Lateral–torsional buckling of Delta hollow flange beams under moment gradient: Fid-Bau Portal

Lateral–torsional buckling of Delta hollow flange beams under moment gradient

Mohebkhah, Amin / Azandariani, Mojtaba G.

Abstract Lateral–torsional buckling (LTB) resistance of an I-beam depends on the minor axis moment of inertia of its compression flange and torsional rigidity of the section. A practical solution to increase lateral buckling of I-beams is to add two Delta stiffeners between the compression flange and web plates to form a hollow compression flange. Although these beams known as Delta hollow flange beams (DHFBs) have been introduced about half a century ago for bridge construction, however, their LTB behavior has not been investigated, yet. This paper develops a three dimensional finite-element model using ABAQUS for the inelastic nonlinear flexural–torsional analysis of DHFBs and uses it to investigate the effects of unbraced length and central off-shear center loading (located at center, top flange and bottom flange) on their moment gradient factor in different behavioral zones. It was found that the C b factor and moment resistance curve given by AISC-LRFD in Specification for structural steel buildings[2] are not accurate for intermediate (inelastic) and short plastic DHFBs leading to an unconservative design. Therefore, a modified moment resistance equation is proposed to be used instead of the code equation in inelastic zone for the investigated load cases in this paper.

Highlights • The moment-gradient factor and moment resistance curve given by AISC-LRFD are just valid for long-span DHFBs (i.e. elastic beams). • A modified moment-gradient factor was proposed for DHFBs as a function of unbraced length. • The AISC moment capacity curve is unconservative for DHFBs.