Evaluation of impact factors for composite concrete–steel cellular straight bridges

This paper presents a method for determining the dynamic impact factors for straight composite concrete deck–steel girder cellular bridges under AASHTO truck loading. The bridges are modeled as three-dimensional structures using commercially available software. The vehicle is idealized as a pair of concentrated forces, with no mass, travelling across the bridge. An extensive parametric study is conducted, in which 120 composite multi-cell bridge prototypes are analyzed. The key parameters considered in this study are: number of cells, number of lanes, span length, number and area of cross-bracing and top-chord systems, and truck(s) speed and truck(s) positioning. Based on the data generated from the parametric study, expressions for dynamic impact factors for moment, reaction, and deflection for such bridges are proposed. The results from this practical-design-oriented study would enable bridge engineers to design new composite cellular bridges more reliably and economically. Furthermore, the results can be used to evaluate the load-carrying capacity of existing composite cellular bridges since even a small increase in strength for live load can make the difference between closing a bridge and leaving it open.