Seismic Analysis of Base Isolated Building Frames with Experimentation Using Shake Table

Abstract

AbstractBase isolation is the most effective and widely used technique for protecting a structure against seismic forces. The base isolation substantially decouples a structure from its base resting on the shaking ground, thus safeguarding the integrity of the structure by making them sustain the seismic forces without damage and also protect the lives of occupants. In the present study, an investigation is done to assess the seismic response of the structure with conventional fixed base and isolated base conditions. The isolation is configured with an elastomeric rubber isolator analyzed and designed in accordance with the International Building Code, IBC:2000. The analytical study is performed using ETAB application software and the experimentation is done using a uniaxial shake table on 1:12.5 scaled-down steel model developed using similitude laws corresponding to G + 3 and G + 5 prototype building frame. The study is carried out by applying three time histories, namely El-Centro, Uttarkashi and Indo-Burma. The fixed base condition is simulated in the laboratory by directly bolting the model on the shake table. The isolated base condition is simulated by mounting the model on an elastomeric rubber isolator. The study reveals that the acceleration produced in the base-isolated structure is reduced in the range of 40–60% in comparison with the fixed base condition. Pseudo spectral acceleration corresponding to fixed and isolated base conditions is obtained, which reveals that the time period of base-isolated structure increased to almost 2.5 s from 0.5 s. The shift in time period resulted in depletion in various parameters such as energy demand, pseudo acceleration and reinforcement requirement. The cumulative energy demand throughout the event of an earthquake is also studied. The reduction in energy demand for the isolated base condition is observed to be 50–90% lesser than in the fixed base condition. The reinforcement demand is reduced to 50% in isolated base condition. Thus, the study reveals that base isolation reduces the seismic demand of structure and enhanced safety, thereby reducing the cost of the structure. KeywordsShake tableBase isolationScaled-down modelElastomeric rubberTime historyTime periodPseudo acceleration