10.12: Numerical modelling of steel sheathed LSF walls under fire conditions

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Abstract
Fire performance of light gauge steel framed (LSF) walls sheathed with gypsum plasterboards has been investigated using experimental and numerical studies by many researchers in the past. Provision of cavity or external insulation, improving the thermal‐mechanical properties of plasterboard, and changing the stud geometry are several options previously employed to enhance the Fire Resistance Level (FRL) of such wall systems. Past studies of steel sheathed cold‐formed steel (CFS) framed walls have shown that the use of steel sheathing improves the shear strength of LSF walls. However, such studies have not investigated the possible improvements to the fire performance of LSF walls due to the use of steel sheathing in addition to plasterboards. This numerical study investigates the thermal performance of three common LSF wall configurations sheathed with steel sheets on both sides under fire conditions. Three steel sheathing configurations (internal and/or external sheathing) were considered for each LSF wall. Thermal Finite Element (FE) models were developed and used to simulate the heat progression across the walls, following validation using previous experimental studies. The walls were exposed to ISO 834‐1 standard fire curve on one side. Results were then compared with those from LSF walls sheathed only with plasterboards. Internal steel sheathing was found to be capable of reducing the ambient side temperatures compared to plasterboard only walls due to the lower emissivity of steel, whereas external steel sheathing increased them further. Although the stud hot flange (HF) temperatures are generally increased with the addition of steel sheets, provision of back‐blocking was able to eliminate this deficiency. A novel arrangement is proposed for back‐blocking which is found to significantly delay the stud temperature rise and improve the FRL. The use of corrugated steel sheet profiles is found to reduce both the stud and ambient side plasterboard temperatures. The results from this study give useful information to develop load bearing and non‐load bearing LSF walls with superior fire performance. This paper presents the details of this numerical study and the results.

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