Application of simulated cyclonic wind loads on roof cladding David Henderson 1 , John Ginger 1 , Murray Morrison 2 , and Gregory A. Kopp 2 1 Cyclone Testing Station, James Cook University, Townsville, Australia, david.henderson@jcu.edu.au 2 Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, London, ON, Canada ABSTRACT Severe tropical cyclones can subject low rise building roofs to large fluctuating pressures. These fluctuating wind loads can cause failure of building elements susceptible to low cycle fatigue. Following the devastation caused by Cyclone Tracy to Darwin, cyclic loading test criteria, such as TR440 and DABM, were developed to enable cladding to be tested for their potential to fail due to low cycle. The previous test criteria have been replaced by the recent introduction of the cyclic Low High Low (L-H-L) test, based on the “design” cyclone derived by Jancauskas et al [1]. The research was conducted using line load sinusoidal loading systems. With the development of real time simulated wind loading actuators (PLA) the performance of a cladding specimen is examined during a simulated “design” cyclone. INTRODUCTION The roofs of low-rise buildings are subjected to large pressures during windstorms. The creation of a dominant opening by debris impact, door failure, etc, in the windward wall can generate positive internal pressures, which, in combination with suctions at the edges of the roof, will generate large net pressures. Cyclone Tracy caused catastrophic damage to housing in Darwin in 1974 [2]. A major component of damage was caused by low cycle fatigue cracking of the cladding under the fixings, which resulted in extensive loss of light gauge metal roof cladding. Fatigue of cladding was also observed following more recent events [3]. Low cycle fatigue was defined by Beck and Stevens [4] as failure typically within 10000 load cycles. Since then, various test regimes and test methods have been proposed and implemented in codes for evaluating cladding systems for Australian cyclonic wind regions. These different test criteria, which were meant to represent the same loading, could result in different outcomes [5]. For effective building code regulation and efficient product design manufacture, a consistent and representative test criteria for evaluating the performance of these building elements is essential. Researchers such as Mahendran [5, 6] and Xu [7, 8] have demonstrated through extensive test programs that the interaction of the cladding and fixing is a crucial part of the cladding’s fatigue response to the applied loading. However, the testing programs were conducted using equipment, which was best practice at that time (15 to 25 years ago), that simulated the wind loads using a sinusoidal load patterns and applied the loads to the cladding using line loads as opposed to air pressure. With the advent of sophisticated loading systems capable of applying realistically varying pressures directly to the cladding surface, the interaction of the cladding and fastener connection is reanalyzed in this paper. LIGHT GAUGE METAL CLADDING Low rise buildings (houses, commercial premises, light-industry sheds, etc), in the northern regions of Australia, predominantly have roofs clad with light gauge pierced fixed metal sheeting. The most common pierce fixed light gauge metal cladding profiles are either