Thin steel webs in plate girders possess strength beyond the elastic buckling load which is commonly referred to as the post-buckling capacity. Semi-empirical equations based on experimental tests of plate girders have been used for decades to predict this post-buckling capacity up to the ultimate shear load. However, these predictions are predicated on a specific set of assumptions regarding the boundary conditions of the plate. Specifically, the rotational and translational restraint provided by the stiffeners and flanges are idealized when calculating the post-buckling capacity of the web. To this end, the current design equations provide an approximate (albeit generally conservative) estimate of capacity relative to the test data upon which they are founded. New research by the authors has examined the impact of web boundary conditions on the post-buckling shear capacity. Analyses of isolated web plates, independent of the flanges and stiffeners with idealized boundary conditions, are compared against the response of webs within a plate girder loaded predominantly in shear. Experimentally validated finite element models are the basis for this study. Outputs such as von Mises stresses and principal stresses are examined for the buckled plate, whose behavior is influenced by both membrane stresses and second-order bending effects. These evaluations are performed for a range of panel aspect ratios, axial (longitudinal) restraint, and initial imperfections, with the goal of exploring changes in post-buckling shear capacity as well as changes in the fundamental mechanics. The results of this study have potential implications for current design-basis approaches.