Behavior of Connections in Cold-Formed Steel Frames under Cycling Loading

Abstract

Cold-formed steel (CFS) sections can be designed in many configurations and, compared to hot-rolled steel elements, can lead to more efficient and economic design solutions. While CFS moment-resisting frames can be used as an alternative to conventional CFS shear-wall systems to create more flexible space plans, their performance under strong earthquakes is questionable due to the inherited low local/distortional buckling of thin-walled CFS elements and the limited ductility and energy dissipation capacity of typical CFS bolted-moment connections. In this paper, the behavior of the connections of CFS frames with bolts has been investigated. A finite element modeling and a nonlinear analysis of the geometry and the materials under the cyclic loads are performed using ANSYS14 and compared to the experimental sample. Afterward, the modeling results are compared using the same model with some specimens in which their connections are of frictional and bearing types. Finally, the stresses created around holes in different types of specimens are compared, and the more appropriate solutions are provided. The results showed that the connections in which the prestress has been applied on the bolts and where the friction factor between the contact surfaces has been defined seem to be more rigid connections, given that the part of the force is borne by the friction before the location of the hole. This can increase the friction factor up to 0.6 without any costs and strengthen the connections of CFS frames. As a result, due to the higher bearing capacity of the bolts, the number of holes in the model can be reduced.