Experiments on local buckling of cold-formed steel lipped channels in compression at elevated temperatures

Cold-formed steel members are widely used in buildings, making it essential to understand their behavior under fire. While extensive research at ambient temperature has led to design methods advancing the use of cold-formed steel load bearing systems, there is still a lack of understanding on the effects of elevated temperatures on the buckling behavior of these thin-walled members, which has hindered the development of fire design methods. This study presents a series of steady-state tests to evaluate the strength and stability of short cold-formed steel lipped channels in compression at uniform elevated temperatures. A novel test rig based on a customizable furnace frame and electrical ceramic heating pads was designed to conduct the experiments, showing high repeatability and accurate control of the steel temperature distribution. Coupon tests were conducted to obtain the elevated temperature material properties, which were compared with provisions in standards. The lipped channels exhibited local buckling of the web, with some specimens also displaying distortional buckling. The channels retained about 88 % of their strength at 300°C but only 34 % at 600°C. Strength evaluations with shell finite element analysis and with the Direct Strength Method led to conservative predictions. This study advances understanding of local buckling behavior for development of performance-based structural fire design methods for cold-formed steel-framed structures.