Seismic base shear of structures on compliant shallow foundations

A simplified method of assessing soil structure interaction (SSI) using a single degree of freedom representation of the structure is presented. The simplified method uses
recommendations from the SEI/ASCE code and implements the response spectra of NZS
1170.5. Three typical structures are analysed, and it was found that SSI effects reduced the base shear in all cases. Reductions in base shear of approximately 30% were found for tall structures with high aspect ratios (h/r=2.8). Structures of a squat nature with aspect ratios of 1.2 yielded a reduction in base shear of 10%. In addition, a nonlinear time domain and linear frequency domain solution is applied in a preliminary manner to the same structures. Using these methods, a reduction in base shear of approximately 50% was found for tall slender structures.