Seismic loading provision changes in National Building Code of Canada 1985

This paper describes the process by which Canadian seismic loading provisions are developed and then details the primary changes being introduced in the 1985 edition of the National Building Code of Canada. The most significant change is the inclusion of new seismic zoning maps, based on a new seismic risk methodology, a new probability level, and additional seismic zones, and incorporating both horizontal ground velocity and acceleration as zoning parameters. The format of base shear calculation is revised to incorporate these changes, including the specification of a new seismic response parameter. The base shear formula is calibrated to ensure that, on a cumulative basis throughout the country, the level of seismic loading remains unchanged. Additional changes discussed in the paper include the removal of dynamic analysis as a specific option in the base shear calculation and some significant changes in the calculation of torsional effects.