SEISMIC UPGRADE OF BC HOUSING'S 20 STOREY NICHOLSON TOWER IN VANCOUVER, CANADA

摘要

BC Housing manages an extensive inventory of subsidized housing mostly in the Vancouver area. They have undertaken a program to carry out seismic retrofitting of key aging facilities that have high tenant occupancy and have been determined to have a high risk of severe damage or collapse for the code specified earthquake. Design of seismic retrofitting of a permanently occupied residential tower is a challenge that must balance cost, maintain fire safety and minimize disruption to the tenants. This paper presents the retrofit design of a 20 storey concrete tower in Vancouver's "West End", an area of dense high rise construction. The concrete shear wall structure was originally constructed in 1969 and houses some 250 tenants. The initial three-dimensional response spectra analysis, using both SAP2000 and ETABS software, determined the load distribution to the existing non-ductile structural components and the capability of the existing structural system to contribute to the final retrofit structural system. The retrofit solution included the construction of external concrete shear walls up to the 17th floor, along with associated foundation requirements both external to the building and within the basement and strengthening of the buildings two internal stairwells using continuous steel plates. A key aspect of the retrofit was the continuous vertical sawcutting of the concrete core within the elevator shaft to modify the stiffness in a manner that best suited the overall structural response. Making provision for adequate fire exiting during construction was key. This and other lessons learned during the construction period are also presented in this paper with conclusions regarding the effectiveness of the various aspects of the retrofit with respect to tenant disruption and constructability.