Mid-scale and full-scale experiments of cavity-insulated gypsum and calcium-silicate sheathed CFS walls under different fire exposures

Abstract

Most previous fire experiments of cold-formed steel (CFS) walls were conducted under ISO834 fire exposure, for which the results can not reflect the fire performance in some special scenarios. Meanwhile, full-scale fire experiments of CFS walls are time-consuming and suffer from high equipment requirements and cost. In this paper, two 1.1 m×1.1 m mid-scale non-load-bearing fire experiments and three 3 m×3 m full-scale load-bearing fire experiments of CFS walls were carried out. The specimens used gypsum plaster (GP) board and calcium-silicate (CS) board as the sheathing boards, and rock wool as the cavity insulation. In addition, the experiments involved four different fire exposures. The results show that the time-temperature profiles between the mid-scale and full-scale specimens, which had the identical dimensions and configuration of wall cross-section, tend to be consistent under the same fire condition. Therefore, a simplified experimental method was proposed to determine the fire resistance time for the structural failure of CFS walls with different load ratios through only one non-load-bearing fire experiment of mid-scale specimen, which avoided the current complex implementation that the fire resistance time of CFS walls with different load ratios was determined by carrying out multiple full-scale load-bearing fire experiments. In addition, the horizontal board joints were identified as the weak parts for the fire resistance of CFS walls under different fire exposures, which would cause stud buckling near the horizontal joints during the fire experiments. Moreover, the experiments under different fire exposures shows extended fire resistance time by substituting GP board with CS board as the base-layer sheathing, and the critical temperatures of stud hot flanges, which corresponded to the structural failure of present cavity-insulated GP-CS sheathed CFS walls and the load ratio of 0.27, were close to each other with the average of 693.8 °C. Finally, it was verified that the equal area method can give a rational prediction of the fire resistance time equivalency after correction by reference temperatures.