Application of uniform hazard spectra in seismic design of multistorey buildings

Abstract

The use of uniform hazard spectra for obtaining the seismic design forces is being considered for the next version of the National Building Code of Canada. Such spectra provide the spectral accelerations of a single-degree-of-freedom system for a range of periods but for a uniform level of hazard. One of the issues that need to be resolved before uniform hazard spectra are used in the design of multistorey buildings is the adjustment required in the base shear to account for the higher mode effects present in a multi-degree-of-freedom system. This issue is examined through analytical studies of the response of idealised elastic and inelastic multistorey building frames to ground motions representative of the seismic hazard in the eastern and western regions of Canada. Representative values are obtained for the adjustment factors that must be applied to the design base shear and to the base overturning moment.Key words: seismic design base shear, uniform hazard spectra, higher mode effects, base shear adjustment factor, base overturning moment reduction factor.