The Design of Modern Steel Bridges - TEDI

124 The Design of Modern Steel Bridges
Figure 5.17 Behaviour of plates in compression, with and without welding
residual stress. Plate with (a) stable post-buckling behaviour, (b) unstable postbuckling
behaviour.
Welding residual stresses are less important for plates subjected to in-plane
shear or bending stress than plates under longitudinal compression. This is
because the applied stresses and the welding residual stresses are likely to be of
different natures in different parts of the plates.
5.4.4 Effects of initial out-of-plane imperfections
Sections 5.4.1 and 5.4.2 dealt with the buckling behaviour of ideally flat plate
panels, i.e. plates without any initial out-of-plane deviations. Plates in real-life
fabricated structures are likely to have some initial out-of-plane deviations.
Instead of the ideal bilinear behaviour shown in Fig. 5.12(b), the real behaviour
of such plates will be as shown in graph (b) of Fig. 5.18. The initial out-ofplane
deviation will start growing in depth from the beginning of loading.
There will not occur any sudden change in the rate of in-plane or out-of-plane
deformation at the theoretical elastic critical buckling stress, but the rate will
gradually increase until the maximum resistance or ultimate strength of the
plate is reached. Thereafter as the resistance falls, the in-plane and out-of-plane
deformations continue to grow.
The in-plane edge conditions of the plate influence its behaviour right from
the beginning. As in the case of perfectly flat plates, the ultimate strength is
reached by a combination of redistribution of the in-plane applied stresses
and the growth of bending stresses due to the out-of-plane deviations. The