Assessment of the seismic performance of a 12-storey ductile concrete shear wall system designed according to the NBCC 2005 and the CSA A23.3 2004 standard

Abstract

A new design philosophy has been integrated in the 2005 edition of the National Building Code of Canada (NBCC 2005) and the 2004 edition of the Canadian Standard A23.3 for design of concrete structures (CSA A23.3-04): the performance-based design. Consequently, these Canadian codes include new performance-based provisions for the seismic design of building structures. Moreover, the NBCC 2005 has been extensively revised from the 1995 edition. Although the new seismic design provisions of the NBCC 2005 and CSA A23.3-04 do not specifically address some likely design issues regarding ductile concrete shear walls, they provide a more rationale design approach for such structures. The purpose of this research project is to assess the seismic performance of a ductile concrete shear wall system used as seismic force resisting system (SFRS) for a multistorey concrete building designed according to the NBCC 2005 and the CSA A23.3-04. In this purpose, a 12-storey ductile concrete core wall building located in the Canadian city of Montreal is adequately designed, two-dimensionally modelled and numerically analyzed through inelastic pushover and time-history dynamic analyses. The core wall consists of a cantilever wall system in one direction and a coupled wall system in the orthogonal direction. A modelling assessment is performed in order to investigate the effects of different structural modelling parameters on response. This assessment shows that the concrete tension-stiffening effect plays a major role on predictions. The dynamic analysis predictions indicate that the seismic demand at design level on the cantilever wall system is slightly to considerably underestimated by that used for design. As a consequence, the shear strength requirement of the CSA A23.3-04 is not satisfied and an additional plastic hinge formation above the base may be expected. The large difference between the predicted and design demands is essentially due to an underestimation by the NBCC spectral response acceleration of the higher mode effects in a cantilever wall system where the seismic response is mostly elastic and dominated by higher modes. This suggests that the NBCC spectral response acceleration may be inadequate for the seismic design of such systems.