LINEAR AND NON-LINEAR STUDY OF THE LATERAL DISTORSIONAL BUCKLING OF CASSTELLATED STEEL BEAM

Abstract

Web-opening beams (WOB) are commonly used in construction due to their several advantages. However, the shape and number of holes significantly impact the general behaviour of such structures. This dissertation is subdivided into main two parts. The first part, from chapters 1 to 3 is dealing with the necessary background on WOB steel structures with an updated literature review (2025) and the different aspects of behaviours of such structures including their potential modes of failure, buckling strength. The second part of this work concerns the assessment of the of webopening on the linear and nonlinear torsional buckling behaviour, while chapter 4 is devoted to linear buckling analysis results and discussion whereas chapter 5 concerns the nonlinear post-buckling analysis results and discussion. Furthermore, chapters 4 and 5 contain the necessary theoretical background for linear and nonlinear buckling F.E. analysis and the way how to perform each type of analysis using software. Also, a detailed study was carried out taking into account several parameters: shape and number of openings; the location of the applied load for linear buckling analysis adding to the sensitivity to imperfection and plastic characteristics in the nonlinear post-buckling analysis. To achieve this goal, dozens of three-dimensional models were built-up in ABAQUS. As detailed in Chapter 4, the numerical models of WOB were validated against the case of a solid beam (LTBeam) and subsequently utilised in a parametric study. From the results of elastic linear buckling, it was found that the strength of a perforated beam to LTB is alternated by the presence of the holes associated to the location of the applied load in the cross section where the top flange being the worst case with a higher stiffness reduction. Furthermore, the number of holes (single or multi), the geometrical shapes (circular, square and rectangular), and the sizes of perforations is seen to be decisive parameters. This explains the significant drop in Mcr values observed in certain cases with multiple rectangular perforations being the weakest configurations. The results showed that a reduction of 1% to 6 % for single web opening to 9% to 24 % reduced the flexural capacity against LTB. RIKS method implanted in Abaqus has been used for nonlinear post-buckling analysis. Except from the first model dealing with a single circular opening which gives an acceptable load- deflection including linear and nonlinear branches with a clear post-buckling behaviour. The remaining models including single and multi-hole fail to give satisfactory results though the same steps were followed. The model seems to stop running when it’s the beam pass through the bifurcation point about a deflection of 10 mm. Despite the efforts made to overcome this problem for more than four weeks by changing the number of increments, LPF, plastic characteristics, transverse maximum displacement the obtained curves remain the same with different values for Pcr