The Design of Modern Steel Bridges - TEDI

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60 The Design of Modern Steel Bridges queues and jams in the early 1980s raised the question whether the assumptions about gaps between vehicles and dilution by light traffic are valid for modern traffic conditions. There have also been some remarkable changes in the freight transport pattern in recent years. For example, between 1962 and Figure 3.4(b) Comparison of National Bridge Loadings for four-lane bridges. (Courtesy OECD.)
Table 3.6 Typical values of U and P for various bridge lengths Loads on Bridges 61 Loaded length (m) P (kN) U (kN/m) for percentage of HGV in traffic 7.5% 30% 100% 15.25 0 38 38 38 122 320 10.4 13.9 17.1 488 534 7.1 10.8 12.3 1950 747 5.8 9.9 10.5 1977, goods moved by road, measured by tonne–km, virtually doubled. Statistics of vehicle population by gross weight indicate that the number of vehicles with gross weight greater than 28 tonnes increased from an insignificant number in 1962 to 90 000 in 1977. Vehicle population with gross weight less than 11 tonnes fell substantially in that period, whereas those between 11 and 28 tonnes also increased, but the rate of increase of over 28 tonnes completely outstripped that of the others. This is the context in which a thorough review of design for live loading of bridges was undertaken in early 1980s. These reviews took into account the growth of traffic and change in traffic mix predicted for the 1990s, and produced new proposals for loading for the entire range of loaded lengths. For the shorter spans, the review was primarily on a deterministic basis, although an element of probability for illegal overloading and lateral bunching was taken into account. The extreme loading obtained from this part of the exercise was considered to be just possible in a rare event, i.e. to be used as design load in the ultimate limit state without multiplying by any further partial safety factor. The results were thus divided by 1.5 to get nominal loading. For the longer spans, a fully statistical basis was used to derive a characteristic loading, i.e. 95% probability of not being exceeded in 120 years. The nominal loading for design, i.e. a 120 year return period load, was taken as the characteristic loading divided by 1.2. A level 3 overall safety analysis was then performed to obtain an appropriate partial safety factor for loading consistent with the assurance that a structure will not have more than 1 in a million chance of collapse in service in its lifetime. The partial safety factor on the nominal load was found to be approximately 1.5, thus confirming the value already in BS 5400. On top of the nominal design loading derived in this fashion, a 10% allowance for future contingencies was provided throughout the whole span range. On a multi-lane bridge deck the loading over the third lane onwards was increased from 33% to 60% of the above design load in the first two lanes. In 1986 the European Commission decided to adopt a single regulation for maximum vehicle weights and dimensions throughout all the countries belonging to the European Economic Community. For the UK this meant an increase in the maximum axle weight from 10.5 to 11.5 tonnes, and in the maximum
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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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Page 58 and 59: Table 2.1 Properties of some commer
Page 63 and 64: Chapter 3 Loads on Bridges 3.1 Dead
Page 65 and 66: 3.3 Design live loads in different
Page 67 and 68: interstate highways are designed fo
Page 69 and 70: a coefficient that depends on the n
Page 71: Loads on Bridges 59 In Germany, a n
Page 75 and 76: 3.5 Longitudinal forces on bridges
Page 77 and 78: wind loading on the traffic. An upl
Page 79 and 80: where r is the air density ¼ 1.226
Page 81 and 82: Loads on Bridges 69 minimum and max
Page 83 and 84: 3.8 Other loads on bridges There ar
Page 85 and 86: References Loads on Bridges 73 wher
Page 87 and 88: Chapter 4 Aims of Design 4.1 Limit
Page 89 and 90: critical components of the structur
Page 91 and 92: But this is an attempt to achieve u
Page 93 and 94: If the basic variables R and S are
Page 95 and 96: educed variables defined by oi ¼ x
Page 97 and 98: will have a probability of failure
Page 99 and 100: Aims of Design 87 g m ¼ g m1 g m2
Page 101 and 102: Table 4.2 Failure probabilities of
Page 103 and 104: Chapter 5 Rolled Beam and Plate Gir
Page 105 and 106: as possible. But deep and thin webs
Page 107 and 108: eam, with an effective area equal t
Page 109 and 110: and stresses caused by lateral defl
Page 111 and 112: Figure 5.3 Beam cross-section. In t
Page 113 and 114: Rolled Beam and Plate Girder Design
Page 115 and 116: Table 5.2 Effective length factors
Page 117 and 118: stress is equal to p 2 E/(Le/r) 2 )
Page 119 and 120: equation (5.16) has been adopted fo
Page 121 and 122: 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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Rolled Beam and Plate Girder Design
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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
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emains flat until an elastic critic
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longitudinal compression is given b
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where Peq ¼ s1tB PE Ps Pcro Peq1
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Figure 5.27 Tension-field forces in
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5.5.6 Design of longitudinal web st
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when Le is the effective length for
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pffiffiffiffiffiffiffiffiffiffiffif
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een derived as a condition for trea
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For interaction of various stress c
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must be at least i.e. 1 IsxbB 4 2 a
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Chapter 6 Stiffened Compression Fla
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Stiffened Compression Flanges of Bo
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cross-section in which the secant s
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longitudinal compression of the lon
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webs of main girders is denoted by
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wherefrom Ms ¼ 2 3 PE P The net be
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Chapter 7 Cable-stayed Bridges 7.1
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Cable-stayed Bridges 185 cables con
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The following is a list of cable-st
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(a) Fan system (b) Harp system (c)
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7.3.2 Ropes causing lateral compres
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The spiral winding of wires around
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polyethylene or even steel tube. Or
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See Fig. 7.7. Imagine a cable-stay
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It may be noted that: Et is higher
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Reference Cable-stayed Bridges 201
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204 The Design of Modern Steel Brid
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206 The Design of Modern Steel Brid
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The Design of Modern Steel Bridges - TEDI

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