Postearthquake fire experiments of cavity-insulated cold-formed steel load-bearing walls lined with plasterboards

Abstract

Postearthquake fire is one of the most frequent secondary disasters facing mankind. This paper presented a detailed postearthquake fire investigation of cavity-insulated load-bearing cold-formed steel (CFS) walls lined with double-layer gypsum plasterboards on both sides. Five identical full-scale specimens with 3.0 m lengths and 3.0 m widths were constructed. The first two specimens were subjected to axial compression under the condition of ambient temperature or fire, respectively. The other three specimens were first tested under cyclic loading to different drift ratios, and then the fire experiment was carried out. The relationship between the drift ratio and fire resistance time (FRT) is presented, and the following conclusions are drawn. (1) When the drift ratios are less than 2.0%, the reduction of postearthquake FRT is insignificant and should be within 10 min. However, when the drift ratio reaches 3.5%, the residual postearthquake FRT is only 8 min, and the failure mode of wall framing changes to local crushing near the bottom of studs; It is because that local buckling near the bottom of stud occurs from cyclic loading before fire tests, leading to the separation of fire-side sheathing from wall studs. (2) The effect of axial thermal expansion constraints provided by rigid floor slabs to the CFS wall studs is significant under fire conditions. It will accelerate the structural failure of load-bearing CFS walls. (3) For the gypsum-sheathed load-bearing CFS walls, the existence of cavity insulation not only reduces the FRT, but also may change the failure mode of wall studs.