Seismic performance of single-storey steel concentrically braced frame structures constructed in the 1960s

Abstract

A general overview of the seismic performance of representative single-storey concentrically braced frame (CBF) buildings designed using the 1965 National Building Code of Canada and the 1965 S16 Canadian Standards Association Steel Structures for Buildings Standard was obtained through the use of nonlinear time history dynamic analyses and the testing of brace elements obtained from buildings constructed in the 1960s. The study comprised 16 representative buildings subjected to 20 site selected ground motions for three locations; Halifax (Nova Scotia) low seismicity, Montreal (Quebec) moderate seismicity, and Abbotsford (British Columbia) high seismicity. Incremental dynamic analyses were performed using various failure criteria as obtained from the test data; brace net-section fracture, bolt shear, block shear, bolt bearing and brace yielding. Fragility curves were created and the probability of failure was defined. The performance of the structures designed for Abbotsford was unsatisfactory for all of the brace connection failure mechanisms. In contrast, because of the lower current seismic hazard in Montreal, the 16 archetypical buildings demonstrated better performance. In Halifax the buildings performed well, based on the identified failure criteria. It was necessary to strengthen the roof diaphragms for all buildings to carry 2010 NBCC design level seismic forces.