Making use of brace overstrength to improve the seismic response of multistorey split-X concentrically braced steel frames

Abstract

This paper presents a study on the inelastic seismic response of multistorey split-X concentrically braced steel frames. Structures with different plan areas and heights are examined for Victoria, British Columbia, and Québec City, Quebec. Structures designed according to current code provisions are found to develop a concentration of inelastic demand over their height, which can lead to dynamic instability. This behaviour was more pronounced for the taller and larger structures located in western Canada. A design method is proposed to mitigate the concentration of inelastic deformations by a proper selection of the bracing members. P–Δ effects also need to be included in the design. Guidelines are also proposed for the accumulation of brace-induced axial loads for column design. Structures up to 12 storeys designed according to the proposed method are found to exhibit a stable inelastic response and storey drifts within acceptable limits.Key words: bracing member, braced steel frame, buckling, instability, seismic, storey drift.