Influence of elastic buckling characteristics on inelastic shear capacity of steel plate girders

Steel I-shaped plate girders commonly rely on slender, stiffened web panels to resist shear, yet the role of initial geometric imperfections in governing their elastic buckling and nonlinear inelastic shear response remains poorly understood. This paper investigates the influence of initial imperfections and web slenderness on the elastic buckling and nonlinear shear behavior of steel plate girder webs. The study is based on a dataset of five web panels from three commercially fabricated girders with field-measured imperfections. Experimentally validated finite element models are used to analyze elastic shear buckling loads, inelastic shear capacities, and associated deformation patterns. Elastic buckling analyses compare the response of models with idealized flat web plates as the initial condition to those with field-measured out-of-flatness imperfections. The results show that elastic buckling loads predicted for imperfect webs are 5 to 7 times larger than those for perfectly flat webs. This indicates that a distinct elastic shear buckling bifurcation is unlikely to occur in real plate girder behavior. Also, the application of different field-measured initial conditions on the same web panel results in similar eigenmode characteristics and negligible differences in V_cr. The nonlinear shear response of webs with field-measured initial imperfections can be accurately captured by instead using eigenmode-based initial imperfections. A study on the effects of web slenderness ratio indicates that only at high slenderness do the trends change in terms of the shape of the deformed web at the shear capacity load. Future work will expand the geometric database and provide insights for developing design recommendations that more accurately account for the role of imperfections in the shear response of steel plate girders.