Seismic analysis of bridge with buckling-restrained brace posttensioned concrete pier

A two-span bridge built with a two-column pier consisting of unbonded posttensioned precast concrete columns and a buckling-restrained brace (BRB) is analyzed using a three-dimensional nonlinear numerical model. Seismic damage to the pier is eliminated through rocking of the posttensioned columns and seismic energy dissipation by the BRB. The numerical model is calibrated with experimental results of posttensioned columns and BRB structural elements. Seismic assessment of the bridge pier is performed using the ratio of BRB axial force to base shear as the parameter of interest. Limits for the seismic performance of the bridge pier are established by means of nonlinear static analysis using OpenSees. Bidirectional ground motions are used to perform probabilistic hazard analysis through nonlinear time history simulations. Three damage limit states are defined in this research: the activation point of posttensioning bars, the maximum base shear capacity or onset of concrete spalling, and collapse defined as the state at 20% loss of maximum base shear capacity. The analysis results are formulated into fragility curves for the three damage states as well as the residual drift. The fragility curves could be used for preliminary seismic bridge design. The analysis shows that the BRB dissipates significant seismic energy and the posttensioned concrete columns reduce residual displacements so that the bridge pier can remain functional after severe earthquakes. The fragility approach for designing bridge piers constructed with posttensioned concrete columns and BRB elements is a significant improvement over conventional seismic bridge design and can contribute to functional recovery after severe earthquakes.