Full-scale experiments of gypsum-sheathed cavity-insulated cold-formed steel walls under different fire conditions

Abstract

Most previous fire experiments of cold-formed steel (CFS) walls focused on ISO 834 fire. The corresponding results may not represent the actual fire performance of CFS walls in some special circumstances. This paper presents a full-scale experimental investigation of gypsum-sheathed cavity-insulated CFS walls under four different fire conditions. The results show that the axial load has an insignificant effect on the heat transfer of such walls in fire. This realization provides a basis for the indirect coupling method of thermal-mechanical analysis of CFS walls, in which the time-temperature profiles of non-load-bearing CFS walls are adopted in the thermal-mechanical analysis of load-bearing walls. In addition, for CFS walls with the same configuration and load level, different fire conditions do not change the failure mode of steel studs; in particular, the stud hot flanges exhibit almost the same temperature when the structural failure of CFS walls occurs. Hence, a new time equivalency method of CFS walls is proposed, which uses the same temperature of hot flange as the principle of equivalency. Meanwhile, both the equal area method and energy-based method are modified by using reference temperatures, and give a good prediction of the fire resistance time equivalency of CFS walls. Moreover, significant opening of gypsum board joints is observed during the fire exposure; however, this phenomenon is an inherent characteristic of heated gypsum boards and has insignificant correlation with the out-of-plane deflection of CFS walls. Furthermore, staggered board joints are recommended as an important and effective fire resistance configuration of CFS walls.