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composite bridges, the design live loads specified in the current codes of
practice are highlighted in this section. The design live loads for railway
bridges depend on the types of trains passing on the bridges, while the design
loads for highway bridges depend on the types of vehicles passing on the
bridge. The design live loads for railway and highway bridges are either con-
centrated loads acting on the axles of the specified trains and vehicles, respec-
tively, or equivalent uniformly distributed loads simulating the case of
several closely spaced vehicles in a jam situation. The specified trains and
vehicles have specified dimensions and axles spaced at definite locations
in the trains or vehicles. Live loads resulting from moving trains or vehicles
are magnified to account for the effect of impact and dynamic application of
the loads on the bridges. Wide steel and steel-concrete composite bridges are
designed on the worst cases of live loads acting on several adjacent lanes.
Long steel and steel-concrete composite bridges are designed to carry mul-
tiple trains or vehicles that should be positioned to provide the maximum
straining actions at a specific section.
3.3.1 Live Loads for Railway Steel Bridges
for railway bridges. EC1 is applicable to railway traffic on the standard track
gauge and wide track gauge Europeanmainline network. According to EC1,
the design load models adopted do not describe actual loads. However, they
have been selected so that their effects, with dynamic enhancements taken
into account separately, represent the effects of service traffic. Where traffic
outside the scope of the load models specified in EC1 needs to be considered,
then alternative load models, with associated combination rules, should
be specified. The live loads specified in EC1 are not applicable for actions
due to narrow-gauge railway, tramways and other light railway, preservation
railway, rack and pinion railways, and funicular railways. EC1 provides three
standard mixes of railway traffic, which are recommended for calculating
the fatigue life of bridges as detailed in Annex D of the code. EC1 specifies
the general rules for the calculation of characteristic vertical load values (static
effects) and eccentricity and distribution of loading and specifies the associ-
ated dynamic effects, centrifugal forces, nosing force, traction and braking
forces, and aerodynamic actions due to passing railway traffic.
According to EC1, railway traffic actions are defined by means of five
load models of railway loading that are as follows: “Load Model 71” and
“Load Model SW/0” for continuous bridges to represent normal railway
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