Low fatigue response of crest-fixed cold-formed steel drape curved roof claddings

Cold-formed steel roof claddings are subjected to significant suction/uplift pressures during high wind events. In New Zealand, the strong prevailing winds makes this a common occurrence. Suction pressures are generated by the turbulence of the wind flow around the building which can vary both spatially and temporally. The weakest link in the roofing system is the connection between roof sheeting and screw fasteners, which if fails, can lead to progressive collapse of the whole roofing assembly. Fluctuating high wind suction pressures can result in either static or fatigue pull-through failure of the roof sheeting at its screw fastener connections. Current literature has covered the static and fatigue wind uplift performance of crest-fixed corrugated and trapezoidal roof claddings. However, no research has been undertaken to understand the wind uplift performance of the typical crest-fixed cold-formed steel drape curved roof claddings used in New Zealand. This issue is addressed herein. In total, 35 large scale experimental tests are presented for crest-fixed drape curved steel roof claddings subjected to static and cyclic wind suction/uplift loads applied using a Pressure Loading Actuator. The material properties of claddings were determined using tensile coupon tests while the initial geometric imperfections of claddings were measured using a laser scanner. The critical fastener reactions were determined using a three axis load cell. Crack initiation, propagation of cracks, crack patterns and the number of load cycles to failure are discussed for such claddings under different load levels. Tests showed that the drape curved roof claddings are also subjected to localised dimpling and pull-through failures at their screw connections under static and cyclic wind uplift loads with the occurrence of low cycle fatigue failures under cyclic loading.