Bridge Hydraulics
Author: Les Hamill | Size: 15.34 MB | Format: PDF | Publisher: E & FN Spon, an imprint of Routledge | Year: 2004 | pages: 347 | ISBN: 0203028414
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This is intended as a useful handbook on the subject of bridge hydraulics. It includes references to articles published in 1997, just prior to its completion, so compared with similar books it is relatively up to date. It explores how to undertake the hydraulic analysis or design of a bridge, either single or multispan, with either rectangular or arched waterways. It describes how to calculate the afflux (backwater), how to improve the hydraulic performance of a bridge, and how to evaluate and combat scour. The intention is to provide a good introduction to the fundamentals for anyone not familiar with this specalised branch of engineering, with enough detailed information to appeal to those who are. This book is, in a way, the result of a mistake. Near my home town many years ago a rather old, untidy, steel truss bridge was replaced by a very elegant masonry structure. The result was that flooding upstream got worse. This raised the question: how is the size of the opening in a river bridge determined? Initial enquiries revealed that estimating the magnitude of the design flood was relatively straightforward; it was converting this into the dimensions of a bridge opening that was difficult. An expert on the subject candidly and charmingly admitted that there was much that he (and practically everyone else) did not know or understand, so if anyone cared to fill in a few gaps… Hence my research interest and the book. Another reason is that bridges are interesting: many people stand on a bridge watching the floodwater pass underneath. Hopefully some of this interest is captured in the following pages. Some engineers may question why a book on bridge hydraulics is needed when it is possible to find computer software that will do all the analysis and design for you. Such people frequently believe, because computers are capable of giving answers to 20 decimal places, that everything that comes out of them is correct and accurate. This is not true. Ignoring the fact that the input data may be inaccurate, there may be mistakes in the computer program. A sobering thought is that someone once said that if a piece of software is worth using then it must have an error in it somewhere! Many years ago the author was invited to use the research facilities of a large, prestigious company. Part of the work involved digitising some
Contents
Preface viii
Principal notation xi
1 Putting things into perspective 1
1.1 Why study bridge hydraulics? 1
1.2 Early developments in bridge hydraulics 3
1.3 Hydraulic causes of bridge failure 9
1.4 The hydraulic design of bridges 19
2 How a bridge affects river flow 34
2.1 Introduction 34
2.2 What happens when water flows through a bridge 36
2.3 Afflux, piezometric head loss and energy loss 41
2.4 Classification of flow types at a bridge 44
2.5 Channel control and structure control 51
2.6 Case study: Canns Mill Bridge 56
3 Factors that affect the hydraulic performance of a bridge 61
3.1 Introduction 61
3.2 The bridge opening ratio, M 61
3.3 Froude number (F), subcritical and supercritical flow 68
Page vi
3.4 Ratio of waterway length to span, L/b 77
3.5 Entrance rounding 78
3.6 Eccentricity, e 79
3.7 Skew, 80
3.8 Depth of flow, Y 86
3.9 Shape of the waterway opening 87
3.10 Channel roughness and shape 88
3.11 Scour 90
3.12 Examples 91
4 How to calculate discharge and afflux 103
4.1 Introduction 103
4.2 US Geological Survey (USGS) method 105
4.3 US Bureau of Public Roads (USBPR) method 134
4.4 Biery and Delleur 152
4.5 Hydraulics Research (HR) method 156
4.6 The accuracy of a hydraulic analysis and numerical models 160
4.7 Examples 166
5 How to analyse flow past piers and trestles 176
5.1 Introduction 176
5.2 The d’Aubuisson equation 177
5.3 The Nagler equation 178
5.4 The work of Yarnell 181
5.5 Examples 186
Page vii
6 How to analyse flow over embankments 189
6.1 Introduction 189
6.2 Road embankments as weirs 192
6.3 Example 6.1 197
7 How to improve flow through a bridge 199
7.1 Introduction 199
7.2 Entrance rounding 200
7.3 Abutment type and extended wingwalls 215
7.4 Spur dykes (or guidewalls) 219
7.5 Minimum energy bridge waterways 226
7.6 Channel improvements 238
7.7 Examples 243
8 How to evaluate and combat scour 251
8.1 Introduction 251
8.2 Types of scour and its classification 257
8.3 Factors affecting scour in cohesionless material and associated
difficulties
263
8.4 Estimation of scour depth in cohesionless material 277
8.5 Designing for scour 292
8.6 Regime theory 305
8.7 Scour in cohesive materials 308
8.8 Scour in tidal waterways 308
8.9 Combatting scour 324
AppendixA
Hydrodynamic forces on bridges 344
AppendixB
Some alternative equations for local scour 347
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