Revisiting the minimum I-section cross-sectional proportions to ensure adequate shear capacity

This paper discusses the conventional assumption of simply-supported boundary conditions in estimating an I-girder web’s elastic shear buckling stress. Some past literature discuss an increase in the elastic buckling stress while considering the restraint from the flanges. However, few have examined the lack of adequate support at the web boundaries shared with flanges and stiffeners. This paper shows that intermediate transfer stiffeners that satisfy the minimum rigidity criteria prescribed in design codes provide adequate restraint to achieve stresses corresponding to the simply-supported edge conditions. However, at stiffener locations not coinciding with lateral or torsional restraints, there are excessive deformations at these web edges despite satisfying the minimum rigidity criteria. Similarly, the paper shows that narrow flanges in long web panels allow excessive deformations at the web-flange junctions, resulting in premature elastic shear buckling, and do not help achieve even simply-supported boundary conditions, thereby making such simplistic assumptions in design codes unsafe. This inadequate restraint, gauged by the large displacement at stiffener locations and the web-flange junctions, further exacerbates the postbuckling behavior of such girders. The paper identifies the flange and stiffener dimensions that dictate the restraint levels at the web boundaries adjoining the flanges and the stiffeners. A brief discussion of the impact of these considerations on the ultimate strength of girders is also presented using finite element simulations.