Number of found documents: 1091
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Mechanical analysis of scarf joint fastened using cylindrical wooden dowel
Tippner, J.; Milch, J.; Kunecký, Jiří; Kloiber, Michal; Brabec, M.; Sebera, V.
2017 - English
Traditional all-wooden woodworking joints play an important role in the behaviour of timber structures. These joints are also widely used when historically valuable constructions are being reconstructed and the connections are usually the masterpieces that testify to the high carpentry skills and knowledges of the overall mechanical behaviour. Within historical timber structures traditional carpentry joints were used while wooden dowel fixed mutual position of elements. Main aim of this study was to contribute to knowledge base about prediction and analysis of the mechanical performance of frequently used scarf joints made from spruce wood fastened using oak dowels. The objectives were to determine the joints' slip moduli and load-carrying capacity by means of theoretical and experimental approaches, in next to assess the mechanical behaviour of dowels through experimental investigation, and finally to perform a strain analysis of dowels. For these purposes, the optical technique employing three-dimensional full-field digital image correlation was used. The experiments were done on the full-scale specimens meeting the requirements of European standards (EN 383 and EN 26891), which were made from Norway spruce (Picea abies L. Karst.) and English oak (Quercus robur L.). The mechanical load consisted in tensile parallel and perpendicular to grain direction within the main components. The results of this study showed good correlation between theoretical approach based on based on Beam on Elastic Foundation theory and European yield model theory and experimental observations. Keywords: all-wooden joints; scarf joint; dowel; spruce; oak; digital image correlation Available at various institutes of the ASCR
Mechanical analysis of scarf joint fastened using cylindrical wooden dowel

Traditional all-wooden woodworking joints play an important role in the behaviour of timber structures. These joints are also widely used when historically valuable constructions are being ...

Tippner, J.; Milch, J.; Kunecký, Jiří; Kloiber, Michal; Brabec, M.; Sebera, V.
Ústav teoretické a aplikované mechaniky, 2017

Deformation behaviour of gellan gum based artificial bone structures under simulated physiological conditions
Krčmářová, N.; Šleichrt, J.; Fíla, Tomáš; Koudelka_ml., Petr; Kytýř, Daniel
2017 - English
The paper deals with investigation of deformation behaviour of gellan gum (GG) based\nstructures prepared for regenerative medicine purposes. Investigated material was synthesized as porous spongy-like scaffold reinforced by bioactive glass (BAG) nano-particles in different concentrations. Deformation behavior was obtained employing custom designed experimental setup. This device equipped with bioreactor chamber allows to test the delivered samples under simulated physiological conditions with controlled flow and temperature. Cylindrical samples were subjected to uniaxial quasi-static loading in tension and compression. Material properties of plain scaffold buffered by 50 wt% and 70 wt% BAG were derived from a set of tensile and compression tests. The results are represented in form of stress-strain curves calculated from the acquired force and displacement data. Keywords: gellan gum scaffold; reinforcement; uni-axial loading; simulated physiological conditions Available at various institutes of the ASCR
Deformation behaviour of gellan gum based artificial bone structures under simulated physiological conditions

The paper deals with investigation of deformation behaviour of gellan gum (GG) based\nstructures prepared for regenerative medicine purposes. Investigated material was synthesized as porous ...

Krčmářová, N.; Šleichrt, J.; Fíla, Tomáš; Koudelka_ml., Petr; Kytýř, Daniel
Ústav teoretické a aplikované mechaniky, 2017

Acta Polytechnica CTU Proceedings 7
Kytýř, Daniel; Zlámal, Petr
2017 - English
The International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences continues the tradition of the Czech-German bilateral symposium founded by prof. Karl-Hans Laermann and prof. Stanislav Holý in 1985. In the following years, the symposium was extensively developed by prof. Josef Jíra. The symposium shall bring together mainly young scientists who are actively involved in experimental solid mechanics, theoretically and practically, in order to exchange experience, to report on the present state-of-art as well as on running research projects, to discuss due questions and problems and to promote the co-operation between individuals as well as between institutions. Therefore in the symposium discussions will play a highly significant role. Keywords: experimental solid mechanics; numerical simulation Available at various institutes of the ASCR
Acta Polytechnica CTU Proceedings 7

The International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences continues the tradition of the Czech-German bilateral symposium founded by prof. Karl-Hans Laermann ...

Kytýř, Daniel; Zlámal, Petr
Ústav teoretické a aplikované mechaniky, 2017

Non-holonomic planar and spatial model of a ball-type tuned mass damping device
Náprstek, Jiří; Fischer, Cyril
2017 - English
The area of tuned mass dampers is a wide field of inspiration for theoretical studies in non-linear dynamics and dynamic stability. The studies attempt to estimate behaviour of diverse damping devices and their reliability. The current paper deals with the response of a heavy ball rolling inside a spherical cavity under horizontal kinematic excitation. The non-linear system consists of six degrees of freedom with three non-holonomic constraints. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appell-Gibbs function of acceleration energy is developed and discussed. Comparison with previous planar (SDOF) model which is based on the Lagrangian procedure is given. The system has an auto-parametric character and therefore semi-trivial solutions and their dynamic stability can be analysed. The most important post-critical regimes are outlined and qualitatively evaluated in resonance domain. Numerical experiments were performed when excitation frequency is slowly swept up and down to identify different modes of response. Some applications in civil engineering as a tuned mass damper, which can be used on slender structures, are mentioned. The proposed device is compared with a conventional pendulum damper. Strengths and weaknesses of both absorbers types are discussed. Keywords: tuned mass damper; moving ball; Appell-Gibbs formulation Available at various institutes of the ASCR
Non-holonomic planar and spatial model of a ball-type tuned mass damping device

The area of tuned mass dampers is a wide field of inspiration for theoretical studies in non-linear dynamics and dynamic stability. The studies attempt to estimate behaviour of diverse damping devices ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2017

Chemical and microstructural characterization of the render, sampled from Gloriette, the US Embassy in Prague 1
Slížková, Zuzana; Frankeová, Dita; Viani, Alberto; Hauková, Petra; Koudelková, Veronika; Svoboda, Milan
2017 - English
The aim of the work was to analyze the mortar taken from the Gloriette (US Embassy, Prague 1). Analyzes were performed for the binder and filler characterization and the sample was also dissolved in HCl to determine the mixing ratio. Keywords: survey; material characterization; chemical composition; binder and aggregate characterization Available at various institutes of the ASCR
Chemical and microstructural characterization of the render, sampled from Gloriette, the US Embassy in Prague 1

The aim of the work was to analyze the mortar taken from the Gloriette (US Embassy, Prague 1). Analyzes were performed for the binder and filler characterization and the sample was also dissolved in ...

Slížková, Zuzana; Frankeová, Dita; Viani, Alberto; Hauková, Petra; Koudelková, Veronika; Svoboda, Milan
Ústav teoretické a aplikované mechaniky, 2017

Three-dimensional characterization of polymer foams using X-ray dark-field imaging
Senck, S.; Plank, B.; Gusenbauer, C.; Salaberger, D.; Vavřík, Daniel; Santer, W.; Kastner, J.
2017 - English
Due to the low cost, the ease of processing, and excellent material properties, polymer foams are used in various applications, e.g. packaging, building and construction, furnitures and bedding, and the automotive and aerospace sector. The mechanical response of polymer foams is primarily influenced by density and morphology. While foam density can be determined with high precision, cell morphology is more difficult to determine since the size distribution of foam cells differs in three dimensions. However, using conventional methods, e.g. optical light microscopy or scanning electron microscopy, it is very difficult to obtain three-dimensional information and to differentiate between the strut system and cell walls. An alternative for the three-dimensional characterization of foam morphology is micro-computed tomography (XCT). But even non-destructive techniques like XCT are not able to characterize anisotropic foams if the thickness of single struts and cell walls is below the physcial resolution of the respective XCT system. In this contribution we therefore investigate different polymeric foam samples using a Talbot-Lau grating interferometer XCT (TLGI-XCT) system. We show that the obtained darkfield contrast images show a high contrast and a strong signal at struts and cell walls, facilitating the segmentation of foam cells in various examples. Keywords: foam; micro-computed tomography; Talbot-Lau grating interferometer XCT; dark-field imaging Fulltext is available at external website.
Three-dimensional characterization of polymer foams using X-ray dark-field imaging

Due to the low cost, the ease of processing, and excellent material properties, polymer foams are used in various applications, e.g. packaging, building and construction, furnitures and bedding, and ...

Senck, S.; Plank, B.; Gusenbauer, C.; Salaberger, D.; Vavřík, Daniel; Santer, W.; Kastner, J.
Ústav teoretické a aplikované mechaniky, 2017

Wind-tunnel simulation of thermally unstable atmospheric flow in complex terrain
Pospíšil, Stanislav; Kuznetsov, Sergeii; Kozmar, H.; Michalcová, V.
2017 - English
The paper presents the characteristics of thermal effects in wind-tunnel simulations of the atmospheric boundary layer (ABL) flow developing above complex terrain. The differences and instable stratification effects between the windward and leeward sides of a hill model were investigated for different wind characteristics. Particularly, the buoyancy effects on the structure of the ABL simulation in a wide range of stability conditions expressed by Richardson number are studied. Keywords: instable stratification; wind tunnel; Richardson number Available at various institutes of the ASCR
Wind-tunnel simulation of thermally unstable atmospheric flow in complex terrain

The paper presents the characteristics of thermal effects in wind-tunnel simulations of the atmospheric boundary layer (ABL) flow developing above complex terrain. The differences and instable ...

Pospíšil, Stanislav; Kuznetsov, Sergeii; Kozmar, H.; Michalcová, V.
Ústav teoretické a aplikované mechaniky, 2017

Analytical approach of slender structure vibration due to random component of the wind velocity
Náprstek, Jiří; Hračov, Stanislav
2017 - English
Along wind random vibration of slender structures represents one of the most important aeroelastic effects resulting from wind - structure interaction. The theoretical model being based on one-dimensional elements with continuously distributed mass and stiffness has been introduced in this paper. The system has been considered to be linear self-adjoint with strongly non-proportional linear damping due to both material of the structure and presence of vibration dampers. The additive random excitation continuously distributed in time and space is Gaussian, therefore the response is Gaussian as well. Consequently, mathematical mean value and correlation function are satisfactory for the full description of the generalized solution of the respective PDE in the stochastic meaning. The general results have been obtained mostly in the form of analytical formulae for important cases of input spectral densities. A numerical example dealing with real structure is presented. Keywords: random vibrations; slender structures; wind load; non-proportional damping; distributed-parameter systems Fulltext is available at external website.
Analytical approach of slender structure vibration due to random component of the wind velocity

Along wind random vibration of slender structures represents one of the most important aeroelastic effects resulting from wind - structure interaction. The theoretical model being based on ...

Náprstek, Jiří; Hračov, Stanislav
Ústav teoretické a aplikované mechaniky, 2017

Materiálové průzkumy pro účel památkové obnovy objektu Nové proboštství, nám. sv. Jiří č.p. 34, Pražský Hrad
Drdácký, Miloš; Slížková, Zuzana; Frankeová, Dita; Hasníková, Hana; Hauková, Petra; Koudelková, Veronika; Kozlovcev, Petr; Ševčík, Radek; Wolf, Benjamin
2017 - Czech
Zpráva obsahuje výsledky materiálových analýz vzorků omítek a kamene, odebraných z fasád a vnitřních omítek objektu Nové proboštství (Pražský hrad, nám. sv. Jiří č.p. 34). Předmětem studia bylo chemické složení a mikrostruktura omítek, petrografie pískovce, pórovitost materiálů rtuťovou porozimetrií, povrchová nasákavost omítek, obsah a distribuce vlhkosti ve zdivu, obsah a chemické složení vodorozpustných solí v omítkách. Výsledky analýz jsou podkladem pro budoucí návrh stavební obnovy objektu a postupy restaurování uměleckých prvků. The report contains the results of the material analyses of plasters and stone samples taken from the facades and interior plasters of the historical building named “Nové Probošství” (Pražský hrad, nám. sv. Jiří č.p. 34).). The topic of the study was determination of the chemical composition and the microstructure of historical plasters and renders, sandstone petrography, porosity of materials by means of MIP, water absorption of plasters by tubes, the water content and the moisture distribution in masonry wall, the content and the chemical composition of water-soluble salts in plasters and renders. The results of the study serves as the basis for the future design of the building renovation and the restoration of the artistic elements.\n Keywords: historic plaster; historic render; chemical composition; survey; historic building; material characterization Available at various institutes of the ASCR
Materiálové průzkumy pro účel památkové obnovy objektu Nové proboštství, nám. sv. Jiří č.p. 34, Pražský Hrad

Zpráva obsahuje výsledky materiálových analýz vzorků omítek a kamene, odebraných z fasád a vnitřních omítek objektu Nové proboštství (Pražský hrad, nám. sv. Jiří č.p. 34). Předmětem studia bylo ...

Drdácký, Miloš; Slížková, Zuzana; Frankeová, Dita; Hasníková, Hana; Hauková, Petra; Koudelková, Veronika; Kozlovcev, Petr; Ševčík, Radek; Wolf, Benjamin
Ústav teoretické a aplikované mechaniky, 2017

Remarks on inverse of matrix polynomials
Fischer, Cyril; Náprstek, Jiří
2017 - English
Analysis of a non-classically damped engineering structure, which is subjected to an external excitation, leads to the solution of a system of second order ordinary differential equations. Although there exists a large variety of powerful numerical methods to accomplish this task, in some cases it is convenient to formulate the explicit inversion of the respective quadratic fundamental system. The presented contribution uses and extends concepts in matrix polynomial theory and proposes an implementation of the inversion problem. Keywords: matrix polynomial; polynomial eigenvalues; structural vibration Available at various institutes of the ASCR
Remarks on inverse of matrix polynomials

Analysis of a non-classically damped engineering structure, which is subjected to an external excitation, leads to the solution of a system of second order ordinary differential equations. Although ...

Fischer, Cyril; Náprstek, Jiří
Ústav teoretické a aplikované mechaniky, 2017

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