Continuous reinforcement of existing simply supported cold-formed thin-walled C-shaped steel purlin

To improve the load capacity of existing simply supported cold-formed thin-walled C-shaped steel purlin, the adjacent simply supported C-shaped purlins were connected to continuous purlins by embedded thin-walled L-shaped steel near the supports. The static loading tests were carried out on the two strengthened C-shaped purlins. One purlin has screw connection only in the web and another purlin has screw connection in the web and flange. The failure mode, stiffness, ductility, bearing capacity, and strain development of the strengthened purlins were analyzed and compared with the mechanical behavior of the simply supported C-shaped purlin. The experimental results show that the global bending deformation occurs for the strengthened two-span purlin specimens. The top flange and compression web of purlins buckle near the mid-span and loading point, and the flange of the thin-walled L-shaped steel yields. The bearing capacity and stiffness of the simply supported purlins have been significantly improved after continuity, but ductility increases less. The stiffness and yield load of the strengthened purlin with screw connection in web and flange are significantly higher than that of the purlin only strengthened with screw connection in web, but the difference of ultimate load and ductility is lower. Using the trilinear steel constitutive model and shell element, a three-dimensional finite element model considering both geometric and material nonlinearity was established for the numerical simulation. The accuracy of the finite element model was validated by the comparison between calculation results and experimental results. The effects of the length of the thin-walled L-shaped steel on the mechanical behavior of the continuously strengthened purlin were analyzed. The results show that when the length of the L-shaped steel increases, the increasing extent of bearing capacity and stiffness of the reinforced purlins is decreasing. The increasing extent of the stiffness is more than that of the load capacity. 10% to 15% of the span of purlin is suitable for the length of L-shaped steel.