Seismic force-modification factors for mid-rise wood-frame buildings with shearwalls using wood screws

Abstract

Wood-screw shearwall (WSS) is generally considered to have limited ductility under seismic load. Conservatively, minimum ductility-related force-modification factor, Rd, of 1.0 and over-strength related force-modification factor, Ro, of 1.3 are used in the National Building Code of Canada for seismic design. In this study, the structural performance of WSS’s with different thicknesses of wood-based panels and sizes of wood screws was investigated by conducting monotonic and cyclic loading tests. The combined force-modification factor RdRo was estimated based on shearwall test results. To verify the estimated modification factors, mid-rise light wood-frame buildings (LWFBs) with different numbers of storeys, wall aspect ratios, magnitudes of gravity and diaphragm flexibilities were designed and analysed numerically. Nonlinear dynamic analyses were performed with 22 scaled Far-Field earthquake time-history records. The seismic response of the mid-rise LWFBs with WSS’s under design hazard level met the design criteria of strength and deformation, and the collapse margin ratios obtained by using a simplified FEMA P695 method complied with the requirements. The study indicates that it is appropriate to use an Rd factor of 1.5 and an Ro factor of 1.7 for seismic design of WSS’s.