Investigation of Base-Isolator Type Selection on Seismic Behavior of Structures Including Story Drifts and Plastic Hinge Formation

Abstract eng:
Seismic base isolation is an earthquake resistant design method that is based on decreasing the seismic demand instead of increasing the seismic capacity. In this paper, the effect of using two different types of seismic isolators in decreasing the base shear and story shears of structure has been investigated. Four structural models with 2, 5, 8 and 12 stories for three cases including fixed-base, lead-rubber isolator and friction pendulum isolator with different stiffness have been modeled. All models have been analyzed under earthquake characteristics of Manjil, Naghan, Tabas and Elcentro using a nonlinear finite element program. The results indicate that by using lead-rubber isolators, maximum displacements of stories in low-rise structures have been increased in comparison with fixed-base model. In contrast, in majority of cases, applying the FPS isolators doesn't guarantee the displacement requirement. Also by using isolators, number of cycles related to displacement response would be decreased especially in models with lower stories. In short base isolated structures, the decrease in plastic hinge formation percent of elements is much more than in fixed-base structures. With regards to the results that are mainly based on Iranian earthquakes characteristics, it could be concluded that seismic isolation is a useful method if being applied in short structures. Finally by comparing the hysteretic responses of structural models in three explained cases, it is revealed that the greater the design period of isolator, the higher level of energy dissipation by isolation system.

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