Near-fault isolation of cable-stayed bridges using RNC isolator

Abstract

This paper investigates the near-fault (NF) seismic performance of a recent isolation system, referred to as Roll-N-Cage (RNC) isolator, considering the cable-stayed Bill Emerson Memorial Bridge in Missouri, USA. Under NF ground motion, the seismic isolation devices might perform poorly because of large isolator displacements caused by long-period large velocity and displacement pulses associated with such strong motion. The RNC isolator is designed to achieve a balance in controlling isolator displacement demands and structural accelerations. It provides in a single unit all the necessary functions of rigid support, horizontal flexibility with enhanced stability and energy dissipation characteristics. Moreover, it is distinguished from other isolation devices by two unique features: (1) it has a built-in energy absorbing buffer to limit the isolated deck displacement under severe seismic excitations to a preset value and (2) it has a built-in linear recentering mechanism that prevents residual displacement after earthquakes. The seismic response of the RNC-isolated cable-stayed bridge is investigated using nonlinear time history analysis under three recorded NF earthquakes and three synthetic ground accelerations that capture many of the kinematic characteristics of recorded NF ground motions. The results show that the RNC isolator is a convenient isolation system in protecting cable-stayed bridges against NF earthquakes.