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Today in Russia 13% of buildings are built on the basis of a metal frame. To increase the energy efficiency of the industry, the use of thin-walled steel structures is one of the most technologically advanced and efficient solutions. To ensure the bearing capacity and reduce the risks of failure of buildings and structures at the design stage, it is important to correctly assess the reliability of the system, taking into account all influencing factors. The technology for the production of thin-walled profiles determines the factors that affect their stress-strain state. Uneven distribution of mechanical properties over the cross-section of the profile: hardening in the bending corners and adjacent zones leads to an increase in the strength of the metal. The article presents the results of numerical modeling of samples from thin sheet steel with and without the effect of hardening. The object of research is a thin-walled sigma profile with a section height of 300 mm, an element length of 4500 mm, operating under compression with bending. Metal hardening values are based on experimental data obtained by the authors. The stresses and displacements obtained as a result of the simulation were analyzed in four sections along the profile length: at a distance of 0.5 m, 2.3 m, 3.0 m and 4.0 m from the support. It is concluded that the supercritical work of the element without hardening of the material occurs earlier than in the element with hardening. The maximum stresses in the element without hardening exceed the stresses in the element with hardening by more than 30%. The maximum displacements in hardening are more than three times.

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The increasing use of light steel thin-walled structures is determined by the efficiency of the production of cold-formed profiles. However, there are problems of calculating the reliability of thin-walled structures. In particular, it is necessary to specify the calculation of the generalized bearing capacity of an element from a thin-walled profile. Such an element is significantly affected by the initial geometric imperfections reducing its bearing capacity. At the same time the element is influenced by an uneven distribution of the mechanical characteristics of the steel over the section of the profile. A thin-walled element of paired sigma profiles with a section height of 300 mm was taken as the object of study. This paper presents the results of the calculation of the effective characteristics of a thin-walled profile operating under axial compression with bending without and with the initial geometric imperfections (additional eccentricity from the element’s initial curvatures). Besides, the paper reveals the results of laboratory studies of the distribution of the mechanical properties of steel over the cross section of a thin-walled profile after using direct and indirect test methods.

The article describes the process of numerical simulation of a composite symmetric section element made of thin-walled Sigma profiles operating under conditions of longitudinal compressive force with bending, taking into account the initial geometric imperfections. At numerical modeling, the main criterion of the load-bearing capacity exhaustion in case of eccentric compression is the stability loss in one of the forms. However, for thin-walled elements, the loss of local stability does not mean that the load-bearing capacity is completely exhausted, since the element continues to carry the load, but to a lesser extent. Therefore, simulation was carried out in two stages: initially, in the elastic formulation, the possible buckling modes were determined, afterwards, there was made calculation on the deformed pattern taking into account possible imperfections.