Imperfection sensitivity of plate girder webs subjected to patch loading

This paper is aimed at studying the influence of initial geometric imperfections on the postbuckling behavior of longitudinally stiffened plate girder webs subjected to patch loading. A sensitivity analysis is conducted herein using two approaches (deterministic and probabilistic) in order to investigate the effect of varying imperfection shape and amplitude on both, the postbuckling response and ultimate strength of plate girders under patch loading. This sensitivity analysis is performed by means of nonlinear finite element analysis. At first, the initial shape imperfections are modeled using the buckling mode shapes resulting from an eigenvalue buckling analysis. Thereafter, the amplitude of the buckling shapes for the various modes is varied, and then introduced in the nonlinear analysis. The results show the influence of these modes and amplitudes on the resistance to patch loading.

Research highlights
► Initial shape imperfection may reduce the patch loading resistance of longitudinally stiffened steel girders.
► The amplitude of the imperfections in most cases leads to a reduction in patch loading resistance.
► There is a more complex interaction between the imperfection shapes and the computed resistances.
► The shape of the initial imperfection that results in the lowest strength for a girder differs for each size of imperfection and stiffener location.
► Keeping the magnitude of the initial imperfection within the usually prescribed tolerances in design codes the drop in the resistance can be avoided.