Site response analysis for dynamic soil–structure interaction and performance-based design

The increasing power of four-dimensional analysis tools and advanced soil models has facilitated performance-based design processes to be followed for foundations in highly seismic areas. Often more efficient foundation solutions result than would be achieved by direct application of codes. Particular care is required in the selection and scaling of input ground motions, applied at an appropriate depth below the foundation system, with properly characterised soil properties and defined hazard level. A performance-based design process that has been applied successfully on many projects is described and is applied to two contrasting situations: a near-fault site in San Francisco where pulse-like ground motions are explicitly considered in seismic hazard assessment and a very soft soil site in Mexico City where amplification and strength mobilisation effects dominate. Outcomes from the analysed examples are examined and compared with the very limited code-based guidance that exists currently for performance-based design of foundations.