The Design of Modern Steel Bridges - TEDI

Recommendations

Info

72 The Design of Modern Steel Bridges forces. The load combinations and the partial load factors for the ultimate limit state are given in Table 3.8. The permanent loads and their factors are not mentioned in the table; these are: 1.05 for dead load of steelwork 1.15 for concrete 1.75 for superimposed dead load, but may be reduced to 1.20 1.50 for earth pressure 1.20 for creep and shrinkage of concrete. The different design parts of the British Standard BS 5400 allow the effects of differential temperature, differential settlement and creep and shrinkage effects of concrete to be ignored in the ultimate limit state in those types of structural design that are capable of redistributing the self-equilibrating internal stresses set up by these effects. Snow load, loading due to stream current and floating ice, earthquake and shipping collision forces are not included in the specified load combinations, as few bridges in the British Isles are subjected to these loadings; where such loading is likely special load combinations and partial load factors are adopted. In the AASHTO specification[5], nine load combinations are specified. Each load is multiplied by one g-factor particular for the load combination under consideration and one b-factor which varies for different loads in the same combination. Thus the total load effect in combination N is given by X ðbFNFÞ g N Table 3.8 Load combinations and partial load factors for ultimate limit state in British Standard BS 5400 Combination LL 1 LF CF CL W T F 1 1.5 – – – – – – 2 (a) – – – – 1.4 – – (b) 1.25 – – – 1.1 – – 3 1.25 – – – – 1.3 2 – 4 (a) 1.5 3 – 1.5 – – – – (b) 1.25 3 1.25 – – – – – (c) 1.25 3 – – 1.25 – – – 5 – – – – – 1.3 Load combination in British Standard BS 5400: LL ¼ live load, LF ¼ longitudinal force, CF ¼ centrifugal force, CL ¼ collision force, W ¼ wind loading, T ¼ temperature effects, F ¼ bearing friction. 1 Factors for HA loading. 2 Load factor for differential temperature effects is 1.0. 3 These factors are used on reduced live loading.
References Loads on Bridges 73 where F represents the load due to dead load, live load, wind load, etc. and b FN is the factor on the particular load for the particular combination N. Dead load, earth pressure, buoyancy and stream flow pressure are considered permanent forces and are included in all the load combinations with the following b-factors: dead load ¼ 1.0 except that a smaller factor of 0.75 is taken for minimum load and maximum moment in columns earth pressure ¼ 1.3 for maximum lateral pressure ¼ 0.5 for minimum lateral pressure ¼ 1.0 for vertical earth pressure buoyancy ¼ 1.0 stream pressure ¼ 1.0. Combination 1 is the main combination with live load, combination 2 is for wind load on unloaded bridges and combination 3 is for wind load on bridges carrying traffic. Combination 4 is for temperature and shrinkage effects with live load and combination 5 is for temperature and shrinkage effects with high wind and no live load. Combination 6 is an omnibus combination with all the above loads, but with a reduced g-factor to represent the reduced likelihood of all the forces acting with their peak values. Combinations 4, 5 and 6 are dominated by the forces due to shrinkage and thermal effects and are thus critical for those structures that are restrained against longitudinal expansion or contraction, i.e. arches and portal frames. Combination 7 is for earthquake forces, to be taken in conjunction with only the permanent loads. Combinations 8 and 9 are for ice pressure on substructures, to be combined with live loads only in the former combination, and with wind load only in the latter. In comparing the g and b factors in the AASHTO specification with the partial load factors in BS 5400, it has to be remembered that in the latter code two other partial factors are to be considered. These are: (1) g f3 – this takes account of inaccuracies in the assessment of load effects, or in the calculation model or in the overall dimensions, and is taken as 1.1 in the ultimate limit state (2) gm – this is the partial factor for material strength and is generally 1.05 for structural steel. 1. Evaluation of Load Carrying Capacity of Bridges: 1979. Organisation for Economic Co-operation and Development, Paris. 2. BS 5400: Part 2: 1978. Steel, Concrete and Composite Bridges: Specification for Loads: British Standards Institution, London. 3. Departmental Standard BD 23/84: Loads for Highway and Foot/Cycle Track Bridges. Department of Transport, London.
Page 1:
The Design of Modern Steel Bridges
Page 5 and 6:
The Design of Modern Steel Bridges
Page 7 and 8:
Contents Preface vii Acknowledgemen
Page 9 and 10:
Preface Bridges are great symbols o
Page 11:
Acknowledgements The figures in Cha
Page 14 and 15:
2 The Design of Modern Steel Bridge
Page 16 and 17:
Page 18 and 19:
Page 20 and 21:
Page 22 and 23:
10 The Design of Modern Steel Bridg
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35: 22 The Design of Modern Steel Bridg
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 and 72: Loads on Bridges 59 In Germany, a n
Page 73 and 74: Table 3.6 Typical values of U and P
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: 3.8 Other loads on bridges There ar
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
Page 123 and 124: Figure 5.6 Buckling of plates in co
Page 125 and 126: Figure 5.8 Buckling of plate under
Page 127 and 128: techniques. It may be noted that th
Page 133 and 134: 5.4.3 Effect of residual stresses R
Page 135 and 136:
Aw ¼ 40 mm 2 , allowing for a smal
Page 137 and 138:
Rolled Beam and Plate Girder Design
Page 139 and 140:
Page 141 and 142:
Basler and Thurlimann were the firs
Page 143 and 144:
Ostapenko/Chern gave the following
Page 145 and 146:
where m ¼ Mp b 2 twsyw ty ¼ syw p
Page 147 and 148:
the case of equal flanges, the tota
Page 149 and 150:
emains flat until an elastic critic
Page 151 and 152:
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 181 and 182:
Page 183 and 184:
wherefrom Ms ¼ 2 3 PE P The net be
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Chapter 7 Cable-stayed Bridges 7.1
Page 197 and 198:
Cable-stayed Bridges 185 cables con
Page 199 and 200:
The following is a list of cable-st
Page 201 and 202:
(a) Fan system (b) Harp system (c)
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
Page 216 and 217:
204 The Design of Modern Steel Brid
Page 218 and 219:
206 The Design of Modern Steel Brid
show all

The Design of Modern Steel Bridges - TEDI

Create successful ePaper yourself

Delete template?

Save as template?