Buckling-Restrained Braces in Bi-Directional Ductile Diaphragms of Multi-Span Bridges

Multi-span bridges having bi-directional ductile diaphragm consisting of Buckling Restrained Braces (BRBs) can provide resilient bridges with damage-free columns, at low cost, while minimizing displacements demands to levels that can be easily accommodated. Towards the goal of better understanding the behavior of such bridges and developing simple procedures for their design, multi-span bridges having ductile diaphragms, considering various layout and implementation strategies, have been investigated to establish their seismic performance. A parametric study has been conducted using nonlinear time-history analyses considering variations in ratio of substructure-to-superstructure stiffness, span length, period, and other factors. These analyses were performed to determine the level of complexity required to predict adequately the bridge response, with the goal of providing design rules as simple as possible to achieve satisfactory seismic performance. This was assessed by subjecting the resulting designs to suites of ground motions accelerations using non-linear time-history analyses. These dynamic analyses allowed to understand the impact of these parameters on global behavior, as well as the magnitude of the local demands and, more specifically, the extent of bidirectional displacements that the hysteretic devices must be able to accommodate while delivering their ductile response.