Buckling Restrained Braces for Ductile End Cross Frames in Steel Girder Bridges

Buckling restrained braces (BRBs) have been shown to be a cost-effective way of improving the seismic performance of moment-frame buildings. In this paper the application of these devices to bridge structures is explored and in particular BRBs are investigated as ductile members of the end cross frames in steel place girder bridges. Component experiments on a series of braces are first described and it is shown that they exhibit good cyclic behavior, although loading history and strain rate affect their performance and ultimate limit state. System experiments on a 0.4 scale model of a two-girder bridge using a pair of shake tables at the University of Nevada Reno are next described. BRBs are used in the ductile end cross-frames of this model and the results show a significant reduction in the shear demand in the bridge. Furthermore, the cross-sectional drift in the superstructures is less than when angle X-braces are used in the end frames. Ductile end cross frames are thus shown to be an effective means of improving the seismic performance of steel girder bridges and believed to be most effective when both the superstructure and substructure are relatively rigid.