System fragility curves for a long multi-frame bridge under differential support motions Jeon, Jong-Su; Shafieezadeh, Abdollah; DesRoches, Reginald
The paper presents the seismic fragility assessment of a long multi-frame bridge subjected to differential support motions. For this purpose, a bridge experiencing the 1992 Landers earthquake is first chosen as the subject bridge and its numerical model is created using OpenSees. Nonlinear time-history analyses for the model under both uniform and multi-support motions recorded during the earthquake are performed and the simulated deck deformations are compared with the recorded sensor data. The results highlight the significance of multi-support motions along with an appropriate bridge model. For the derivation of fragility curves of the bridge, the conditional simulation of spatially variable ground motions is undertaken to obtain a set of acceleration time histories at different supports, which are converted into a set of displacement time histories. A set of analyses for the simulated motions are conducted on statistical realizations of the bridge model reflecting material and structural uncertainties to monitor the seismic demand of components. Accordingly, a new analytical formulation for the intensity measure is introduced to consider the spatial correlation of ground motions. Given the demands and limit states, component fragility curves are developed on the basis of the closed form, and system fragility curves are developed using Monte Carlo simulation. The fragility results reveal that a reduction in the average shear wave velocity results in an increase in the exceedance probabilities at higher limit states and thus the increase of bridge vulnerability.
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