Critical Buckling Coefficient of Tapered Web Plate Girders Under Compression and Bending Stresses

Abstract

The tapered girders were developed as a cost-effective solution to the problem of long-span building construction. These systems are very attractive from an economic viewpoint, combining wide spans, quick erection, and easy access to services between the shallow parts of the beam and the ceiling below. Elastic local buckling is one of several modes of failure that must be considered during the structure design. Although elastic local buckling has been studied for decades, there is still a need to develop quick and comprehensive procedures that will reduce product design time, particularly during the presizing stage. Most design codes have no specific provisions for the particular case of non-rectangular panels, stating that they may conservatively be treated as rectangular panels with a larger width. This paper presented an extensive numerical analysis to estimate the critical local buckling coefficient of two typologies for trapezoidal tapered steel web plate girders with simply supported end conditions. The considered loading conditions are compression and bending stresses. Moreover, the study identifies the relative importance of several parameters that influence the local buckling phenomenon, such as the tapering ratio of the panel, normalized plate length, and ratio of minimum and maximum compressive stresses. Numerical results are used to propose approximate closed-form ex-pressions that can be used to compute the local buckling coefficient. In addition, the elastic local buckling coefficients obtained from the proposed formulas were compared with the buckling coefficient predicted by both AISC and ECP-LRFD specifications. The proposed formulas are also verified against results obtained from nonlinear numerical analysis based on the finite element technique. The results indicate that the proposed formulas are valid for directly estimating the critical local buckling coefficient of trapezoidal tapered steel web plates. However, it is worth noting that the AISC and ECP-LRFD specifications have been shown to provide conservative predictions when calculating the local buckling coefficient for trapezoidal tapered steel web plate girders under stress gradients.