Strength and Stiffness of Cold-Formed Steel Purlins with Sleeved and Overlapped Bolted Connections

A series of nine cold-formed steel Z sections with sleeved and overlapped bolted connections were tested in bending. These types of cross-section and connections are largely used in continuous multi-span cold-formed steel purlin systems. This paper aims to analyze the strength and stiffness of semi-continuous purlins subjected to flexure. Results show that strength is often limited by a plastic mechanism failure that develops at the end of the overlap or sleeve caused by a combination of distortional and local buckling. Out-of-plane forces introduced by the beam undergoing distortional buckling to the connection reduce the web rigidity. The loss of web rigidity induces an early development of local buckling in the compressed flange, which leads to a bending strength lower than the one found in a continuous beam; this observation contrasts with the common practice of considering sleeved and overlapped purlins as continuous purlins. However, the rotational stiffness of the system is highly affected by the length of the connection and by the bearing deformations around the bolt hole. In addition to the experiments, this paper also presents a numerical and analytical study of the strength and stiffness of sleeved and overlapped bolted connections. 

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