Strength design criteria for steel members at elevated temperatures

Design equations for structural steel members at elevated (fire) temperatures are evaluated through comparisons with nonlinear finite element simulations. The study includes comparative analyses of the American Institute of Steel Construction (AISC) and European Committee for Standardization (CEN) design provisions for laterally unsupported I-shaped columns, beams, and beam–columns at temperatures between ambient to 800 ∘C. The Eurocode 3 provisions are shown to predict the simulated finite element results within about 10%–20%. On the other hand, the AISC specification predicts strengths that are up to twice as large (unconservative) as the simulated results. The discrepancies are largest for members of intermediate slenderness and temperatures above 300 ∘C. Modifications to the AISC equations are proposed that provide improved accuracy with calculated strengths typically within 20%–30% of the simulated results. Limitations of the member-based assessments and future research and development needs for structural fire engineering are discussed.