Wind Induced Fatigue of Metal Roof Cladding during Severe Tropical Cyclones

The corner regions of roofs of low-rise buildings are subjected to large fluctuating pressures during windstorms. Damage investigations of metal cladding following hurricanes and cyclones in the US and Australia have shown loss of cladding due to wind induced fatigue cracking. To mitigate for low cycle fatigue failures, cladding systems are required to demonstrate compliance to dynamic wind loading test criteria such as the Low-High-Low (L-H-L) test detailed in the Building Code of Australia. The test criteria's loading sequences are a simplification of the dynamic wind loading environment, where assumptions such as building orientation, cyclone duration, wind direction and cycle range have been made. For example, when applying the Australian test criteria, the L-H-L test, the maximum negative external and maximum positive internal pressures are combined and applied across the load cycles. However, when analysing external and net pressure cycles for various windward and side-wall dominant opening cases, the numbers of cycles vary along with the mean and range, indicating a potentially conservative test criteria. An advanced pressure loading actuator (PLA) developed by UWO, is used to apply the fluctuating pressures of a design cyclone to sections of roof cladding. The PLAs permit the application of actual temporally varying wind pressures to a representative test section of the building envelope. The test method is able to replicate cladding failures as observed following severe cyclones and demonstrate conservative aspects of the L-H-L test criteria.