Influence of site effects and period-dependent force modification factors on the seismic response of ductile structures

A foundation factor, F, is incorporated in the National Building Code of Canada (NBCC) design base shear formula to account for amplification of bedrock ground motions as these propagate upwards through the local soil deposit (site effects). In the NBCC, the value of F is specified as a function of the local soil type and depth, irrespective of the ductility capacity for which the structure situated at the surface of the soil deposit is to be designed and detailed. On the other hand, the ductility capacity of the structures is taken into account in the code by the force modification factor, R, for which values are specified depending on the type of the structural system. The current study investigates the influence of the ductility capacity of engineering structures in mitigating the site effects. Simple bilinear single-degree-of-freedom models are used to simulate the seismic response of structures, underlain by soft or stiff soil deposits and subjected to seismic ground motions. These structural models ...