Seismic response and design of steel multi-tiered buckling-restrained braced frames

This paper examines the seismic behaviour of steel Multi-Tiered Buckling-Restrained Braced Frames (MT-BRBFs) and proposes analysis and design methods to improve their seismic stability response. A set of 16 prototype frames, part of a single-storey building, are selected and designed. The fibre-based numerical model of the frames is then developed and used to analyze the frames under earthquake accelerations. The effects of influential design parameters on the seismic response of the prototype frames are interrogated using local and global response parameters, including storey and tier drifts, BRB force-deformation response, column axial force and flexural demands. The results of the dynamic analyses show that frame lateral deformation tends to concentrate in the tier(s) undergoing tensile yielding, creating larger inelastic deformation in tension-acting BRBs compared to those yielding in compression and imposing in-plane bending on the columns. Two analysis and design methods, including a detailed method and a computer-aided (alternative) technique are proposed and demonstrated for a four-tiered BRBF. The proposed methods can predict with sufficient accuracy column flexural and tier drift demands, while leading to an improved seismic response.