Strength and ductility of steel box girders under cyclic shear

This paper presents practical methods for predictions of strength and ductility capacity of thin-walled steel box girders with longitudinally stiffened webs predominantly loaded in shear. The shear behaviors of the girders under monotonic and cyclic loadings are simulated through inelastic large deformation analysis, in which a modified two-surface model is incorporated to trace the material nonlinearity. Geometric and material imperfections are taken into account. During the analysis, the variation of stresses in the webs and flanges is monitored, and the observed shear-resisting mechanisms of the girders are discussed. An extensive parametric study is carried out to investigate the effects of structural parameters on the shear strength and ductility capacity. From these investigations, the application of available shear strength prediction methods, originally developed for plate girders, to box girders is verified. Some method is found to be appropriate for practical design, since it gives satisfactory predictions and relies on rational assumptions regarding the shear-resisting mechanism. Considering key structural parameters, a simple formula is proposed for the assessment of the ductility capacity.