Ústav kovových a dřevěných konstrukcí

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    Influence of Creep on Torsional Restraint Provided to Cold-Formed Z-shaped Purlins by Sandwich Panels
    (Swedish Institute of Steel Construction, 2024-06-24) Balázs, Ivan; Belica, Andrej; Misiek, Thomas
    Sandwich panels supported by purlins are widely used as the main load bearing part of roof and wall cladding systems of steel buildings. Beside of their main function as building envelope, sandwich panels provide lateral and torsional restraint to purlins which positively influences the member resistance. Lateral restraint provided by sandwich panels is equal for both gravity and uplift loads applied on the panel’s surface, however, the torsional restraint may have a different behaviour depending on the direction of loading. While gravity loads increase the contact pressure between the panels and purlins so that the torsional restraint is ensured up to a relatively large rotation of the purlin, uplift loads reduce the contact area which can result in smaller torsional restraint. The paper discusses and compares the different behaviour and addresses the resulting requirements for the experimental setups. Another aspect that is noticeable in torsional restraint, but not in lateral restraint, is the influence of the materials of the insulation core (usually PUR-, PIR- or EPS-foam or mineral wool) of the sandwich panel. These materials significantly differ in their properties from the materials of faces as they exhibit complex behaviour with time-dependent response. Deformations from compressive stress increase over time which is referred as creep. This behaviour is evident both under gravity loads and under uplift loads, which reduces torsional restraint. Creep of the core can also result in the reduction of the preload force in screws, as the core is under compression after tightening. The paper focuses on the influence of creep on torsional restraint provided to cold-formed Z-shaped purlins by sandwich panels. Results of experimental tests are presented, and the influence of creep is evaluated for various types of the core materials of the sandwich panels
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    Modelling of bolted joints in fire using the component-based finite element method
    (Ernst & Sohn, 2023-09-12) Der, Batuhan; Wald, František; Vild, Martin
    This paper presents a study using the component-based finite element method to analyze the behavior bolted joints in fire. The model was verified and validated on analytical and experimental results at elevated temperature. In this work, the plates are modelled using shell elements and the bolt is represented by non-linear springs. The elements are analyzed by geometrically and materially nonlinear analysis with imperfections (GMNIA). Consequently, the method used in this work can give reasonable results to predict the behavior of joints at elevated temperature. It is predicting the resistance and the stiffness for design of steel structure at elevated temperature by 3D model with members represented by 1D or 2D elements.
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    The effect of cross-section geometry on the lateral-torsional behavior of thin-walled beams: Analytical and numerical studies
    (ELSEVIER SCI LTD, 2023-01-17) Haffar, Muhammad Ziad; Horáček, Martin; Ádány, Sándor
    In this paper, the elastic lateral-torsional behavior of simple beams is discussed by presenting a novel analytical solution and performing numerical studies. The motivation of the presented research is the observation that classic analytical prediction and finite element prediction are, typically, significantly different when the second -order nonlinear behavior of beams with initial imperfections is analyzed. To understand and explain the observed differences, a novel analytical model is worked out for the geometrically nonlinear analysis of beams with initial geometric imperfections. The advancement in the presented analytical solution is the explicit consideration of the changing geometry as the load increases. The most important steps of the derivations are summarized, and the resulting formulae are briefly discussed. The derivations are done for general cross -sections, however, the bending is assumed to act in one of the principal planes. Numerical studies are also presented, focusing on mono-symmetric cross-sections. As part of the numerical studies, first, the results of the new analytical formulae are compared to those from shell finite element analysis. The results suggest that the new formulae can capture the most essential elements of the behavior observed in the shell finite element calculations, justifying that the cross-section shape might have a significant effect on the nonlinear lateral-torsional behavior of beams. Then the effect of the lateral-torsional buckling is predicted by calculating buckling reduction factors, using the results of the geometrically nonlinear finite element calculations. The capacity prediction results, again, justify that the cross-section shape, as well as the sign of the assumed geometric imperfection, might have a non-negligible effect on the buckling reduction factors, and on the capacity of the member.
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    Theoretical research of dimensional optimization and choice of material strength in steel-concrete composite beams
    (IOP Publishing, 2021-12-21) Hrabovská, Kristýna; Břečka, Jan
    The aim of this study is to find out how the change of individual parameters will affect the flexural strength of steel-concrete composite beams. The project was focused on the choice of strength of materials and the choice of dimension, specifically the height of the concrete slab and the size of the steel profile. The resaearch aim is to reveal which parameters have dominant influence on the flexural strength and thus facilitate the optimazation of the design in practic.
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    Advanced analysis of members with gusset plate joints
    (Taylor & Francis, 2021-06-16) Vild, Martin; Chalupa, Vojtěch; Šabatka, Lubomír; Wald, František
    The compressive resistance of truss members connected by gusset plates is estimated by taking the buckling length of the member equal to the member length. Usually, no check is provided for the gusset plate, although several design methods were proposed in the past. The paper presents an advanced member analysis, a design-oriented finite element method of a member including its joints. Geometrically and materially nonlinear analysis with imperfections is used to determine the load resistance of the joint-member-joint subsystem. Component-based Finite Element Method is used for joints; i.e. bolts and welds are modeled by nonlinear springs with properties based on design codes. The advanced analysis is demonstrated on two cases. The buckling length of angles, vastly used for masts, may be assumed smaller than the theoretical length if the boundary conditions determined by bolted gusset plates provide sufficient stiffness. The experiments and detailed numerical analysis performed at the Graz University of Technology are used for validation of the advanced analysis. The buckling resistance of gusset plates may govern the compressive resistance of the bracing. The experiments performed at the Czech Technical University in Prague (Vesecký), together with analytical design methods, are used for validation of buckling resistance of bolted eccentric gusset plate joints of circular hollow section braces. The results depend on the chosen shape and amplitude of initial imperfections. Using recommended procedures, the proposed method provides results very close to the experiments.