Three dimensional seismic analysis of buildings supported on elastomeric bearings

The study presented herein aims at investigating the effectiveness of elastomeric bearing isolation systems in reducing the translational as well as the rotational story-displacements and story-forces of buildings subjected to earthquake forces. The rotational displacement principally occurs because of eccentricities between the mass center and the shear center of a building, and these eccentricities may sometimes be accidental, or naturally may exist because the shape of the building is unsymmetric.; To carry out the investigation, we first have to provide a solution that would include the rotational properties of a building. This study deals with such a solution which as we shall see would be iterative and time dependent. The force-displacement relationship of the elastomeric bearings will be considered (1) as linearly elastic, and (2) as bilinear hysteretic where the results from both considerations will be compared at the end. Furthermore, the study will implement the assumption that the upperstructure remains linearly elastic which enable us to solve the bearings equations of motion separately from the upperstructure equations of motion and ultimately reduce the (time cost) of the solution. The responses of a single-story building and a 4-story building with strong coupling between the torsional degree of freedom and the lateral degrees of freedom will be studied. Different response quantities of these buildings mounted on elastomeric bearings will be compared with those of the same buildings with the traditional fixed-base. Upon such comparison, a conclusion could be drawn on the effect of the torsional-lateral coupling, the inclusion of upperstructural stiffness, and the modeling of the bearing stiffness (linear and nonlinear) on the performance of elastomeric bearing isolation systems.