Moment gradient factor for steel I-beams with sinusoidal web openings

Abstract

The moment gradient factor is an important parameter to be considered in the design of beams subjected to failure by Lateral-torsional Buckling. The analytical formulation to obtain the critical moment for the LTB is based on the assumption of applying a constant bending moment along the free span of the structural element. This loading situation is not usual in engineering projects, so it is necessary to correct the value of the critical moment according to the different loading situations that can be found in practical cases. Thus, many design codes worldwide assign values to perform this correction. The moment gradient factor, Cb, is determined by comparing the elastic critical moment of a beam subject to varying moment condition with that subject to a constant moment condition. When considering beams with web openings, there are currently no recommendations or proposals for calculating the moment gradient factor, considering loads applied outside the shear center. There are also no explicit recommendations in standards regarding the design of this type of structure. Recent research deals with the influence of cellular beam parameters on the moment gradient factor; however, they do not present explicit proposals for its calculation in structures of this nature. The research scenario in the literature becomes even more scarce when considering beams with sinusoidal web openings. Thus, the paper investigates this for a wide range of I-beams with openings, with the goal of analyzing the influence of the openings on the Cb, as well as proposing formulae for usual design situations. The proposals were obtained through prediction models derived from an extensive parametric study using the ABAQUS finite element software, in which 34,020 models were developed.