Behaviour of Cold-formed Steel Claddings under Static and Constant Amplitude Cyclic Wind Loading

Abstract

Cold-formed steel (CFS) roof and wall claddings are subjected to significant wind uplift or suction pressure during high wind events. In New Zealand, the strong prevailing winds makes this a common occurrence. Suction pressure is generated by turbulence of the wind flow around the building which can vary both spatially and temporally. The weakest link in the cladding system is the connection between cladding sheeting and screw fasteners. Should this fail, it can lead to a progressive collapse of the whole cladding assembly. Fluctuating high wind suction pressures can result in either static or fatigue pull-through failure of the cladding sheeting at its screw fastener connections. Current literature has covered the static and fatigue wind uplift/cyclic performance of crest-fixed corrugated and trapezoidal roof claddings. However, no research has been undertaken to examine the wind uplift/ cyclic performance of the various roof/wall claddings used in New Zealand, which include drape curve cladding, super seam cladding, interlocking cladding, and weatherboard cladding. This issue is addressed herein. In total, 120 large scale experimental tests are reported. These were conducted on four different types of cladding profiles under static wind uplift and cyclic pressure using a Pressure Loading Actuator (PLA). Two different cladding thicknesses (0.48 mm and 0.55 mm), along with different cladding pan widths and spans were considered in the experimental investigation. The material properties of the claddings were determined using tensile coupon tests and the initial geometric imperfections of CFS claddings were measured using a specially designed laser scanner. Failure load at the fixings was determined by measuring the load at the critical fixings by using a 3-axis (x-y-z) load cell. Tests showed that the claddings are subjected to local failure in the vicinity of the fixings initially, followed by the global failure of the cladding profile at ultimate wind pressure. Shear failure of fixing clips was observed under static wind uplift pressure. The clips failed under bending for most of the specimens subjected to cyclic wind uplift pressure for super seam claddings. Nonlinear finite element (FE) models were also developed for all four different cladding profiles under static wind uplift pressure, which showed good agreement with the experimental results. The FE models include material nonlinearity, initial imperfections, buckling effects, and contact modelling of screws. A splitting criterion was also included in the FE model of CFS drape curved claddings under static wind-uplift pressure. The FE models were validated against the test results, which showed good agreement, both in terms of wind uplift-capacity and deformed shapes. The validated FE models were then used to conduct extensive parametric iii studies for all four different cladding profiles to include the effect of material properties and geometric parameters on the wind-uplift capacity of four different cladding profiles. Based on the results of the parametric study for CFS drape curved claddings, design formulas have been derived for pull-through failure loads of CFS drape curved claddings. These can be used by researchers and practising engineers for design and optimization purposes. For super seam, interlocking and weatherboard claddings, load-span tables are proposed for ultimate limit state of failure under wind-uplift pressure.