Postearthquake fire performance of cavity-insulated CFS shear walls with gypsum and calcium-silicate sheathing

This paper presented a detailed postearthquake fire investigation of cavity-insulated cold-formed steel (CFS) shear walls lined with face-layer gypsum (GP) boards and base-layer calcium-silicate (CS) boards on both sides. Four identical full-scale specimens with 3.0 m lengths and 3.0 m widths were constructed. The first specimens were subjected to 150834 fire without earthquake damage. The other three specimens were first tested under cyclic loading to different drift ratios, and then the fire experiments were conducted. Three types of failure modes of CFS frame are identified and the corresponding generation mechanism is discussed. The relationship between the drift ratio and fire resistance time (FRT) is presented for the shear walls with the load ratio of 0.27. Meanwhile, by substituting GP board with CS board as the base-layer sheathing, the FRT was extended from 48 min to 66 min, and the shear strength and initial stiffness were increased by 21.5% and 39%, respectively; moreover, the postearthquake FRT was extended from only 8 min to 40 min when the drift ratio reached 3.5%. The degradation mechanism of postearthquake FRT is also discussed. In addition, it is found that the fire experiments of the same CFS walls can have good repeatability, especially regarding the FRT, failure mode and time-temperature curves. Finally, for the fire design practice, the overlapped board joints on the same side of double-layer sheathing should be avoided to the greatest extent and the CFS walls with GP and CS board sheathing on either side are recommended in mid-rise CFS buildings.