CONCRETE BRIDGE PRACTICE Analysis, Design and Economics SECOND EDITION Dr V.K RAINA Ph D (London), DIC (London), MICE (London), ©. Eng., P. Eng. (Ontario) Civil Engineering Adviser Tata McGraw-Hill Publishing Company Limited New Delhi MoGraw-Hil Offices New Delhi New York St Louis San Francisco Auckland Bogota Guatemala Hamburg Lisbon London Madrid Mexico Milan Montreal Panama Paris San Juan $a0 Paulo Singapore Sydney Tokyo Toronto© 1994, 1991, RAINA, VK [No par of this publication can be reproduced in any form or by any means ‘without the prior written permission ofthe publishers “This edition can be exported from Indi only by the publishers, ‘Tata McGraw-Hill Publishing Company Limited ISBN’ 0-07-462362-1 Published by Tata McGraw-Hill Publishing Company Limited, 4/12 Asat Al Road, New Delhi 110002 aserypeset at Laser Words 13, Prithvi Avenue, Madias 600018 and printed at Rakamal Electric Press, 3835/9 GT Kamal Rosd, Delhi 110033for the development of the so-called THIRD WORLD COUNTRIES ‘many of which, in the past were physically conquered, politically subjugated, culturally oppressed, and economically exploited I dedicate this work to THE INTERNATIONAL BANK FOR RECONSTRUCTION AND DEVELOPMENT and THE UNITED NATIONS ORGANISATION ‘for their pious and commendable efforts whether ‘they’ be the ‘wealthy’ poor, the ‘well-to-do’ poor, or the ‘rock-bottom’ poor, their continued dependence on alien ownership of technology must be checked so that these peoples are reasonably protected against commercial exploi- tation. There is no alternative for these countries but to search from within to strengthen their own infrastructures! We, as today's well-wishers, have an urgent job to do. We must take a leap-of-faith and remember that the only thing dark about these countries is our own ignorance about them! Technologies must be bent to suit the indigenously available manpower, ‘materials and equipment as far as viable, and simultaneously the infrastructure must be strengthened by massive manpower training programmesForeword ‘The twentieth century heralded a new era in bridge building ‘concepts with large improvements in materials and methods, Structural steel and reinforced concrete began to be used extensively. Rapid developments in the theory of structures along with the advent of the computer made it possible to pioneer innovative designs. Sophisticated mathematical and ‘model analysis was increasingly used to predict the behaviour of structures. With the massive knowledge explosion and the eagemess of creative men to develop large and more daring spans, there have been many pioneering achievernents in the USA and Europe, which are indeed marvels of engineering. ‘The design of bridge structures has become intricate with the changeover from the conventional girder slab bridges to the complex interchanges requiring curved units or cable stays or suspended units, The analysis of such structures, hhaving different forms and shapes, requites ingenuity of @ high order as research may lag behind practical possibilities. How then can we, builders of bridges, calculate and design those daring structures to safely support the loads of railway trains or heavy vehicles and to withstand the often unpredict- able forces of wind and water. ‘The emphasis on theory and too little consideration for structural detailing and on-site realities have resulted in bridge collapses in the not-too-distant past, To desist from using ‘new methods and materials seems tobe a wise way of reducing the risk of error and consequent failures. Thanks to the dynamism of the professionals, bridge builders continue to build spans larger or attempt forms of construction more elegant and more economical than ever before. In the words of Paul Bonatz and Fritz Leonard, “Every new difficulty challenges the human spirit to think of new solutions which in turn push forward the threshold of what can be done.” Undoubtedly. the public and even some engineers believe that the ultimate in bridge design and construction has been reached for the present. OF course, this remains to be seen; history would indicate otherwise. ‘The engineering work on large bridge projects of today {sso complex that many engineers are involved in the design and construction activities. The eredit cannot go primarily to one person as it did in the past. Large firms of specialists in many areas are involved, Nevertheless, one man has to make the final decision. These decisions, of which there may be several, call for a wealth of technical knowledge and sound judgement based on many years of experience, ‘This book by Dr V K Raina—Concrete Bridge Practice: Analysis, Design and Economics te fourth book in his series of six books treating various facets of bridge engineering— provides a comprehensive coverage on the subject for both the designer and the constructor. The book is like a programmed text giving discrete steps to decision making. It is based on the author's experience both in India at abroad. His present assignment is as United Nations Exper in Saudi Arabia. He says, “It is no exaggeration to state that more bridges of many varieties, including some flyovers exceeding 10 km in length each, have been designed and built in Saudi Arabia in the late seventies and eighties than anywhere else in the world. If there ever existed in the world a feast of designing and building prestressed and reinforced concrete bridges, it was in Saudi Arabia during this period and it was not for nothing that so many internationally operating consultants and contractors converged in.” It is this setting that inspired Dr Raina to write this Santasiic book providing an integrated coverage of the structural analysis and design of both conventional and modern bridges. It was his passion for the bridge art, which Jed him to take up this study. Dr Raina has written in the language of the engineer. The reader, on going through this ‘book, will acquire a far-reaching insight into design procedures, and methods and the interpretation and use of design specifications. It furnishes the practising engineer with much needed data to meet the challenges in his work Hfe. It is can excellent source of reference. Dr TN Susana Rao Managing Director Gammon India Limited, BombayAWord to the Reader Talking alone never pulled out a stump! Many try to throw about the weight of their purely academic degrees, non-productive publications, classroom or staid-office experiences, and even the thunder of their committee- memberships. In the end, only those that have finally actually been moulded on the professional anvil, are of real value—those that have had protonged but succeseful exposures to furiously resultoriented and profit-bearing competitive practical commercial experiences where the next month's survival depends on the previous month’s turnover. ‘My aim in writing this book is two-fold. One is to benefit those who may wish to receive exposure to actual professional practice from the ‘scene of action’ standpoint as distinct from a ‘theoretical’ classroom hyperbole that belongs to an almost imaginary ‘air-conditioned’ world that is fr and remote from the sleeves up workmanlike life-size actuality! Second is to try and ‘talk’ to the engineer in short straight steps, ‘explaining the subtleties en route, in the vein of a story narrated informally, without ‘mystifying’ him with exotica Descriptions have been written with clarity and brevity s0 that the engineer is neither overawed nor bored with jargon that i either too theoretical or oozing with impressive looking useless detail. This book takes the reader by the finger through the labyrinths of the subject in a workman-like manner, and thus caters for the contractor, the client and the practice- oriented engineer student alike! OF the numerous works that have been written upon the subject of bridge analysis and design, many ate excellent examples of mathematical gymnastics rather than of ‘engineering application! In this book the steps of the reader are guided in paths often trodden by and therefore familiar to the author, who, thereby, is able to recommend a straight course without the designer having to waste time in search Jor a route. If Ihave succeeded in some measure, it is not only by being a encyclopaedic, but because the presentation is fresh in treatment, and, above all, easy to study and follow. It concisely provides what the designerengineer wants, without making demands on his energy. However, the subject being what it is, and the wark involved being awesome (as suggested by the title of the book), I have had to presume that the reader already has some experience in the analysis, design and detailing of concrete bridges, with a reasonable exposure to competitive professional practice. Engineering is not just doing theoretical sums, nor is it ‘a matter of biind adherence to graphs and formulae. One ccan ran the danger of becoming too concemed with “leaming” and not be concemed enough with ‘practical realities.” tis more meaningful to have an approximate solution to an exact problem than an exact solution to an approximated problem. A useful book does not have to be the graveyard ‘of dead Ph Ds! As a prolific practitioner who has operated in so many countries and has worked with myriads of contractors and consultants, 1am disturbed if a book purports to be ‘practical’ when it is packed with pages of iterative ‘empicics and impressive looking graphs that are only of very restricted use and, worse still, is written by someone who has never stayed, survived and surfaced in the merciless world of competitive practice in construction and design. ‘That is where all the fun is and where one grapples with the survival situations that can cause ulcers! A good musician is far superior to a music-critic! Practical engineers must bbe conceptual more than perceptual, creative more than analytical and more visual than merely mathematical. They have to have a wide breadth of experience rather than an isolated narrow specialisation alone, Originality comes out of understanding, and understanding comes out of relentless practice, not from mere information. Last but not the least, 00d judgement comes out of experience and experience often comes out of bad judgement! Da VK Raaé Acknowledgements As acknowledged in my other books. one of the prices a professional practitioner has to pay is that he, unlike those involved in research and laboratory work, classroom lectures, or staid-office work, hacdly has time to write. A chronic practitioner would rather spend the time in designing (and still more designing) and constructing (and still more constructing) than just writing! But of course it would be very useful if such a real-life practising-professional, who has his fingers on the pulse of practice and in fact has a lot to write about, could squeeze tite in order to ‘also write” for the profession, however hard it might be for him to find that time! It would be even more meaningful if he, ‘additionally, had a practical research background that would help him sift grain from husk. Fired by this feeling, I took up writing the present book in the humble hope that it may provide an amalgam of practice and theory, with the former subordinating the latter in order that the book be of gainful use to the practising engineer. With the mind boggling and unparalieled spree of fast growth of world-class super-expressway and highway ‘networks in Saudi Arabia, I, seconded by the United Nations (Department of Technical Cooperation for Development) as the in-house adviser to the Ministry of Communi the Saudi Government, was involved first-hand with optimised design and construction of several bridges in many interchanges, crossings and flyovers, of various types, spans, skews and curves, with many consultants and contractors, (it is no exaggeration to state here that more bridges of many varieties, including some flyovers exceeding 10 kim in length each, have been designed and built in Saudi Arabia in the late seventies and the eighties than anywhere else in the world! If there ever existed in the world a feast of designing and building prestressed and reinforced concrete bridges, it was in Saudi Arabia during this period and it was not for nothing that so many internationally operating Consultants and contractors converged in.) am indeed grateful both to the United Nations and to the Saudi Government for this challenging responsibility and the additional satisfying and revealing practical experience this opportunity afforded. In tum, I gratefully acknowledge the trust, confidence and appreciation shown by them. If I have acquitted myself creditably in their eyes, the credit is all theirs. It is this additional important experience that further prompted me to write this book. Apart from drawing upon my own. experience end interaction with others, in preparing this book, I have also drawn on some of the material published by the British Standards, the Indian Standards, the American Concrete Institute, the American Association of State Highway and ‘Transportation Officials, the C&CA London, the FIP, CEB, the Indian National Group of the [ABSE (Zarich), the Indian Roads Congress, New Delhi, the British Steel Designer's Manual, CS Reynolds, AH Allen, A Witecki, B Richardson etal, GH Ryder, Podolny & Muller, Freyssinet Intemational, Paris, PK Thomas, GN Smith and EN Pole, E Pennels, MJ Tomlinson, PW Ables et al., Fisher Cassie, W Teng, and various proprietary firms. to all of whom I am greatly indebted and owe grateful thanks. 1 am thankful to various consulting engineering firms ‘and contractors (Dar Al-Hendasah, London, UK), Wilson Murrow (Salina, USA), Ital-Consult (Rome, Italy), Sauti- Renardet (Rome, Italy), Technic (Rome, Italy), Saudi-Consult Riyadh (KSA), R. Travers Morgan and Ptas, (London, UK), Arabian Engg: Bureau (Riyadh, KSA), Rhein-Rubr Ingenieur (Dortmund, W. Germany), Dar Al-Riyadh (KSA), Doxiadis (Athens, Greece), Ove—Arup (London, UK), Gilcon PS Ltd, (New Delhi, India) Gammon India Ltd. (Bombay, India), US Dugal & Co. P. Ltd. (New Delhi, India), CCC (Lebanon), ‘Al-Mashrik Contracting (KSA), Naser Haza & Bros. (KSA), Han Yang (S Korea), Edok-Eter (Athens, Greece), Tanmia (Riyadh, KSA) and J & P (Cyprus), to name only some), with whom T worked in different capacities in different countries. I also wish to acknowledge the opportunity I got of designing some of the first class curved and skew conti: ‘uous prestressed concrete bridges in Canada while working with the Ontario Department of Transportation (previously, ‘The Department of Highways), Toronto. These experiences 1 assiduously sifted and stored over the long years with a view to sharing them with others through this book. Last but certainly not the least, I wish to express my heartfelt gratitude to Vinita, my dear wife, for ber limit state endurance. While we both tried to serve the underserved through our respective professions, engineering and medicine (she has a Doctorate from London University in Bone Patho~ logy), but perhaps we did this too devotedly..since this led to the neglect of priorities on our domestic front. Perhaps the cost to us in terms of common and worldly-mundane equations of understanding has. been high, but it took us strength to stand the oneness of self-inflicted individual solitudes and solitude is always an exercise in agony! Ican never pardon myself enough for causing to my wife (and tox Acknowledgements rn eel some extent to my parents) silent suffering and loneliness, with all its consequences and resulting despatch from (what to most people are) essential worldly norms though in reality only transitory, indeed illusory, in the ultimate mortal sense! ‘This was due 10 my professional commitments taking me away ofien-times, often to different lands, for long periods of time for years not just months, while her own professional commitments kept her tied back. The only solace was that int the resulting void I invested the time for five years in writing this book and my other four books (and various papers), vtilising literally each available minute every single day (outside my crowded official work schedule), shunning the time-consuming and generally frivolous social get- togethers, and denying myself even the minor indiscretions of relaxation, (Only a bit of yoga kept me going.) Judgement is left o posterity Dr VK RasaContents Foreword vii A Word to the Reader vith Acknowledgements ix 1, The Basic Principle of Practical Structural Analysis and Design 1 1.1 Introduction 1 1.2 Summary of the tool-kit approach for analysis and design of a usual type of bridge J 2. Forces to be Considered in the Analysis for the Design of a Bridge 6 21 Main forces 6 2.2 Some relevant considerations 6 3. Live Load on Road Bridges 9 3.1 General background 9 3.2 Loadings of different countries 10 3.3 Some interesting comparisons in the different types of loadings 17 3.4 Details of some national (highway) bridge loadings 15 References 25 4, Structural Concrete 26 4.1 Concrete for construction 26 42° Some rough-and-ready information 28 5. Details of Structural Reinforcement Bars and Mesh Fabrics 32 6. Details of Prestressing-steel, Tendons and Anchorages 41 6.1 Types of steel 41 62. Prestressing tendons 43 7. The Substructure oo 7.1 Introduction 60 7.2. Important definitions 60 7.3. Open foundations 63 74 Pile foundations 64 7.5 Small diameter single and double under-reamed and relatively short bored piles 67 7.6 Caissons or ‘well'foundations 70 7.7 Pier and abutment 80 9. 10. nL Distribution of Externally-Applied and Self- Induced Horizontal Forees among Bridge- Supports in Straight-Decks 83 8.1 Introduction | 83 8.2. Simply supported non-skew straight decks on unyielding supports 83 8.3. Distribution of longitudinal horizontal forces among bridge-supports in straight-decks in simple and continuous spans on unyielding or flexible supports 84 8.4 Application 85 85 Conclusion 91 Distribution of Externally Applied and Self Induced Horizontal Fores among Bridge- Supports in Curved and/or Skewed Decks {Simple or Continuous Spans) 2 9.1 Introduction 92 9.2 Analysis 93 9.3 Application 96 94 Conclusion 98 Estimation of ‘Design Values’ of Axial Load and Bending Moment in a Tall Stender Bridge Support—Guarding against Buckling Effect 99 10.1 2nd order theory 100 10.2 Conclusion 104 References 104 Analysis and Design of Stender Exposed Piles in a Group 105 H1.1 Introduction 105 11.2 Analysis for column action by second order theory 106 11.3 Application 105 114 Recommendations 109 ILS Numerical example 117 References 114 Annexures 115 Estimating Safe Bearing Capacity of Soils for Footings, Caissons and Piles 118, 121 Introduction 118————————— xii Contents 2B. 4 18. 16. 1. PART I (Workman-like Approach) 1/9 (A) Various preliminaries, and obtaining quickly a rough-estimate of the safe bearing capacity (S.B.C) of soil 1/9 More accurate estimation of S.B.C. of soil under a footing or a caisson 127 (©) Soil resistance to a pile 125 (D)_Soil resistance to a group of pites PART Il (Some Relevant Details) 130 (Improving the bearing capacity of soil ‘and making foundations on weak soils 130 Various in-situ penetration tests employed in the estimation of sub-strata bearing capacity 132 Safe bearing capacity of rocky substrata B7 Soil parameters: Some typical values 138 By 17 a «ud ayy Estimating the Net Dependable ‘Passive Less Active’ Earth-Pressure Relief from Undisturbed Soil Mass Gripping the Foundation-Bulkhead between the Maximum-Scour Level and the Founding-Level 13.1 Case A 141 132 Case B 144 13.3 Active earth-pressure on abutment or on retaining. wall, founded on footing or piles 146 Mi Evaluation of Base-Pressure and Contact-area under Foundations Subjected to Direct Load and Any-Axis Bending a7 Friction Slab for Stabilising Abutments and Retaining Walls 150 15.1 Procedure 150 Reinforced Earth Structures 152 16.1 Principle of reinforced earth 153 16.2 Current design and construction systems 156 16.3 A note about ‘costing’, ‘construction time” and ‘care needed during construction’ 162 16.4 The British versus the French codes of practice 163 16.5 Testing of fill material 16.6 The problem of corrosion References 165 163 164 Bearings for Bridges 166 17.1 Bearings 266 17.2. Bridge superstructure movements 17.3 Development of Bearings 167 166 VD. 17.4 Types of Bearings recommended for various span-lengths and support-flexibility conditions 169 17.5 Practical considerations in the specification, design, manufacture and quality control of mechanical bridge Bearings 171 17.6 Lessons from some actual distress experiences 173 17.7 Structural design of various types of Beatings 174 178. Design of linear concrete hinge (rocker) Bearing 184 179. Details of laminated neoprene Bectings 189 17.10. Some of the versatile and modern larger capa- city Bearings 194 17.11 Anticulasion systems 204 References 205 ‘The Superstructure 206 18.1 Introduction 206 18.2 General comparison of reinforced concrete and prestressed concrete superstructures 209 18.3 Slab type superstructure (Solid or voided), Statically determinate or indeterminate 209 18.4 Beam-and-slab and box-type superstructures 210 18.5 Economie spacing between beams 2/1 18.6 Balanced cantilever type superstructures 2/2 18.7 Continuous type superstructures 212 188 Segmental deck construction 2/3 189 Frame bridges 217 18.10. Brief check-list for structural analysis, desiga and construction for various types of super- structure 221 ‘Transverse Distribution of Live Load among Deck Longitudinal 19,1 Introduction 229 19.2 Basic features related to transverse load distribution 237 Transverse distribution of loads (as per ACI Committee 343 Report and AASHTO specifi- cations) 235 Courbon’s method for estimating transverse distribution of live load among deck longitu- dinals in a beam-and-slab type deck 238 Little and Morice method (for estimating transverse distribution of live load among the deck longitudinals in a solid-slab type or a ppseudo-slab type or a beam-and-slab type deck) 239 Grillage method (for estimating the appor- 229 193 194 195 19.6aL, 2. 2B. Contents xiii tionment of the applied toad effect in the longitudinal and the transverse members of the deck) 243 19.7 Transverse distribution of live toad in box sections 257 References 260 . Practical Structural Analysis 261 20.1 Aim 261 is—fundamental concepts. 26/ 20.3 “Area moments’ method of analysis 270 20.4 ‘Strain energy’ method of analysis 274 205 ‘Moment distribution’ method of analysis 278 206 Slope deflection’ method of analysis 288 20.7 “Flexibility method of anaiysis (jk or Vrs method) 29 208 Beams on elastic foundations 306 20.9 Simplified aids for rapid hand-analysis 308 Baker’s Method for Ultimate Load Analysis of Indeterminate Concrete Structures 382 References 353 Effect of Differential Settlement of Supports ina Statically Indeterminate Structure 354 22.1 Effects of (an assumed) pier settlement on the ‘moments in the superstructure 354 22.2 Calculating the effect of differential settlement of supports in a statically indeterminate structure by the flexibility method 354 Reinforced Concrete Design 387 23.1. General background and principle of reinforced concrete design 357 23.2 Elastic design method 358 233 Load-factor design method 360 234 Detailing 376 References 376 |. Practical Design against Shear and Torsion and Design of Short-cantilevers and Deep-beams 37 24.1 Principle of design against shear 377 24.2. Design of short-cantilevers, corbels and brackets 578 24,3 Design of an articulation (ie. a halving joint) 379 24.4 Design of deep beams 387 24.5 Design against combined shear and torsion 582 References 386 25, Design of a Reinforced Concrete Section Subject to Combined Axial Thrust and Any-axis Bending—Simplified Practical Method 387 25.1 Introduction 387 25.2 Theory 387 25.3 Examples 389 Conclusion 396 26. Post-tensioned Prestressing of Concrete 397 26.1 General principles of prestressed concrete 397 26.2 Stages of loading 397 263 Prestressed versus reinforced concrete 398 26.4 Systems 400 26.5 Cable frietion calculations 407 266 Effect of cable-blockage 412 26.) Design of cable-anchorage zones (end blocks) in post-ensioned prestressed concrete 42 268 Concordant cable profiles in continuous prestressed concrete beams 4/5 269 Non-concordance and estimation of secondary prestress moment, shears and reactions in continuous prestressed concrete beams 417 26.10 Linear transformation of continuous prestre- ssing tendon profiles in continuous beams 419 26.11. Limits of linear transformation of cable profiles in continuous beams 42 Reference 421 27, Behaviour of a Structure during the Loading History all the way up to Collapse, and Estimation of Moments Attained at ‘Ultimate’ taking ‘Redistribution’ into account 22 27.1 Deformation characteristics 422 27.2 Collapse behaviour of continuous beams 423 27.3. Proposed method for estimating true ultimate bending moment distribution 423 27.4 Bffect of tendon transformation on ultimate strength 427 21.5 Importance of workman-like “detailing” 428 27.6 Estimation of various limiting moments and stress-strain relationship 428 References. 429 28. Effect of Tendon Transformation on Ultimate Strength of Continuous Prestressed Concrete Beams 430 28.1 Analytical derivation of the proposed formula #30xiv Contents 29, Simplified Method for the Analysis of Torsional Moment as an Effect of a Horizontally Carved Multispan Continuous Deck 436 29.1 Introduction 436 29.2 Longitudinal analysis 29.3 Torque analysis 438 References 442 437 30, Temperature Stresses in Concrete Bridge Decks—Simple Design Method 30.1 ‘Introduction 445 30.2 The three causes 445 30.3 Predicting temperature distribution through deck-depth (for evaluating eigenstress) 447 30.4 ‘Thermal crack pattern 449 30.5 Thermal stresses 450 30.6 Recommendations 451 30.7 Numerical examples 452 References 453 Annexure 455 445 31. Transverse Analysis of Some Typical Concrete Deck-Sections, i.e. Analysing a Deck Cross- Section 31.1 Background 457 Case (A): Twin-box-section with an inter- connecting top slab 458 Malticell box-section with equal- thickness webs 463 Multicell box-section with stub central web 466 Two-cell box-section with solid central spin 473 Voided deck section 475 Analysis of “deck-slab in ordinary “beam-and-siab" type of deck and ordinary ‘slab’ type of deck 476 478 479 487 Case (B): Case (C): Case (D): Case (B): Case (F): References Annexures 32, Expansion Joints for Bridge Decks 483 32.1. Sources of movements and loads at expansion joints 483 32.2 Functional requirements of expansion joints 485 323 Compression seals 488 32.4 Large movement expansion joints 32.5 Installation of Waboflex SR systems References $1! Parapets and Railings for Highway Bridges $12 33.1 Definitions 5/2 496 $504 38. 36. 37. Ls 33.2. Classification of highway bridge parapets 512 333 Various Details 513 Construction Techniques sz Construction Considerations 523 Cantilever Construction of Bridges 528 36.1 A modern construction technique 525 36.2 Various details 525 Considerations in the Design of Prestressed Concrete Box-Girder Decks with Spectal Reference to Cantilever-Construction 37.1 Initial design 531 37.2 Analysis $32 37.3 Final design 535 374 Detailing 537 37.5 Construction 539 37.6 Deflection of cantilever bridges and camber design 539 Practical problems in castsin-sita construction camber control 540 Characteristics of precast segments and match- cast epoxy joints 544 su 317 378 37.9 Fatigue in prestressed concrete bridges 546 References 546 Design and Construction of Cable-stayed Bridge Decks—Some Information 548 38.1 38.2 383 384 38.5 386 38.7 388 38.9 38.10 38.11 38.12 38.13 38.14 38.15 38.16 Brief history 548 ‘The evolution of the stays Analysis (brief note) 550 Deflection criteria 550 Operation of a cable stay 551 Alternate stresses in cable-stays Cable stay reliability 555 General cable stay arrangement 555 Different types of cable-stays 558 ‘The Freyssinet cable stay 559 BBR stay and anchorage 567 Freyssinet stay anchorage 562 Strength of the stays 562 Specification of strands for ceble-stays 564 Specification of anchorage for cable-stays. 564 Specification of protective materials for cable stays 564 38.17 Supply of ‘stay’ steel 565 38.18 Installation of a cable stay 565 Salient details of certain cable-stay bridges 568 References 569 548 $5239. Vibration of Bridge Decks 370 4 39.1 Introduction $70 392 Studies 571 39.3 Codal provisions 571 394 Human aspect $72 39.5. Frequencies causing physiological amd psyeho- logical effects 573 396 Fatigue and tolerance levels $73 39.7 Work already done and its relation to present problem 573 398 Practical facts 574 39.9 Practical approach for vibration analysis 574 Use of Freyssinet Flat Jacks 576 40.1. Introdus 576 40.2 Adaptation and combinations 576 40.3. Force exerted according to the opening 576 40.4 Methods of ‘installation’ $77 40.5 ‘Inflation’ technique $77 40.6 Recovery and re-use of jacks 577 40.7 Applications 578 Fire Resistance of Structural Concrete 581 411 General 587 41.2 Simply supported (unrestrained) slabs and beams 58) 41.3. Continuous slabs and beams 58/ 414 Fire endurance of floors and roofs which have restraint to thermal expansion 582 415 Heat transmission 582 416 Fire endurance of walls 583 41.7 Reinforced concrete columns 583 41.8 Properties of steel at high temperatures 584 41.9 Properties of concrete at high temperatures 585 41.10 Temperature distribution within concrete members exposed to fire 588 Selected bibliography. 591 Economics and Quantity-Trends in Alternative Bridge Structure Schemes 594 42.1 Synopsis 594 42.2 Introduction 594 42.3 Economics—various considerations 596 424 Some useful inferences 602 425 Additional factors 604 42.6 Typical comparison-Case Study 1 605 42.7 Typical comparison-Case Study 2 607 428 Quantity-trends 608 Guidelines for Professionally Preparing and Submitting ‘Detailed Structural Analysis and 4s. 47. 48. Coments_xy Calculations’ and ‘Construction Drawings’ for Client's Counter-checking and Record 617 . Engineering Drawings and Working Drawings 619 44.1 Engineering drawings 6/9 44.2 Working drawings 621 44.3 Caution 623 Pre-Tender Data-Questionnaire—Design-cum- Construct Bridge-Tender 624 ‘Maintenance Management System for Highway Bridges 626 46.1 Introduction 626 46.2. Elements of the agreement 526 46.3 Inception report 626 46.4 Inventory and condition survey of the entire highway network 627 46.5 Maintenance and rehabilitation of bridges and ‘other structures 627, 46.6 Bridge maintenance team 628 46,7 Structure—Inspections 629 468 Guidance for BMT 630 46.9 Outline of bridge surveys 635 46.10 Inspection procedures 639 46.11 Means of access and the required equipment 639 46.12 Schedule of unit rates for investigative structural computations for bridges and culverts 642 46.13 Schedule or unit rates for static load and material tests 642 46,14 Structure-maintenance reports and records 6a3 Bridge-Distress Reporting—A Workman-like ‘Approach 647 47.1 Introduction 647 47.2 Bridge-distress reponing 647 Bridge Engineering—Some Topical Reflections 655 48.1 Inoduction 655 48.2 The "Bridge Culture’ (A brief historical note) 655 48.3 Rational approach to structural design 659 48.4 New codes of practice (split ‘load-factors'!) 661xvi Contents 48.5 Design education 663 Appendix 3 Properties of Geometric Sections and 48.6 Cure against cracking of concrete—not by Shapes 696 calculations alorie! 664 Appendix 4 Mathematical Data 704 48.7 _Life-care of road bridges 666 Appendix 5 Estimation of Bursting Tensile Stress in 48.8 Concrete structure—deterioration and rehabi- ‘Caisson-Steining’ under ‘Pneumatic- litation 668 Sinking’ Conditions 708 48.9. Appropriate technology for developing Appendix 6 Extracts from the A.C.L Committee countries 672 Report 343 and the AASHTO Design 48.10 Biue-print for guiding technical development Specifications 70 in the field of civil engineering public works References 724 in developing countries 676 Appendix 7 Some of the U.K. (DTp.) Department of 48.11 Inspection checklist 687 Transport Bridge Engineering Technical ‘Some useful references 685 Appendix 1 Appendix 2 Metrie Units and Conversion Factors 687 Some General Data 690 Appendix 8 Index Memoranda TBI Additional Bibliography 734 237hvoaar (SH “wpetns suoneowumuwep Jo Aus: As01ne9) SONYHOUSLM LuOUUIYAL al “eeCHAPTER 1 The Basic Principle of Practical ‘Structural Analysis and Design 11 INTRODUCTION After deciding the type of bridge, span arrangement and span lengths, assunie suitable firstrial cross-sections of foundations and deck in concert with the method of construction. Hence, establish the loading sequence. For each load in the sequence see what it acts on, or what span of spans it acts on and under what end-conditions. From this find out what moments, etc. it causes at various sections, and which of these act on what section properties at those sections, and hence cause what stresses. The resultant stresses at every load stage at each section must not exceed their permissible valves that are set out in the relevant Code of Practice (the design specification). This, in a nutshell, is the essence of structural analysis and design. ‘A good design can be produced only if developed along with scaled sketches and drawings with an eye for practical detail. Indeed design is guided by drawings ‘made i parallel. For a regular workmanlike practical design, the designer must not lose sight of the overall requirement which is, ‘to produce a workable and practical structure in a limited amount of time at the minimum cost” keeping in mind the recent state of art and the contractually binding specifications. There is a large gap between a purely theoretical approach and a down-to-earth competitive practising professional's approach. It is more useful to carry ‘out a practical design and produce a workman-like detailing, in an execution drawing, rather than, for instance, merely be able to lecture on the. ‘ultimate strength of a nut" for ‘hours! One has to appreciate the difference between husk and the grain, between the so-called ‘coach’ and the actual player, between the music critic sitting on the sidelines ‘and the actual performing musician, berween the class- Tom teacher and the practising professional working in 8 commercial, result- and profit-oriented scene of action, At the end of the day it is more important to have ‘an approximate solution to an exact problem rather than tty for an exact solution to an approximated problem. Very few theoreticians, lecturers, and those in staid office services have ever produced competitive practical structures. themselves. Indeed, it should not be surprising if some Of them, left to themselves, may even find the existing structures unsafe! In fact merely writing of papers and books, based on litle practical experience and with no step- by-step; tool-kit applicability for a competitive practical end-product, often times is a manifestation of frustrated academics, and is.no substitute for intelligent, long and hard drawn, cold, commercial practical experience resulting from swimming against the cuirent covering the whole gamut of work from reconnaissance and feasibility through alternative working ‘designs and actual construction and maintenance. Creativity cannot be taught. It is an experienc one must five through to Jeamn with one’s own two hands in a cold competitive practice. (For more on this subject, see the ‘Reflections’ on ‘Design Education’ in Ch, 46 of this book.) 2 SUMMARY OF THE TOOL-KIT APPROACH FOR ANALYSIS AND DESIGN OF A USUAL ‘TYPE OF BRIDGE, General Steps Step | Knowing the required road-formation level, establish the permissible structural deck-depth {afier allowing for (i) the minimum vertical clearance needed between the affluxed high flood level and deck, soffit, and (i) the wearing-coat thickness below the road-formation level) Depending upon the depth of foundations, the height of deck above bed level (and above low water level), average depth of standing water during construction season, method of construction adequately suited to the site and the construction expertise available, decide: the type of bridge, span- Jengths and arrangement, the type of foundations, the type and cross-section of the deck, method of construction and the loading sequence in the entire construction. (Considerations described in Chs. 7, 18 and 42 have direct bearing here.) Finally, the optimum type of bridge may well have to be decided by weighing between relevant alternatives. Decide the firsttrial cross-sections and sizes of various elements of the substructure and superstructure, draw these to scale and establish Step 2 Step 3TS 2 Concrete Bridge Piactive: Analysis, Design and Economics the Preliminary General Arrangement Drawing (PGAD) of the bridge. (Some sizes and proportions, when seen to scale, will attract_modifications and will be decided better through such sealed drawings. This is necessary so as to “feel’ the order in the transmission of forces and moments and the flow of stress trajectories that are to be surrounded by elegant enveloping proportions bby practical detailing. Various ‘rials lead to a structural form with optimum placement of its load- asses. Relative proportions and approximate sizes of certain members as well as their shapes will be best decided only through these scaled sketches, provided they are drawn by an experienced practical designer with an eye for detail.) Decide the type of bearings to be used and their locations (xed, fre, ete), Establish the preliminary member sections and sizes of various structural elements from a quick preliminary analysis and design. This is necessary for the subsequent detailed analysis and design work, Substructure Design Steps Stop 4 Step 5 Step 6 Step 7 Establish deck dead load reaction and. the ‘maximum and minimum live load reactions on the pierfbutment under consideration. Also estimate the co-existing moments due to these loads, about the transverse and longitudinal axes of the bridge due to the maximum possible eccentric transfer of these dead and live load reactions, as also the braking and temperature forces. Estimate total vertical load at base of foundation (at Soffit of pile cap in case of piles) under maximum, minimum and no live load conditions, taking into account the upward buoyancy force equal to 100 or 50% weight of water in volume equal 10 that of the submerged miass (100% in case of saturated soil and fissured or weak rock, 50% in ease of good rock). Estimate total moment about the bridge's longitudi- nal axis and horizontal force in the transverse drec- tion, at various levels and at the base of the foun- dation, due to possible eccentricity of live and dead loads, flood water force and afflux if any (usually 10-15 em). Estimate total moment about the bridge’s transverse axis and horizontal force in tongitudinal direction, at various levels and at the base of the foundation, {due to possible eccentricity of live and dead loads, braking and temperature forces, and flood water force (or altematively in case of an unerodible Step 8 bed, the cross current effect of 25 em static head difference across pier thickness, if this is greater than the flood water effect). (2) In case of simply supported spans'on rocker/oller bearings, braking force from the live load on one complete span may be assumed to goto its rocker bearing alone so that the foundation under it will take either ‘braking- temperature" or ‘half of braking + temperature”®, the later usually applying to an abutment or a pier supporting unequal spans. (ii) In case of simple spans with identical neoprefe-bearings under each end of an individual span, the foundation will take the sum of half of braking from the live loads on each of the two spans supported by it and_the horizontal temperature force equal to (Spmz — Sq-m). where Sy is the shear- rating of the neoprene bearings supporting the left side span, Sq that of those supporting the right side span, and mz and mp the deck movements above them, respectively. (ii) Refer to Chs. 8 and 9 for the method of distributing the extemally applied as well asthe self-induced horizontal forces ‘among various bridge supports with different types of bearings (taking into account both the shear- rating of each support as well as the location of the zéro-movernent-point in the deck) the deck being continuous, or curved and/or skewed (simply supported or continuous), respectively Estimate the wind force in the transverse direction that can be attracted by the exposed surface area of the bridge with or without the live load on deck. Generally, it is enough t0 consider wind on the deck surface area between its soffit and top of the solid parapet or up to mid-height of parapet in case of an open-type parapet, and that on the body of live load at the rate of 300 kayim length of live load under maximum and minimum live load conditions. ‘Wind pressure on deck surface area depends on the height of the centroid of its exposed surface area (indicated above) above the mean retarding surface, i, above the bigh flood level or the bed level, as the case may be. With live load on bridge, 4 wind force of 450 kgiim length of deck alone (gnoring that on live load) is also considered an alternative to ‘wind on the deck exposed area and (on the body of the live load’, Under “no tive load” conditions directly the effect of a wind pressure of 240 kg/m? on the exposed area of the deck is, Temperature force here wil be equal 0 u(V —V"}, where p= coeff of ‘ction atthe rol (oe sling) bearing, and V and V" are the "ead + live Toad reactions atthe to roller (siding) bearings on the tw sides ofthe rocker bearing on the Foundation under considerationPractical Structural Analysis and Design 3 Step 9 considered, assuming no live loads would ply under sucha wind. (In coastal and certain specific areas, higher wind pressures (generally 100% extra or as, pertinent) have to be considered.) Since wind. can also hit the bridge obliquely, therefore, as an altemative to the above-mentioned purely transverse wind condition, a combination ‘of simaltancous wind forces in transverse and longitudinal directions, in magnitudes respectively qual to 67 and 33% of the said purely transverse ‘wind force, should also be considered, (Estimate the static equivalent of the horizontal seismic force as can be attracted by the mass fof the structure above the embedment level (maximum scour level in case of hydraulic bridges). Earthquake force is based on the full weight, even of the submerged portions of the structure (50 long as they are above the embedment level). Gi) Horizontal seismic force on a mass may be taken as a certain fraction of its weight, acting through its centroid. This fraction may vary between 0.10 for severe seismic zones 19 0.05 for moderate seismic zones to zero for non- seismic zones, depending on the seismicity of the area, In addition, 2 vertical seismic force, upward or downward, equal to half the aforementioned horizontal value, can also co-exist and should be catered for—panicularly when maximum or minimum base pressures are critica Gil) If the earthquake is in bridge transverse direction, then, as far as the contributions of the live load and the deck dead load to it are concemed, the aforementioned fraction may be applied on the magnitude of their reactions on the support under consideration, acting respectively at 1.2 m height above road surface and at the deck centroid level (The lings of bearings in this direction effectively act as one fixed bearing.) However, -if the earthquake is in bridge ongitudinal direction, then, the contribution of live toad to it can be ignored since braking force is already considered and any further longitudinal horizontal force on live load will only cause skidding of its wheels. As for the longitudinal seismic force coming on the foundation from the weight of the deck and footpath tive toad, it will depend on whether the bearings are tocker and roller-rocker (sliding) type of shearing (elastomeric) type. In the former case the seismic fraction may be applied on the entire weight of & simple span deck on the rocker (fixed) beating and the footpath live joad on it, and this be assumed to oto the rocker bearing and to the foundation under it (roller-rocker bearing only takes the temperature force). However, in te latter case the fraction may be applied on the sum of the deck dead load and footpath live load reactions from the two simple spans sitting on the foundation under consideration. In each ease, he point of action willbe the bearing level NoTE that for distribution of externally applied longitudinal horizontal forces (e.., seismic, wind and braking) in straight, simple or continuous decks and in curved and skewed (simple or continuous) Gecks, reference may be made to Chs. 8 and 9 as indicated earlier Step 10 Estimate the ‘active’ earth pressure force and ‘moment (at various levels and at the base of foundation) on account of the retained fill above the soffit level of Footing/pile cap. Passive relief from the front fill is generally to be ignored, but if i is well protected dependably then a fraction of it may be taken as dependable (but accounting for the negative surcharge angle effect if sloping downwards). This depends on the actual conditions in stu, case by case, the fraction may be such as (0 limit the magnitude of passive coefficient equal to the active coefficient If par of the foundation has been taken down ‘well into permanent and unexcavated soil” (c.g. 2 caisson taken below the maximum scour level), estimate and take into account the net ‘passive less active’ earth pressure relief (force and moment) from such assisting soil grip. For this purpose, reference may be made to Ch. 13. Step IT (i) Summarise the net vertical load, the net horizontal forces in the wo orthogonal directions and the net moments about these two directions, at the base of the foundation (at soffit of pile cap in case of piles), under each critical load combination. Jn other than piled foundations, establish the base pressures and the safety factors for stability against overturning and sliding and ensure that the requirements are satisfied, and if necessary redesign with revised dimensions. (Guidance on substrata bearing capacity... from Ch. 12.) (ii) In case of piled foundations estimate the ‘maximum and minimum axial loads in the piles by the traditional rivet-group approach (takiog account of rakes if piles are raked). Ensure that no pile is Fer minimum depth of oundstion reter to the book Consultancy and Consiraction Agreements or Bridges Including Field Investigations by the author.