested and a final selection made. Color choices are complex decisions requiring specialized technical knowledge and refined visual sensibility. Architects and especially landscape architects frequently make color selections for outdoor environments. They can be helpful consultants. 4.4 Texture. Ornamentation and Details Ornamentation, texture, and details are elements that can add visual interest and emphasis. Structural elements themselves, such as stiffeners and bearings, can serve this function. Indeed, traditional systems of architectural ornament started from a desire to visually emphasize points where force is transferred, such as from beam to column through an ornamental capital. Patterns of grooves or insets and similar details are other examples. Surface texturing, often produced by formliners, can be used to create patterns, add visual interest and introduce subtle surface variations and shading, which in turn soften or reduce the scale or visual mass of abutments, piers and walls.
Fig. 12: Rather than pasting on bulky, vaguely historical ornament, the designers of the Wilson Street Bridge in Batavia, Illinois have dealt with a historic setting in a different way. They have combined a structure of amazing thinness, only possible because of modern high strength concrete and post tensioning, with traditional details that reflect the nature of its setting. Both the past and the future are expressed, while views up and down the river are reopened that had been blocked for decades by the previous earth-filled concrete arch.
Utilitarian details, such as electrical conduits or bridge drainage, often create major and unforeseen visual impacts on bridge appearance. Every visible element of the bridge, no matter how utilitarian or seemingly inconsequential, must be anticipated and integrated into the concept. If it’s visible, it must be designed to be seen.
Ornament is best used sparingly. Less is generally better than more. As bridge engineer J.B. Johnson put it in 1912: “In bridge building…to overload a structure or any part thereof with ornaments... would be to suppress or disguise the main members and to exhibit an unbecoming wastefulness. The plain or elaborate character of an entire structure must not be contradicted by any of its parts.” 62 Volume 45
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Fig. 13: This angular pier geometry and afterthought of a drainage system and clash with an otherwise attractive overall aesthetic scheme. Union Pacific Railroad Bridge over I-25, Castle Rock, Colorado.
The Bridge and Structural Engineer
4.5 Lighting, Signing and Landscaping Though not actually part of the structural system, these elements can have great influence on the aesthetic impression a bridge makes. Lighting Roadway lighting is governed by the illumination requirements of the owner, but still requires multiple choices of pole type, height and spacing as well as fixture and lamp type. While an individual pole may not seem to be much of a visual element, a row or array of them on a bridge will exert surprising influence on the appearance of the bridge. Close coordination with the lighting engineer is necessary to make sure that this influence is positive. The most important step is to simplify the array. For example, place all of the poles on either the median or the sidewalk, but not both. Another goal is to coordinate the pole location with bridge features by, for example, lining the poles up with pier locations or, at the very least, centering the longitudinal pattern of pole placement at the midpoint of the bridge. Lighting of the bridge itself is a good way to draw attention to the bridge and make it an asset to the nighttime environment. Such lighting must be sensitive to motorists, pedestrians, boaters and other users. It should be selected and located to enhance and highlight the structure, yet minimize glare and unnecessary distraction. The lighting must respond appropriately to the context, both in terms of surrounding structures and environmental conditions. Considerations of impact on wildlife and light pollution in the night sky should be weighed together with those of aesthetics.
Fig. 14: Linear LED fixtures outline the unbraced arch of US Route 61 over the Mississippi River in Hastings, Minnesota.
Aesthetic lighting design for bridges requires The Bridge and Structural Engineer
specialized technical knowledge and refined visual sensibility beyond the capabilities of many lighting engineers. It is a consulting specialty of its own. Engineers should consider including such specialists when developing an aesthetic lighting design. Signing There are two types of signs mounted on bridges. The first and most common is where the bridge itself is used as a support for a sign serving the underpassing roadway. The second is when a sign structure is erected on a bridge to serve the bridge’s own roadway. This is often necessary on long viaducts and ramps. In both situations the sign usually blocks and/ or complicates the lines of the bridge itself. The result is rarely attractive. Thus, the most desirable option is to keep signing off bridges. Saddling a bridge with an unattractive sign or sign structure defeats the purpose of creating an attractive aesthetic bridge design in the first place. The goal should be to seek alternate locations for signs away from bridges. This will inevitably mean more specialized structures for the signs themselves. Landscaping Landscaping is defined here to include planted areas and hardscape: stone, brick, or concrete paving, often colored and/or patterned, used primarily for erosion control or pedestrian circulation. Landscaping should enhance an already attractive structure. It should not be relied upon to cover up an embarrassment or hide some unfortunate detail. Conversely, it should not be allowed to grow up to hide some important feature that is crucial to the visual form of the bridge. Landscaping can be a more economical and effective
Fig. 15: This bridge from I-5 in Olympia, Washington conceals an ordinary concrete abutment wing wall.
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way to add richness and interest to a design rather than special surface finishes or materials. For example, a large, plain concrete abutment can be effectively enhanced by well-chosen landscaping.
5. Case Study: The Rich Street Bridge, Columbus, Ohio 5.1 Understanding the Goals and the Site For many years the three bridges carrying Broad Street, Town/Rich Street and Main Street across the Scioto River in downtown Columbus have been an important part of both the city’s traffic infrastructure and its self image. All were built in traditional architectural styles influenced by historic architecture. The bridges are surrounded by the monumental public buildings of the city’s Civic Center, all built in traditional architectural styles. So, in the 1980’s when it became obvious that all three bridges would have to be replaced soon, the city was determined to build new bridges equal in aesthetic quality to the old. The first of the three to be replaced was the Broad Street Bridge, a seven span earth filled concrete deck arch. An extensive community outreach program resulted in a design that reduced the number of spans to three full arches and two half arches in the end spans. Using half arches in the end spans allowed for river walks to be built on both banks. In keeping with the Civic Center tradition the new bridge was built with similar architectural features to the previous bridge, including pilasters and overlooks at the piers and monumental pylons at the abutments. The bridge has the circular curves of traditional arches, even though structurally the “arches” are concrete plate girders with very deep haunches.
Fig. 16: The Broad Street Bridge, Columbus, Ohio
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Soon after the new Broad Street Bridge was completed one of the Civic Center’s historic buildings, the Central High School, was converted to the Center of Science and Industry (COSI). A new wing was built in an ultramodern style on the land side of the existing building. Its facade is curved in plan and it is covered in white precast concrete panels that are curved in two directions and separated by stainless steel strips. Its construction signaled that the community was no longer wedded to the historical architectural styles used in the Civic Center for the previous 80 years.
Fig. 17: The Center of Science and Industry (COSI) ca 1996. The new Broad Street bridge is on the left, the previous Town/Rich Street bridge is on the right, the Ohio Judiciary Building is across the Scioto River.
The Main Street Bridge was the next of the historic bridges to reach a deteriorated state. With the example of COSI now in place, a much wider range of options were considered, moving way beyond conventional deck arches, though the arch theme remained a constant. The city decided to replace the historic bridge with an ultra-contemporary three span bridge with a tilted through arch in the long center span. The bridge is patterned after several bridges by Santiago Calatrava. This structure was opened to traffic in 2010 (Fig. 18).
Fig. 18: The new Main Street Bridge, Columbus, Ohio
The Bridge and Structural Engineer
5.2 Developing a Design Intention That left only the Town/Rich Street Bridge to be replaced. Since all three bridges are seen at once their appearance as a group had to be considered. However, the radical differences in appearance between the traditional Broad Street Bridge and the ultra-contemporary Main Street Bridge made this a significant challenge. The city established a goal to make the three bridges a “Family of Bridges”. As the middle bridge of the three, the intention for Rich Street became to establish a visual link with both the Broad Street Bridge and the Main Street Bridge. At the same time the city realigned the bridge to connect it to Rich Street, bringing the skew angle of the crossing to almost 90 degrees. The city also established guidelines identifying arches as the overriding theme and suggesting certain features of the Broad Street Bridge that should be emulated. The design of COSI, which is at the west end of the Rich Street Bridge, also suggested a vocabulary of contemporary details. Unfortunately, cost overruns on the Main Street Bridge had severely depleted the city’s budget. The team was asked to complete the Rich Street Bridge at roughly one-third the cost of the Main Street Bridge, which is about the same length and width. From the beginning the team had to concentrate on economy as well as efficiency and elegance. 5.3 Conceptual Engineering Study In order to establish a visual link with the new Broad Street Bridge, the team decided to emulate several of its features. Regarding the alignment geometry, the new bridge was given a rise of about three feet from the abutments to the center of the bridge, created by a gentle crest vertical curve stretching the length of the bridge, to give it an overall shape similar to Broad Street. Taking advantage of the near symmetry of the new Rich Street alignment, the team raised the west end of the bridge by about 1.5 feet and rotated the bridge slightly to achieve a skew angle of exactly 90 degrees. This established two axes of symmetry for the bridge, about its own centerline and about the center of the river. The goal was to simplify and speed up construction. In the event it simplified the precasting. In order to establish the visual link with the new Broad Street Bridge, the team decided the new bridge would use the same span arrangement, three full arch The Bridge and Structural Engineer
openings and two half arched openings. This allowed for the extension through the bridge of the river walk on the west bank. Finally, certain of the railing features and other details of the Broad Street Bridge would be emulated as suggested by the guidelines. In order to establish the visual link with the new Main Street Bridge, the team decided to emulate the open structural system and the angular, streamlined design of its structural members. The team initially considered both cast in place and precast options. However, because the deterioration of the existing bridge was at such an advanced state the decision was made to focus on using precast concrete members. The precast members could be manufactured during foundation and site preparation work, thus accelerating the completion of the project. The selected concept uses four lines of precast concrete arch ribs supporting four lines of precast haunched girders (Fig. 19). The space above the piers is left completely open. That combined with the thinness of the ribs gives this concept the openness and grace of the Main Street structure. The geometry of the arch rib is defined by two circular arcs, one forming the top of the rib and one forming the bottom of the rib. The resulting shape is a rib of variable thickness, with the thickest section occurring at the crest and the thinnest section at the base. This matches their dimensions to their structural needs as well as visually minimizes their thickness. The edges of the ribs are formed by two intersecting surfaces, oriented at angles of 30 and 45 degrees from the top surface of the rib. The upper one reflects more light and the bottom one less, so that when seen from the side the arch shapes are split into two facets of different brightness. This visually minimizes their thickness still more. (See Fig. 21 for the arch leg cross section). The radii of the ribs and all other relevant dimensions are standardized from span to span. That combined with the biaxial symmetry of the structure meant that all 68 pieces of the precast structural members could be cast with just three custom steel forms. This concept looks like an arch bridge consistent with the arch theme established for the Family of Bridges. However, like the Broad Street Bridge, the new Rich Street Bridge does not structurally act like an arch. It is basically a rigid frame. Loads applied between the over the piers create moments and shears in the rigid frame formed by the beams and arch ribs. This Volume 45 Number 3 September 2015 65
system allows the “spandrel” areas over the piers to be left completely open. Observers can see right through the bridge from most angles. (It also allows the bridge to more easily pass the river’s periodic floods.) The bridge has the span arrangement and general shape of the Discovery Bridge while having the open, contemporary appearance of the new Main Street Bridge, thereby making the three bridges truly a Family of Bridges.
The arch ribs, beams, and composite deck are longitudinally post-tensioned. Four 19-strand tendons are contained in each arch rib, passing through a tight (3.25 ft radius) bend in the arch block at each pier location. Each set of rib tendons passes through one arch block, with anchorages located at the abutments and in the cast-in-place closure beyond the arch crest in each span. Full - length longitudinal tendons are used in the beam segments and in the cast-in place deck. These tendons are tensioned from both ends of the bridge. The superstructure of the bridge consists of three segment types: the arch leg segments (B1 to B8), the arch crest segments (C1 to C5), and the drop-in beam segments (A1 to A4). A diagram showing the layout of the precast segments for the structure is shown in Fig. 22.
Fig. 19: Structural Form, Railings and other Details of the Rich Street Bridge
5.4 Structural Design and Analysis The Rich Street Bridge is a 562-foot long five-span precast concrete open rib arch structure. Diagrams showing plan and profile views of the bridge and a bridge typical section are shown in Fig. 20 & 21. The superstructure consists of four individual lines of precast arch ribs and deck beams using 7,000 psi sand lightweight concrete (125 lb/ft3). At the piers, the arch rib segments are linked by a cast-in-place arch block. The riding surface of the bridge is a 10-inch cast-in-place concrete deck with a 1 ½” micro-silica modified concrete overlay. The cast-in-place deck is composite with the precast beam segments. Strip seal expansion joints are provided at each abutment.
Fig. 21: Typical Section
The arch leg segments (B1 to B8) make up the portion of the rib that connects the pier arch block to the arch crest. A single set of custom forms was used for all of the B1 to B8 segments. Individual pieces were cast by shifting the bulkheads within the forms. Details for the arch leg segments are shown in Fig. 22.
Fig. 22: Precast Segment Layout
5.5 Details and Finishes Pylons and Railings
Fig. 20: Plan and Elevation
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Four pylons are placed at the four corners of the bridge. In response to the Family of Bridges guidelines. These emulate large circular pylons that are a prominent feature of the Broad Street Bridge. However, the shape of the Rich Street pylons emulates the curved panels of COSI, projecting its contemporary aesthetic to the east bank of the river. The pylons also house electrical equipment that serves not only the bridge The Bridge and Structural Engineer
lighting and the adjoining park but also the temporary power for the periodic festivals hosted on the bridge. The four pylons are visible in Fig. 19. The pier arch block nosings are covered by a stainless steel shield (Fig. 23). Aesthetically the shield draws attention to the point of force transfer, a traditional function of ornament, but with a modern form. The shield also helps the piers shed river debris, a constant problem in the Scioto River.
Fig. 23: Modern Ornament: Stainless Steel Pier Nosings
The railings emulate the pattern of the Broad Street Bridge. The railing posts are spaced in a short-longshort pattern. However, in order to match the open, contemporary design of the bridge, the railing design itself is more contemporary, with a wide horizontal band that emphasizes the line of the deck from abutment to abutment, similar in some ways to the railing of the new Main Street Bridge. The horizontal band is made from aluminum industrial grating, an unusual use of a durable and sturdy material. The railing is topped by a visually dominant handrail, as on the Broad Street Bridge, but it is aluminum, not bronze. Lighting The features of the Broad Street and Main Street bridges are lighted at night, as are many of the buildings adjoining the river. The lighting for many of the buildings includes lighted corporate titles or logos. Taken together, all of these lighted elements make the nighttime environment of the Civic Center a rich and interesting visual experience. The Rich Street Bridge has a varied and prominent aesthetic lighting program so it can hold its place in the center of this environment. The lighting of the Broad Street Bridge uses both blue
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and white light. The Main Street Bridge uses entirely white light. Blue is also the dominant color used in the night lighting of COSI. To unify these different sources the Rich Street Bridge uses both blue and white lighting. The arch ribs are floodlit from fixtures mounted just under the deck, between the inner ribs, and near the arch apexes. The inner surfaces of the ribs are bright while the fascia surfaces of the bridge are dark and silhouetted against them. This brings out the structural system and transparency of the bridge while making the river and riverwalk seem a more inviting place. Each railing post has a pair of small blue fixtures at the same height as the aluminum grating band, a fluorescent fixture facing outward toward the river and a Light Emitting Diode (LED) fixture facing inward toward the sidewalk. These bring out the short-long-short spacing rhythm of the railing posts. Taken together they form a line of bright spots that emphasize at night the sweep of the bridge from abutment to abutment, highlighting the arching profile line of the deck and giving the bridge another layer of interest. Finally, short LED strips in blue are placed in the vertical rustications of the pylons near their tops. These draw attention to the pylons and signify the beginning and end of the bridge at night (Fig. 25). Landscaping Simultaneously with the construction of the Rich Street Bridge the parks on both river banks were completely reconstructed. The abutment wing walls, sidewalks and railings on each end of the bridge were customized to fit into these projects. 5.6 Costs The Rich Street Bridge was constructed for just under $13 million, $1 million less than the city’s budget.
Fig. 24: Rich Street Bridge in the Post Card View of Downtown Columbus
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5.5 Sources of Aesthetic Form for Rich Street All three sources of aesthetic form influenced the Rich Street Bridge. The circular deck arch geometry traces back to the Broad Street Bridge, which in turn traces back to the concrete deck arch bridges that previously occupied the site, which in turn trace back to traditional stone masonry arch bridges all the way back to the Pont Neuf. However the dominant source of aesthetic form is obviously the engineers aesthetic. By taking advantage of the load carrying capability of high strength posttensioned concrete a minimum amount of material could be used. The volume under the bridge is mostly empty space, allowing views through the bridge in all directions, in marked contrast to the massiveness of the Broad Street Bridge girders or all of the earth filled concrete arches that came before. The structural material that is present is shaped to meet the structural demands upon it as a rigid frame. The deck girder is thickest at the points where it intersects the curved diagonals of the arch legs and thinnest at the points in between. The arch legs themselves taper to their thinnest point where they meet the pier block. The bridge strays into the manipulation of structure in the arch legs, which require a slight curve in order to meet the geometrical requirements of the circular arch form established at the beginning. This adds a small bending moment to the legs. Whether this takes the bridge out of the realm of structural art I will leave to others to decide. 5.6 Awards and Recognition This is a magnificent bridge design, the FINEST of our downtown collection of bridges. Great job!!! –Brian Kinzelman, Columbus landscape architect The bridge has won more than a dozen awards, including most notably the Columbus Landmarks Foundation’s 2012 Design and Preservation Award, the Portland Cement Association’s 2014 Design Award of Excellence and two awards from the Precast Concrete Institute, the 2014 Best Medium Span Bridge Award and the 2014 All Precast Design Award. The bridge is the site of several annual civic festivals in Columbus, including the Fourth of July celebration, and is the focus of the “postcard view” of the Columbus skyline. 68 Volume 45
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Fig. 25: Rich Street Bridge on the Fourth of July
6.
The Possibilities of Aesthetic Success
Following the ideas set forth in this article will improve most everyday structures, but they will not guarantee structural art. There are no hard and fast rules or generic formulas that will guarantee outstanding visual quality. Each bridge is unique and must be studied individually, always taking into consideration all the issues, constraints and opportunities of its particular setting and environment. Nevertheless, observing the successes and failures of other bridges and using design guidelines such as these can improve an engineer’s aesthetic abilities, help avoid visual disasters and encourage the creation of structural art.
Acknowledgements Much of this article is based on my book Bridgescape. Readers are encouraged to see the book for more detail on the ideas discussed and especially for a series of additional case studies that are presented therein. Much of the photography and some of the discussion in Sections 3 and 4 resulted from my work on the Bridge Aesthetics Subcommittee of the U. S, Transportation Research Board, for which I am especially indebted to my subcommittee colleagues Joseph Showers, Robert Shulock and Dean van lan Duyt. The Case Study of the Rich Street Bridge in Section 5 is based on the design of that project that I did jointly with John Shanks and Travis Butz of Burgess & Niple of Columbus, Ohio and Siegfried Hopf of Leonhardt, Andra und Partners of Stuttgart, Germany. The lighting concept for the Hastings, Minnesota bridge portrayed in Section 4.5 was developed by Illumination Arts of Bloomfield, New Jersey. The Bridge and Structural Engineer
References 1.
Frederick Gottemoeller, 2004. Bridgescape, the Art of Designing Bridges, 2nd Ed. John Wylie & Sons, Inc., New York, NY
2. Allen, E. and Zalewski, W. 2010. Form and Forces, Designing Efficient, Expressive Structures, John Wylie & Sons, Inc., New York, NY 3. Leonhardt, F. 1983. Brucken, MIT Press, Cambridge, MA 4.
David Pye, D. 1999. The Nature and Aesthetics of Design, 5th Reprinting, Cambium Press, Bethel, CT
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5. Man-Chung Tang, M. C. 2001. 36 Years of Bridges, Tango International, New York, NY 6. Schlaich, J. and Bergermann, R. 2003. Light Weight Structures, Prestel Publishing, New York, NY 7. Bridge Aesthetics Subcommittee of the Transportation Research Board, 2010. Bridge Aesthetics Source book, American Association of State Highway and Transportation Officials, Washington, DC 8. Frederick Gottemoeller, Travis Butz and John Shanks, Design and Construction of the Rich Street Bridge, Proceedings of the 2013 International Bridge Conference, Pittsburgh, PA
Volume 45 Number 3 September 2015  69
Living Root Bridges: State of knowledge, Fundamental Research and Future Application “Paper selected for ‘outstanding young engineers’ award at International Association for Bridge and Structural Engineering Conference in Geneva on September 25th 2015”
Sanjeev SHANKAR Founder, Studio Sanjeev Shankar Bangalore, India sanjeev@sanjeevshankar.com
Sanjeev Shankar received Bachelors in Architecture (with distinction) from School of Planning and Architecture New Delhi in 2004, a Masters in Design from Indian Institute of Technology Bombay in 2006, and a Masters in Science from Architectural Association London in 2010. His researchbased studio explores an inclusive and collaborative agenda by blurring boundaries between architecture, science, craft and engineering. A recipient of the Chevening fellowship from Britain and the DAAD fellowship from Germany, his critically acclaimed works have featured at the Royal Institute of British Architects London; Centre for Architecture New York and Hyde Park Art Center Chicago. He was shortlisted for the Emerging Architecture award at the Royal Institute of British Architects London, and has won the ‘10 Great Ideas to change the world’ competition at Indian Institute of Technology Bombay.
Abstract Living root bridges are Ficus elastica1 based suspension bridges within dense tropical rainforests of Meghalaya in the North Eastern Indian Himalayas (25° 30’ N and 91° 00’ E). Ranging in span from 15 feet to 250 feet, these bridges are grown by Khasi2 tribes over a time period of 15 to 30 years, and last for several centuries. With 1) exceptional robustness3 under extreme climatic conditions, 2) minimal material and maintenance cost, 3) no environmental damage, 4) progressive increase in load-bearing capacity, 5) carbon sequestration, 6) remedial properties on surrounding soil, water and air, 7) collective grass root involvement based on human-plant interaction across multiple generations, 8) support to other plant and animal systems, and 9) keystone4 role of Ficus plant species in local ecology, living root bridges offer an extraordinary model for long-term socioecological resilience5 and sustainable infrastructure solutions, and warrant further scientific study. Keywords: Ficus; living root bridges; biological systems; resilience; robustness; redundancy; sensitive environments; developing economies; collaborative approaches; human-plant interaction.
1 Introduction The indigenous Khasi tribes of Meghalaya in the 70 Volume 45
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Fig. 1: Location diagram of living root bridges
North Eastern Indian Himalayas exemplify a unique relationship with their environment. Demonstrating a high degree of self-sufficiency, which in part is owing to their remote location and distinctive environment6, Khasis have developed numerous sustainable practices based on collective and planned cooperation. One such practice is the ‘living root bridge’. Locally known as jing kieng jri, this indigenous technology uses the aerial roots of Ficus elastica to grow bridges ranging in spans from 15 feet to 250 feet over a time period The Bridge and Structural Engineer
of 15 to 30 years. Situated in heavily forested and wet places, which are prone to unexpected environmental disturbances, the underlying growth process of these plant-based structural systems involves nurturing the aerial roots of Ficus elastica, and guiding them across deep gorges and rivers. The supporting horticultural technique was developed using locally available materials, skills and tools at a time when concrete and steel were non-existent. Recent attempts to build steel suspension bridges in these fragile eco-systems have highlighted their limitations, and underlined the potential of hybrid structures, which combine advantages of both technologies for an overall improved performance. Key advantages of the living root bridges include exceptional structural robustness and resilience, progressive increase in load bearing capacity with time and use, remedial impact on surrounding soil, water and air, grass root community involvement in the growth process across multiple generations, carbon sequestration, low cost, and support for other plant and animal systems. Key challenges of this technology include a long growth phase, low safety during initial growth stage, need for appropriate growth conditions (soil, water, sunlight and nutrients), and a sensitized community support for nurturing its growth and maintenance. Comparatively, conventional bridges are extremely safe, precisely calculable for load and performance, can be installed quickly and have a long history of documented knowledge. However conventional bridge building methods have certain limitations especially in ecologically sensitive remote tropical regions in developing countries. These include high material and maintenance cost, relatively short life span (40 to 50 years as compared to several centuries for living root bridges), extensive environmental damage (caused during material transport and construction), and use of specialized materials (steel and concrete) with high carbon footprint. In addition, traditional engineered structures are driven by principles of efficiency, optimization and strength, with a precise economy of materials applied for specific environmental conditions. Conversely living root bridges, which are fibre based natural biological structures, use high degree of redundancy7 and complexity to respond to extreme environmental stresses and dynamic loads. This paper discusses the potential of fusing these structural systems for The Bridge and Structural Engineer
a plant-based hybrid system, which can withstand climatic imbalances and have significant remedial impact on its environment.
2.
State of knowledge
2.1 Living root bridges Khasis, who follow an oral tradition, have limited written documentation about their history and customs. This also applies to the living root bridges. No scientific documentation or analysis of these bridges has been found. This paper is based on author’s independent field visits in 2013 and subsequent ongoing research. The author has documented 11 living root bridges and these are listed below for reference: Table 1 Location [india]
Span [feet]
Growth stage
Safety level [5 is safest]
Riwai
75
Mature
5
Wahryngkoh
15
Mid life
3
Mawkyrnot
250
Early life
1
Mawkyrnot
150
Early life
1
Mawkyrnot
250
Mid life
3
Nongthymmai
60
Mid life
3
Nongthymmai
80
Early life
1
Nongthymmai
20
Mature
5
Nongriat
40
Mature
5
Nongriat
50
Mature
5
Nongriat
60
Mid life
3
Based on witnessing these eleven bridges at different growth stages, it can be said that the technique used to grow these bridges is still practiced by the Khasis. The underlying growth process (Fig 2) involves recurring inosculation (joining by twining8) of Ficus aerial root fibres over a gorge or river. The process begins with placing of young pliable aerial roots growing from Ficus trees in hollowed out Areca catechu trunks9. These provide essential nutrition and protection from the weather, and also perform as root guidance systems by redirecting the positive gravitropic movement of the aerial roots. This assemblage is structurally supported by a bamboo scaffold, which spans the river and performs as a temporary river crossing for the community. Over time, as the aerial Volume 45 Number 3 September 2015  71
roots increase in strength and thickness, the Areca catechu trunks are no longer required. Periodic replacement of green bamboo poles is essential with increase in aerial root thickness and gradual deterioration of bamboo owing to wet tropical conditions of Meghalaya. Gradually, more roots are inosculated to the primary root system with morphological variations like steps and handrails integrated at a later stage. Dead load, in the form of heavy stones, timber planks, leaves and soil is added in succession to plug the gaps and to test the entire living root structure for weight (Fig 3). Heavy humidity, ambient moisture content and pedestrian movement together contribute to soil compaction. Eventually, over 15 to 30 years, the root assemblage becomes strong and stable enough to support substantial human and material weight without the bamboo scaffolding. The author has witnessed the mature bridges in Riwai (Fig 4) and Nongriat (Fig 5) carrying upto 35 and 20 people at one time. Unlike contemporary construction materials and structures, these living root structural systems become stronger, more robust and resilient with time and use. Despite turbulent weather conditions, the author did not witness any mechanical failure of these bridges under external water or wind loads. In addition, no disease or attack from insects or fungi has been observed. Further, Khasi tribes’ sacred worldview and unique understanding of ‘time’ with respect to material strength and shelf life is a key aspect of the growth process. Precise synchronisation of periodic changing of bamboo and Areca catechu trunks, with progressive addition of dead load is a critical step in the growth process, and ensures a continual relationship between the living bridge and the local community.
2.2 Living plant-based construction Historic precedents in the domain of living plantbased construction include ‘tanzlinden’ lime treetops of Europe, and unrealized proposals of gardener and landscape engineer Arthur Weichula (Fig 6). Recent works by Terreform (founded by Dr. Mitchell Joachim) and Baubotanik10 (founded by Dr. Ferdinand Ludwig) have explored the potential of living plant-based constructions as structural systems within architecture and infrastructure. Additionally, research of Inca natural fibre suspension bridges by Prof. John Ochsendorf has highlighted the potential of appropriate local technologies, which combine social integration with environmental performance for sustainable solutions. Ongoing research by Baubotanik is specifically relevant for understanding and investigating living root bridges. The group has employed the growth processes of living woody plants within construction, through the integration of design, structural engineering, biological research and horticultural procedures11. Through full scale prototypes (Fig 7 and Fig 8) and accurate analysis, the group is developing an understanding of the challenges involved in designing living plant based constructions.
Fig. 6: (i) Drawing by Weichula A. (ca. 1925); (ii) Tanzlinde Peesten ©www.tanzlindenmuseum.de; (iii) Terreform, Fab Tree Hab (Joachim M., 2009)
Fig. 7: Footbridge (Ludwig F. and Storz O., 2005); Tower in the first and second year of development (Ludwig F. and Hackenbracht C., 2009); Plane Tree Cube Nagold (Ludwig. schoenle, 2011) Fig. 2: Growth process of living root bridges
Fig. 3: Early stage, Nongthymmai Fig. 4: Mature bridge, Riwai Fig. 5: Mature bridge, Nongriat
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Fig. 8: Experimentation for adequate construction techniques: Vegetal-technical joint (Storz O., 2010); Crosswise inosculation with Salix Alba and cross cut showing development stage (Ludwig F., 2010); Crosscuts through parallel inosculation showing different development stages (Ludwig F., 2010)
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3.2 Biological systems
Fig. 9: Bamboo bridge failure Fig. 10: Steel suspension bridge failure Fig. 11: Ficus-steel twining
3
Fundamental research
Understanding the performance of living root bridges and its underlying technology will require a precise in-situ analysis of the bridges and the Ficus elastica plant specie used for growing these structures. 3.1 Comparative analysis Based on eyewitness accounts, onsite documentation and information provided by Meghalaya Basin Development Authority12, it can be said that the structural resiliency of living root bridges is comparatively superior to steel suspension bridges and vernacular bamboo bridges in Meghalaya’s remote, vertical and wet tropical landscape. Annual failure and deformation of bamboo bridges is common when impacted by heavy water loads during the monsoon season (Fig 9). There are recorded cases of bamboo bridges being swept away causing loss of life and severely impacting rural connectivity. In steel suspension bridges, failure is caused by high wear and tear, and corrosion of the cables (Fig 10). This is due to the extremely wet conditions of this region, and gradual decline in cable strength. These bridges also require periodic maintenance, which needs specialized expertise,government approval and financial resources. As a result numerous steel suspension bridges remain in a precarious condition. Comparatively, living root bridges withstand heavy dynamic water loads in the form of flash floods and storm surges, and avoid resonance catastrophes13 with minimal maintenance over many centuries. In many cases they are the only means of connectivity in the monsoon season. Their success and relevance is demonstrated in case studies where Khasis’ have applied this technology to the damaged steel suspension bridges by using the corroded cables as a scaffold for root guidance, support and growth (Fig. 11). The Bridge and Structural Engineer
Ficus elastica is a living biological system. Investigating the growth and physiology especially morphology and biomechanics of the aerial root fibres along with their inosculation is a prerequisite to understand, improve and replicate the performance of these plant-based structures. Research on plant systems has revealed that a high degree of redundancy at multiple scales within the hierarchical arrangement of cells and tissues produces sufficient excess capacity for adaptation to changing environmental stresses14. Additional attributes of material self-organisation, complexity, non-linearity, anisotropy, differentiation and visco-elasticity contribute to variable stiffness and elasticity, which is useful for resisting dynamic and unpredictable water loads. Recent scientific investigations have established that all aerial roots of Ficus elastica are under tensile stress, which is an essential aspect for the efficiency of fibrous structures in biological systems.15 The tensile stress in Ficus aerial roots is inversely proportional to the diameter of the aerial root, and its distance from point of connection to soil or another aerial root.16 This stress is generated due to gelatinous fibres within the roots, which are in turn produced by stimuli in the form of attachment or anchorage.17 Although yet to be confirmed, it is estimated that at a macro level the principle of multiple resonance damping noticed within Douglas Fir (Pseudotsuga menziesii)18 can be applied to understand energy dissipation of the Ficus elastica based living root bridge assemblage. The constituent aerial root fibres are grown in successive layers over 15 to 30 years resulting in a complex root network, where each fibre is at a different growth stage, and possesses different material properties and capacity for energy dissipation. This high degree of differentiation contributes to higher overall damping. A material property chart, which estimates the stiffness and density of Ficus aerial roots in comparison to contemporary construction materials is included here for reference (Fig 12). The author recognizes that the stiffness and density values of Ficus plant specie are time dependent, vary with local conditions and need precise scientific tests for validation.
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growth conditions (especially moisture and light) in these nurseries19, 3) engineering the aerial root inosculation process using different joining methods, 4) applying engineered stress to aerial root fibres in early growth stage, 5) engineering the bamboo scaffold and Areca catechu root guidance system using structural topology optimization, 6) increasing anchorage based stimuli to enhance gelatinous fibre production and tensile stress within the aerial roots, and 7) developing a digital planning tool based on growth principles of Ficus elastica20. Fig. 12: Modulus-Density chart (Modified and redrawn) Ashby M., Shercliff H. and Cebon D. Materials Engineering, Science, Processing and Design, Elsevier, Pg 57, 2007.
Second key challenge of the living root bridge technology is its low-safety during early growth stage. This can be addressed by developing symbiotic hybrid structures, which combine living plant based matter with inanimate matter.
3.3 Optimization
3.3.1 Value addition
Despite demonstrating extraordinary structural and socio-ecological resilience (Fig 13), living root bridges are being replaced by inappropriate solutions owing to increasing resource needs, and the nexus of poverty, population explosion and environmental degradation in North Eastern India. The author proposes systematic optimization and value-addition for technology revival.
Living root bridges perform as rural pedestrian bridges for remote mountain villages. The author proposes strategic interventions, which will build local enterprise and align rural development with Ficus ecology. Key interventions discussed with local stakeholders include redesign and widening of the bridge to support vehicular movement, and potential adaptation of the bridge as a host biome for orchids, other epiphytic plants, food for humans and other biota.
structural resiliency and robustness
living root bridges
4. new fibres become primary structure
steel suspension bridges
fibres become primary structure
bamboo
aerial root fibre growth 0 12 3
5
10
100
1000
Time (in years: logarithmic scale)
Fig. 13: Structural resiliency-time chart
The primary challenge of living root bridge technology is its long gestation period of 15 to 30 years. Although yet to be confirmed through scientific analysis for Ficus plant specie it can be said that possible methods for expediting the growth process include 1) producing (breeding) of Ficus saplings, which fulfill several physiological - especially morphological and biomechanical prerequisites, in off-site nurseries before replanting them onsite, 2) providing ideal 74  Volume 45
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Concluding remarks
Living root bridges offer an exemplary model for sustainable community-based infrastructure solutions. This paper consolidates the author’s findings and puts forth future research directions for the global engineering community. The author acknowledges that he is not in possession of full scientific facts and the estimates in certain cases may be incorrect or at least simplistic. Findings from a precise scientific investigation would lay a foundation for understanding these structures, upgrading the technology and adapting it for other tropical and sub-tropical regions using appropriate native plant systems e.g. Ficus benghalensis. It may also lead to novel design strategies based on redundancy and irregularity for achieving structural robustness in classical engineered structures. The author envisages establishment of a trans-disciplinary consortium for initiating in-situ research of living The Bridge and Structural Engineer
root bridges through a research and demonstration station in Meghalaya. This platform will engage all stakeholders in a participatory process to leverage this knowledge for rural connectivity, conservation, education and livelihood.
5. Acknowledgements The author is indebted to the Khasi tribes of Meghalaya for sharing their knowledge about the living root bridges and for guiding him through Meghalaya’s challenging geography. He would also like to thank Dr. Ferdinand Ludwig, Prof. A G Rao, Prof. Anna Dyson, Prof. Renee Borges, Prof. Ananthasuresh, Prof. Arup Kumar Sarma, Dr. Tejas Gorur Murthy, Dr. Rekha Shangpliang and Mr. Aiban Swer for critical information about living plant-based constructions. Gratitude also goes to other scientists, engineers, architects and government representatives who have inspired the author with their suggestions and support.
6. References 1.
2.
Native from the Himalayas to Malaysia, Sumatra and Java, Ficus elastica (or India rubber tree or India rubber fig) is a broadleaf evergreen shrub or tree that may grow to 50-100’ tall in its native habitat. With high drought tolerance, pest resilience and diverse soil tolerance it is widely grown in the tropics as an ornamental tree. Mature Ficus elastica trees (family: moraceae) develop Ficus benghalensis (banyan)-like aerial roots. http://www.missouribotanicalgarden.org/ gardens-gardening/your-garden/plant-finder/ plant-details/kc/b597/ficus-elastica.aspx The term “Khasi” means “born of the mother”. For a detailed elaboration, see Shangpliang R. Forest in the Life of Khasis. New Delhi, Concept Publishing Company, p. 1, 2010.
3. Robustness is used to describe a system that can survive extreme external variations. For a detailed elaboration, see Weinstock M. SelfOrganization and the Structural Dynamics of Plants, AD Emergence: Techniques and Technologies in Morphogenetic Design, Vol 76, No 2, 2006. 4. A keystone species is a plant or animal that The Bridge and Structural Engineer
plays a unique and crucial role in the way an ecosystem functions. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. http:// education.nationalgeographic.com/education/ encyclopedia/keystone-species/?ar_a=1 5. Resiliency is the ability of a system to change and adapt to external disturbances and yet remain within critical thresholds. http://www. stockholmresilience.org/21/research/what-isresilience.html 6. North East India is a global hot spot for biodiversity. Characterized by varied physical geography, it is marked by distinct orography, heavy monsoon rains and a diverse range of flora and fauna. Mawsynram and Cherrapunjee receive the highest annual rainfall in the world. Shangpliang R., Forest in the Life of Khasis. Concept Publishing Company, New Delhi, p. 5, 2010. 7. In biological systems, redundancy occurs when the same function is performed by identical elements. For a detailed elaboration, see Weinstock M. Self-Organization and the Structural Dynamics of Plants, AD Emergence: Techniques and Technologies in Morphogenetic Design, Vol 76, No 2, 2006. See also Guilo T., Olaf S. and Gerald M.E. Measures of degeneracy and redundancy in biological networks, Proceedings of the National Academy of Science USA, Vol 98, Issue 6, pp. 3257-3262, 1999. 8. Twining is a type of weave structure, which involves the twisting of two or more linear elements around another set of linear elements, which are perpendicular or inclined to the first set. Dunkelberg K., IL 31, Bamboo, Kraemer Karl Gmbh + Co, p. 357, 1985. 9.
Areca Catechu (betel nut) is a slender, single trunked palm that can grow to 30 m (100 ft). It is cultivated from East Africa and Arabian Peninsula across tropical Asia and Indonesia to the central Pacific and New Guinea. http:// agroforestry.org/images/pdfs/Areca-catechubetel-nut.pdf
10. The term “Baubotanik” was developed at the Institute for Architectural Theory, University of Volume 45 Number 3 September 2015 75
Stuttgart and describes an approach to engineer with living plants. It is a German neologism that can be translated as “Living Plant Constructions”. http://www.baubotanik.de/index_en.html
16. Abasolo W.P., Yoshida M., Yamamoto H. and Okuyama T. Stress generation in aerial roots of ficus elastica (moraceae), IAWA Journal, Vol. 30 (2), pp. 216-224, 2009.
11. Ludwig F., Storz O. and Schwertfeger H. Living Systems. Designing Growth in Baubotanik, Architectural Design Journal, Vol 82, No 2, 2012.
17. Mellerowicz E.J. and Gorshkova T.A. Tensional stress generation in gelatinous fibres: a review and possible mechanism based on cellwall structure and composition, Journal of Experimental Botany, Vol. 63, No. 2, pp. 551565, 2012.
12. Meghalaya Basin Development Authority: Integrated Basin Development and Livelihood Promotion Programme. http://mbda.gov.in 13. Resonance phenomenon can be thought of as a vibration that is caused by the tendency of a system to absorb energy from an external force that is in harmony with the natural frequency of the structure. For a detailed elaboration, see Weinstock M. Self-Organization and the Structural Dynamics of Plants, AD Emergence: Techniques and Technologies in Morphogenetic Design, Vol 76, No 2, 2006. 14. Ibid. 15. Jeronimidis G., Biodynamics, AD Emergence: Morphogenetic Design Strategies, Vol 74, No 3, 2004. See also Elices M., Structural Biological Materials, Pergamon Press, Amsterdam, 2000.
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18. Spatz H.C., Bruchert F. and Pfisterer J. Multiple resonance damping or how do trees escape dangerously large oscillations?, American Journal of Botany 94(10), pp. 1603-1611, 2007. 19. Ludwig F., De Bruyn G., Thielen M. and Speck, T. Plant stems as building material for living plant constructions, In: Thibaut, B. (ed.) Sixth Plant Biomechanics Conference, Cayenne, French Guyana, France, UMR EcoFoG, 2009. 20. Ludwig F., Mihaylov B. and Schwinn T. Emergent Timber: A tool for designing the growth process of Baubotanik structures, Transmaterial Aesthetics: Experiments with Timber in Architecture and Technology, ANCB The Metropolitan Laboratory, Berlin, 2013.
The Bridge and Structural Engineer
SYNTHESIS FOR ULTIMATE LIMIT STATE OF INDUCED DEFORMATIONS (SECTION 11 OF IRC:112)
V.N. HEGGADE Sr. Vice President & Member Board of Management Gammon India Limited, Mumbai venkat.heggade@gammonindia.com
V.N. Heggade, presently is a Member, Board of Management of Gammon India Limited. He has more than 20 years of experience of furthering the cause of standardization in the country by being an active member of various code making committees of IRC and BIS, relating to Bridges, Marine structures and Special structures like Cooling towers and Chimneys. He is also a member of FIB commissions relating to Pre-cast segmental construction and Sustainability. By being one of the authors of the currently under preparation explanatory handbook on IRC:112 , he is also a speaker in workshops conducted all over India on new IRC:112. His contribution in earlier foundation committee of IRC and present special structures committee of BIS has been officially recognized.
Summary The recent limit state code for concrete bridges IRC: 112 have 4 sections (Sections 8 to 11) on ultimate limit states. The IRC:112 has dedicated a separate section on Ultimate limit state of induced deformation which testifies the importance as no other code has dedicated a separate chapter on this. The code gives simple guidelines for ignoring the 2nd order effects and simple method for calculating 2nd order effects as the same is very complex. In the paper below the background of these guidelines are discussed in detail.
1.
in the Section of ultimate limit state of induced deformation. The buckling is mentioned only when a nominal buckling load is used as a parameter in certain calculation methods. First order effects or deformations are due to transverse/lateral loads and also include the Effect of imperfections, interpreted as physical deviations in the form of inclinations or eccentricities. The compression resultants with eccentricities and curvature variation significantly influenced by 2nd order effects are shown in Fig 1.
Introduction
By virtue of its high compressive strength, concrete was considered in the beginning as building material for massive and sturdy structures.With the advancement of Concrete technology and also very high increase in strength, concrete structural members are becoming leaner, slimmer and slender. Unfortunately with the increase in strength of the concrete, proportionately modulus of elasticity there by stiffness is not increasing to the same extent. As such axially loaded slender structural members are vulnerable to sudden failure due to instability which is generally termed as buckling failure.
Load deformation behavior and ultimate capacity of structural members and structures is significantly affected by Second order effects.
The word buckling is meant for the “pure”, hypothetical buckling of an initially straight member or structure, without load eccentricities or transverse loading. The pure buckling is not a relevant limit state in real structures, due to the presence of imperfections, eccentricities and/or transverse loads. This is also a reason why the word “buckling” is avoided generally
Second order effects are additional action effects caused by the interaction of axial forces and deflections under load. First order deflections cause additional moments which in turns lead to further deflections (Fig 2). Sometimes these effects are also called P-∆ effects as they are the products of axial forces and deflections of the elements or system. Normally
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Fig. 1: Compression resultants with eccentricities and curvature variations (Source: FIB Model code 2010)
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second order effects are calculated by second order analysis. Majority of commercially available structural soft wares has the capability to carry out second order analysis. In this analysis, in addition to the invalidity of the principle of superposition the flexural rigidity of reinforced concrete structures EI is not constant. As the moment increases for the same load, EI reduces
concrete structure is not constant. EI reduces with increasing moment due to cracking
The above de-merits introduces complexities in 2nd order analysis as such the code gives two simple criteria for not carrying out the 2nd order analysis.
•
Cases where second order effects are less than or equal to 10% of the first order effects.
•
If the slenderness λ is below a certain value λlim, i.e., λ < λlim (λ limitation criteria)
2.1 Less than or equal to 10% criterion2 Before adopting this 10% criterion, two different ways of defining 10% criterion for ignoring 2nd order effects were investigated by Bo Westerberg et al •
≤ 10 % increase of the corresponding first order effect,
•
≤ 10 % reduction of the load capacity, assuming a constant eccentricity of the axial force.
Fig. 2: Interaction Chart showing Second Order effect
due to cracking of concrete and inherent non-linearity in the concrete stress-strain response also increases. Thus it involves both geometry and material nonlinearity for reinforced concrete elements and has to be taken in to account while choosing the method for 2nd order analysis.
The cross section resistance (Fig 3) was calculated for rectangular cross section 400 x 600 mm concrete C35, ω = 0.1 (total mechanical reinforcement ratio), edge distance of reinforcement 60 mm.
The terms sway – non-sway is not used in section 11 of IRC: 112. The words in themselves are misleading, since all structures are more or less “sway”. A structure that would be classified as “sway” could be just as stiff as one classified as “non-sway”. These terms are in fact now replaced by unbraced – braced. The distinction braced – bracing is simple. The units or systems that are assumed to contribute to the stabilization of the structure are bracing elements, the others are braced. Bracing units/systems should be designed so that they, all together, have the necessary stiffness and resistance to develop stabilization forces. The braced ones, by definition, do not need to resist such forces.
Fig. 3: Interaction diagram for two diffrent 10% criteria
2 Criteria for ignoring 2nd order effects
During the conversion process2, the first criterion of 10% less than or equal to first order effects was found to be suitable for the following reasons:
Significant disadvantages of second order analysis are:
•
In a column or a structure it is the bending moment that is influenced by second order effects.
•
The axial force is governed by vertical loads, and is not significantly affected by second order effects.
•
Most design methods are based on calculating
•
The principle of superposition is not valid in second order analysis and all actions must be applied to the bridge together with all their respective load and combination factors.
•
The flexural rigidity (EI) of the reinforced
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a bending moment, including a second order moment if it is significant.
These effects are accounted for by the terms A, B and C respectively in the λlim equation.
The above criterion is not much of a use to practising designers as the 2nd order analysis has to be carried out to determine whether the 2nd order effects are with in the 10% of 1st order effects. In view of this perhaps, the alternative criterion of λ limitation is more useful for designers for ignoring 2nd order effects and analysis.
2.2.1 The term “A” accounts for creep as
2.2
MoEqp= First order B.M. in quazi-permanent load combination in SLS.
λ limitation criterion
While determining the second order effects by simplified methods instead of non-linear second order analysis, the effective length concept can be used to determine slenderness. On determination of slenderness, the requirement of second order analysis itself may be deduced. The slenderness ratio is defined as λ= le/i where ‘le’ is effective length and ‘i’ is the radius of gyration of the uncracked concrete section. This criterion states that second order effects may be ignored if the slenderness λ is below a certain value λlim, i.e., λ < λlim.
below:
A= 1/(1+0.2øef) φef is effective creep ratio.
MoEd = First order B.M. in design load combination in U.L.S. Where φef defined above is not known, ‘A’ may be taken as 0.7 which corresponds to φef = 2.0 that would be typical of concrete loaded at relatively young age, such that φ∞ = 2.0 with a loading being entirely quasi permanent. Using the default value of A = 0.7 is reasonably conservative as the same is in any case not sensitive to realistic variation of φef. 2.2.2
The term “B” accounts for ratio:
reinforcement
Where, n= is the relative normal force n = NEd /(Acfcd) As the axial force ‘n’ becomes greater, the section becomes more susceptible to development of second order effects and, consequently limiting slenderness value become lower. After receiving the comments and examples from Prof Hellesland2 during the evolving stage in 2001, a systematic investigation of the slenderness limit was made, with focus on the effects of reinforcement, normal force, creep and moment ratio (different end moments) and these parameters were added in λlim equation finally. Higher limiting slenderness can be achieved where: •
There is low creep (because the stiffness of the concrete part of the member in compression is then higher)
•
There is a high percentage of reinforcement (because total member stiffness is then less affected by the cracking of the concrete)
•
The locations of the peak first order is not the same as the location of peak second order moment.
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Fig. 4: Column in double curvature
B= Where ω= Asfyd/(Acfcd)is the mechanical reinforcement ratio. If the same is not known, ‘B’ may be taken as 1.1, that is equivalent to ω =0.1. This value would Volume 45 Number 3 September 2015 79
usually be achieved in a slender column; however this is generous in comparison to minimum reinforcement provisions in the codes. In establishing the λlim, the effective creep ratio φef and the relative normal force n were included as parameters in the initial stages, however the reinforcement ratio ‘ω’ was not included then, since it was considered unpractical. 2.2.3 The term “C” accounts for bending curvature: •
C = 1.7-rm, where moment ratio rm = M01/M02.
•
M01 & M02 are the first order end moments at two ends of member as calculated from the analysis of structure.
•
If the end moments give tension on the same side, rm should be taken as positive (i.e. C≤1.7), otherwise negative (Fig 4) (i.e. C >1.7).
•
If ‘rm’ is not known, C may be taken as 0.7 which corresponds to uniform moment throughout the member.
•
‘C’ also should be taken as 0.7 where there is transverse loading, where first order moments are predominantly due to imperfections and where the members are not braced
2.2.4 Effective Length of compression members in regular frames (le) For compression members in regular frames, the effective length is determined in the following way Braced Members:
members at a joint for unit bending moment M EI = is the bending stiffness of compression member Io = is the clear height of compression member between end restraints. For the unbraced members with rotational restraint at both ends, the second equation above can be used. Quick inspection of this equation shows that for the theoretical case of a member with ends built in rigidity for moment (k1 = k2 = 0), but free to sway in the absence of positional restraint at one end, gives the effective length l0 = l It is the relative rigidity of restraint to flexural stiffness of the compression member i.e. important in determining effective length. Consequently, using the uncracked value of stiffness for the pier will be conservative as the restraint will have to be relatively stiffer to reduce the buckling length to a given value. This also is in line with the definition of radius of gyration, ‘i’, given in the in IRC: 112 which are based on the uncracked section. However it is apt that the cracking needs to be considered in determining the stiffness of a restraint, such as reinforced concrete pier base, if it significantly affects the overall stiffness of restraint offered to the pier. It is seen that quite often the overall stiffness is governed by the soil stiffness rather than Reinforced Cement Concrete element. Further fully rigid restraint is rare in practice that minimum value of the ‘k’ should be taken as 0.1, even if the joint is fully restrained.
Unbraced members:
Where
Fig. 5: Buckling modes for braced & unbraced situation
k1, k2 are the relative flexibilities of rotational restraints at ends 1 and 2 respectively.
θ / M = is the rotation of restraining 80 Volume 45
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Unlike While in building frames the degree of restraint can be easily assessed, in bridges it is difficult to assess the degree of restraint as the superstructure is supported on bearings (Fig 5) which creates boundary conditions within the bridge system by virtue of its layout making the assessment of braced or un braced complex. The Bridge and Structural Engineer
The value of the end stiffness to use for piers in integral construction can be determined from a plane frame model by deflecting the pier to give the deflection relevant to the mode of buckling and determining the moment and rotation produced in the deck at the connection to the pier.
warrants thorough understanding of the background deliberations for accurate application.
The case shown in the Fig 5 (b) above do not permit any rigidity of positional restraint in sway cases. However, this case is very hard to exist in reality and practicality. If significant lateral restraint is available, as might be the case (b) of Fig5 where one pier is very much stiffer than the other or carrying more axial force ignoring this restraint will be very conservative as the most flexible piers may actually be braced by the stiffer one. In such cases elastic critical buckling analysis carried out by computers give reduced value of effective length. The analytical method could also be carried out for such situations to deduce accurate effective lengths by applying coexisting loads to all columns and increasing all loads proportionately until a buckling mode involving the pier of interest is found, then the buckling load is the axial load in the member of interest at buckling. 2.2.5 Effective heights of isolated piers (le)
Fig. 7: Effective heights of isolated piers
Fig. 6: Effective Lengths as per model & euro codes
FIB model code 2010 and euro code2 for bridges give recommendations for isolated members of effective lengths as given in the Fig 6. While arriving at the above recommendations, it appears that the members were assumed to be infinitely rigid at bottom for the cases b) to e) and also some of the peculiarities of cantilever bridge piers supporting decking through bearings with in the bridge system were not considered as such the provisions appear to be on liberal side. On the other hand, the table (Fig.7) in IRC: 1121 borrowed from 1985 version of BS 5400 are on conservative side and
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Effective lengths to be used for cantilever bridge piers have been bone of contention even in the earlier version of codes. While traditionally, the effective height to be used for the piers which are held in position at both ends are based on realistic end conditions meaning, for the slender piers which are fixed at both ends 0.70 times of actual length of the pier, for one end fixed and other end pinned slender piers 0.85 times the length of the pier. For the cantilever piers which are supporting the deck through bearings, the effective lengths were said to be between 1.0 times the actual lengths of the pier to 2.00 times. The value between 1.0 times the actual length to 2 times is based on the assumption that the base pier is infinitely rigid for restraint while at the top of the cantilever pier, the degree of restraint varies depending upon the type of bearings used from various degrees of restraint to no restraint at all. Volume 45 Number 3 September 2015â&#x20AC;&#x192; 81
•
Linear strain distribution
•
Equal strains in reinforcement and concrete at the same level
•
Given stress-strain relationships for concrete and steel
Fig. 8: Translation and rotation functions in bearings
For the piers which are not in regular frame and supporting decks through bearings, finding out the extent of restraint at top is very complex as such there will be always a tendency to advocate and adopt the highly conservative and uneconomical effective lengths of 2.30 lo as proposed under the case 7 of Fig 7. In fact, after much deliberations, the said table was adopted in the code from BS:5400 part 4 which was based on a scientific investigation as brought out by P.A. Jackson in his technical report no. 561 for cement and concrete association viz. ‘The buckling of slender bridge piers and the effective height provisions of BS:5400:Part 4’3. The effective length of cantilever piers are the function of the behavior of bearings (Fig 8) giving rise to buckling mode of the cantilever. The readers are requested to refer to B&SE_Volume 44_Number 2_June 20145 for detailed deliberation on this.
3. Analysis for 2nd order effects There are three methods of analysis for 2nd order effects deliberated in codes. 1.
General Method.
2.
Nominal stiffness method.
3.
Nominal curvature method.
While the first method of analysis ‘General method’ is a nonlinear method of analysis more suited for computers, the 2nd and 3rd are simplified methods meant for manual calculations. For some reasons, ‘nominal stiffness method’ is not recognised in IRC: 112. 3.1 General method of nonlinear analysis Non-linear analysis of slender compression members includes material and geometric nonlinearity (second order effects). The method used rests on the following basic assumptions: 82 Volume 45
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Fig. 9: Accurate (Left) & Simplified (Right) version of General method
These assumptions are “classical” and are known to give realistic results. In the stress-strain relationships, a tensile strength of the concrete can be included, or disregarded. If a tensile strength is included, the effect of tension between cracks (tension stiffening) can also be taken into account. However, usually no effects of concrete tension are included. This is more or less conservative, “less” rather than “more”, and furthermore, it is a common principle to disregard the direct effect of tension in concrete in ultimate limit state design. “General” here refers to the fact that the method can be used for any type of cross section, any variation of cross section, axial load and first order moment, any boundary conditions, any stress strain relations, uniaxial or biaxial bending etc. The limiting factor is the capability of the computer program. In the accurate method as can be seen from Fig 9 (Left), conditions of equilibrium and deformation compatibility are satisfied in a number of cross sections, and the deflection is calculated by double integration of the curvature, having an assumed variation between the selected sections. Inelastic rotations are generally concentrated in these assumed critical sections. Deformation due to shear are generally neglected and axial deformations are considered only if absolutely necessary. Since principle of superposition is not applicable due to non-linearity, the calculations are The Bridge and Structural Engineer
carried out for each load condition where it is assumed that ULS is reached through a single proportional increase of load.
Esd=Esm/1.05 would be logical, considering that variations in the E-modulus are negligible. However, a factor 1.0 has been chosen as simplification.
In the simplified version (Right in Fig 9), only one cross section (or certain critical sections) is studied, and the curvature is pre-assumed to have a certain variation in other parts of the member. This enables simpler computer programs and faster calculation compromising a bit on accuracy.
In all the methods of analysis the following additional assumptions, related to the time-dependent properties of concrete, have been made:
Any stress-strain relations can be used. A continuous curve with a descending branch is considered to be the most realistic alternative for the concrete while the same is also convenient for computational reasons. The safety format is particularly important in second order analysis, where the absolute magnitude of deformations has a direct influence on the ultimate load. This has been taken care of by satisfying 2 basic criteria2: •
By using the same set of material parameters in all parts of the member, in order to avoid discontinuities and computational problems.
•
By adopting a format compatible with the general design format based on partial safety factors.
Both these criteria have been satisfied in IRC: 112 by use of design values directly in ultimate analysis. For concrete, λc = 1.5 for strength takes into account not only strength variation, but also geometrical deviations in the cross section. Assuming a factor 1.1
1.
The effect of concrete creep has been taken into account by extending the concrete stress strain curve according to Fig 10, i.e. all strain values are multiplied by (1+ φef). φef is a so called effective creep ratio, based on the final value of the creep coefficient and reduced with regard to the relative effect of long-term load in a load combination.
2. The shrinkage of concrete has been neglected. 3. The strength increase of concrete with time has been neglected. 3.1.1 Treatment of time dependent parameter creep2 Creep can be taken into account in different ways. The most accurate model would be to increase load and time in steps, for each step taking the stresses, strains (and corresponding deflections) from the previous step as starting values for the next increment. For each step, strains would be calculated taking into account their time-dependence. A simplified model is to multiply all strain values in the concrete stress-strain function with the factor (1+ φef), as in Fig.10, where φef is an effective creep ratio relevant for the load considered. With this model, the analysis can be made either in steps for loads of different duration or directly for the design load combination in one step.
Fig. 10: Simple way of taking creep in analysis. Source: Euro code 2 commentary, Published by the Europeon Concrete Platform ASBI, June 2008
for these deviations, and considering the relationship between strength and E-modulus, a reasonable value of the factor for Ec is λce = 1.1*(1.5/1.1)1/3 =1.2.
Fig. 11: The concept of effective creep ratio (φef) Source: Euro code 2 commentary, Published by the Europeon Concrete Platform ASBL, June 2008
For steel, λs = 1.15 includes a factor of about 1.05 for geometrical deviations. Thus, a design value
Through the Fig.11 the relevance of the effective creep ratio for slender columns are examined. A
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slender column behaves in a non-linear way, due to both material and geometrical non-linearity. The load history can be divided into three steps: 1. For the application of long-term load QL, immediate deformation is y1, for φef = 0 2.
For the long-term load QL during time t-t0, total deformation is y2, for φef = ϕ
3. For the load increase up to design load QD, additional deformation is y3 - y2, for φef = 0 The calculation representing the above load history involves three steps, including the relevant first order moments or eccentricities for each step. For simplification, steps 1 and 2 can be combined into one, using a stress-strain diagram with the strains multiplied by (1+ φ). This corresponds to line AC, and the calculation is then reduced to two steps.
creep deformations will mainly be governed by total moments. With this alternative, however, iteration is inevitable since second order moments depend on stiffness, which depends on effective creep ratio, which depends on total moments etc. Therefore, alternative a. will be the normal choice in practical design. Alternative a. is always more or less always the safe side, as the second order moment is a non-linear function of the axial load. Therefore, the moment increase due to second order effects will be greater under design load than under long-term load, and the ratio ML/MD will be lower if second order moments are included. Apart from creep, other parameters have a fundamental effect on the ultimate capacity of a slender compression member with a given cross section, which are
The last step can be calculated in further two alternative ways:
•
Amount and configuration of longitudinal reinforcement
1. After calculating point C, the additional load QD – QL is added, with deformation starting from y2. See line CD in Fig 16.
•
Slenderness
•
Boundary conditions
•
Magnitude and distribution of first order moment (or eccentricity of axial load)
•
In case of biaxial bending:
2. After calculating point C, the total load QD is applied “from scratch”, but with y0 = y2 - y1 as an initial deflection added to other first order effects. See line ED in Fig.11. Alternative 2, can be used in two-step calculations in the following way. The distribution of y0 along the column should in principle be the same as the distribution of y2 – y1. For a pin-ended column, however, a sinusoidal or parabolic distribution shall be adopted as a simplification. A further simplification is a one-step calculation, using an effective creep ratio φef; (line AD in the Fig.11). For the definition of ef there are two main options:
a. based on first order moments M0L and M0D, i.e. φef = *M0L / M0D
b. based on total moments ML and MD, including 2nd order moments, i.e. φef = *ML / MD
The relevant deformation parameter in second order analysis is curvature, which depends primarily on bending moment. Therefore, the axial load should not be included in the definition of effective creep ratio. Alternative b. is the most realistic one, since 84 Volume 45
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another first order moment, independent of the first one
proportions of cross section
3.1.2 Effect of shrinkage on analysis of compression member Shrinkage is a material property of concrete which is as inevitable as creep. Taking into account the effect of shrinkage is self-evident in many design situations, e.g. with regard to cracking in members with restraint to shortening, time-dependent losses of prestress and in accurate calculations of deflections. These design situations represent serviceability limit states. However, in ultimate limit states the effect of shrinkage, like many other types of imposed deformations, is usually disregarded. This is justified in most cases, due to the possibility for redistribution of stresses and moments. Slender compressive members are seldom restrained in such a way that it could give any effect of shrinkage on the member as a whole; The Bridge and Structural Engineer
furthermore, if there were such a restraint, it would rather be a favourable effect since it would reduce the axial force. This may be a reason why shrinkage is never discussed as a factor of importance for the load capacity of slender columns. However, shrinkage will have an effect on the internal stress distribution, which might in turn have an effect on deflections and hence on the ultimate load. Shrinkage leads to a transfer of compression from concrete to reinforcement, much like the effect of creep but independent of stress. This can be both favourable and unfavourable, depending on the concrete and reinforcement compressive stresses, cracking etc. It is difficult to say whether favourable or unfavourable effects will dominate. 3.1.3 Effect of increase in strength on analysis of compression members It is well established that the strength of concrete, at least the compressive strength, increases with time, due to the continued hydration of the cement. The tensile strength may not increase to the same extent, it may even decrease due to tension in the cement paste when the aggregates resist the shrinkage, but as long as the tensile strength is not relied upon for direct tension in ultimate limit state design this can be ignored. When there are second order effects, in which case other time dependent effects like creep and shrinkage become important, the problem is different. In the beginning of the service life, there is little strength increase but, on the other hand, deflections are not yet much influenced by creep (and shrinkage). Therefore, the critical design condition is normally assumed to occur at the end of the service life, when deflections are at their maximum due to the creep and to some extent shrinkage. On the other hand, at that time we also have the maximum effect of strength increase, and it is no longer self-evident that the most critical design condition is always to be found at the end of the service life; in principle it may occur at any time within the service life. Whatever possible unfavourable effect on the load capacity due to neglecting of shrinkage can be considered to be neutralised by the favourable effects that could have occurred due to strength increase. The Bridge and Structural Engineer
3.1.4 Simplified method of analysis for 2nd order effects In simplified methods the difference between cross section resistance and first order moment, Mu - M0 is used as a second order moment. When this moment is added to the first order moment, a design moment is obtained for which the cross section can be designed with regard to its ultimate resistance. There are two principal methods to calculate this second order moment: •
Estimation of the flexural stiffness2 EI to be used in a linear second order analysis (i.e. considering geometrical non-linearity but assuming linear material behaviour); this method is called stiffness method.
•
Estimation of the curvature 1/r corresponding to a second order deflection for which the second order moment is calculated; this method is called curvature method, recognised in IRC: 112.
The total moment (Fig. 12) including second order moment for a simple isolated member is:
1 l2 M=M0+M2=M0+N.y=M0+N ⋅ ⋅ r c •
M = total moment
•
M0 = first order moment including imperfections. M2 = second order moment
•
N = axial force
•
y = deflection corresponding to 1/r
•
1/r = curvature corresponding to y
•
l = length
•
c = factor for curvature distribution
Fig. 12: Simplified methods for pin ended column Source: Euro code 2 commentary, Published by the European Concrete Platform ASBL, June 2008
Volume 45 Number 3 September 2015 85
IRC:112 requires to consider geometric imperfections in to account in many places. The effect of imperfection as per fib model code and euro-code are represented by an inclination, θ1 =
αh 200
Where is the reduction factor for the clear length (lo): ah=2/ lo ≤″ 1
Where, •
Ned is the design value of axial force
•
e2 is the deflection
•
1/r is the curvature.
•
le is the effective length.
•
c is a factor depending on the curvature distribution. For constant cross section, c=10 = (�2) is normally used. If the first order moment is constant, a lower value should be considered (8 is a lower limit) corresponding to constant total moment
As per IRC :112 imperfections has to be treated as first order effects as the code recognises nominal curvature method for second order analysis. As there is a link between imperfections and tolerances, an analysis ( Table 1) has been carried out up to 60 m tall piers, both for imperfection as per euro-code and tolerances as per EN 13670 during the convergence process and finally the best fit is recommended as e =
Fig. 13: Accounting for 1/r while calculating M2 (Source : Euro code 2 commentary, Published by the European Concrete Platform ASBL, June 2008)
l 15 + o imited to 50mm in the latest IRC. 800
In the stiffness method 1/r is expressed in terms of an estimated nominal flexural stiffness, i.e. 1/r=M/ EI, while in curvature method curvature is estimated directly on the basis of assuming yield strain in tensile and compressive reinforcement i.e. 1/r = ɛyd/0.45d. Differing first order end moments M01 and M02 may be replaced by an equivalent 1st order end moment Moe: where,
As mentioned in the Fig.14, 1/r is estimated on the basis of reaching yield strain in tensile and compressive reinforcement. Here correction factors Kr and Kφ are included. Where there is unambiguous definition of d, the effective depth is worked out as per Fig.14 in which is is the radius of gyration of the total reinforcement area. Kr is a correction factor depending on axial load. In order to reduce the curvature in cases where yielding is not reached in the tensile reinforcement, a factor Kr is introduced.
M0e=0.6 M02 +0.4M01 ≥ 0.4 M02. M01 and M02 should have the same sign if they give tension on the same side, otherwise opposite signs. Furthermore | M02 | ≥ | M01 |.
•
η = relative axial force = NEd/Acfcd
•
NEd = design value of axial force.
The 2nd order moment M2 is deduced by the expression
•
ηu = 1 + ω
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The Bridge and Structural Engineer
•
ηbal = value of n at maximum moment of resistance; the value 0.4 may be used (Fig.14)
•
ω = Asfyd/Acfcd
•
As = total area of reinforcement.
•
Ac = area of concrete cross section
any of the above methods, including imperfections. It is only necessary to consider imperfections in one direction, but the direction should be chosen to determine the most unfavorable overall effect.
Kφ is a factor for taking account of creep which is given by Fig. 15: Different slenderness in 2 direction (Source: Euro code 2 commentary, Published by the Europeon Concrete Platform ASBL, June 2008).
Where
Comparisons with the general method indicate that in certain cases the method can give unsafe results if allowance for creep is not considered, and the factor Kφ has been introduced for this purpose. It has been calibrated against calculations with the general method. •
φef = is the effective creep ratio
•
λ = is the slenderness ratio.
There are areas where biaxial bending moments can be neglected, like after considering bending in each direction separately, if the slenderness ratios in the two principle directions do not differ by more than a factor of 2 and the ‘relative eccentricities’ do not differ by more than a value of 0.2 as represented in Fig.15. Where this is not satisfied, the moments in the two directions (including second-order effects) must be combined, but imperfections only need to be considered in one direction such as to produce the most unfavorable conditions overall. Section design under the biaxial moments and axial force may be done either by a rigorous cross-section analysis using the strain compatibility method or by simple interaction a
Mx My + M Rx M Ry
Fig. 14: ηbal as 0.4 at maximum moment of resistance (Source: Fib model code 2010)
3.1.5
Biaxial bending
The effects of slenderness for columns bent biaxial are most accurately determined using non-linear analysis. The simplified methods can also be used for the case of biaxial bending. The second-order moment is first determined separately in each direction following
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a
≤ 1
•
Mx/y design moment in the respective direction, including nominal 2nd order moment
•
MRx/y corresponding moment resistance of cross section
•
a exponent varying up to 2.
For circular columns, it is possible to take the vector resultant of moments in two orthogonal directions, thus transforming the problem into a uniaxial bending problem with M2 considered only in the direction of the resultant moment. In general, however, it is recommended here that M2 conservatively be calculated for both directions. Bending should then be checked in each direction independently, and then biaxial bending should
Volume 45 Number 3 September 2015 87
be considered (with M2 applied in both directions together) unless second-order effects can be neglected in one or both directions. Imperfections should only be considered in one direction.
4.
Lateral stability of slender beams
below by illustration of an example as shown in Fig.16. The improper lifting hook placement and casting imperfection can cause the beam to be tilted at an initial angle θ1 near the lifting hook location about the roll axis. Normally the casting imperfections
IRC 112 requires to investigate lateral instability of precast bridge girders before it becomes a part of the finished bridge system, during casting, transportation and erection. It specifies l/300 as casting geometric imperfection for unbraced conditions where l = total length of beam. While carrying out investigation for lateral instability, the 2nd order effects could be neglected on fulfillment of following empirical conditions •
in persistent situations: and h/b ≤ 2.5
•
transient situations: and h/b ≤3.5
I0t is the distance between torsional restraints
h is the total depth of beam in central part of lot
be is the effective width of compression flange
The IRC:112 proposes the clear distance between the restraints of 60 be or , whichever is the lesser, for the lateral stability of simple or continuous beams, where ‘d’ is the effective depth ‘be’ is the breadth of the compression flange of the beam midway between restraints. For cantilevers with lateral restraint provided only at the support, the clear distance from the free end of the cantilever to face of the support is limited to 25bc or
, whichever is the lesser.
The above empirical expressions seem to be applicable for non-pre stressed beams. The pre stressed beams have more complexities due to induced pre stress resulting in locked up compressive and flexural stresses in beams. Robert F Mast6&7 deliberates extensively on ‘Lateral stability of long prestressed concrete beams’ in two parts i.e. part 1 and part 2, published in PCI Journals Lateral stability aspects of PSC beams are discussed 88 Volume 45
Number 3 September 2015
Fig. 16: Equilibrium of PSC beams on supports (Source Robert F Mast, Lateral stability of long beams, PCI Journal/January-February 2993)
considered gets manifested itself by way of curvature in plan of beam after transfer of prestress force. Lifting hook placement tolerance needs to be considered during casting. The above tilting of beam induces the lateral deflection about weak axis of the beam. Because of the transfer of prestress, there is already tension at the top fiber of the beam for which the tensile stress caused about the weak axis by the component of the self-weight due to tilt gets added which needs to be within the permissible limits and in fact decides the maximum tilt ( θmax) to which the beam can be subjected to. After the tilting is initiated by the initial angle θ1 near the support locations, the beam achieves its equilibrium with a uniform lift angle θ (shown at midspan) with CG of the mass of the deflected beam right under the roll axis. In the figure as Zo approaches Yr, the beam starts rotating and becomes totally unstable even without the initial imperfection and without improper location of lifting hook. Thus the safety against the lateral buckling is a measure of Yr vis-à-vis Zo and is called gross factor of safety (FOS = Yr/Zo) for a perfect beam without imperfection. If one has to account for imperfections causing the initial angle θ1 and limiting the maximum . lift to θmax, the factor of safety reduces to However, it is more logical to deduce the factor of safety against lateral stability by dividing maximum The Bridge and Structural Engineer
possible tilt θmax with that of equilibrium rotation θ at midspan. Moving the lifting position inwards improves the factor of safety against lateral stability by virtue of reduced deflections caused by rotations about the weak axis. However, it has to be ensured that the stresses are within the limits in overhang portions. Classic studies of lateral buckling of beams are based on the assumptions that the supports are restrained for rotations. However for prestressed beams in the casting yard, the same has to be supported on elastic pads as the prestressing has to be induced. Due to the casting imperfections buckling is caused by the middle part of the span twisting relative to the support creating a sideway deflection. In case of the beams that are lifted by lifting hooks the roll axis is at top while the beams that are supported during casting as well as during transportation have the roll axis at the bottom. Thus the value Yr for the beam being lifted is below the roll axis whereas for those beams laterally buckling and bottom supported have Yr above the roll axis, all the other other principles and concepts of lateral buckling being the same.
5. Conclusions In the paper above, the background of clauses for Ultimate Limit State for induced deformations have been presented which will help the users to understand the intent of the clauses there by avoiding the misinterpretations. As there is always bone of contention about the effective heights of cantilever piers, the same has been deliberated in detail. The
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provisions made in IRC: 112 for lateral instability of beams seem to cater for only non-prestressed concrete beams as such the aspects of lateral buckling of pre stressed beams are discussed which may be useful for the readers. Most of the deliberations including the figures are taken from background documents prepared by the project team for EN 1992-1-1(2004) as such the same is acknowledged very profusely.
References 1.
IRC: 112: Code of practice for Concrete Bridges.
2. Euro code 2 commentary, Published by the European Concrete Platform ASBL, June 2008. 3.
P.A. Jackson, the buckling slender bridge piers and the effective height provisions of BS: 5400: part 4, CECA Technical report 561, June 1985.
4.
BS EN 1992-2 : 2005, euro code 2 – Design of concrete structures – part 2 : concrete bridges – design and detailing rules
5. V N Heggade, A vision of modern structural code of practice: bridge between code making and practice, the bridge & structural engineer, B & SE_Volume 44_Number 2_June 2014. 6. Robert F Mast, Lateral stability of long prestressed concrete beams Part 1, PCI Journal/ January-February 1989. 7. Robert F Mast, Lateral stability of long prestressed concrete beams Part 2, PCI Journal/ January-February 1993.
Volume 45 Number 3 September 2015 89
INDIAN NATIONAL GROUP OF THE IABSE OFFICE BEARERS AND MANAGING COMMITTEE – 2015 Chairman 1. Shri DO Tawade, Chief Engineer (CoordinatorII), Ministry of Road Transport and Highways Vice-Chairmen 2. Shri Divakar Garg, Director General, Central Public Works Department
Past Member of the Executive Committee and Technical Committee of IABSE 11. Prof SS Chakraborty, Past Vice-President, IABSE 12. Dr BC Roy, Vice President & Member, Technical Committee, IABSE Honorary Secretary
3. Shri MP Sharma, Member (Technical), National Highways Authority of India
13. Shri RK Pandey, Chief Engineer (Planning), Ministry of Road Transport and Highways
4. Shri Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt. Ltd.
Members of the Executive Committee
5. Shri MV Jatkar, Executive Director (Technical), Gammon India Ltd. Honorary Treasurer 6. The Director General (Road Development) & Special Secretary to the Government of India, Ministry of Road Transport and Highways Honorary Members 7.
Shri Ninan Koshi, Former DG (RD) & Additional Secretary
8. Prof SS Chakraborty, Honorary Member & Past Vice-President, IABSE Persons represented ING on the Executive Committee and Technical Committee of the IABSE 9. Dr BC Roy, Vice President & Member, Technical Committee, IABSE 10. Dr Harshavardhan Subbarao, Member, Technical Committee of IABSE & Chairman and Managing Director, Construma Consultancy Pvt Ltd
90 Volume 45
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MEMBERS OF THE MANAGING COMMITTEE – 2015 Rule-9 (a): A representative of the Union Ministry of Road Transport and Highways 1.
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Rule-9 (b): A representative each of the Union Ministries/Central Government Departments making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time 2.
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3.
NHAI - nomination awaited
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36. Shri AK Banerjee , Former Member (Technical), NHAI
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37. Shri AV Sinha, Former DG (RD) & Special Secretary
51. Shri AD Narain President, ICT Pvt Ltd
38. Shri RP Indoria, Former DG (RD) & Special Secretary 39. Shri V Velayutham , Former DG (RD) & Special Secretary 40. Shri Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt Ltd
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