Seismic Response of Rc Buildings Incorporating Effective Soil Isolation With Sustainable Materials

Abstract

Seismic isolation is a technique that has been adopted worldwide to protect building structures, non-structural components, and content from the damaging effects of earthquake-induced ground shaking. Geotechnical seismic isolation is a kind of isolation technique that has recently emerged as a possible solution to reduce the effects of earthquakes. The present research investigates the effectiveness of different materials such as natural material (coir mat), elastomeric material (rubber mat) and polymer material (epoxy polystyrene, polyethylene foam) as a medium for soil isolation to limit seismic energy transfer and thus the dynamic response of buildings. Finite element analysis is carried out on low-rise reinforced concrete buildings, resting on raft foundation over reinforced soil subjected to various earthquake motions. Two kinds of soil, namely soft and stiff soil, are considered based on their flexibility to study the dynamic soil-structure interaction (DSSI) effects. The linear elastic as well as non-linear inelastic behavior have been assumed for the analysis of the integrated building-foundation-soil system. The nonlinear analysis is carried out by incorporating the material non-linearity in the soil and isolation materials. The response of SSI system subjected to ground motions corresponding to the elastic design spectrum for Zone III as per the IS code, El Centro earthquake (1940), Northridge earthquake (1994) and Chi-Chi earthquake (1999) is analysed. The results indicate that soil isolation provided by the coir mat substantially reduces the earthquake energy transmission to the superstructure compared to other isolation mats. The optimum values for the depth of embedment, width and thickness of the coir mat were analysed and identified as B/18, B and B/36 respectively from the parametric analysis of the soil-structure system, where, B is the width of foundation. The coir composites such as coir-rubber and coir-polymer foam are proposed to increase the durability of the coir mat by preventing coir mat from biodegradation. Further, a pore water pressure analysis of soil bed also has been carried out in Cyclic 1D software and PLAXIS 3D software to study the efficacy of these materials to reduce ii the excess pore water pressure generated in soil under earthquake loading. The isolation efficiency of reinforcement materials in reducing the excess pore water pressure generated in soil under different earthquake motions obtained is 75-82%, 71-80% and 67-72% with coir, coir-polymer and coir-rubber composites respectively. Among various isolation mats, the coir mat and coir-polymer foam composite mat are recommended as the efficient soilisolation medium, especially at soft soil sites.