Seismic performance of steel girder bridges with ductile cross frames using buckling-restrained braces

Ductile end cross frames have been proposed in the past for seismic design of steel plate girder bridges. In this paper buckling-restrained braces (BRBs) are investigated as ductile end cross frames and compared against the performance of yielding X braces. Component experiments on the BRBs showed that these braces dissipated energy very efficiently and have stable hysteretic behavior. Shake-table experiments on a large scale bridge model investigated the performance of braces with both pin-ended connections and fixed-end connections. Despite slippage, the pin-ended connections are considered more effective as flexural action in the relatively short braces is prevented. The base shear in the bridge model in response to 2.0 times the El Centro earthquake was 69% of the elastic base shear at an average drift of 2.5% during experiments. The relatively large deformation capacity of the BRBs, although not as great as the X braces, is necessary to achieve a significant reduction in base shear. The maximum cross frame displacements with the BRBs are consistently smaller than those in X braces at the same level of base shear.