Better connection details for strap-braced CFS stud walls in seismic regions

Buildings composed of cold-formed steel (CFS) framing systems have become popular in many parts of the world. Light-gauge CFS frames can be built up from C-shaped sections and laterally braced with tension-only thin strap members. Recent research has raised many concerns about the lateral performance of these light wall systems in regions of high seismic activity. This paper focuses on the failure modes of different systems and on the main factors contributing to the ductile response of the CFS walls. The aim is to ensure that the diagonal straps yield and respond plastically with a significant drift, thereby preventing any risk of brittle failure such as connection failure or column buckling. Several superior connection details are then proposed, which provide a reliable lateral performance even in large lateral deformations by using perforated straps and/or bracket members in four corners of the wall. Performance of the proposed systems is evaluated by experimental tests on full-scale 2.4 m x 2.4 m and 1.2 m x 2.4 m specimens under a particular cyclic load regime. Method B of ASTM E2126-05 standard was selected as lateral loading regime, which introduces a progressively increasing cyclic loading with two stabilized cycles at each displacement amplitude. In order to maximize the precision of the result, each specimen was connected to the testing rig by high strength bolt. The tests showed that all of the new proposed systems can provide reliable response with good ductility and maintain their lateral and vertical load-bearing abilities up to a relative lateral displacements of 3.3%, which was the limit of the testing rig.