Elastic lateral-torsional buckling of single-span doubly symmetric I-section beams with intermediate discrete lateral support considering prebuckling deflections

• Lateral-torsional buckling of beams is investigated. • The combined effect of the prebuckling deflection and an intermediate support is considered. • New analytical formulae are derived for beams with discrete intermediate lateral support. • Numerical studies are completed using analytical solutions and finite element calculations. • The results show that the efficiency of an intermediate lateral support strongly modified by the prebuckling deflection. In this paper the elastic lateral-torsional buckling of simple beams is investigated. The beams are single-span, the cross-sections are doubly symmetric, the beam is subjected to uniform moment. Moreover, the middle cross-section is laterally supported by a rigid support, the position of which varies within the cross-section. In the investigations, the effect of prebuckling deflections is considered. First, the critical moments are obtained by an iterative linear buckling analysis, completed by the finite element method, using both beam and shell finite elements. Analytical solutions are provided, too, and the results from finite element computations and from analytical formulae are compared. The numerical and analytical results show good coincidence. The results prove that the critical moment can efficiently be calculated by classic numerical methods, even if the effect of prebuckling deflection is considered. The existing literature suggests that the critical moment increase due to prebuckling deflections is influenced primarily by the ratio of minor-to-major moment of inertia, however, the presented results show that when the beam is laterally supported in the middle, the type and position of the lateral support as well as the beam length has important effect, too. Depending on these parameters, the critical moment values show a significant scatter, and the values with and without considering the prebuckling effect can be strongly different. Moreover, the suggestion from previous literature that the prebuckling effect is positive, cannot be justified in general. The experienced tendencies can be explained by the buckling shapes, as proved in the paper.