This paper presents a calculation method for axially compressed cold formed stainless, high strength and carbon steel profiles. Results of different authors in this field published in international journals depict current trends in this field. Paper also presents author’s numerical and experimental analysis of cold-formed centrally compressed elements. Numerical analysis was carried out by finite element method and program for the nonlinear static and dynamic structural analysis - PAK. The results obtained by experimental and numerical methods included boundary conditions, maximum force, buckling curve etc. Small difference observed in the values obtained by these different methods. Results werw compared to values predicted by international designing code in order to analyze if they are too conservative for cold formed steel sections.

Experimental and numerical research on axially compressed columns made from built-up two-chord concrete-filled steel tubes (TCCFSTs) is presented in this study. The columns were constructed from two parallel circular high-strength steel tubes connected by five batten tubes. The chord tubes were filled with high-strength concrete. The yield stress of the steel used was 600 MPa, while the cylinder compressive strength of the concrete was 95 MPa. Hollow specimens were also tested to serve as a control group. An experimental analysis investigated the influence of the compressive strength of the concrete fill on the load-bearing capacity of the column and the influence of the concrete fill on the slenderness of the column. The behavior under load, stress and strain development, and the failure modes of the specimens were also analyzed. The results of the tests showed that all parts of the built-up column participated in the load-bearing process. The load-bearing capacity of the hollow two-chord columns was improved by around 1.74 times, and the slenderness increased by 16% with the concrete infill. The columns filled with concrete exhibited almost linear behavior with a higher ultimate strength and stiffness than the hollow built-up steel columns. Furthermore, the application of three calculation codes to forecast the capacity of the TCCFST columns was evaluated. Additionally, finite element method (FEM) modeling was used to investigate the stresses, strains, deformations, and ultimate capacity of the TCCFST column models loaded with axial compressive force. The FEM model showed good predictions of strength, stresses, deformations, and buckling.

Because of different production technology, the calculation of cold-formed profiles significantly differs from that of hot-rolled profiles. Formation of various section shapes from the basic sheets induces changes in material mechanical properties, which manifest themselves through different yield point, ultimate tensile strength, modulus of elasticity and reduced elongation percentage. Yield stress distribution over the cross section also changes, the largest values are in the corners of the profile. This paper presents testing results obtained from tensile coupons taken from different regions within profiles and compression tests on complex stub columns. Results are shown on cumulative diagrams and compared with those obtained from the base strip coupons. Before testing, a detailed measurement of real geometric properties of profiles was performed to determine the initial geometric imperfections of samples. The obtained results represent important parameters in determining appropriate buckling curves of centrically compressed members made from cold-formed profiles.

Analysis of axially compressed steel members made of cold formed profiles presented in this paper was conducted through both experimental and numerical methods. Numerical analysis was conducted by means of "PAK" finite element software designed for nonlinear static and dynamic analysis of structures. Results of numerical analysis included ultimate bearing capacity with corresponding middle section force-deflection graphs and buckling curves. Extensive experimental investigation were also concentrated on determination of bearing capacity and buckling curves. Experiments were conducted on five series with six specimens each for slenderness values of 50, 70, 90, 110 and 120. Compressed simply supported members were analyzed on Amsler Spherical pin support with unique electronical equipment and software. Besides determination of forcedeflection curves, strains were measured in 18 or 12 cross sections along the height of the members. Analysis included comparisons with results obtained by different authors in this field recently published in international journals. Special attention was dedicated to experiments conducted on high strength and stainless steel members.