Elastic Critical Moment of Lateral Distortional Buckling of Castellated Composite Beams under Uniform Hogging Moment

Continuous and semicontinuous castellated composite beams can present a global buckling mode in the hogging-moment regions known as lateral-distortional buckling. In this mode, the lower portion of a steel section is compressed and the bottom flange undergoes lateral displacement and torsion as the web distorts. A common standard contains no equations for the calculation of the elastic critical moment of regular I beams, while another standard indicates a procedure for the assessment of this moment, which is used to calculate the resistant moment of these beams, based on the inverted U frame mechanism. This phenomenon also occurs in steel-concrete composite castellated beams, but there is no design procedure in current standards. In this paper, a new design procedure is presented for the purpose of determining the critical moment of castellated composite beams under a uniform hogging moment. Finite-element simulations in ANSYS commercial code were performed and compared to the proposed procedure. Results indicate the this procedure is adequate for achieving the elastic critical moment and satisfactorily considers the variation of a slab's stiffness and the displacement of the neutral axis position in steel sections. The presented procedure led to excellent agreement with numerical results, with an average deviation lower than 3.5%. (c) 2020 American Society of Civil Engineers.