COMPARATIVE CALCULATIONS OF THE STABILITY OF SINGLE-SPAN METAL BEAMS USING DIFFERENT CALCULATION METHODS

Abstract

The calculation of metal structures, along with the use of current regulatory documents, in particular “DBN V.2.6-198:2014”, can be performed according to the standards “Eurocode 3 EN 1993-1-1:2005/AC:2009”, while the vast majority of structures are designed according to the standards “SNiP II-23-81*”. It is worth noting that similar approaches are used in strength calculations, so the results of strength calculations are quite close. What cannot be said about the calculation of the stability of bending metal elements. This calculation significantly affects both the selection of the final cross-section and its unbending from the plane. All this affects the final cost of metal structures, in view of this issue, comparing the results of stability calculations using different methods is quite relevant. The purpose of the work: to perform comparative calculations of the bending stability of singlespan metal beams according to DBN V.2.6-198:2014, Eurocode 3 (EN 1993-1-1:2005/AC:2009) and SNiP II-23-81*, to determine the load at which the loss of stability occurs, and to assess the influence of the rod and plastic methods (finite elements, elastic formulation) of modeling on the critical load value. For comparative calculations, we will consider a single-span metal beam of I-beam cross-section with a hinged movable support on one side and a hinged fixed support on the other. The beam cross-section is taken in the form of a welded I-beamThe beam is  made of steel. A uniform distributed load is applied to the beam, the load is applied to the upper chord of the beam. The beam is supported at the supports. The calculation was performed using the LIRA-SAPR 2024 software package using the finite element method. When calculating according to regulatory methods, rod elements were used, a type 2 rod finite element (SE of a flat frame) was adopted. The calculation was performed by the iterative method, by selecting a uniformly distributed load that corresponds to a utilization factor of 100%. Also, for comparison, a spatial scheme made of plate finite elements of type 41 (universal rectangular SE) was simulated. The shell elements were modeled along the median planes of the flange and wall ofthe I-beam. The calculation was performed taking into account moments according to the first form of stability costs. The  smallest load corresponding to the loss of stability of a single-span metal beam corresponds to the type of calculation when the element is modeled by finite elements in the form of plates SE 41. This is explained by the fact that the calculation of such elements is performed in an elastic setting, without allowing the development of plastic deformations. The main advantage ofthis method is the ability to perform the calculation of damaged metal elements. The highest load corresponds to SNiP II-2381*. The difference between SNiP II-23-81* and the current design standards is 1.3%. What should be paid special attention to when reconstructing existing objects that were designed according to SNiP II-23-81*: such objects will require either an increase in the cross-section or the installation of additional reinforcements from the plane. This applies to elements that may lose stability. We also note that the Eurocode 3 EN 1993-1-1:2005/AC:2009 standards are the most conservative, when switching to this regulatoryelement it will also be necessary to carry out certain structural strengthening. Calculations of the stability of a beam loaded with a uniformly distributed load were carried out according to various regulatory documents. The need to strengthen beams that may lose stability, which were designed according to SNiP II-23-81*, is indicated when switching to new regulatory documents. All regulatory methods allow elastic-plate work when calculating beams for stability, the most conservative is the calculation according to Eurocode 3 EN 1993-1-1:2005/AC:2009.