Efficient design of overlapped purlins loaded by gravity

Abstract

Cold-formed steel represents a competitive solution for a wide range of structural applications due to its efficient use of material and its rapid manufacturing and installation. Concerning the purlin systems, continuous Z-shaped steel purlins overlapping over the intermediate rafters are the best choice to minimise material use. The connection between two purlin segments can be achieved by overlapping the profiles over the supports. Using a finite element model validated against experimental data, an extensive study was performed to identify the parameters that influence the design of overlapped purlins loaded by gravity. The analysis is performed on a two-span continuous beam under gravity loading. To capture as much as possible the real behaviour of the purlin, the sheeting is included in the model. The design of lapped purlins was found to be primarily influenced by the length of the span and the overlap length. The detail of the lapped connection is relevant only for short overlaps. A material efficiency study was performed to determine how the overlapped purlin should be designed to minimise material use. Numerical results demonstrate that short overlaps behave poorly from a material efficiency point of view. The optimal overlap length Lp1 + Lp2 was found to be between 15 and 25 % of the length of the span. Connection details or the use of unsymmetric overlaps do not bring a significant increase in terms of material efficiency. However, the use of higher-grade steels bring great improvements.