Evaluation of the seismic response factor introduced in the 1985 edition of the National Building Code of Canada

Abstract

The seismic loading provisions included in the 1985 edition of the National Building Code of Canada simulate the dynamic response of structures using a seismic response factor, which has three branches depending upon the relationship between the velocity-related seismic zone Zv and the acceleration-related zone Za. This paper utilizes three ensembles of actual seismic strong motion records to evaluate the seismic response factor; each ensemble has acceleration/velocity ratios corresponding to one of the three branches of the seismic response factor. These strong motion time histories are used as input to relatively simple elastic models of frame and wall structures in order to obtain dynamic seismic response factors. The comparison of these dynamic factors with those specified in the NBCC 1985 indicates that the code factors are generally quite satisfactory, with the exception of the case of frame structures with low fundamental periods located such that Za is two zones higher than Zv. The paper references several other investigations that produce similar results. In that instance, it is recommended that the seismic response factor should be increased, particularly if the structure is located on stiff soil rather than on rock. Key words: structures, loading, seismic, code, earthquake, dynamic, elastic, acceleration, velocity, spectra.