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.
NZGS Symposium