A displacement-based seismic design procedure for concrete bridges having deck integral with the piers

A multi-step displacement-based seismic design procedure is presented and exemplified for concrete bridges having piers integral with a continuous prestressed deck, which is restrained transversely at the abutments but free to slide there longitudinally. It includes a simple estimation of inelastic deformation demands (chord or plastic hinge rotations in piers, curvatures for the deck) via elastic 5%-damped modal response spectrum analysis and normally entails very few design-analysis iterations. Prescriptive detailing and minimum reinforcement rules are relaxed. Instead, the vertical reinforcement of piers is tailored to seismic deformation demands for uniform ductility ratios across the piers, while their transverse reinforcement is detailed on the basis of explicit checks of their integrity under the design earthquake. The procedure is applied to eight different bridges with three or five spans, box girder deck and piers of various cross-sections with about equal or very different heights. Nonlinear response-history analyses are carried out under ground motions well beyond the design earthquake, in order to evaluate the seismic performance of the resulting designs and compare with that of force-based Eurocode 8 designs of the same bridge. The displacement-based procedure is shown to give more cost-effective and balanced designs than Eurocode 8, without loss in seismic performance.