Seismic performance of low- and medium-rise chevron braced steel frames

This paper describes the seismic behaviour of chevron steel braced frames f or 2-, 4-, 8-, and 12-storey steel building structures. Two different desig n approaches were considered: one that corresponds to current CSA-S16.1 sei smic provisions for braced frames with nominal ductility with an R factor o f 2.0, and one in which the beams are sized to develop a fraction of the yi eld tension capacity of the bracing members. In this second approach, an R factor of 3.0 was used for determining the seismic loads and chevron bracin g with stronger beams capable of developing 100%, 80%, and 60% of the brace yield load were examined. The results show that current S16.1 provisions f or chevron braced frames may lead to systems that are prone to dynamic inst ability for 4-storey and taller structures. Chevron bracing with stronger b eams exhibits a more stable inelastic response and can be used for structur es up to 8 storeys in height. For 2- and 4-storey buildings, chevron braced frames with beams designed to develop only 60% of the brace yield resistan ce can be used. The analyses also show that the force demand in brace conne ctions, beams, and columns as determined from capacity design provisions ag ree well with that anticipated under strong ground motions.