1. Use 3 thick steel plates to make a C-shaped joint, add a 3 mm thick steel plate to the main purlin, and connect it with bolts.

2. For overlapping purlins, just ensure that the length of the overlapping is not less than 1.5 times the height of the C-shaped steel. Use bolts to fix the purlins. The purlins are stress-bearing components, 2.5 mm thick. According to the specification, welding is not allowed.

3. The steel purlins are made of hot-rolled plates and cold-bent. They have thin walls, are lightweight, have excellent cross-sectional properties, and have high strength. The material is Q195-345. Common steel purlins include Z purlins and C purlins. Steel purlins are the secondary load-bearing components in the roof structure system, which transfer the roof load to the steel frame.

4. The overlapping length 2a of continuous purlins should not be less than 10% of the purlin span. The purlins in the nested overlapping part should be connected by bolts, and the bolt connection strength should be checked according to the bending moment at the continuous purlin supports.

The rational design of the overlap length of continuous purlins can greatly reduce the bending moment of the purlin supports and mid-span, reduce the number of purlins, and thus achieve good economic benefits. Continuous purlins are currently widely used in the design of lightweight roofs.