Fire resistance of LSF floors made of hollow flange channels

•FE models of LSF floor made of HFC joists were developed and validated using fire test results.•Investigated numerous HFC joist parameters on the FRR of LSF floors using validated FE models.•Obtained load ratio versus failure time and temperature curves for different joist parameters.•Joist thickness and mechanical property reduction factors affected the FRR of LSF floors.•Load ratio versus failure time curves can be used to predict the FRR of LSF floors.

Light gauge Steel Frame (LSF) floor systems are generally made of conventional lipped channel section (LCS) joists and lined using fire resistive gypsum boards. Although the use of LSF floor systems has significantly increased in the construction of fire rated buildings, it is limited to those made of LCS joists. Since the fire resistance ratings (FRR) for steel sections other than LCS joists are not available, engineers are reluctant to use innovative steel joists in LSF floor systems exposed to fire conditions. To overcome these limitations, a new LSF floor system recently developed using a welded hollow flange channel (HFC) section as joists was investigated using both experimental and numerical studies under standard fire conditions. Both these studies demonstrated higher fire resistance ratings in comparison to those made of LCS joists. However, they were limited to one welded HFC joist section. Hence a detailed parametric study of LSF floor systems made of HFC joists was undertaken to investigate the effects of joist sizes and shapes, steel types and service openings on the FRR using the validated finite element models. This paper presents the details of this finite element analysis based parametric study and the load ratio versus time curves. These results can be used in designing the LSF floors made of HFC joists with varying sizes for different industry applications without the use of expensive fire tests.