Probabilistic Seismic Demand Assessment of Steel Moment Resisting Frames Isolated by LRB

Seismic isolation is an effective approach used in controlling the seismic responses and retrofitting of structures. The construction and installation of such systems are expanded nowadays due to modern improvements in technology. In this research, the seismic performance of steel moment resisting frames isolated by Lead Rubber Bearing (LRB) is assessed, and the seismic demand hazard curves of the frames are developed using Probabilistic Seismic Demand Analysis (PSDA). In addition, the effects of LRB on overstrength, ductility and response modification factor of the frames are studied. To achieve this, Incremental Dynamic Analyses (IDA) are conducted using 10 records of near field earthquake ground motions on the intermediate steel moment resisting fixed base frames with 3, 6 and 9 storeys retrofitted by LRB according to ASCE 41. The results show that in the case of isolated frames, the values of ductility and response modification factor are decreased in comparison with those of fixed base frames. Moreover, based on the developed fragility curves, seismic isolation is more effective in improving structural performance in extensive and complete damage states compared to slight and moderate damage states. However, increasing the height of both structural groups (i.e. fixed base and base isolated) results in reduction in performance level. Besides, the probability of occurrence of a certain demand is reduced by base isolation.