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Currently, there are different options to increase the ultimate resistance of plate girders subjected to patch loading. Some of these alternatives include the use of closely spaced transverse stiffeners and the use of longitudinal stiffeners. Nevertheless, recent investigations have demonstrated that the resistance is also improved by using delta stiffeners, which are obtained by welding two plates between the web plate and the loaded flange. This paper aims at studying the elastic buckling behavior of slender plate girders designed following AASHTO norms with delta stiffeners subjected to patch loading. The research is carried out by means of eigenvalue analysis using the finite element method. A parametric study is performed to evaluate the influence of various geometrical parameters on the buckling coefficient of the girder. Finally, design recommendations are suggested based on the obtained results. [ABSTRACT FROM AUTHOR]

Currently, in the EN1993‐1‐5 the ultimate strength of a longitudinally stiffened webs is calculated based on a design procedure which considers the ratio between the yield resistance and the critical buckling load. In the available formulation which is based on numerical modelling, the critical load increases with the relative position of the longitudinal stiffener. This behaviour contrasts with that observed at ultimate limit state, several experimental results have shown that the ultimate strength increases when the longitudinal stiffener is placed closer to the loaded flange. To solve this problem, new hypotheses of boundaries restrictions at the stiffener location are presented to model the elastic buckling behaviour of webs subjected to patch loading. A comprehensive finite element model is presented in this study to evaluate theses hypotheses by varying the web and longitudinal stiffener dimensions. Finally, a methodology to model the buckling behaviour of stiffened webs is presented. [ABSTRACT FROM AUTHOR]

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. • The patch loading resistance of plate girders with one longitudinal stiffener is investigated. • Critical loads are calculated considering various displacement restrictions offered by the stiffener. • Imposing a nodal line at the stiffener location improves the calculation of the web slenderness. • Compliance between the behavior of the critical buckling and ultimate load is attained. • Results show an improvement in the predicted resistances for strong stiffeners (γ s ≥ γ t ). [ABSTRACT FROM AUTHOR]