Evaluation of the AISI S213 seismic design procedures through testing of strap braced cold-formed steel walls

摘要

The North American standard for the design of lateral systems constructed of cold-formed steel (CFS) (AISI S213), which is published by the American Iron and Steel Institute (AISI), was updated in 2007. Included in this update were changes to the provisions related to strap braced walls. The 2007 version of AISI S213 includes requirements for the brace material and the use of capacity design principles; as well, the engineer is directed towards using welded connections to avoid possible net section fracture of the braces. Screw-connected braces may be used if shown to perform in a ductile fashion. The research described herein was undertaken to evaluate typical weld and screw-connected single-storey strap braced wall configurations with respect to their ability to resist lateral in-plane loads in the inelastic range of behaviour; that is, the results were used to verify the new strap braced wall seismic design provisions in AISI S213. A total of 44 tension-only X-braced walls ranging in size from 610 × 2440 mm~2 to 2440 × 2440 mm~2 (aspect ratios from 4:1 to 1:1), designed and detailed following a capacity-based approach, were tested under lateral loading using monotonic and reversed cyclic protocols. The strap braces were expected to undergo gross cross-section yielding along their length, while the other elements in the seismic force resisting system (SFRS) were selected to be able to carry the probable brace capacity. A summary of the test program is provided, including design approach, failure modes and ductility measures. The scope of the research also included the determination of "test-based" seismic force modification factors based on the measured ductility and overstrength of the test walls for comparison with the R-values recommended in AISI S213.