Lapped joints of cold-formed steel Z-shaped purlins are extensively used in metal building roof construction to create multi-span purlin systems. Conventionally, round holes are used in the lapped purlin connections. With the advantage of providing extra installation tolerance, vertical slotted holes are widely used in the lapped joints of cold-formed steel Z-shaped purlin systems to simplify and expedite the erection of multi-span purlin roof systems. However, the current design practice is based on the research for the lapped connections with round holes. Almost no research has been conducted to investigate effects of vertical holes on the flexural behaviour of cold-formed steel Z-shaped purlins. To investigate the effects of vertical slotted holes on the structural behaviour of lapped cold-formed steel Z-shaped purlins, tests were performed on the lapped purlins with different lap lengths, purlin depths, thicknesses and spans. The results show that the flexural strength and stiffness of the lapped purlins with vertical slotted holes are primarily influenced by three parameters, i.e., the ratio of lap length to purlin depth, the ratio of lap length to purlin thickness, and the ratio of purlin depth to purlin thickness. Based on the test results, design recommendations are proposed for designing lapped cold-formed steel Z-shaped purlins with vertical slotted holes.
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