Cold-formed steel properties at elevated temperature: review and proposed equation
Abreu, Jean C. Batista
Glauz, Robert S.
Schafer, Benjamin W.
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Cold-formed steel members are increasingly used in the construction industry due to their favorable strength-to-weight ratio and cost efficiency. Knowledge of the elevated temperature behavior of cold-formed steels is fundamental for the fire design of cold-formed steel members. The literature describes experimental tests on different types of cold-formed steels under different elevated temperature regimes, but no specification pertaining to elevated temperature behavior of cold-formed steel is currently available in the United States and no unified model has established itself for grades commonly used in the US. In this work, we conducted a review of available test data and specifications in other countries (including the Eurocode 3 and the Australian AS/NZS 4600), complemented with previously unpublished test data obtained at Johns Hopkins University. Reviewed data covered steady-state and transient-state tests performed on a wide range of material grades and thicknesses. The data was analyzed to characterize the reduction in stiffness and strength with temperature, including the effects of testing regime, material grade, and plate thickness. Then, a unified three-coefficient equation was formulated to capture the reduction of mechanical properties of cold-formed steels with temperature. Four sets of coefficients of the unified equation were calibrated to characterize, respectively, the reduction of elastic modulus, 0.2% proof stress, 2.0% yield stress, and ultimate stress at elevated temperature. The reduction factors obtained with the proposed equation generally agree with the Eurocode 3 and AS/NZS 4600 factors. Yet, the proposed equation is a continuous function of temperature in the range 20°C-1000°C, provides a single curve for a given mechanical property, is more exhaustive (capturing also ultimate stress), and applies to cold-formed steels typically used in the U.S. The proposed equation is suitable for steel grades up to G550 and thickness up to 3.5 mm.