Research on Critical Moment of Lateral Restrained Beams Under End Moments

In order to establish the calculation method for the critical moment of simply-supported steel beams with lateral restraints equally distributed along the span, the segments between two lateral restraints were treated as simply-supported steel beams firstly. Then, the characteristic of the end moment ratio for these segments were revealed for variable number of lateral restraints and end moment ratio of lateral restrained steel beams. A segment with the maximum end moment of the lateral restrained steel beam, which named as the calculated segment, was selected for determining the critical moment. The interaction between the calculated segment and other segments were analyzed and revealed for pure bending and impure bending theoretically and numerically. Values of the coefficient C₁ and the expressions of the interaction coefficient α were proposed, by which the calculation of the critical moment for lateral restrained steel beams was transformed to the calculation of the critical moment for the calculated segment. Finally, comparisons were carried ont between the critical moments obtained from the proposed method, the method in current design standards and the numerical results. The results showed that the values of the coefficient C₁ and the expressions of the interaction coefficient α were accurate enough for determining the critical moment of lateral restrained steel beams subjected to end moments, while the β_b coefficient provided in Standard for Design of Steel Structures (GB 50017-2017) and the C₁ provided in Technical Code of Cold-Formed Thin-Wall Steel Structures (GB 50018-2002) were accurate for pure bending, but for impure bending, unsafe or too safe predictions were generated.