Direct Displacement Based Design of RC Frame With Based Isolation

From long time ago, various solutions have been proposed to reduce earthquake damages, including increasing ductility and reducing structural mass. New methods are based on separating the structure from the foundation, to reduce the shear force of the base of the structure. In other words, seismic isolation is a new method for designing buildings against earthquakes, which is based on reducing the forces entering the structure due to earthquakes, instead of increasing the capacity of the structure to withstand lateral loads. This paper is a focused on the study of the effect of the placement of rubber separators with lead cores in the behavior of reinforced concrete structures under the influence of remote earthquakes. Therefore, for rubber separators with lead core in two samples of concrete structures of 3 and 5 floors, a double damping of 10 and 15% has been considered. Separating structures and fixed base structures were modeled in “Opensees” software. Afterwards, under the influence of distant earthquakes, a time history analysis was performed on them. Finally, the results of time history analysis for designs by force and direct displacement method are exposed, which include, maximum drift of floors, maximum shear of base and period of structures. Results obtained from the analysis of time history show that with the increase of the rotation time, the shear of the bases and the maximum drift in the buildings with isolators designed by direct displacement method are more than the buildings designed by force method. Buildings with separators designed by direct displacement method have sections with less capacity than buildings designed by force method.