Bending behaviors of quasi-closed trapezoidal box girders with X-type internal cross-frames

Abstract

During the construction of composite trapezoidal box girder bridges, steel tub girders with top lateral bracing systems, so-called quasi-closed box girders, are expected to carry non-composite dead loads in addition to other construction loads. Although quasi-closed box systems with internal cross frames mainly serve to increase the torsional resistance of tub girders and preserve the original box shape, significant forces are developed in both top lateral and internal bracing members due to bending. The coupling action that occurs between the single-diagonal-type lateral bracing system and internal cross frames depends on the panel spacing of the internal cross frames. Although either internal K- or X-frames can be used in trapezoidal box girders, their interaction behaviors with top lateral bracing systems differ because of their different configurations. In this study, matrix equations were formulated to calculate the brace forces developed in both single-diagonal-type top lateral bracing and internal X-frame members in trapezoidal box girders subjected to bending action. Member forces computed using the new equations were then compared with those from three-dimensional finite element analyses, and an excellent correlation was found.