Pull-through failure of crest-fixed steel claddings under combined wind and bushfire conditions

Cold-formed steel (CFS) roof and wall cladding systems are commonly used in Australia and around the world. The use of CFS claddings in bushfire prone areas is becoming more popular due to their non-combustibility and is recommended in the Australian standard AS 3959 for construction in bushfire areas. However, severe fire events occur more frequently and in recent bushfire events, strong winds and fire–wind interactions have been observed. Thus, the behaviour of CFS claddings exposed to a combined action of fire and wind needs to be considered for the safe design of buildings in bushfire prone areas. In this study, a small-scale test set-up was developed and used to simulate the wind suction loading on crest-fixed CFS roof and wall claddings while also being exposed to elevated temperatures. Experiments were conducted on three commonly used 0.42 mm high strength (G550) CFS cladding profiles at ambient and elevated temperatures and their critical localised pull-through failures of the crests under the screw heads were investigated at increasing temperatures. The results showed that the failure mode of trapezoidal cladding profiles changed from a transverse splitting type to a localised dimpling type pull-through failure. They also showed different rates of reduction in the pull-through capacity with increasing temperatures and the type of cladding profile. This paper has proposed a suitable equation for the pull-through capacity reduction with increasing temperatures and made suitable recommendations in relation to the use of CFS cladding systems in bushfire prone areas.