Numerical study of high strength LSF floor systems in fire

Light gauge steel frames (LSF) are commonly used in floor systems. The LSF floor systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. However, limited research has been undertaken on LSF floor systems, particularly on those made of high strength steel joists, and hence a thorough understanding of their fire resistance behaviour is not available. Recently a new composite floor system was also developed to provide higher fire resistance rating. But its increased fire rating could not be determined using the currently available design methods. This paper presents the details of finite element models of high strength LSF floor systems developed to simulate their structural performance under standard fire conditions. The numerical analyses of LSF floor joists were undertaken using the finite element program ABAQUS based on the measured time–temperature profiles obtained from full scale fire tests under both steady state and transient state conditions. Finite element models were calibrated using full scale fire test results and used to further investigate the structural fire behaviour of LSF floor systems. Numerical analyses provided a good understanding of the structural fire behaviour of LSF floor systems and confirmed the superior performance of the new composite floor system. This paper has shown that fire resistance ratings of a range of LSF floor systems can be predicted from the critical average joist temperature obtained from finite element analyses