Imperfection analysis on the patch loading resistance of girders with open section longitudinal stiffeners

Previous studies proved that the patch loading resistance model of the EN1993-1-5 can lead to significant underestimation of the patch loading resistance in case of longitudinally stiffened girders. Recently there are several research activities to improve the design method. In the current study experimental research program is executed on 8 large scale test specimens having different longitudinal stiffener configurations and loading lengths to extend the available background and to verify advanced numerical model. In parallel to the experiments a finite element model is developed considering the geometrical and material nonlinearities and geometric imperfections. The current paper presents the experimental tests and focuses on the modelling technique of the geometric imperfections, which can have large importance in case of coupled instabilities. Based on the experiments and numerical investigations design recommendations are given for equivalent geometric imperfection shapes and magnitudes for girders with longitudinally stiffened web. The measured resistances are compared to different resistance models found in the international literature and their accuracies are evaluated.