Main Article Content
Base isolations are acknowledged as an effective seismic protective system for structural systems of buildings. This study investigates the effectiveness of lead rubber bearing (LRB) on the nonlinear response of the steel moment resisting frames subjected to real ground motions. To this aim, 12-storey regular and irregular steel frames in elevation upgraded with LRB were studied by evaluating the local and global deformations. LRB was modeled by considering three key parameters of isolation period, effective damping ratio, and stiffness ratio. Two-dimensional model of the base isolated frames were created and a series of time-history analyses were carried out by different earthquake ground motions. The seismic behaviour of the base and isolated frames was measured by the variation of isolator displacement, acceleration, inter storey drift ratio, relative displacement, roof drift ratio , normalized base shear, base moment, and hysteretic curve. The supremacy of the base-isolated frames over the base frames was discussed accordingly. The results prove a substantial elongation of the building period, as well as a reduction in the building displacement, the roof acceleration, the inter-storey drift ratio and the base shear force of isolated building relative to fixed-base building.