The Design of Modern Steel Bridges - TEDI

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188 The Design of Modern Steel Bridges 7.3 Cable types (c) two vertical planes, with twin-leg tower (d) two inclined planes, with A-shaped tower. With (a) or (b), the stiffening girder must be torsionally strong and must be supported at the tower on bearings to resist torsion. With (c) or (d), the cables can be attached to the deck either at its edges or within its width; in the latter case the configuration/clearance of the traffic paths will have to be safeguarded. The width of the tower foundation normal to the bridge direction could be shorter with (a) or (b) than with (c) or (d). It is not essential to support the stiffening girder at the tower on bearings if cable supports are provided all along its length and in two planes; that way a hard point on the stiffening girder with high hogging bending moment is avoided. However, if the stiffening girder is supported on bearings at the tower and by multiple cable-stays in either a single or twin planes, stays can be omitted for some distance either side of the tower. That solution creates a window in the cable net either side of the tower, which is often admired as an attractive architectural feature. The tower need not be vertical; it can be tilted towards the side span, with both architectural and structural advantages; but the tower will have to be supported by temporary stays in the bridge direction during construction. There could also be different stay arrangements in the central and side spans; for example, stays in a single central vertical plane in the central span and in two inclined planes in the side spans meeting at the tower was adopted for the Ebro bridge in Spain. All the possible arrangements for stay cables described above for three-span cable-stayed bridges with two towers are also possible for two-span bridges with one tower on one bank of a river. As outlined in Section 7.1, the earlier cable-stayed bridges had only a few cable-stays but modern bridges tend to have a large number of small diameter cable-stays. Figures 7.1 and 7.2 show, in conceptual forms, various arrangements of stays in cable-stayed bridges. The basic element of the cable-stays is the steel wire 5 to 7 mm diameter with proof (or yield) and ultimate strengths of the order of 1200 and 1600 N/mm 2 , respectively, as against 450 and 600 N/mm 2 for high-tensile structural steel. These steel wires are cold-drawn from high-carbon pearlitic rolled rods. The tensile strength of such wires has improved from about 1000 N/mm 2 in the 1880s, when Brooklyn Bridge was built, to about 1300 N/mm 2 in the 1900s, and then to around 1500 N/mm 2 in the 1930s. No great advance has been achieved since then. Wires with tensile strength of 1600 N/mm 2 are now available. In Japan attempts are being made to produce wires of 1900 N/mm 2 tensile strength. Such high strengths are obtained by a high percentage of carbon in
(a) Fan system (b) Harp system (c) Modified fan system Figure 7.1 Cable arrangements. Tower Cables (a) Cable stays in one central plane Tower Cables Tower Cables (c) Cable stays in two vertical planes. Tower Cables (b) Cable stays in one off-centre plane (d) Cable stays in two inclined planes Figure 7.2 Cable planes. Cable-stayed Bridges 189
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The Design of Modern Steel Bridges
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The Design of Modern Steel Bridges
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Contents Preface vii Acknowledgemen
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Preface Bridges are great symbols o
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Acknowledgements The figures in Cha
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2 The Design of Modern Steel Bridge
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10 The Design of Modern Steel Bridg
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Table 2.1 Properties of some commer
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Chapter 3 Loads on Bridges 3.1 Dead
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3.3 Design live loads in different
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interstate highways are designed fo
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a coefficient that depends on the n
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Loads on Bridges 59 In Germany, a n
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Table 3.6 Typical values of U and P
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3.5 Longitudinal forces on bridges
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wind loading on the traffic. An upl
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where r is the air density ¼ 1.226
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Loads on Bridges 69 minimum and max
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3.8 Other loads on bridges There ar
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References Loads on Bridges 73 wher
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Chapter 4 Aims of Design 4.1 Limit
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critical components of the structur
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But this is an attempt to achieve u
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If the basic variables R and S are
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educed variables defined by oi ¼ x
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will have a probability of failure
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Aims of Design 87 g m ¼ g m1 g m2
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Table 4.2 Failure probabilities of
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Chapter 5 Rolled Beam and Plate Gir
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as possible. But deep and thin webs
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eam, with an effective area equal t
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and stresses caused by lateral defl
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Figure 5.3 Beam cross-section. In t
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Rolled Beam and Plate Girder Design
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Table 5.2 Effective length factors
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stress is equal to p 2 E/(Le/r) 2 )
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equation (5.16) has been adopted fo
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The strain energy of the elastic re
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Figure 5.6 Buckling of plates in co
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Figure 5.8 Buckling of plate under
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techniques. It may be noted that th
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5.4.3 Effect of residual stresses R
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Aw ¼ 40 mm 2 , allowing for a smal
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Basler and Thurlimann were the firs
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Ostapenko/Chern gave the following
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where m ¼ Mp b 2 twsyw ty ¼ syw p
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the case of equal flanges, the tota
Page 149 and 150: emains flat until an elastic critic
Page 151 and 152: Rolled Beam and Plate Girder Design
Page 153 and 154: longitudinal compression is given b
Page 155 and 156: where Peq ¼ s1tB PE Ps Pcro Peq1
Page 157 and 158: Figure 5.27 Tension-field forces in
Page 159 and 160: 5.5.6 Design of longitudinal web st
Page 161 and 162: when Le is the effective length for
Page 163 and 164: pffiffiffiffiffiffiffiffiffiffiffif
Page 165 and 166: een derived as a condition for trea
Page 167 and 168: For interaction of various stress c
Page 169 and 170: must be at least i.e. 1 IsxbB 4 2 a
Page 171 and 172: Chapter 6 Stiffened Compression Fla
Page 173 and 174: Stiffened Compression Flanges of Bo
Page 175 and 176: cross-section in which the secant s
Page 177 and 178: longitudinal compression of the lon
Page 179 and 180: webs of main girders is denoted by
Page 183 and 184: wherefrom Ms ¼ 2 3 PE P The net be
Page 195 and 196: Chapter 7 Cable-stayed Bridges 7.1
Page 197 and 198: Cable-stayed Bridges 185 cables con
Page 199: The following is a list of cable-st
Page 203 and 204: 7.3.2 Ropes causing lateral compres
Page 205 and 206: The spiral winding of wires around
Page 207 and 208: polyethylene or even steel tube. Or
Page 209 and 210: See Fig. 7.7. Imagine a cable-stay
Page 211 and 212: It may be noted that: Et is higher
Page 213: Reference Cable-stayed Bridges 201
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The Design of Modern Steel Bridges - TEDI

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