Optimal design of superelastic-friction base isolators for seismic protection of highway bridges against near-field earthquakes
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AbstractThe seismic response of a multispan continuous bridge isolated with novel superelasticfriction base isolator (SFBI) is investigated under nearfield earthquakes. The isolation system consists of a flat steelTeflon sliding bearing and a superelastic NiTi shape memory alloy (SMA) device. The key design parameters of an SFBI system are the natural period of the isolated bridge, the yielding displacement of the SMA device, and the friction coefficient of the sliding bearings. The goal of this study is to obtain optimal values for each design parameter by performing sensitivity analysis of a bridge isolated by an SFBI system. First, a threespan continuous bridge is modeled as twodegreesoffreedom with the SFBI system. A neurofuzzy model is used to capture rate and temperaturedependent nonlinear behavior of the SMA device. Then, a set of nonlinear time history analyses of the isolated bridge is performed. The variation of the peak response quantities of interest is shown as a function of design parameters of the SFBI system and the optimal values for each parameter are evaluated. Next, in order to assess the effectiveness of the SFBI system, the response of the bridge isolated by the SFBI system is compared with the response of the nonisolated bridge and the same bridge isolated by purefriction (PF) sliding isolation system. Finally, the influence of temperature variations on the performance of the SFBI system is evaluated. The results show that the optimum design of a bridge with the SFBI system can be achieved by a judicious specification of design parameters. Copyright 2010 John Wiley & Sons, Ltd.
