Live load distribution factors for simply-supported composite steel I-girder bridges

Abstract

The Canadian Highway Bridge Design Code (CHBDC) provides formulas for determining the live load distribution factors for composite slab-on-girder bridges. These formulas were developed by neglecting the contribution of secondary elements such as lateral bracing in bridges, leading to conservative design in some cases and unsafe design in others. This paper presents a practical-design-oriented parametric study, using three-dimensional (3D) finite-element modeling, to investigate the live load distribution factors of composite braces steel I-girder bridges under CHBDC truck loading conditions at ultimate, serviceability and fatigue limit states. The key parameters considered in this study included girder stiffness and spacing, span length, number of girders, and number of design lanes. The comparison of results suggested that the CHBDC equations underestimate the girder moments for the 15 m spans and overestimates the response for greater spans. On the other hand, CHBDC generally overestimates the shear distribution factors, with significant difference observed at fatigue limit state. Based on the database generated from this study, a set of empirical expressions were developed for the moment and shear distribution factors for rational prediction of the girder design moment and shear force. A design example is presented to illustrate the use of the developed equations.