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The paper presents the analysis of the influence of fasteners and connections flexibility on displacements of symmetrical single-bay pitched-roof steel building, including trapezoidal cladding acting as a diaphragm. The purpose of the article was to compare numerical models with and without taking into consideration fasteners and connections flexibility in order to observe the differences in transverse stiffness of the building during modifying model from the simple one to more complex and precise. The analyses were carried out for the 3D structure. Fasteners and connections were substituted by equivalent beam finite elements. Corrugated sheets were replaced by three types of equivalent orthotropic shell models and the influence of the choice of the model on the stiffness of the building was observed. The results showed that in the analysed structure the flexibility of fasteners and connections has negligible effect on transverse displacements of the building in the case of four sides fastening of the sheeting, however in the case of two sides fastening the influence significantly increases.

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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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