Experimental and numerical studies of LSF truss floor-ceiling systems under standard fire conditions

• Investigated the behaviour of LSF truss floor-ceiling systems under ambient and fire conditions. • Evaluated the mechanical properties of fibre cement board sheathing and used in FE models. • Developed structural and sequentially coupled FE models of sheathed trusses and validated against test results. • Developed advanced heat transfer models incorporating critical plasterboard fall-off and cavity convection. • Investigated the effects of cavity insulation and joist types on the failure times of floor-ceiling systems in fire. Light gauge steel-framed (LSF) truss floor systems are increasingly utilized in low to mid-rise buildings due to their lightweight nature, high load-bearing capacity, and ease of installation. However, exposure to fire can severely diminish their structural performance. Full-scale fire testing is costly and limited to specific configurations. This study addresses a significant gap on the fire behaviour of LSF truss floor-ceiling systems by conducting ambient temperature and fire tests of short-span LSF floors made of trusses fabricated from cold-formed steel top hat and C-sections, gypsum plasterboard ceiling and non-combustible fibre cement board flooring and associated thermal and structural finite element (FE) modelling of tested floors. Elevated temperature mechanical properties of fibre cement board flooring were also assessed for integration into the truss FE models with sheathing. Heat transfer and structural FE models were developed and validated using fire test results. Findings from this study were compared with previous studies revealed that temperature-time responses and failure times of LSF floor systems with a particular ceiling configuration under fire conditions do not depend on truss or joist type but are primarily influenced by the presence or absence of cavity insulation and ceiling boards. The use of short-span fire testing and validated FE models offers a cost-effective alternative to expensive and time-consuming full-scale fire testing to obtain the failure times and fire resistance levels of truss floor assemblies.