SEISMIC SHEAR DEMAND OF DUCTILE CANTILEVER WALLS - A CANADIAN CODE PERSPECTIVE

During severe earthquakes, ductile flexural walls are expected to exhi bit inelastic flexural behaviour while other brittle deformation mecha nisms, such as shear, should remain elastic. The philosophy of the Can adian seismic provisions for flexural walls is based on the assumption that the force reduction factor is applicable to both flexure and she ar. If the bending moments are limited because of the flexural strengt h of a wall, then the shear forces are considered to be limited by the same ratio. Recent case studies have not confirmed this philosophy. B rittle shear failures in walls are still possible even if their shear strengths are established by the Canadian standards. This paper presen ts an analytical investigation on the shear demand of ductile flexural walls designed for three different seismic zones in Canada. For each zone, an ensemble of code compatible historical earthquake ground moti ons is identified. The shear demand of each structure, under each eart hquake record, is obtained by nonlinear time-history dynamic analyses. In 77% of the cases, the computed dynamic shear demand is higher than the current code shear strength. To address this issue, a force modif ication factor for shear, different from the one for flexure, is sugge sted for the Canadian code.