The Design of Modern Steel Bridges - TEDI

Recommendations

Info

52 The Design of Modern Steel Bridges 6 m for shear force, are governed by single axles or bogies with closely spaced multiple axles. The worst loading for spans over about 20 m is often caused by more than three vehicles. The worst vehicles are often the medium-weight compact vehicles with two axles, and not the heaviest vehicles with four, five or six axles. The criteria thus change from axle loads to worst vehicles as the span increases, with the mixture of vehicles in the traffic being an important factor for the longer spans. When axles or single vehicles are the worst case, the effect of impact has to be allowed for, but several closely spaced vehicles represent a jam situation without significant impact. The adjacent lanes of short span bridges may all be loaded simultaneously with the worst axles or vehicles, but this is less likely for long spans. Apart from the design loading for normal traffic, many countries specify special bridge design loading for the passage of abnormal vehicles of the military type or carrying heavy indivisible industrial equipment like generators. The passage of such heavy vehicles on public roads usually involves special permits from the highway authorities and often supervision by the police. In addition to these legal heavy loads, there is the growing problem of illegal overweight vehicles weighing as much as 40% over their legal limits. In each country traffic regulations limit the wheel and axle loads and gross vehicle weights, and impose dimensional limits on axle spacing and size of vehicles. Goods vehicles may be of the following types: vehicles with two axles rigid vehicles with three or more axles articulated vehicles with two or three axles under the tractor and one or more axles under the trailer road trains comprising a vehicle and trailer. The maximum legal axle weights[1] are 9.1 tonnes in the USA, 10.0 tonnes in Japan, Germany, Scandinavia, Holland, Canada and Switzerland, 10.5 tonnes in the UK (increased to this value in 1983), 12.0 tonnes in Italy and 13.0 tonnes in Belgium, France and Spain. The total weight limit for tandem axles is 15.4 tonnes in the USA, 16.0 tonnes in Scandinavia, Germany and Holland, 18.0 tonnes in Switzerland, 19.0 tonnes in Italy, 19.8 tonnes in Canada, 20.0 tonnes in Belgium, 20.3 tonnes in the UK, and 21.0 tonnes in France and Spain. The gross vehicle weight limits in these countries vary from 12.7 to 20 tonnes for two-axle vehicles, 19.1 to 28.1 tonnes for three-axle vehicles, 21.8 to 50.0 tonnes for articulated vehicles and 32.5 to 63.5 tonnes for road trains. Maximum widths, lengths and heights are also controlled by these regulations, but for bridge loading minimum possible lengths and widths are the critical parameters. For example, in Britain the four-axle 30.5 tonne 8.3 m long rigid vehicle is more critical on bridge spans of 10 to 40 m than the five-axle 38 tonne articulated lorry, which must be at least 12 m long. It can be seen from the above figures that at present the weight limits on vehicles are very diverse in different countries.
3.3 Design live loads in different countries Bridge design loadings in different countries vary a great deal and they do not necessarily follow the patterns of the vehicle weight limits in the countries. In the UK, bridge design loading is given in BS 5400 Part 2: 1978[2], with some amendments to it prescribed by the government authority. Type HA loading consists of a uniformly distributed lane loading, together with a knifeedge loading of 120 kN placed across the lane width. For loaded lengths in the direction of the traffic up to 30 m, the value of the uniformly distributed lane loading is 30 kN/m; for greater loaded length (L) it is given by 151(L) 0.475 , but not less than 9 kN/m. As an alternative to HA loading for short loaded lengths and areas, a wheel load of 100 kN distributed over a circular or square area with pressure of 1.1 N/mm 2 has to be considered. An impact factor of 1.25 on any one axle of one vehicle has been taken into account in the prescribed design loading. The whole carriageway, including hard shoulders if any, is divided into an integral number of notional traffic lanes of width not less than 2.3 m or more than 3.8 m. Any two such lanes are to be loaded with the full HA loading, the remaining lanes with one-third HA loading, which was increased to 0.6 HA by the government in 1984[3]. Type HB loading represents abnormal vehicles; it is a hypothetical vehicle with 16 wheels on four axles; the heaviest HB loading is for 45 units representing 180 tonnes. HA loading was originally derived in the 1950s for the drafting of the first British Bridge code BS 153[4]. It was based on the following sets of vehicles: Vehicle sets for design loading in BS 153 Loaded length Vehicles (@ tonnes) ft m Gap 1 (ft) Total weight (tonnes) UDL (tonnes/m) 75 23 3 @ 22 3 66 2.9 200 61 5 @ 22 18 110 1.3 480 146 5 @ 22 plus 8@10 18 190 1.3 3000 915 (i) 5 @ 22 plus 8 @ 10 72 @ 5 18 550 or 0.6 (ii) 21 @ 24 21 @ 1 55 536 1 2 1 A 2 s gap at 18 mile/h speed is 55 ft and at 6 mile/h speed is 18 ft. Loads on Bridges 53 It may be seen that up to 23 m a jam situation was envisaged with heavy and compact lorries. Between 23 and 61 m a column of heavy and compact lorries
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 22 and 23: 10 The Design of Modern Steel Bridg
Page 58 and 59: Table 2.1 Properties of some commer
Page 63: Chapter 3 Loads on Bridges 3.1 Dead
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 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
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 129 and 130:
Rolled Beam and Plate Girder Design
Page 131 and 132:
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:
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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?