Influence of Warping on Bearing Capacity of Steel I-Beam with Non-Fork Support

The European Standard 3 does not provide a direct answer about how to verify the bearing capacity of a beam with non-fork support. For a pinned beam it assumes, that there is no constraint on lateral bending and warping or full restraint. But in the most of design cases the constrainment is somewhere between them. There are some guidelines in scientific literature and computer programs that enhance the calculation of the value of a Critical Moment (which governs the Lateral-Torsional Buckling and as a result - the Bearing Capacity of Bending) for a flexible support. But there is no official information about which of method is the best for a certain case. To confine the variables only an influence of warping on a Lateral-Torsional Buckling was taken into the consideration. It was created by adding an endplate on one or both ends of a beam. Few approaches to calculate the Critical Moment were compared. A beam based on cross section of IS-300/150/10.7/7.1 with the length of 5.0m were taken into the consideration. The first method is the General Formula from pre-code of the European Standard 3 (1992) with the additional equations for calculating the stiffness of endplates according to Lindner (1994). The second approach bases on the General Formula, but with modification of C-1 factor derived by Lopez, Yong and Serna (2006). The third method uses very similar equation to the G. F., but with other value of C-1 factor. It was derived by Lindner (1994). Those approximated formulas were compared with Finite Element Method calculation. It was conducted using three different computer programs. In the first one, ABAQUS CAE, the spatial shell model of a beam was created. An influence of a type of a discretisation on results was validated. Secondly, LTBeamN, the dedicated program for calculating the value of Critical Moment written by CTICM, was used. Thirdly, computing was made using the RFEM - an application for civil engineers which allows to create models of beams with seven degrees of freedom in each node. The results show that an endplate's influence on a value of a Critical Moment is significant. Even the thinnest plates can noticeably increase the bearing capacity of a cross-section. But over the certain value of plate's thickness there is no further growth of the Critical Moment value. The results from equations based on the General Formula and calculations with the FEM are approximate for endplates below 4.0cm of thickness. It is very important to take few approaches to discretise the model of beam with endplates using ABAQUS, because there could be a major difference between them in outcomes.