Seismic Design of Precast I-Beam Bridges Based on Ductility

Abstract

This study proposes a new configuration for the longitudinal direction of precast I-beam bridges aimed at the improvement of their earthquake resistance. The longitudinal response of the new bridge system is different from the response of the usual "floating deck" bridge configuration, the main characteristic of which is the different seismic movements between the deck and pier head. The proposed configuration includes the application of seismic stoppers that are used to transmit the longitudinal design seismic action to three contiguous piers, provided that serviceability requirements are preserved. The aforementioned seismic stoppers are combined with elastomeric bearings that allow the free rotation of the supported nodes. The deck is connected to the other piers through sliding bearings permitting its free movement in the longitudinal direction, while its transverse movement is constrained by stoppers. This methodology offers the opportunity to design precast I-beam bridges as ductile structures, provided that the longitudinal seismic action is transmitted to the three piers of the bridge. The result is that values of the behavior factor q ≤ 3,5 are obtained in both directions. The suggested modification is necessary before integrating a restraining system. This restraining system consists of four symmetrical bundles of steel bars, whose function is to improve the seismic behavior of the whole bridge system. These bundles are applied in the bridge sidewalks; they are anchored at their ends and bind the deck with the abutments’ wing walls, while their length between the anchorages is unbounded. The steel bundles act as a longitudinal struts and ties system. This proposed method improves the earthquake resistance of the structural system as the steel bundles are activated during earthquakes and restrain the seismic displacements. The above-mentioned procedures were applied in a precast concrete I-beam bridge and the results showed a significant reduction in the seismic displacements and loads of the bridge.