The required moment of inertia for steel plate girders is commonly provided by using relatively slender webs to achieve high strength-to-weight ratio. A large part of the shear capacity of such plate girders depends on the post-buckling reserve strength of the web panels due to the diagonal tension field mechanism. The effectiveness of the tension field significantly depends on geometrical and mechanical properties of the panel as well as on the boundary conditions. This research study includes two experimental tests which have been conducted considering both rigid and non-rigid end posts. The acquired data in addition to the previous experimental studies were then used to verify the numerical models. Furthermore, the ultimate post buckling capacity of the plate girders are compared with the current specification codes. Findings show a good agreement between codes and numerical analyses for the web slenderness between 120 and 220. However, there is a rather large discrepancy in the results for the web slenderness outside this range.
