There is increasing awareness in earthquake engineering of the need to consider the structure, foundation, and underlying soil in an integrated fashion. The traditional design scenario, where the geotechnical and structural considerations are dealt with separately, results in inefficient and sometimes less effective foundation systems. Integrated numerical models provide a means to more appropriately capture the earthquake response of buildings; however, this does not necessarily require the development of evermore complex models. Spring-bed models used to capture the interaction between the foundation and the soil provide a balance between ease of implementation and theoretically rigorous solutions. By incorporating nonlinear interaction effects associated with soil-foundation-structure interaction (SFSI) into a spring-bed model, the earthquake response of buildings can be appropriately captured.
A structure-foundation model on a bed of nonlinear springs has been developed for a multistorey building on a shallow raft foundation in Christchurch, New Zealand. A widely-used structural design software package (SAP2000) was employed to model this integrated system and existing features of the program were used to capture the nonlinear effects of foundation uplift and soil yielding in the springs. Time history data from the 22 February 2011 Christchurch Earthquake was used to investigate the earthquake response of the building. The results of analysis of this integrated SFSI numerical modelling showed that the earthquake response was very different when loss of contact was allowed between part of the foundation and the underlying soil.