Structural and thermal performance of cold-formed steel studs with slits

Abstract

Cold-formed steel (CFS) studs in lightweight construction increasingly incorporate web slits to limit thermal bridging, yet these openings can reduce axial strength. This thesis integrates structural and thermal assessments through validated non-linear elasto-plastic finite element analysis (FEA) and complementary heat-transfer modelling. Shell-element FEA models were developed and validated against tests, then used in a 960-case parametric study spanning section dimensions, slit geometry, thickness, and member length to establish the influence of slits on concentric axial capacity. The results were evaluated against the Direct Strength Method (DSM) in AS/NZS 4600, leading to strength-reduction recommendations and modified DSM expressions that achieve reliability indices β ≥ 2.5. The programme was extended to combined axial compression and minor-axis bending using 1,134 FEA models with six eccentricities, demonstrating a systematic discrepancy in current AS/NZS 4600 interaction checks: strengths are generally underestimated at eccentricities of 10–25 mm and overestimated at 50 mm. A new interaction equation incorporating element and web slenderness ratios is proposed and verified within the AISI S100 reliability framework. Subsequently, a parametric three-dimensional heat-transfer study quantified the dependence of heat flux on geometry and slit parameters, providing a quantitative basis for thermal performance gains and their balance with strength. The thesis proposes design recommendations and revised equations for slitted CFS studs that satisfy codified reliability targets and support informed selection of slit configurations to balance energy efficiency and structural capacity in practice.