Impact of variability in thermal properties of SFRM on steel temperatures in fire

For structural steel components protected by spray-applied fire-resistive materials (SFRMs), variations in the thermal properties and thickness of SFRM may influence steel temperatures during fires. This paper presents a sensitivity analysis of the influence of assumed thermal properties and thickness of SFRM on predicted steel temperatures in fire. For this purpose, material test data in the literature on the thermal properties of SFRMs were used to determine reasonable bounds for three variables: thermal conductivity, volumetric heat capacity, and insulation thickness. Fifteen material models were developed assuming temperature-independent values for these variables based on a face-centered central composite experiment design. Finite element models were developed for three structural fire experiments. In addition, a fourth model of a composite beam was developed with localized hole in the SFRM representing an ID tag, which in practice is affixed to beam webs. Each model was analyzed using the fifteen material models. The choice of SFRM thermal properties had a significant influence on steel temperatures, and statistical analysis of the experimental design showed that steel temperatures increased with increasing thermal conductivity, and decreased with increasing thickness and volumetric heat capacity. The influence of volumetric heat capacity was smaller than that of thermal conductivity and thickness.