Compressive strength equations for box-girder flanges stiffened with U-ribs in cable-supported bridges

Abstract

Abstract When primary bending moments and axial forces are applied to a wide steel box girder in a long-span cable-supported bridge, top or bottom flanges are subjected to longitudinal in-plane compressional forces. In order to evaluate the ultimate compressive strength of such U-rib stiffened flanges, a total of 36 geometrically different numerical finite element models were carefully established taking into account the practical ranges of panel length and plate thickness of wide box girder flanges. Ultimate strength analyses were accordingly conducted on these hypothetical models incorporating local and global modes as possible initial geometric imperfections and different methods of imposing residual stresses. According to the resulting relationships between strengths and plate-like or column-like behavior, a set of functions is proposed to predict compressive strength and their coefficients are numerically determined by a regression analysis. The nominal strengths obtained from the proposed equations are then quantitatively compared to those of the FHWA (Federal Highway Administration) provisions, Eurocode 3, and KHBDC–CSB (Korea Highway Bridge Design Code–Cable-Supported Bridges) specifications. The strength equations developed in this study are expressed as simple equations and provide reliable strength predictions without any inherent subjectivity.