Numerical modelling and fire testing of gypsum plasterboard sheathed cold-formed steel walls

Gypsum plasterboards are used in Light-gauged Steel Framed (LSF) walls as the primary fire-resistant material. In addition to thermal protection, they provide restraints to the cold-formed steel studs at the screw locations and improve the load-bearing capacity. In this study, three full-scale standard fire tests were conducted first to investigate the thermal and structural behaviour of LSF walls in fire. Close examination of the plasterboard joint opening up and plasterboard fall-off phenomena showed that most of the plasterboard joint compound fell-off after 17 min of fire exposure and the joint gap gradually widened afterwards. A multi-step heat transfer finite element (FE) model was developed incorporating the physical changes observed during the fire tests and validated using the test results. The important time–temperature profiles obtained from this study and past literature were compared, and idealised time–temperature profiles of wall studs were developed for use in structural FE models. Past studies involving elevated temperature structural FE models considered mainly the in-plane restraints provided by plasterboard sheathing. Hence the effects of their out-of-plane restraints were investigated using structural FE models and fire tests, and suitable out-of-plane restraint values were proposed for numerical analysis. This study has shown that out-of-plane restraints significantly reduced the lateral deflections of LSF walls and improved their fire resistance levels (FRL) when double layers of plasterboards were used. However, excessive out-of-plane restraints could adversely affect the FRL. Overall, this research has used the fire test results to enhance the understanding of the thermal and structural behaviour of LSF walls and provided useful data and recommendations for more accurate thermal and structural modelling of LSF walls.