Inelastic performance of screw-connected cold-formed steel strap-braced walls

Cold-formed steel, screw-connected strap-braced walls (15 specimens, 2.44 m x 2.44 m each), designed following a capacity-based approach, were tested to evaluate their performance in the inelastic range of behaviour. Gross cross-section yielding of the tension braces was the specified failure mode in the design procedure. Extended tracks and additional shear anchors were installed, such that inelastic deformations would be limited to tension yielding of the braces. Walls without extended tracks were able to reach their yield level; however, damage to other frame elements occurred, thus reducing the ductility level that was attained. Cyclically loaded walls (0.5 Hz) with track extensions showed that wall performance is also dependent on the strain rate experienced by the braces. An F-u / F-y ratio greater than 1.2 is necessary to limit the possibility of brace fracture under seismic loading. Preliminary force modification factors, R-d = 2.0 and R-0 =1.3, are recommended for walls designed and detailed to achieve ductile performance.