Post-buckling shear resistance of slender girder webs: Stiffener participation and flange contributions

A series of validated finite element models are used to parametrically evaluate the participation of flanges and transverse stiffeners in the post-buckling web shear mechanics of welded I-shaped steel plate girders. The models are validated against the results of six large-scale web shear-buckling tests from the existing literature on highly slender plate girders (with web slenderness ratios of 250–267) and varying transverse stiffener spacing (with web panel aspect ratios from 1 to 4). All girders exhibited a 3-stage web shear-buckling response: 1) an initial linear elastic stage, 2) a post-buckling stage I during which shear stiffness begins to progressively decrease, and 3) a post-buckling stage II with either significantly reduced or negative stiffness after the buckled web panel has formed a yield mechanism. Increasing the flange thickness in a given girder configuration can change the mode of the post-buckling stage II response from gradual unloading (with ultimate shear reached at the end of post-buckling stage I) to positive hardening (with ultimate shear instead reached during post-buckling stage II at much larger displacement and with a 5–15% increase in shear resistance from the end of post-buckling stage I). At ultimate shear, the transverse stiffeners develop axial forces that equal only 10–30% of the applied shear load depending on their sizing, the panel aspect ratio, and the web plate thickness. The stiffeners are primarily engaged in the web's out-of-plane direction to impose panelization and less as an axial strut for the post-buckling load path.