Web slenderness for longitudinally stiffened I-girders subjected to patch loading

Abstract

In the current edition of the EC3 Part 1–5, the design provisions for longitudinally stiffened plate girders subjected to patch loading result in an enhanced resistance for an increasing distance of the stiffener, measured from the loaded flange. This is in contrast to the actual behavior observed experimentally, which shows a decreasing resistance for an increasing distance of the stiffener. The problem lies in the determination of the critical buckling load, which increases with the stiffener location, also affecting the calculation of the slenderness of the plate girder. At ultimate load level, the longitudinal stiffener restricts the vertical and the out-of-plane displacements of the web panel. This paper investigates the impact of various hypotheses regarding these displacements on the determination of the critical buckling load of plate girder webs with a single longitudinal stiffener. At first, the study is performed through linear buckling analysis using the finite element method, in which various displacements restrictions are applied to investigate their influence on the buckling response of the stiffened girders. The results show that a full restriction of the displacements of the stiffener in the vertical, as well as in the out-of-plane direction, lead to an improvement in the determination of the slenderness of the web panel, and hence the resistance to patch loading at ultimate load level. Finally, experimental results are compared to those obtained with a validated methodology attaining a good agreement.