Numerical study of slender I-girders with one longitudinal stiffener under patch loading

Abstract

Slender plate I-girders are steel members widely used in bridges, viaducts and heavy industrial buildings, which are subjected to combined bending and shear, making the web panel susceptible to stability problems. Therefore, longitudinal stiffeners are sometimes placed along the web. This paper aims at investigating the load carrying capacity of girders submitted to patch loading (common in bridge launching), using finite element models. A nonlinear stability analysis was carried out considering the initial geometric imperfection as the first buckling eigenmode, with amplitude defined according to EN 1993-1-5 recommendations. The performance of girders with different stiffener locations was evaluated, discussing the structural behavior and associated failure modes. If the stiffener is effective and properly placed, the failure mode is the local buckling of the two web subpanels (which increases the patch loading resistance), although it was verified that the optimal position for patch loading is mainly governed by the web crippling resistance of the upper subpanel. The numerical results are in accordance with the experimental results available in the literature. For the studied girder configurations, the optimal stiffener position for patch loading resistance is closer to the loaded flange when compared to girders under dominant bending. Depending on the cross-sectional shape of the buckling mode, the stiffener can be unfavorable to the patch loading resistance for certain range of positions. Furthermore, the definition of positive or negative cross-sectional imperfections, i.e., the inversion of the curvature of the buckling mode shape, has impact on the load capacity for larger patch loading lengths.