Seismic assessment of existing steel braced frames designed in accordance with the 1980 Canadian code provisions

Steel concentrically braced frames are designed for 4- and 10-storey commercial build- ings according to the provisions of the 1980 National Building Code of Canada and the CSA-S16.1- M78 steel design standard to identify potential deficiencies compared to current Canadian seismic design requirements. Tension-only X-bracing and tension-compression chevron bracing built with back-to-back double angle braces are selected being most commonly used some 30 years ago. No ductility verifications are considered in design, consistent with Canadian seismic design practice prior to 1989. Seismic design loads prescribed in the 2010 code are higher than the 1980 values, especially for the 10-storey building. Nearly all braces and all brace connections of all frames studied have insufficient capacity compared to the demand from current codes. Failure of beams and columns is also a possibility for the 10-storey frames. Beams in the 4-storey frame are adequate and excessive demand on columns of this structure is only observed at its base.