Seismic Response of Buildings Resting on Raft Foundation with EPS Geofoam Buffer

Seismic isolation is a technique that has been used around the world to protect building structures, non-structural components and content from the damaging effects of earthquake ground shaking. The present study deals with analysing the efficiency of Epoxy Polystyrene (EPS) geofoam buffer as a soil isolation medium to reduce the seismic energy transferred, thereby reducing the dynamic response of building under earthquake loads. The behaviour of an integrated soil isolation-building system has been investigated analytically, by using recorded accelerogram of El Centro earthquake. Finite element simulation of transient response has been carried out on three-dimensional field-scale models of one-storey, two-storey, three-storey and four-storey buildings resting on raft foundation in sand beds of different stiffnesses, with and without soil isolation mechanism. Four sets of three-dimensional buildings of single bay moment resisting concrete frames with 4 m bay length in either directions and 3 m storey height have been considered for the estimation of seismic response. EPS geofoam buffer of thicknesses 0.05, 0.10, 0.15 and 0.20 m and stiffnesses 22, 16, 10 and 5 MPa are placed at a depth of 0.15 m below the raft foundation of dimension 5 m × 5 m × 0.5 m. Different soil stiffnesses are considered to study its effects on the seismic response of building. Size of the soil stratum considered is 55 m × 55 m with a depth of 20 m. Absorbent boundaries have been used to eliminate the problem of reflection of the waves back into the soil from lateral boundaries. The interface between the underneath soil and EPS geofoam is formulated with a coefficient of friction 0.3. The results under field-scale conditions indicate that soil isolation provided by the EPS geofoam buffer substantially reduces the earthquake energy transmission to the superstructure during a strong earthquake.