Experimental investigation of the quantified influence of gypsum plasterboard joints on the fire performance of cold-formed steel walls

Abstract

The fire-induced width development of a joint and the corresponding impact on the fire performance of cold-formed steel (CFS) walls were not quantified in previous investigations. Six non-cavity-insulated mid-scale CFS walls lined with artificial board joints were tested under ISO 834 fire conditions. Specimens were sheathed with double layer gypsum plasterboard (GP) on both sides and contained three types of GP board joints (face layer joint, base layer joint and overlapped joint). Moreover, 5 mm and 30 mm initial joint widths were set for each type of board joint to quantitatively investigate the negative impact of joints on the fire performance of walls and identify the positions on the wall that are vulnerable to fire-induced structural failure. Based on pixel comparison, the curves of the time-joint width are given, which can provide supporting data for investigating the heat transfer numerical simulation of CFS walls with joints in fire. In addition, the conventional numerical heat transfer model of CFS walls assigns the thermal boundary to the GP board joint surface. However, during the initial 30 min of fire exposure, temperatures at both the face layer joints and overlapped joints were significantly lower than the fire-side temperatures of the walls. Hence, the temperature results at the board joint of conventional numerical heat-transfer simulation results tend to be too conservative. It is suggested that the numerical heat transfer model of CFS walls should consider the development of GP board joint width and the flow-thermal coupling effect in the joint area. In addition, for a typical CFS load-bearing wall lined with double layers of GP boards on both sides, although each wall stud has the same vertical load (load ratio 0.65), fire-induced structural failure can occur when the HF critical temperature reaches 453 °C. Therefore, the wall stud adjacent to the overlapped joints will be the first to display fire-induced structural failure. Subsequently, the studs near the face layer joints will fail, and the wall studs near the base layer joints will fail last.