Investigating the Effect of Vertical Component of Earthquake on Variation of Axial forces in RC Bridge Pier with FPS Isolators

Bridges are key elements in the highway transportation system. Many bridges collapsed or were extensively damaged in past earthquakes, which highlighted the vulnerabilities of existing bridges. Therefore, different rehabilitation methods have been developed for mitigating earthquake hazards in new bridges or retrofitting existing ones. Isolation systems are one of the most commonly used devices that have been developed to dissipate earthquake energy and improve the seismic behavior of bridges. Friction pendulum System (FPS) is a sliding-based isolator, widely used in the seismic design of bridges. Recent investigations show that bridges with FPS isolators exhibit good performance against seismic forces due to the energy dissipation of the isolation device. The purpose of this study is to assess the effects of the vertical component of the earthquake on variations of axial forces of piers in a three-span continuous deck reinforced concrete(RC) bridge, seismically isolated by the FPS. To this end, incremental dynamic analyses (IDA) are conducted using a suite of 24 near-fault ground motions to evaluate the dynamic behavior of the bridge piers. IDA curves and Fragility curves are generated with peak Ground acceleration and column drift as intensity measure and Engineering Demand Parameter (EDP), respectively. The results showed that the vertical component of earthquake can increase the axial forces of piers significantly. Moreover, the damage probability of the moderate and extensive damage states showed 6% and 24% increase, respectively, And The damage probability of Isolators increased by 21% considering the vertical component of the earthquake.