Thermal Modelling of Load Bearing Cold-Formed Steel Frame Walls Under Realistic Design Fire Conditions

Abstract

Cold-formed Light gauge Steel Frame (LSF) walls lined with plasterboards are increasingly used in the building industry as primary load bearing components. Although they have been used widely, their behaviour in real building fires is not fully understood. Many experimental and numerical studies have been undertaken to investigate the fire performance of load bearing LSF walls under standard fire conditions. However, the standard fire time-temperature curve given in ISO 834 [1] does not represent the fire load present in typical modern buildings that include considerable amount of thermoplastic materials. Some of these materials with high in calorific values increase the fire severity beyond that of the standard fire curve. Fire performance studies of load bearing LSF walls exposed to realistic design fire curves have also been limited. Therefore in this research, finite element thermal models of LSF wall panels were developed to simulate their fire performance using the recently developed realistic design fire time-temperature curves [2]. Suitable thermal properties were proposed for plasterboards and insulations based on laboratory tests and available literature. The developed finite element thermal models were validated by comparing their thermal performance results with available realistic design fire test results, and were then used in a detailed parametric study. This paper presents the details of the developed finite element thermal models of load bearing LSF wall panels under realistic design fire time-temperature curves and the results. It shows that finite element thermal models of LSF walls can be used to predict the fire performance including their fire resistance rating with reasonable accuracy for varying configurations of plasterboard lined LSF walls exposed to realistic design fire time-temperature curves.

Fire design rules for load bearing cold-formed steel frame walls exposed to realistic design fire curves

“…15(b) and 16(b)). Only the LSF wall panels exposed to Fire Curves Cp-EU5, Cp-EU6, Cp-BFD1 and Cp-BFD2 failed at load ratios less than 0.5, as their stud hot flange temperatures are less than 500°C [26]. This indicates that studs will sustain the above fire curves if they are axially loaded to lower load ratios ( o0.5).…”

“…The studs failed due to local buckling and the failure load was 68.50 kN for 1.15 mm G500 steel stud when nominal mechanical properties were used. The stud time-temperature curves were obtained from the finite element thermal model developed in [26] using SAFIR [27]. In fire conditions steady state non-linear analysis was performed in two steps.…”

“…Further, all of them have a decay phase. The corresponding stud hot and cold flange time-temperature curves were obtained using the validated finite element thermal model [26] and are shown in Fig. 7(a) and (b).…”

“…12(a) and 13(a)). The hot and cold flange temperatures of the studs in LSF walls exposed to these fire curves were obtained from finite element thermal analyses reported in [26]. Unlike LSF walls lined with double plasterboards, the ultimate failure loads in this case rapidly reduce even in the early stage of the fire.…”

“…2). For this study the finite element model developed in [25] was used with stud temperatures obtained from the finite element thermal model developed by Keerthan et al [26] using SAFIR [27]. Based on the parametric study results a simplified design method was developed to obtain the FRR of LSF walls exposed to realistic fire curves.…”