Assessment of the flexural buckling resistance of bisymmetrical I-section beam-columns using FEM is widely discussed in the paper with regard to their imperfect model. The concept of equivalent geometric imperfections is applied in compliance with the so-called Eurocode’s general method. Various imperfection profiles are considered. The global effect of imperfections on the real compression members behaviour is illustrated by the comparison of imperfect beam-columns resistance and the resistance of their perfect counterparts. Numerous FEM simulations with regard to the stability behaviour of laterally and torsionally restrained steel structural elements of hot-rolled wide flange HEB section subjected to both compression and bending about the major or minor principal axes were performed. Geometrically and materially nonlinear analyses, GMNA for perfect structural elements and GMNIA for imperfect ones, preceded by LBA for the initial curvature evaluation of imperfect member configuration prior to loading were carried out. Numerical modelling and simulations were conducted with use of ABAQUS/Standard program. FEM results are compared with those obtained using the Eurocode’s interaction criteria of Method 1 and 2. Concluding remarks with regard to a necessity of equivalent imperfection profiles inclusion in modelling of the in-plane resistance of compression members are presented.

The analysis of web-corrugated and trapezoidal profiled web girders focuses on the description of buckling resistance, possibly the ultimate resistance neglecting the post-buckling resistance reserve of girders. The problem is still the post-buckling resistance reserve and its possible application in practice. For this purpose this paper presents the analysis of tests on shear resistance of the corrugated web of SIN girders with the support stiffeners in the pre- and post-buckling zones. There are also presented values of the post-buckling resistance zone and the mutual relationships between pre- and post-buckling resistance zones. Values of these zones are related to optimization of the web-corrugated girders, which consists in enlarging the zone of pre-critical resistance and balancing between shear resistance and bending resistance. The experimental tests were performed on 20 girders with the following web depth: 500, 1000, 1250, and 1500 mm, composed of three pre-assembled units. The girders with a simply supported beam system and a simply supported beam with a single cantilever were made of pre-assembled units joined by means of high strength preloaded bolts. The numerical analysis by FEM was conducted for the models with web depth from h_w = 500 to 1500 mm at the full range of web thickness 2,0; 2,5, and 3 mm. The tests showed that stiffness of the support stiffeners in the web-corrugated girders had an impact on the size of pre- and post-buckling resistance zones, which consequently reduced the zone of post-buckling resistance. Because the initiated loss of stability of the corrugated-web girders is an irreversible and rapid process, and the resulting displacements in the non-linear area are permanent, the application of the post-buckling resistance zone in practice can be troublesome. From the standpoint of the structural reliability, however, the post-buckling zone provides a yield delay, i.e. it may be regarded as a safety margin. Therefore, its most possible reduction is required.

Metal columns of hollow and smoothly variable cross-sections, simply supported at their ends are considered in the paper. Columns of such shapes are recently frequently designed by architects in public utility buildings of various types. In thiswork authors present the comparatively simple method of buckling resistance assessment which can be used by designers of metal columns of such shapes. The formula on critical force required in the procedure was derived for columns of variable cross section by means of Mathematica™system. The closed formulae were obtained for a rod with a certain, predefined geometry being the surface of revolution. Critical forces obtained by means of derived formulae were compared with results of numerical solutions. To assess the compression resistance of considered rods the general Ayrton–Perry approach was applied and bow imperfection with assumed amplitude was used in the analysis. Results of numerical simulations and experimental tests inserted in the paper confirm the correctness and the effectiveness of the proposed procedure of buckling resistance assessment of considered struts.