Numerical modelling of LSF floors under fire conditions

The demand for cold-formed steel frame systems has steadily increased in low and mid-rise buildings in recent years. Fire can significantly impair the performance of cold-formed light gauge steel framed (LSF) floors due to reduced bending capacity and stiffness. However, previous studies on Australian LSF floor systems in fire are limited. Although standard fire tests of LSF floor systems could offer valuable data on their behaviour and Fire Resistance Level (FRL), their utility is constrained by high costs, time requirements, and applicability only to tested configurations. This paper presents the development of finite element (FE) models of LSF floors to simulate their structural and thermal behaviour under standard fire conditions. Initially, the behaviour of LSF floors at ambient temperature was investigated using advanced structural FE models alongside simplified unsheathed models. The verified ambient joist-only model was then expanded to replicate the structural responses of LSF floors exposed to standard fire. Predicted FRLs, failure modes, and deflection patterns demonstrated close alignment with fire test outcomes. Additionally, thermal FE models were developed employing innovative techniques to model convection and plasterboard fall-off for five commonly used LSF floor configurations. These thermal FE models were verified against fire test results of sheathing and joist temperatures, showing good correlation between the FE models and fire tests. The combined use of sequentially coupled thermal and structural FE models developed in this study allows for detailed parametric investigations to establish FRL data for LSF floor systems, avoiding the need for full-scale fire tests.