Lateral-torsional buckling performance of I-section cellular beams

The lateral-torsional buckling (LTB) performance of cellular members subjected to uniform moment, uniform transverse load and mid-span concentrated load was studied, based on a hypothetical continuous model developed using a new theory system for constrained torsion of thin-walled structures, the Plate-Beam theory. The LTB energy functional models consisting of strain energy, initial stress potential energy and load potential energy for cellular beams were first established. The equilibrium differential equation models and analytical solution for the LTB critical loads were then derived. In the process, the warping constant and free torsion constant of cellular beams were concomitantly obtained. A numerical program validated against existing experimental data was conducted in parallel to examine the predication accuracy of the theoretical equation. Based on these findings, the moment gradient factor specified in the design codes for cellular beams was further discussed. Given the significant gap of over 30 % between the relevant clauses in the design specifications and the analytical and numerical solutions, a new evaluation formula was proposed and validated against the analytical and numerical data.