Dynamic Evaluation of Overturning Moment Reduction Factor Used in Static Seismic Loading

The static seismic loading provisions of the 1975 National Building Code of Canada include, as do a number of other seismic codes, an overturning moment reduction factor in order to recognize that the overturning moment computed from the static load distribution is likely to be larger than the actual maximum dynamic moment. The reduction factors specified in the various codes have been based on empirical data and on relatively simplistic evaluations of the contributing effects. The purpose of this paper is to make a dynamic evaluation of the dynamic shear moment relationship and the reduction factor for a class of uniform shear wall–frame buildings subjected to earthquake motions as specified by several design spectra. The results are presented to show the effect of damping, natural period, and the particular response spectrum for different shear wall–frame stiffness proportions.