Studies Of Seismic Responses Of Framed Steel Structure With Spring-Rubber Isolators

For a few decades, the use of the base isolation technique has achieved significant success in reducing the structural damage to buildings from earthquake attacks. Despite the overall effectiveness of base isolators, further study and development are required for improving the mean of protecting structures and their contents against earthquakes.On background of the practical engineering, a one-four three story steel model was used. The seismic characteristics of a three-storey steel model isolated with Spring-Rubber (SR) Isolators have been studied using a shake table. Shaking table of MTS Corporation, with computer control system were used to identify dynamic parameters of the Steel model with and without SR bearings. The natural frequencies, damping ratios and mode shapes as well as structural properties, namely, the mass, stiffness and damping matrices, were obtained. In order to evaluate the efficiency of the base isolation system and the effect of earthquake ground motions, both numerical analysis and shake table testing of the model with and without the isolation system were carried out under four different strong ground motions, namely El-Centro 1940, Spitak (Armenia) 1988, Shanghai artificial wave and Kobe 1995 earthquakes.1. It was found, from both numerical analysis and shake table testing, that the isolation effectiveness offered by the SR bearings to earthquake inputs is strongly dependent on the type of earthquake motion.2. Test results of fixed-base model and the SR isolator model were compared to confirm the effects of Isolator system. The comparison showed that the response of the model with isolated system reduced than the responses of fixed-base model and damping increased due to SR isolators. The results confirmed that model with Isolated system can withstand and behave well under high intensity earthquakes.3. The maximum acceleration for all floors was significantly reduced with the addition of a SR isolation system, regardless of ground motion input. However, the relative displacements of the SR isolated model are strongly dependent on the type of earthquake excitation. The seismic responses of the isolated model were improved when subjected to the Kobe 1995 earthquakes, with best results obtained when El Centro earthquake was applied.4. The maximum accelerations, displacements, inter-storey drifts and base shear force as well as over-turning moment for the SR isolated model were significantly reduced, and the vibration amplitude of the accelerations, and inter-storey drift decreased much more quickly with time than those without SR bearings. The present base isolation system was not effective in combating the Shanghai Wave earthquake. A reasonable agreement between results obtained from numerical analysis and those of shake table testing was also observed.The idea of this paper is to isolate structures from earthquakes by incorporating the rubber and spring in one device which is new in civil engineering. The new devices were used to test framed steel structure and to study its seismic responses. Believe suggested system of isolation will provide safety to structures and guarantee of saving lives from earthquake attacks.