Top-Lateral Bracing Systems for Trapezoidal Steel Box-Girder Bridges

Trapezoidal steel box girders are becoming increasingly popular as a bridge system due to their torsional efficiency and aesthetic appearance. These bridge systems utilize one or more trapezoidal steel girders with a cast-in-place composite concrete roadway. The critical design stage occurs during pouring of the bridge deck, when the steel superstructure must support the weight of the fresh concrete. Top-lateral bracing systems are used to provide both strength and stiffness during construction.

A method for the design of top-lateral bracing systems was developed through field and laboratory experiments conducted on fullscale trapezoidal steel box-girders. The top-lateral bracing systems investigated included traditional single-diagonal truss systems and stay-in-place metal deck forms used during deck casting. Results include torsional girder stiffnesses, brace forces, and loaddeflection responses. Design issues, limitations, and guidelines for truss, metal-deck, and combined top-lateral systems are presented.