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The proposed 2005 edition of the National Building Code of Canada (NBCC) will contain very significant changes in the provisions for seismic loading and design. A brief history of the NBCC seismic provisions is presented followed by a discussion of the reasons for introducing such major changes in the next edition of the code. The major changes to the seismic provisions are summarized; this includes updated hazard in spectral format, change in return period (probability of exceedance), period-dependent site factors, delineation of effects of overstrength and ductility, modified period calculation formulae, explicit recognition of higher mode effects, rational treatment of irregularities, triggers for special provisions incorporated directly in classification of structural systems, and placing dynamic analysis as the normal "default" method of analysis for use in seismic design. The impact of these changes on the seismic level of protection is considered by comparing the 2005 NBCC and 1995 NBCC base shear coefficients for a selection of common structural systems located on a range of site conditions in three urban areas having low to high levels of seismic hazard, i.e., Toronto, Montréal, and Vancouver.Key words: seismic, design, loading, code, hazard, buildings, structures, foundations, period, analysis.

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SUMMARYA statistical analysis is performed to investigate the significance of peak ground acceleration to velocity ratio ( u h ) on the displacement ductility demand of simple bilinear hysteretic systems. Three groups of earthquake records representative of low, normal and high a/v ranges are used as input ground motions. The design yield strength of the inelastic systems is specified from the base shear formula in the 1980 National Building Code of Canada (NBCC 1980) and that in NBCC 1985 respectively. The former case represents the common practice of specifying seismic design base shear based on a peak site acceleration, while in the latter case the base shear is specified based on peak ground velocity and u/u ratio. Mean displacement ductility demands are obtained for the three groups of ground motions; and the corresponding dispersion characteristics are examined. The results show that the ground motion u/u range has a significant effect on the displacement ductility demand, and it should be accounted for in design strength specification.

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