STEEL BRIDGES

328 Pages·2007·9.82 MB·English

by  METWALLY ABU-HAMD

STEEL BRIDGES

METWALLY ABU-HAMD
Head of Structural Engineering Dept
Professor of Bridge and Steel Structures
Faculty of Engineering, Cairo University
Any part of this book may be reproduced by any means
WITHOUT the written permission of the author.
Preface
___________________________________________

Bridges have always fascinated people, be it a primitive bridge over a
canal or one of the magnificent long span modern bridges. People built
bridges to challenge nature where some obstacles like rivers, valleys, or
traffic block the way they want to pass through. Our transportation system
would not exist without bridges. Their existence allows million of people,
cars, and trains to travel every day and everywhere they want to go. It is
obvious that both our economy and our society could not function without the
technology of bridge engineering.

Bridge building is one of the difficult constructional endeavors that both
attracts and challenges structural engineers. The design of such complex
structures requires a great deal of knowledge and experience. Depending on
the bridge span to be covered, several types of bridge systems exist.
Examples of bridge systems are beam bridges for short and moderate spans,
arch bridges for moderate spans, and cable stayed bridges and suspension
bridges for long spans.

This book covers the design of steel bridges in general with emphasis on
bridge systems commonly used to cover short and moderate spans, namely
plate girder bridges, box girder bridges, and truss bridges. The book is
intended for senior year college students and practicing bridge engineers.

The contents of the book are organized into two parts: the first four
chapters cover the design of steel bridges in general while the other four
chapters cover the design of specific bridge types. Chapter 1 describes the
different structural systems of steel bridges. Chapter 2 presents the design
loads on roadway and railway bridges. Chapter 3 presents the design
considerations. Chapter 4 covers the design of roadway and railway bridge
floor. Chapter 5 covers the design of plate girder bridges. Chapter 6 covers
the design of composite plate girders. Chapter 7 covers the design of box
girder bridges. Chapter 8 covers the design of truss bridges.

The author hopes that this book will enable structural engineers to design
and construct steel bridges with better safety and economy.

Dr Metwally Abu-Hamd
Professor of Steel and Bridge Structures
Faculty of Engineering
Cairo University
Giza, 2007
CONTENTS
___________________________________________

1: INTRODUCTION

1.1 GENERAL 2
1.2 TYPES OF BRIDGES 5
1.3 MATERIALS FOR BRIDGE CONSTRUCTION 20

2: DESIGN LOADS ON BRIDGES

2.1 INTRODUCTION 26
2.2 ROADWAY DESIGN LOADINGS 26
2.3 RAILWAY DESIGN LOADINGS 32
2.4 OTHER LOADS ON BRIDGES 36

3: DESIGN CONSIDERATIONS

3.1 DESIGN PHILOSOPHIES 42
3.2 ALLOWABLE STRESSES FOR STRUCTURAL STEEL 43
3.3 FATIGUE 65
3.4 ALLOWABLE STRESSES FOR WELDED JOINTS 106
3.5 ALLOWABLE STRESSES FOR BOLTED JOINTS 107

4: BRIDGE FLOORS

4.1 INTRODUCTION 116
4.2 STRUCTURAL SYSTEMS OF BRIDGE FLOORS 117
4.3 DESIGN CONSIDERATIONS 122
4.4 DESIGN EXAMPLES 125
5: PLATE GIRDER BRIDGES

5.1 INTRODUCTION 146
5.2 GENERAL DESIGN CONSIDERATIONS 148
5.3 INFLUENCE OF BUCKLING ON GIRDERS DESIGN 154
5.4 ACTUAL STRENGTH OF PLATE GIRDER ELEMENTS 173
5.5 FLANGE PLATE CURTAILMENT 181
5.6 DESIGN DETAILS 183
5.7 FLANGE-TO-WEB CONNECTION 183
5.8 STIFFENERS 187
5.9 SPLICES 194
5.9.4 DESIGN 200
5.10 BRIDGE BRACINGS 203
5.11 BRIDGE BEARINGS 208
5.12 DESIGN EXAMPLE 218

6: COMPOSITE PLATE GIRDER BRIDGES

6.1 GENERAL 240
6.2 COMPONENTS OF COMPOSITE GIRDERS 243
6.3 DESIGN CONSIDERATIONS 245
6.4 SHEAR CONNECTORS 257

7: BOX GIRDER BRIDGES

7.1 INTRODUCTION 276
7.2 CROSS SECTION ARRANGEMENTS 278
7.3 BEHAVIOR OF BOX GIRDER BRIDGES 282
7.4 EFFECT BENDING 284
7.5 EFFECT OF TORSION 291
7.6 DESIGN EXAMPLE 306

8: TRUSS BRIDGES

8.1 TRUSS TYPES & CHARACTERISTICS 312
8.2 DESIGN OF TRUSS MEMBERS 318
8.3 GENERAL DESIGN PRINCIPLES 320
8.4 DESIGN OF TRUSS MEMBERS 322
8.5 DESIGN OF TRUSS CONNECTIONS 329

Chapter 1: Introduction

1
CHAPTER

INTRODUCTION
Steel Bridges

1

CHAPTER

INTRODUCTION

1.1 GENERAL

1.1.1 Historical Background

People have always needed to transport themselves and their goods from
one place to another. In early times, waterways were used wherever possible.
Navigable waterways, however, do not always go in the direction desired or
may not be always available. Therefore, it has been necessary to develop land
transportation methods and means of crossing waterways and valleys.
Roadway and railway development have therefore become an absolute
necessity for economic development. The rapid economic development in
Europe, USA, and Japan could not take place until land transportation was
developed. Even today, one important factor that has caused many countries
to lag behind in economic development is the lack of good land
transportation systems.

An important element of land transportation systems is the bridge. A
bridge is a structure that carries a service (which may be highway or railway
traffic, a footpath, public utilities, etc.) over an obstacle (which may be
another road or railway, a river, a valley, etc.), and then transfers the loads
from the service to the foundations at ground level.

The history of bridge engineering, which began with stone and wooden
structures in the first century BC, can be said to be the history of the
evolution of civil engineering. It is not possible to date humanity’s
conception and creation of the first bridge. Perhaps people derived the first
concept in bridge building from nature. The idea of a bridge might have
developed from a tree trunk that had fallen across a canal. Early bridges
consisted of simple short spans of stone slabs or tree trunks. For longer spans,
Chapter 1: Introduction 3
strands of bamboo or vine were hung between two trees across a stream to
make a suspension bridge.
The introduction of new materials – plain, reinforced, and pre-stressed
concrete; cast iron; wrought iron; and steel – evolved gradually within the
last two centuries. According to known records, the first use of iron in
bridges was a chain bridge built in 1734 in Prussia. Concrete was first used in
1840 for a 12-m span bridge in France. Reinforced concrete was not used in
bridge construction until the beginning of the twentieth century. Pre-stressed
concrete was introduced in 1927. These developments, coupled with
advances in structural engineering and construction technology, led to the
introduction of different forms of bridges having increasingly longer spans
and more load carrying capacities.

1.1.2 Bridge Components

In Figure 1.1 the principal components of a bridge structure are shown.
The two basic parts are:

(1) the substructure; which includes the piers, the abutments and the
U U
foundations.
(2) the superstructure; which consists of:
U U

a) the bridge deck, which supports the direct loads due to traffic and all
the other permanent loads to which the structure is subjected.
In roadway bridges it includes the deck slab, Fig. 1.1b.
In railway bridges it includes the rails and sleepers, Fig. 1.1c

b) the floor beams, which transmit loads from the bridge deck to the
bridge main girders. They consist of longitudinal beams, called
stringers, and transversal beams, called cross girders, Fig. 1.1c.

c) the main girders, which transmit the bridge vertical loads to the
supports.

d) the bracings, which transmit lateral loads to the supports and also
provide lateral stability to compression members in the bridge, Fig.
1.1b.

The connection between the substructure and the superstructure is usually
made through bearings. However, rigid connections between the piers (and
sometimes the abutments) may be adopted, such as in frame bridges, Figs.
1.4a and 1.4b.
Steel Bridges

a) Bridge Elevation

Bridge deck
stringer
main girder
bracing

b) Cross Section of a Roadway Bridge

c) Cross Section of a Railway Bridge

Fig. 1.1 Principal Components of a Bridge Structure