Development of fragility curves for localised pull-through failures of thin steel roof battens

Abstract

Recent extreme wind events such as tropical cyclones and severe storms have shown that thin steel roof battens fail prematurely at their screw connections to the rafters or trusses. The screw heads connecting the bottom flanges of thin steel roof battens to the rafters or trusses often pull through the roof batten bottom flanges. Since such localised pull-through failures occur in the lower level of roof connections, they often cause the loss of the entire roofing system during extreme wind events. Therefore detailed experimental and numerical studies were conducted at the Queensland University of Technology, and suitable test, design and strengthening methods were developed to accurately design the roof batten to rafter/truss connections and to enhance the roof batten performances under wind uplift loads. However, the levels of possible damages at community level due to the pull-through failures of roof battens are still unknown. Therefore fragility curves were developed in this study to determine the likely level of roof damage during extreme wind events, based on the governing pull-through failures of thin steel roof battens. Detailed probabilistic analyses and Monte Carlo simulations were conducted for this purpose. Fragility curves were also used to evaluate the effects of roof batten span and spacing and, levels of enhancement that could be achieved with the strengthening method proposed for roof battens. This paper presents the details of this study on the development of fragility curves and the results.