Performance-based seismic design and assessment of multi-storey CFS strap-braced frames

Abstract

Cold-formed steel (CFS) structures typically rely on diagonally braced stud walls to withstand lateral forces. While the response of CFS single-wall panels has been extensively investigated, limited studies focused on the seismic performance of multi-storey CFS strap-braced frames. Previous research highlighted that the presence of vertical loading can significantly reduce the lateral load and ductility capacity of strap-braced walls by amplifying the secondary moments due to P-Δ effects. While this effect is generally ignored in current design practice, it may lead to premature failures and poor seismic performance. This study aims to investigate the efficiency of a new design methodology to take into account the vertical load effects on the performance of multi-storey CFS strap-braced frames. Detailed experimentally validated FE models of CFS panels were developed in ABAQUS and used to obtain equivalent hysteretic models in OpenSees. The seismic performance of 6-storey strap-braced frames designed based on the Eurocode 8 and the proposed design methodology were then investigated under a set of artificial spectrum-compatible records. While the code-base design did not satisfy the ASCE/SEI 41–17 Life Safety (LS) and Collapse Prevention (CP) ductility limits, all performance targets were met using the proposed design methodology. The results of Incremental Dynamic Analyses (IDA) also indicated that meeting the code capacity requirements could not prevent extensive global damage in the strap-braced frames, due to soft-storey failure modes associated with the premature buckling of chord studs. Finally, the efficiency of the proposed design compared to its code-compliant counterpart was demonstrated under a set of 20 real spectrum compatible records, showing higher ductility capacity and considerably lower damage levels.