# Seismic Response and Damage Analysis of an Isolated Bridge Subjected to Near-Fault Ground Motion
## 1 Introduction  
The earthquake damage investigation found that reinforced concrete piers would suffer severe damage or even collapse under near-fault ground motions [1; 2; 3; 4]. CAO [5] studied the damage to piers under near-fault ground motions and found that more than 91% of the 200 near-fault ground motions caused the piers to collapse, while far-fault motions rarely caused the piers to collapse. More severe damage often occurs in engineering structures in near-fault zones. Isolation bearings can effectively reduce the seismic response of structures, and have been used widely. However, In the 1999 Duzce earthquake in Turkey, the seismic isolation system of the Bolu Viaduct completely failed [6]. Then, under near-fault ground motions, the applicability of seismic isolation bearings has attracted more attention.  
Under near-fault ground motions, the isolated bridges will be damaged due to the large displacement of the bearings [7]. [PERSON] et al. [8] found that compared with far-fault motions, the displacement of the isolation bearings under near-fault motions will increase significantly. Similarly, [PERSON] et al. [9] found that the isolation bearing has a more significant displacement requirement under near-fault motions. [PERSON] et al. [10] suggested that energy dissipation devices should be installed to reduce the displacement of the isolation device under near-fault motions. [PERSON] [11] provided an elastic-gap device to decrease the isolator displacements under near-fault ground motions. [PERSON] et al. [12] found that a sliding-lead rubber bearing isolation system can reduce the base forces of the piers, and employing the shape memory alloy devices can reduce the peak displacement of the isolation system. [PERSON] et al. [13] found that the PGV/PGA ratio of near-fault ground motions has a significant influence on bridge response. The effect of the isolation bearing to reduce the shear force of the pier is not evident under near-fault ground motions. [PERSON] et al. [14; 15] analyzed the response of a three-span bridge with mid-span isolation undernear-field pulse-like ground motion and studied the difference between parallel fault and vertical fault ground motions to the structural response. [PERSON] et al. [16] found that the roll-in-cage isolator had a good seismic isolation effect under near-field and pulse-like ground motions. [PERSON] et al. [17] studied the pulse effect on the isolator optimization of bridges in near-fault zones. Most current studies focus on the seismic response of isolated bridges under near-fault and far-fault ground motions. There are few studies on the local damage state, damage evolution process, and potential failure modes of the isolated and non-isolated bridges.  
The main purpose of this paper is to study the seismic response and damage evolution process of the isolated and non-isolated bridges under near-fault ground motion and then to explore the failure modes of bridges. Based on the Refined Simulation and Analysis Platform for Structures (RSAPS) [18] developed previously, the fiber beam-column element model combined with the previously established damage constitutive model of steel and concrete materials [19] is used to simulate the nonlinear mechanical behavior and damage behavior of the piers. The isolation bearing model, with the horizontal bi-directional coupling effect and bearing instability failure considered, is used to simulate the nonlinear mechanical behavior and failure behavior of the isolation bearing. Then, the damage analysis model of the reinforced concrete bridge is established. The TCU068 ground motion of the Chi-Chi earthquake obtained from the Pacific Earthquake Engineering Research Center database [20] was selected as the input of the near-fault ground motion to study the seismic response and damage of non-isolated and isolated bridges. The present study can provide a theoretical basis for the seismic and isolation design of bridges in near-fault areas.