System fragility analysis of roof cladding and trusses for Australian contemporary housing subjected to wind uplift

This paper describes a reliability-based fragility method to evaluate the wind damage to roof cladding and trusses for contemporary houses in non-cyclonic regions of Australia. The fragility assessment considers roof sheeting loss and roof truss failure due to overloading of cladding-to-batten, batten-to-rafter/truss and rafter/truss-to-wall connectors that are typically the ‘weakest links’ of a roof system under wind uplift pressure. The wind fragility herein is expressed by the mean extent of roof sheeting loss and roof truss failures as a function of gust wind speed. Monte Carlo Simulation in conjunction with a finite element approach are employed to carry out the wind fragility assessment, which enables the probabilistic characterization of spatially varying wind uplift pressure, connection resistances, structural response, failure progression of roof connections and internal pressure evolution with increasing roof sheeting loss. The proposed fragility method was illustrated on representative contemporary housing built in Brisbane and Melbourne with complex hip-roof geometries and corrugated metal roof sheeting. It was found that, for the gust wind speed corresponding to a 500-year return period, the mean proportion of roof sheeting loss and roof truss failures is negligible for the representative contemporary house built in Melbourne, whereas considerable roof damage is predicted for those built in Brisbane when windward dominant openings exist.