Thermal performance of LSF floors made of hollow flange channel section joists under fire conditions

• Developed FE models to simulate the thermal performance of LSF floors made of HFC joists.
• Compared the time–temperature profiles from FEA and fire tests.
• FE model with plywood subfloor was developed and validated.
• A thermal parametric study was performed to study the effects of important parameters.
• Time–temperature profiles can be used to determine the fire resistance ratings of LSF floors.

Light gauge steel frame (LSF) floor systems used in the building industry are made of cold-formed lipped channel section (LCS) joists and lined using gypsum plasterboards. The recently developed LSF floor systems made of welded hollow flange channel (HFC) section joists exhibited superior fire performance in the full scale fire tests. Since full scale fire tests are expensive and time consuming, finite element (FE) models were used in this research on LSF floor systems. In this paper 2-dimensional FE models were developed using a finite element analysis software SAFIR to predict the thermal performance of LSF floors made of HFC joists, and validated using the fire test results. The developed FE models predicted the thermal performance of LSF floor systems exposed to standard fires reasonably well. The validated model was then modified to include plywood subfloor and was used to investigate the effects of important parameters such as joist size, shape and subfloor thickness on the time–temperature profiles of the outer hot and cold flanges of HFC joists. These time–temperature profiles can be directly used to estimate the fire resistance ratings (FRR) of LSF floors made of HFC joists without performing expensive full scale fire tests. This paper presents the details of this thermal analysis study and the results.