Experiments on load-bearing cold-formed steel sheathed studs at elevated temperatures

This paper assesses the stability and strength of sheathed cold-formed steel studs at elevated temperatures. Short and intermediate-length studs braced with gypsum, fire-rated gypsum, and oriented strand board were subjected to compressive axial load and temperatures ranging from 20 degrees C to 600 degrees C. A total of 40 tests were conducted in the steady-state regime, where the studs were first heated, then a compressive axial load was applied until failure occurred. Results show that the load-carrying capacity of the structural members decreases with increasing temperature, as the mechanical properties of the cold-formed steel reduce, and the bracing provided by the sheathing degrades. Local and distortional cross-section buckling failures are observed in the cold-formed steel member. The stabilizing effect and increase of load-carrying capacity attributed to the sheathing at ambient temperature is eventually lost at elevated temperature and the behavior of the sheathed studs becomes similar to the behavior of unsheathed members. Direct Strength Method design equations provided in the U.S. AISI S100 design specification are used with experimentally determined elevated temperature properties to predict the load-carrying capacity of the studs, then compared to experimental results to explore the feasibility of current design methods for performance-based fire design applications.