Seismic performance assessment of highway bridges equipped with superelastic shape memory alloy-based laminated rubber isolation bearing

Abstract

Seismic performance analysis is conducted for an isolated three-span continuous highway bridge, which is subjected to moderate to strong earthquake ground accelerations in the longitudinal direction. Two types of isolation bearings are used in the analysis: high damping rubber bearing (HDRB) and combined isolation bearing consisting of shape memory alloy (SMA) wires and natural rubber bearing (NRB) entitled as SMA-based rubber bearing (SRB). Two types of SMA wires, such as Ni–Ti and Cu–Al–Be, are used in fabricating the combined isolation bearings. In the first step of the work, analytical models for HDRB, NRB and SRB are introduced. Then, a three-span continuous highway bridge is modeled in a simplified form, using 2-DOF bridge pier-bearing system isolated by either HDRBs or SRBs. The hysteretic behavior of HDRB is evaluated using a strain-rate dependent constitutive model (i.e. visco-elasto-plastic model), while in the case of SRBs the hysteretic behavior is modeled by a nonlinear elasto-plastic model for NRB and a simplified visco-elastic model for SMAs. A standard bilinear force–displacement relationship is employed in the analytical model of the bridge pier to consider its nonlinear characteristic behavior. Nonlinear dynamic analysis of the bridge, based on the direct time integration approach, is conducted to evaluate the seismic responses of the bridge. This study shows that the seismic responses of the bridge are affected by the use of different types of isolation bearings; more specifically, residual displacement of the deck are noticeably reduced after earthquakes in the case of SRBs compared to HDRB for moderate and strong earthquakes; however, pier displacements are smaller in the cases of SRBs for moderate earthquakes and higher for strong earthquakes. Other response parameters of the system, such as deck displacement, bearing displacement and deck acceleration, are significantly larger in the cases of SRBs compared to those of HDRB. This study also depicts the effect of modeling of isolation bearings on the seismic responses of the system.