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Due to the technological reasons in modern lightweight steel trusses, fabricated from coldformed sections, positive eccentricities appear in the truss nodes what induce additional forces in the truss chords. To account for the real load-carrying capacity of truss node area the steel structure research in scale 1:1 were conducted. The experiments consisted of two parts: preliminary and proper one, when conclusions from the first part were applied. Carrying out preliminary studies helped to identify of the research station drawbacks and eliminate most of them, what ensure the appropriate research results. The initial numerical analysis were also conducted what was presented in the paper. 108Małgorzata GORDZIEJ-ZAGÓROWSKA, Elżbieta URBAŃSKA-GALEWSKA, Patryk DENIZIAK, Łukasz PYRZOWSKI more and more emphasis on the rational development of both the elements crosssections and designed with these elements thin-walled structures. The aim of this paper is to present the methodology of proceeding with the preparation of experimental studies mapping the behaviour of truss elements made of coldformed sections and research results presentation. Research problemResearch issue concerns design solution used in structural systems of single storey steel buildings made of cold-formed open cross-sections as a whole. In the construction of a typical, mono-pitch, trapezium lattice girder, assuming a fixed spacing between the nods, the angle of inclination of brace members change due to technological reasons. The angle increase causes the appearance of the positive eccentricity in the truss joint and therefore occurrence of the bending moment in the presence of shear. In accordance with the current state of knowledge [7], when dimensioning the lattice girder's chord, one should take into consideration the eccentricity occurrence that leads to the necessity for local increase in the chord's section in the joint area. Practically, this is done by strengthening the chords through the use of channel-section covers (Fig. 1) or by increasing of the crosssection wall thickness over the entire length of the element. Both solutions are uneconomical what caused that research on real load-carrying capacity of the compressed and bent chord of the lattice girder made of coldformed open cross-sections was undertaken.The study aimed to clarify whether the bolted connection of the brace members to the walls of the hat cross-section chord locally stiffen the joint area providing increase of its capacity relative to this determined by traditional methods.

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This work describes the restraints in the optimization problem. This is an important and complicated issue because it requires taking into account a vast range of information related to the design and production. In order to describe the relations of a specific optimization problem, it is essential to adopt appropriate criteria and to collect information on all kinds of restraints, i.e. boundary conditions. The following paper verifies the various restraints and defines three subsets: design assumptions, technological limitations and standard conditions. The provided classification was made with reference to the analysis of the construction applicability of the newly patented cold-formed profile.