Thermal behavior of gypsum-sheathed cold-formed steel composite assemblies under fire conditions

Gypsum-sheathed cold-formed steel (CFS) composite assemblies consisting of CFS framing and gypsum plasterboard are widely used in modern buildings. This paper presents a detailed investigation of the thermal response of such assemblies under fire conditions. Limited to the accuracy of test devices for high-temperature low-thermal-conductivity material, previous results obtained from direct thermal conductivity tests of heated gypsum plasterboard may be unsatisfactory. Therefore, some transient-state thermal conductivity tests of post-heated gypsum plasterboard have been conducted, and the results truly reflect the tendency of thermal conductivity of gypsum plasterboard at elevated temperatures. Subsequently, six fire experiments on gypsum-sheathed composite assemblies were conducted under the ISO834 time-temperature curve. Significant local buckling is observed along the longitudinal direction of stud web, and the assembly cannot recover from the local deformation after the fire exposure. The fall off of fire side gypsum plasterboard occurs from approximately 690 °C to 750 °C. The aluminum silicate wool insulated gypsum composite panel is recommended for use as the sheathing of CFS composite assemblies for severe fire-resistance demand. Besides, a two-dimensional heat transfer model was built using the finite element method. The present thermal conductivity of post-heated gypsum plasterboard is verified by the heat transfer model and is recommended for use in the thermal response simulation of such assemblies under fire conditions, instead of the thermal conductivity tests of heated gypsum plasterboard. In addition, the fall off of fire side gypsum plasterboard is successfully simulated by using the birth-death element technique and the definition of critical temperature of gypsum plasterboard.