Influence of endplates on the value of critical moment

The article analyses the lateral-torsional buckling of a double symmetric, steel I-beam with an assumption of a non-fork support. The fork support assumes free lateral bending and free warping what is described by factors kz and kw. In the Eurocode 3 there is no solution concerning how to calculate the value of a critical moment for steel structures. Information about it can be found in the pre-code for European Standard 3, the German Standard and scientific papers. In the calculations assumed the loads generating a non-uniform shape of bending moment diagram what is connected with a value of C1 factor. Calculations were conducted using equations derived by Lindner, Lopez and others and the applications such as LTBeamN and ABAQUS which allows to use a scheme with 7 degrees of freedom in boundary conditions. The non-fork support is created by adding endplates which reduce the possibility of warping by blocking the rotation between the flanges. A stiffness of endplates was calculated using the Saint-Venant's formula and was incremented into the equations and LTBeamN. In ABAQUS the I-beam was modelled as a shell structure with endplates discretized with a mesh of solid elements. The type of Finite Elements was chosen in accordance to previous research, where an influence of a mesh scheme on result was taken under consideration. To check the lateral-torsional buckling in ABAQUS a “buckle” analysis was conducted.