H Toopchi-nezhad - Assistant Professor, Department of Civil Engineering, Razi University, Kermanshah, Iran,
M.A Sharafiani - PHD Student in Civil Eng., Department of Civil Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran,
Ehsan Khosravi - PHD In Civil Eng., Department of Civil Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran,

Base isolator is a device which decuples a structure from earth movements, and decreases responses of the structure during earthquakes. The main task of this device is causing difference between the natural period of the structure and the main period range of the excitation. Therefore, by helping the structure experiences lower excitation, the base isolator reduces damages. It is clear that the effects of near-fault (NF) ground motions with large velocity pulses can bring the seismic isolation devices to critical working conditions. In this article, a four-story steel structural frame was modeled, analyzed anddesigned in SAP2000 software, then the lateral displacement of the structure was controlled. In the second part, the pushover analysis was applied on the structure, and both the capacity curve of frame and the performance point of structure were calculated. In the third part, three earthquake records applied on the structure, and nonlinear time history analyses were done for fixed- base structure (without using isolator), after that based on dead and live loads lead rubber isolators were designed and modeled in software. Finally, three earthquake records applied on the structure which was equipped by isolator, and nonlinear time history analyses were done, after that the responses of the structure were compared with and without the presence of isolators. The results showed positive effect of lead rubber bearing on seismic performance of the structure.

lead-rubber bearing, capacity curve, nonlinear time history analysis, near-fault motions