Classical soil-structure interaction and the New Zealand structural design actions standard NZS 1170.5 (2004)

The purpose of this paper is to evaluate the provisions of the New Zealand structural design actions standard (NZS 1170.5 (2004)) with respect to classical elastic soil-structure interaction effects on the earthquake design of shallow foundations supporting multi-storey buildings. Work by earlier researchers had led to the suggestion that for tall buildings the lengthening of the structure-foundation period caused by soil-structure interaction might give reduced foundation design actions. The results of numerical modelling using the modal response spectrum method did not reveal any evidence for such a reduction, in fact generally there was an increase. We suggest that the jumps between the design spectra when moving from a rock site, to a shallow soil site, to a deep soil site are more significant than the subtle soil-structure interaction effects caused by the modest period lengthening of the structure-foundation system.