Performance-based design of structures Performance evaluation of three pre-qualified steel systems in Canada

Abstract

A prototype five-story (seven bays by five bays) office building without basement level was selected for this study. The building has a fixed bay width of 9 meters, a first-floor height of 4.25 meters and a floor height of 3.65 meters at other floors. The building is symmetric in both the NorthSouth and East-West directions and has 6 SFRS bays in each direction. Figure 1 shows a typical1 INTRODUCTIONSteel structures are prevalent structural systems for seismic applications around the world. Among different Seismic Force Resisting Systems (SFRS), Moment Resisting Frame (MRF), Concentrically Braced Frame (CBF) and Buckling Restrained Braced Frames (BRBF) are found throughout North America. Selection of the structural system is usually based on engineering judgment. The typical approach is to select a structural system which satisfies the minimum standard specified by the local building code(s) and which carries the minimum initial construction cost. However, the relative seismic performance of the system throughout its life cycle is not usually considered. To compare the seismic performance of the MRF, CBF and BRBF systems at different levels of earthquake shaking, a five-story office building located in Vancouver, British Columbia is designed and analyzed. The prototype building is designed with the assistance of a renowned Vancouver-based structural engineering firm according to the requirements specified in the National Building Code of Canada (NBCC 2011) and Canadian Steel Code CSA S16-09 (CSA 2010). A detailed performance assessment of the prototype building using each of these three systems was analyzed using the performance-based assessment methodology presented by Yang et al. (2009a). This methodology uses a Monte-Carlo simulation procedure in which the building is analyzed under numerous earthquake ground motions, with repair costs aggregated to determine rates at which different repair costs occur. To carry out the procedure,floor plan and perspective view of the structure. The SFRS bays are shown in bold in Figure 1a. All structural members were designed according to the National Building Code of Canada 2010 (NBCC 2010) and the Canadian Institute of Steel Construction design standard (CSA 2010). Three code pre-qualified SFRS are included in this study. These include: a) Type D-Moment Resisting Frame (MRF); b) Type MD-Concentrically Braced Frame (CBF); and c) Type D-Buckling Restrained Braced Frame (BRBF). Figure 2 shows the member sizes and configurations for the SFRS bays and the typical gravity bays. Note that gravity columns for the MRF structure are different because the columns were designed with a column effective length factor of K = 1.2, whereas the gravity columns of the braced frames were designed with K = 1.0. This reflects the ability of the gravity frame to sway laterally in the MRF. Overall, the building equipped with the BRBF system uses 21% less total structural steel than the MRF, while the CBF system uses 7% less total structural steel than the MRF.