Number of found documents: 886
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Proposal for loading tests of bridges - simulation and laboratory experiments
Bayer, Jan; Urushadze, Shota; Černý, Miloš
2018 - English
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient solution of piecewise linear mechanical structures were developed to assess the effects of the proposed dynamic load on a bridge model. According to the first laboratory experiments, it seems that the proposed travelling impulse load could surpass some of the shortcomings and limitations of the currently applied methods of bridge testing. The investigation is a part of a project aimed at drive-by identification of dynamic properties of bridges and further experimental and analytical research will follow. Keywords: dynamic loading tests; transient analysis; vibrations; vehicle-bridge interaction Available at various institutes of the ASCR
Proposal for loading tests of bridges - simulation and laboratory experiments

A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient ...

Bayer, Jan; Urushadze, Shota; Černý, Miloš
Ústav teoretické a aplikované mechaniky, 2018

Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu
Göringer, J.; Hračov, Stanislav; Macháček, Michael
2018 - Czech
S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo podpory. Zatížení větrem u takovéto konstrukce nevystupuje pouze jako náhradní statický účinek, ale zejména je nutné posoudit případné ztráty aerodynamické stability. Příspěvek předkládá postup stanovení problematiky podle EN 1991-1-4 včetně porovnání s výsledky z větrného tunelu. Due to the atypical design of the footbridge in Radotín the procedures for evaluation of the force coefficients presented in EN 1991-1-4 were experimentally verified in the wind tunnel. For the lack of the information about the structure behaviour on the edge of the aerodynamic instability the critical velocity for flutter was experimentally verified as well. The paper presents comparison of the approaches from EN 1991-1-4 with the results of the experiment. Keywords: wind load; footbridge; wind tunnel experiments Available at various institutes of the ASCR
Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu

S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo ...

Göringer, J.; Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2018

Asymmetry of the response probability density of a system with parametric random noises
Náprstek, Jiří; Fischer, Cyril
2018 - English
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These parasitic processes are usually of the random character and, consequently, they exercise as parametric noises. Moreover, the input signal mostly consists of a useful signal which can be taken as composed from deterministic and random additive part. Various combinations of these noises are the origin of random and also systematic measuring errors which can have under certain circumstances a cumulative character, deteriorate the output signal quality and can lead finally to the stochastic stability loss. These effects can be theoretically described using differential systems with stochastic coefficients and stochastic right hand side considering all input and output processes to be of the Markov type. Keywords: random vibration; signal reconstruction; parametric noise; response asymmetry Available at various institutes of the ASCR
Asymmetry of the response probability density of a system with parametric random noises

Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2018

Forced movement of a ball in spherical cavity under kinematic excitation
Náprstek, Jiří; Fischer, Cyril
2018 - English
In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic constraints is considered. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appel-Gibbs function of acceleration energy is developed and discussed. The most important post-critical regimes are outlined and qualitatively evaluated on the frequency axis. Numerical experiments have been performed when excitation frequency is slowly swept up and down. Results obtained by means of semi-analytical investigation and numerical simulation are evaluated and physically interpreted. Some applications in civil engineering as a tuned mass damper used on slender structures is outlined. Strengths and weaknesses of solution method are evaluated. Keywords: nonlinear dynamics; non-holonomic systems; Appell-Gibbs formulation; singular states; tuned mass damper Available at various institutes of the ASCR
Forced movement of a ball in spherical cavity under kinematic excitation

In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2018

Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device
Hračov, Stanislav
2018 - English
The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of perturbation and incremental approaches and is applicable to the classically damped structures equipped with a specialized passive damping device. The numerical efficiency in terms of the required calculation times and the accuracy is demonstrated on a model of an existing structure for various combination of computational parameters. Wide numerical simulations revealed the selection of real eigenmodes of undamped system used in the approximate eigensolution as the most important parameter affecting the final accuracy. Keywords: non-classical damping; complex eigensolution; perturbation method; passive damper Available at various institutes of the ASCR
Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device

The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of ...

Hračov, Stanislav
Ústav teoretické a aplikované mechaniky, 2018

Tradiční opracování a kvalita dřeva při opravách dřevěných konstrukcí.
Kloiber, Michal; Růžička, Petr
2018 - Czech
Rozsáhlé terénní zkušenosti při opravách dřevěných konstrukcí ukazují na dva základní limitující faktory kvality odvedené práce, které se často různými obcházejí či zjednodušují. V první řadě je to kvalita dřeva při opravách (výměny, protézy) a z ní vyplývající problémy při nedodržení doporučených kritérií pro výběr vhodného materiálu, s ohledem na dlouhodobou koexistenci nového dřeva s původním materiálem. Ve druhém případě jsou velmi vlivným faktorem způsoby opracování dřeva, kdy se pro své výhody preferované tradiční způsoby z různých důvodů nahrazují podvrhem. V tomto článku se budeme vzhledem k jeho omezenému rozsahu věnovat pouze nejkřiklavějšímu případu, a tím je opracování kulatiny tesáním. Extensive field experience with repairing timber structures shows two main limiting factors for the quality of work that are often circumvented or simplified. First, it is the quality of the timber for the repairs (replacements, additions) and the resulting problem when the recommended criteria for the selection of suitable material are not met, with regard to the long-term coexistence of the new timber with the original material. Second, a critical factor is the way in which the timber is worked - the preferred traditional working is for various reasons replaced by counterfeits. Due to the limited scope of this paper, we can only pay attention to the most blatant case, which is working of logs by hewing. Keywords: wooden structures; old carpentry tools; timbers Available at various institutes of the ASCR
Tradiční opracování a kvalita dřeva při opravách dřevěných konstrukcí.

Rozsáhlé terénní zkušenosti při opravách dřevěných konstrukcí ukazují na dva základní limitující faktory kvality odvedené práce, které se často různými obcházejí či zjednodušují. V první řadě je to ...

Kloiber, Michal; Růžička, Petr
Ústav teoretické a aplikované mechaniky, 2018

Crystallization force of sodium chloride
Koudelková, Veronika; Wolf, Benjamin
2018 - English
Soluble salts are one of the most deteriorating factor causing damage of historical building materials due to generation of crystallization pressure inside pore space. Direct measurement of crystallization force is quite challenging, hence we developed at our institute a novel device able to detect the force of growing crystal. The device is based on the monitoring of force developed with upper microscopic glass on the growing crystal to maintain constant position. The crystal could generate force because of the existence of thin liquid layer of solution between both surfaces come into contact. The driving force for the subsequent growth of crystal against obstacle is supersaturation, which is mainly induced by evaporation of the salt solution. In this experiment, the crystal of sodium chloride generated force 16.8 mN and the corresponding crystallization pressure was equal to the value 0.48 MPa. Keywords: crystallization force; sodium chloride; salt deterioration Available at various institutes of the ASCR
Crystallization force of sodium chloride

Soluble salts are one of the most deteriorating factor causing damage of historical building materials due to generation of crystallization pressure inside pore space. Direct measurement of ...

Koudelková, Veronika; Wolf, Benjamin
Ústav teoretické a aplikované mechaniky, 2018

Možnosti využití rentgenové tomografie ke kvantifikaci poškození teplotně namáhaného betonu
Rozsypalová, I.; Kumpová, Ivana; Daněk, P.; Šimonová, H.; Keršner, Z.
2018 - Czech
Působení vysokých teplot na beton ovlivňuje vnitřní strukturu tohoto kompozitního materiálu. V příspěvku se otevírá otázka možnosti využití výpočetní rentgenové tomografie ke kVantifikaci míry poškození betonového tělesa, které bylo odvrtáno z vybraného experimentálního panelu zatěžovaného vysokými teplotami na požární peci Centra AdMaS (Advanced Materials, Structures and Technologies) FAST VUT v Brně. Nominální hodnota maxima teploty v peci činila 1000 °C. Pokročilé zařízení TORATOM (Twinned Orthogonal Adjustable Tomograph) v Centru excelence Telč (CET) kombinuje dva páry „rentgenka–detektor“ v ortogonálním uspořádání, které umožňuje dvojnásobné zrychlení procesu sběru dat pro tomografické rekonstrukce. Zařízení má plně motorizované osy pro nastavování vzdáleností „rentgenka–vzorek–detektor“. Tím lze měnit zvětšení zhruba od 1,2× po 100× (ve speciálních případech i více). Při dané velikosti pixelů detektoru je možné měnit rozlišení CT rekonstrukcí, tj. velikost jednoho prostorového bodu modelu, od 0,2 milimetrů až po mikrometrické. Další výhodu zařízení TORATOM představuje možnost paralelního zobrazování objektu ve dvou spektrech RTG záření. Tento postup umožňuje zvýraznit rozdíly mezi materiálovými komponentami, které mají v plném RTG spektru podobný útlum. Pokud se vzorek skládá pouze ze dvou materiálů, lze tyto materiály jednoznačně odlišit. U vícesložkových materiálů lze rozdíly pouze zdůraznit. The effect of high temperatures on concrete affects the internal structure of this composite material. The paper opens the question of the possibility of using a computed X–ray tomography to quantify the degree of damage of a concrete specimen that was drilled from the selected experimental panel loaded in a fire furnace with high temperatures at the AdMaS (Advanced Materials, Structures and Technologies) research centre at Faculty of Civil Engineering Brno University of Technology. The nominal value of the maximum temperature on the heated side of the panel was 1000 °C. Advanced workstation computer X–ray tomography TORATOM at Centre of Excellence Telč (CET) is parallel imaging of an object in two spectra of X–ray radiation, that allows to highlight differences between the material components to the full X–ray spectrum similar to the attenuation of the radiation. Keywords: TORATOM; concrete; high temperature; computed tomography Available at various institutes of the ASCR
Možnosti využití rentgenové tomografie ke kvantifikaci poškození teplotně namáhaného betonu

Působení vysokých teplot na beton ovlivňuje vnitřní strukturu tohoto kompozitního materiálu. V příspěvku se otevírá otázka možnosti využití výpočetní rentgenové tomografie ke kVantifikaci míry ...

Rozsypalová, I.; Kumpová, Ivana; Daněk, P.; Šimonová, H.; Keršner, Z.
Ústav teoretické a aplikované mechaniky, 2018

Iron alloys outdoor corrosion and laboratory simulation - comparison
Majtás, Dušan; Mácová, Petra; Kreislová, Kateřina; Příhoda, J.
2017 - English
Simulation of iron alloy corrosion is widespread used to predict corrosion resistance. The simulation using corrosion chambers or climatic chambers provides reasonable information on corrosion resistance, the corrosion rate however must be compared to real exposition as the corrosion in simulated environment is accelerated compared to real situation. However the composition of corrosion products and its structure is different question. The corrosion products composition is dependent on corrosion process. The phases present are most likely the same, most voluminous hydrated oxides and oxy-hydroxides on the outside where the less voluminous oxides are present in the lower layers. However this macroscopic phase structure may not fully describe the layered structure of corrosion products, thickness of corrosion products or mechanical properties. In the vicinity of crack in corrosion products the structure is more likely to be similar to the structure near the surface. Keywords: corrosion; wrought iron; accelerated ageing; corrosion simulation Available at various institutes of the ASCR
Iron alloys outdoor corrosion and laboratory simulation - comparison

Simulation of iron alloy corrosion is widespread used to predict corrosion resistance. The simulation using corrosion chambers or climatic chambers provides reasonable information on corrosion ...

Majtás, Dušan; Mácová, Petra; Kreislová, Kateřina; Příhoda, J.
Ústav teoretické a aplikované mechaniky, 2017

Analysis of Baroque sculpture based on X-ray fluorescence imaging and X-ray\ncomputed tomography data fusion
Vavřík, Daniel; Kumpová, Ivana; Vopálenský, Michal; Lauterkranc, J.
2017 - English
It is advantageous to combine information about geometry and the inner structure of historical artifacts with information about the elemental composition of decorative layers, typically covering historical wooden sculptures. X-ray computed tomography describing artifact structure is quite common and easy. Standard X-ray fluorescence (XRF) analysis of decorative layers is typically done for several selected spots of the artifact’s surface utilizing single pad detector. XRF imaging fully describing the surface’s elemental composition is commonly done for flat objects, while time consuming XRF tomography is applied to relatively small objects. It will be shown in this work that an effective fusion combination of XRF imaging and X-ray tomography describing the whole object can be realized even when using a limited number of XRF images. Keywords: X-ray computed tomography; X-ray flourescence imaging; cultural heritage; data fusion Fulltext is available at external website.
Analysis of Baroque sculpture based on X-ray fluorescence imaging and X-ray\ncomputed tomography data fusion

It is advantageous to combine information about geometry and the inner structure of historical artifacts with information about the elemental composition of decorative layers, typically covering ...

Vavřík, Daniel; Kumpová, Ivana; Vopálenský, Michal; Lauterkranc, J.
Ústav teoretické a aplikované mechaniky, 2017

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