The equivalent static force procedure is a fundamental part of seismic design provisions of the National Building Code of Canada (NBC). This procedure simplifies the seismic design process by approximating the complex nonlinear dynamic response of structures using an equivalent linear problem. Two key input parameters in the equivalent static force procedure are the ductility-related and overstrength-related force modification factors. The ductility-related factor accounts for the ability of a structure to dissipate energy through inelastic behaviour. The overstrength-related factor considers the reserve strength of a structure due to material properties and redundancy in the system. The seismic force modification factors of the NBC were originally determined based on engineering judgment and a qualitative approach.
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