Localised pull-through failures of thin steel roof battens subject to wind uplift loads


High wind events such as tropical cyclones, severe storms and tornadoes can be extremely destructive to low-rise buildings with lightweight steel roofing systems. Recent post-disaster investigations showed that significant roof damages are caused by localised pull-through failures of thin steel roof battens in which the screw fastener head that connects the rafter/truss below pulls through the bottom flanges of roof battens. Currently available design rules in the cold-formed steel standards do not address the specific pull-through failures in thin steel roof battens. Since the climate predictions indicate the likelihood of severe storm events with increased intensity in the future, they are more likely to cause static pull-through failures of roof battens. A thorough understanding of the static behaviour is first needed to evaluate the fatigue behaviour and strength of roof battens. Hence this research was aimed at investigating the localised pull-through failures of thin steel roof battens under simulated static wind uplift loads, using experiments and finite element modelling.

An experimental study (70 tests) was first conducted using full scale air-box tests and three different small scale tests such as two-span, cantilever and short batten tests and, suitable small scale test methods were identified to accurately simulate the localised pull-through failures of roof battens. The main experimental study was then undertaken using suitable small scale test methods (220 tests) and, the effects of many critical parameters on the pull-through failure loads of roof battens were investigated in detail.

The finite element models of both two-span batten and short battens were modelled and analysed using ABAQUS. A suitable failure criterion was developed based on constitutive model inputs and used in the analyses to predict the pull-through failures of roof battens. The finite element models were validated using test results, and detailed parametric studies were conducted. A large pull-through capacity data base was developed from the tests and finite element analyses. Suitable design rules were then developed and recommended for the accurate determination of the pull-through capacities of thin-walled steel roof battens.

This study also investigated the strengthening methods that are currently being used and, a suitable strengthening method was proposed to enhance the roof batten performances under high wind events. Suitable fragility curves were developed using detailed probabilistic analyses and Monte Carlo simulations based on the governing pull-through failures of thin steel roof battens to predict the likely level of roof damages to a community for a given wind speed. Fragility curves were also used to evaluate the achievable enhancement level with the strengthening method proposed in this research.

In summary, this research study has developed suitable test, design and strengthening methods and fragility curves for thin steel roof battens subject to localised pull-through failures under high wind uplift loads. They can be used by roof system manufacturers and designers to not only eliminate premature roofing failures, but also to enhance the disaster resilience of residential, industrial and commercial buildings in high wind regions.