A numerical study of rotational capacity of steel beams in fire

Abstract

The chapter presents a numerical study of the rotational capacity of steel beams in fire. The study identifies the key factors affecting the available rotational capacity of steel beams in fire and also studies the interaction of these key factors. A series of UBs, UCs, and fabricated sections having different spans subjected to midspan point load are studied in the chapter. The numerical analysis is conducted using the commercially available finite element program MSC.MARC Mentat. It is found that the rotational capacity reduces at elevated temperatures because the highly non-linear stress-strain curve with reducing tangent modulus results in beams achieving its plastic moment capacity at a higher strain, thus reducing the inelastic rotation thereafter. Besides, three key factors that affect the rotation capacity are identified, namely, the local buckling of flange, the local buckling of web, and the lateral torsional buckling. Lateral torsional buckling often develops rapidly after the onset of flange buckling if there is no sufficient lateral restraint.