Shape-memory alloy-friction isolator enhanced with inertia pendulum for seismic mitigation of bridges

Abstract

Research has demonstrated that shape-memory alloy-based friction bearings (SMAFBIs) can obtain significant seismic response reduction and self-centering performance of isolated bridges. However, SMAFBIs, similar to conventional isolation techniques, reduce seismic forces at the cost of increasing deck drift. Excessive deck drift will increase the probability of the deck unseating, while large seismic forces such as base shear of piers will increase the risk of damage to piers. To limit the deck drift and the pier base shear of bridges isolated with SMAFBIs at the same time, an inertia pendulum (IP), which can amplify the inertia of a pendulum mass by a lever to effectively tune the natural period of structures, is proposed to enhance the bridge isolated with SMAFBIs. The seismic design spectrum of the linearized SDOF system with IP is proposed and examined by direct integration method. Based on this seismic design spectrum, the performance-based seismic design procedure for bridges isolated with IP-SMAFBIs is proposed. The two bridges isolated, respectively, with SMAFBIs and IP-SMAFBIs are designed according to this procedure, and their seismic responses obtained by elastic–plastic time history analysis are examined and compared. The research results show that IP-SMAFBIs have significant advantages in terms of reducing maximum deck drift not at the cost of increasing the pier base shear. In addition, the effects of the mass ratio and leverage ratio of the IP on seismic performance of the isolated bridge are investigated in detail, and the optimal parameters are suggested.