Direct Displacement Based Design for Reinforced Concrete Framed Structures with Seismic Isolation

Abstract

Direct displacement-based design is a nonlinear static procedure and has to check the suitability of the method against different types of ground motions namely far field, near field forward directivity and near field fling step. The method is applied for the buildings supported on a fixed base and hysteretic isolation bearings. Seismic isolators are provided between the foundation and the superstructure to minimize the influence of ground motion on the superstructure. The method is applied for four, eight and twelve storey reinforced concrete frame structures equipped with and without seismic isolators. Lead rubber bearing is used as seismic isolators. An equivalent damping ratio, derived from the particular characteristics of buildings supported on isolation bearings, is suggested. The energy dissipation mechanism in the isolators controls the displacement of the structure within acceptable limits at the level of the isolator. The results were validated with nonlinear time history analysis and were found to be in good agreement with the Direct displacement-based design methodology for far field ground motions. The performance of the building was measured for interstorey drift ratio, time period, acceleration of top floor, base shear, isolator displacement. This is an attempt to link the direct displacement-based design of the reinforced concrete building with seismic isolators subjected to the far field, near field forward directivity, near field fling step ground motions.