Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 154

of the bridge independent of the width of the bridge. EC1 [ 3.3 ] recom-
mends that care should be exercised in the design of large concrete box
girder bridges where significant temperature differences can occur between
the inner and outer web walls of such structures. The National Annex may
specify numerical values for the temperature difference. The recommended
value for a linear temperature difference is 15 C.
3.6 LOAD COMBINATIONS
3.6.1 General
The different loads acting on steel and steel-concrete composite bridges,
previously highlighted, should be grouped and superimposed to determine
the worst case of loading that induce highest straining actions and conse-
quently stresses at critical sections of the bridges. Grouping of the different
loads acting on the bridges is commonly known as load combinations. The
load combinations are dependent on the approaches adopted to design the
bridge components, for example, allowable (permissible) stress design, limit
state design, plastic design, and load and resistance factored design. The
methods of design will be highlighted in the succeeding sections; however,
in general, the concept of grouping different loads acting on the bridge is
based on multiplying nominal or characteristic values of loads by partial
safety factors to obtain the design value of the load. When several loads
are to be grouped or combined, the partial safety factors should be reduced
from their values for individual application of the loads in order to attain the
same probability of occurrence of the combination as that of the individual
loads.
3.6.2 Groups of Traffic Loads for Highway Bridges
Let us look at the grouping of traffic loads for highway bridges adopted in
Europe, which is addressed in EC1 [ 3.1 ] . The code recommends that the
simultaneity of the loading systems (Load Model 1, Load Model 2, Load
Model 3, Load Model 4, and horizontal forces) and the loads of footways
should be taken into account by considering the groups of loads defined
in Table 3.13 specified the code. Each of these groups of loads, which are
mutually exclusive, should be considered as defining a characteristic action
for combination with nontraffic loads.The frequent action should consist
only of either the frequent values of LM1 or the frequent value of LM2