Advanced non-linear analysis of composite cold-formed steel and reinforced concrete floor systems

This study presents an advanced non-linear finite element analysis (FEA) of composite flooring systems comprising cold-formed steel (CFS) joists and reinforced concrete slabs, aiming to address the limited representation of such hybrid systems in current design standards. The research develops a validated 3D ANSYS model incorporating multi-linear material behaviour, contact interactions, and large deformation effects under static and cyclic loading. Key phenomena—including bolt slip, plastic hinge formation, and strain redistribution—were captured, with validation against benchmark experiments yielding a mean absolute error (MAE) of 23.75 kN and root mean squared error (RMSE) of 33.72 kN. Fatigue performance was assessed using both stress-life (S–N) and strain-life (ε–N) methods, with results showing a critically low life of 0.85 cycles at the upper slab in stress-based analysis and 75.45 cycles at support zones in strain-based analysis, validating the latter's applicability for brittle concrete fatigue modelling. Crack sensitivity was investigated using a J-Integral fracture approach applied to a 25 mm notch at mid-span, revealing high stress intensity prior to arrest by reinforcement. A targeted numerical investigation of different reinforcement layouts indicated that reducing rebar spacing by 10 mm produced an average 8% decrease in peak J-Integral, underscoring the importance of layout configuration in fracture control. The study