Implications of soil–structure interaction effects on the NBCC 1990 base shear provisions for high-rise buildings

This study is carried out on a site-specific basis for three locations in Canada, namely Ottawa, Vancouver, and Prince Rupert. Soil models are developed to correspond to the soil classifications used to define the foundation factor, F, in the 1990 edition of the National Building Code of Canada (NBCC). Structural models are developed to represent both 20-storey ductile moment-resisting frames and ductile flexural walls. Three initial sets of actual ground motion records are scaled, in the frequency domain, to represent the postulated bedrock motions for each of the three sites. The computer program FLUSH is used to perform the numerical analyses of the various soil–structure systems. Results from the current study indicate that the code F values generally underestimate the site effects associated with the respective soil deposits, but appear to be reasonably adequate, in most cases, when soil–structure interaction effects are taken into consideration. In spite of some deficiencies in the code F values, the 1990 NBCC design base shear is shown to be quite conservative for regular high-rise reinforced concrete buildings. A simple measure to account for inertial interaction effects in uncoupled analyses is shown to provide a significant improvement, as compared to conventional uncoupled analyses, in the prediction of the coupled base shear demand. Key words: seismic, hazard, site, soil, structure, interaction, code, design, base, shear.