Structural performance of cold-formed steel wall systems incorporating sustainable composite sheathing

Abstract

Cold-formed steel (CFS) wall systems are widely adopted in low- and mid-rise buildings due to their high strength-to-weight ratio and construction efficiency. The structural behaviour of these systems is governed by the interaction between thin-walled steel framing, sheathing materials and mechanical fasteners. In recent years, sustainable composite boards manufactured from recycled packaging and plastics—commercially available in New Zealand under the name SaveBOARD—have been proposed as alternative sheathing materials; however, their structural performance in load-bearing CFS walls has not been systematically investigated in peer-reviewed research.

This thesis presents a multi-scale experimental investigation into the structural performance of CFS wall systems incorporating sustainable composite sheathing (SaveBOARD). The research integrates material characterisation, connection-level testing, full-height single-stud wall subassembly tests under axial compression, and full-scale wall tests under quasi-static cyclic lateral loading. Key parameters include sheathing type, stud thickness, screw spacing configuration and axial load interaction.

The results demonstrate that sustainable composite boards can provide effective restraint against local and distortional buckling within the tested configurations. In the axial subassembly tests, the gypsum-sheathed specimen increased ultimate axial resistance by 36.8% relative to the bare frame, while the PIL- and EPL-sheathed specimens achieved increases of 36.5% and 27.0%, respectively. Under cyclic loading, the tested composite-sheathed walls exhibited reduced pinching and more stable hysteretic behaviour than the gypsum reference specimens, primarily because the response was governed by progressive bearing deformation at screw connections rather than abrupt brittle panel fracture. Screw spacing is identified as a primary structural parameter, with diminishing returns observed under excessive densification. A stability–connection coupling interpretation is developed to explain the interaction between connection degradation and global wall response.

Overall, the findings support the structural feasibility of using sustainable composite sheathing in CFS wall systems within the tested configurations and provide a mechanistic basis for performance-informed design considerations and future analytical modelling.