Localised screw connection failures in cold-formed steel roofing systems

Lightweight roofing systems made of thin and high strength steel roof sheeting and battens are commonly used in low-rise buildings. However, they often fail frequently at their screw fastener connections during wind storms due to inadequate connection capacities. Two localised failures, known as pull-through and pull-out failures at the screw fastener connections, have been the root cause for extensive loss of roofing systems under high wind uplift loads. Such premature connection failures often cause partial or even complete loss of steel roofing systems and severe damage to building contents. Therefore many experimental studies have been conducted to investigate the pull-through failures of roof batten to purlin/rafter connections and the pull-out failures of roof sheeting to batten and roof batten to rafter connections. The roof batten connections involve multiple (two or four) screw connections between the two bottom flanges of roof battens and rafters. This paper reports the details of experimental studies on one of the localised screw connections failures, the pull-out failures. More than 750 small scale pull-out tests were conducted for this purpose using a range of screw fastener sizes and many thicknesses of thin steel roof battens and purlins. This paper presents the important details of the experimental studies and the pull-out capacity data obtained from the tests. It then presents suitable design equations and capacity reduction factors to accurately determine the pull-out capacities of both single and multiple screw fastener connections commonly used in steel roofing systems. They can also be used for the screw fastener connections in steel wall cladding systems.