Longitudinal-direction design of buckling-restrained braces in resilient multi-span bridges

Multi-span bridges having a bidirectional ductile diaphragm consisting of buckling-restrained braces (BRBs) can provide resilient bridges with damage-free columns, at low cost, while minimising displacement demands to levels that can be easily accommodated. Towards the goal of better understanding the behaviour of this type of bridge and its advantages, a parametric analysis was performed considering regular multi-span simply supported bridges with variations in pier stiffness, BRB target displacement, BRB yield displacement and numbers of spans. The bridges were analysed in the longitudinal direction. BRBs were designed using non-linear response history analysis. The demands of the designed bridges were analysed to understand the influence of the various parameters considered. The proposed system was able to reduce the demands in piers so as to keep them elastic and limit the displacement demands in expansion joints (making it easier to prevent unseating in retrofit situations). It was also found that, according to fatigue damage calculations, it is not necessary to replace BRBs after an earthquake.