Seismic Performance of Conventional Construction Braced Steel Frames Designed According to Canadian Seismic Provisions

This paper presents an ongoing research project on the seismic performance of concentrically braced steel frames of the Conventional Construction category designed according to Canadian seismic provisions. A preliminary test program performed on typical brace connections indicated that a governing bolt bearing failure mode can lead to ductile connection response. Nonlinear time history analyses were carried out for 4- and 8-storey structures to assess the force and deformation demand from earthquakes on brace connections. The building height, the location in Canada, and the site class were varied. The median brace axial forces obtained from the analyses were found to exceed the code design force level specified for non ductile brace connections, except for the buildings located on site Class C in Montreal. These structures however possessed increased overstrength due to building code provisions. The excessive force demand observed in the other structures is mainly attributed to the difference in damping levels assumed in analysis and design. For the 4-storey structures, the computed median inelastic connection deformation values are small enough to be accommodated by properly detailed connections exhibiting a bolt bearing failure mode. The 8-storey structures experienced larger deformations, in excess of the tested connection capacity, as well as marked demand concentrations over the building height.