Seismic response of low-rise buildings with eco-rubber geotechnical seismic isolation (ERGSI) foundation system: numerical investigation

The 2010–2011 Canterbury Earthquake Sequence caused extensive damage to over 6000 residential buildings in Christchurch and highlighted an urgent need to improve the resilience of the housing sector. As a result, the authors have developed the eco-rubber geotechnical seismic isolation (ERGSI) foundation system for new low-rise buildings. It is a cost-effective and sustainable technology that integrates a horizontal geotechnical seismic isolation (GSI) layer—i.e. a deformable seismic energy dissipative filter made of gravel–rubber mixtures (GRMs)—and a flexible rubberised concrete (RuC) raft footing. The present study aims at evaluating the performance of an ideal ERGSI system in dissipating seismic energy and assessing the seismic response of two-storey RC framed structures placed on the ERGSI system. Firstly, results of laboratory investigations are presented and ideal GRM and RuC for use in ERGSI systems are identified. Hence, OpenSees finite-element numerical investigations and spectral acceleration analyses are undertaken for a 900 mm-thick GRM layer with 40% rubber content by volume. Further, time-history dynamic analyses—carried out by SeismoStruct software—are presented and discussed for two ERGSI-isolated RC framed structures having natural period of 0.3 s and 0.5 s. The results obtained for the ERGSI-isolated structures are finally compared with those obtained for two non-isolated framed structures placed on a traditional foundation (i.e. RC footing placed on a compacted gravel layer). This study demonstrates that the seismic demand (i.e. peak acceleration measured at the structure top-floor, lateral deformation at each floor and base shear) on low-rise buildings can be significantly reduced by using ERSGI foundation systems.