Optimum joint gap size in bridges with Ductile Piers

The present study puts forward a novel approach for seismic design of bridges, wherein the optimum joint gap size is one of the design parameters of the bridge; the methodology integrates the optimization of the joint gap with a ‘mainstream’ seismic design for energy dissipation in the piers. Another contribution of this study is the assessment of the effect of bridge configuration on the selection of the optimum joint gap sizes, focusing on the effect of pier height for bridges with ductile piers. It is found that designing bridges for optimal gap sizes in both directions leads to a notable reduction in pier reinforcement requirements when the aim is to satisfy the Code criteria while, at the same time, the safety margin against exceeding the specified performance criteria (limit states) remains practically unaffected. On the other hand, the required design effort inevitably increases. Regarding the effect of pier height, an interesting finding is that as piers increase in height, leading to increased flexibility and, hence, larger displacements, other components of the bridge, such as the abutment-backfill system, tend to become the critical ones in identifying the optimum gaps.