Retrofitting of Structural Steel Channel Sections Using Cold-Formed Steel Encasing Channels

Abstract

A four-point bending test was carried out to examine the feasibility of using cold-formed steel (CFS) channel for retrofitting of open hot rolled steel (HRS) channels. The retrofitting technique using CFS section transforms the open-channel HRS section to a closed composite (HRS–CFS) section, thereby increasing its torsional rigidity to inhibit failure due to lateral–torsional buckling (LTB). The integrity of the HRS–CFS section was ensured by adequate spot welding of the CFS section to the HRS at regular intervals along the length of the member. This technique has the advantage of accumulating minimum residual stress (spot welding) in addition to reduced manpower required for section fabrication. The test results, in general, indicate that this technique can significantly increase the load-carrying capacity (up to 6% compared to the control specimen) without deformation when local buckling of the CFS sections can be prevented by providing adequate thickness and smaller weld intervals. In addition, the test results indicate that the current specification for both HRS and CFS requires modification to adopt the same for a built-up section made of both HRS and CFS. Based on the test results, a new interconnection spacing limitation to avoid the local buckling of the CFS channel is suggested.