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Moving dynamic test loads for road bridges - a case study
Bayer, Jan; Urushadze, Shota
2019 - English
Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact elements and in MATLAB using a modal solution together with coupling force were performed. Equations for the estimation of the impulse load caused by a rolling cogwheel were suggested. The experiments confirmed that a driving impulse load is more efficient in exciting bridge vibrations. This, together with the fact that impulse loading is not sensitive to surface roughness, leads to the conclusion that, as a method for bridge health monitoring, impulse loading is more promising than using a driving sprung mass
Keywords:
drive-by identification; bridge testing; moving sprung mass; impulse loading; vibration measurements; laboratory experiments
Available at various institutes of the ASCR
Moving dynamic test loads for road bridges - a case study
Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact ...
System response with random imperfections in coefficients on the space of realizations
Náprstek, Jiří; Fischer, Cyril
2019 - English
The contribution is concerned with the analysis of the simultaneous effect of a random perturbation and a white noise in the coefficient of the system. The excitation of the system of the 1-st order is described by the sum of a deterministic signal and an additive white noise which is partly correlated with the parametric noise. The random perturbation in the parameter is considered as a statistics in a set of realizations. It reveals that the density of probability of perturbations must be limited in the phase space, otherwise the system would lose the stochastic stability in probability. The width of the permissible zone depends heavily on the intensity of the parametric noise, the extent of correlation with the additive excitation noise and the type of probability density. The general explanation is demonstrated on cases of normal, uniform and truncated normal densities of probability.
Keywords:
noisy signal; filtration; random imperfections
Available at various institutes of the ASCR
System response with random imperfections in coefficients on the space of realizations
The contribution is concerned with the analysis of the simultaneous effect of a random perturbation and a white noise in the coefficient of the system. The excitation of the system of the 1-st order ...
Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
Vinařský, V.; Martino, F.; Forte, G.; Šleichrt, Jan; Rada, Václav; Kytýř, Daniel
2019 - English
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. PDMS based material is used for construction of microfluidic organ on chip devices for cell culture due to ease of device preparation, bonding, and possibility of surface functionalization. However it has stiffness orders of magnitude out of physiological range. Therefore, we adapted recently available protocol aiming to prepare substrates which offer stiffness in physiological range 5−100 kPa using various mixtures of Sylgard. An in-house developer loading device with single micron position tracking accuracy and sub-micron position sensitivity was adapted for this experimental campaign. All batches of the samples were subjected to uniaxial loading. During quasi-static experiment the samples were compressed to minimally 40% deformation. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data and elastic moduli are estimated.
Keywords:
quasi-static loading; hyperelasticity; polydimethylsiloxane substrates; in-situ loading device
Available at various institutes of the ASCR
Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. PDMS based material is used for construction of ...
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
Trush, Arsenii; Pospíšil, Stanislav; Kuznetsov, Sergeii
2019 - English
A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of residual life of these structures. Guyed masts and particularly guy ropes have significant dimensions and comparatively low mass and damping with high flexibility. Therefore, aerodynamic and aeroelastic loads, such as vortex induced vibrations, galloping, wind gusts, etc., are key for them. As a tensile construction elements (guy ropes) for guyed masts the traditional open wire spiral strand cables are used. This type of cable has a characteristic helical surface roughness pattern that can act as vortex suppressor, high fatigue endurance, although somewhat lower corrosion resistance comparing to modern locked coil cables with non-circular shaped wires of outer layer and cables with protective polymer coatings. At the same time, on numerous bridges with the above-mentioned modern cable types the fatigue damage to wires in anchorage zones and destruction of protective coatings was detected. Present paper provides results of wind tunnel testing of three models of helical strake cable in order to evaluate separately impact of lay angle and surface roughness factors and reference smooth cylinder model in flow with grid generated turbulence of different intensities. The reduction of the lock-in range of helical strand cables comparing to reference smooth model was observed whereby the greatest impact was an increase of lay angle.
Keywords:
bridge cable; wind tunnel; vortex shedding
Available at various institutes of the ASCR
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of ...
In-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography
Glinz, J.; Kytýř, Daniel; Fíla, Tomáš; Šleichrt, Jan; Schrempf, A.; Fürst, D.; Kastner, J.; Senck, S.
2019 - English
In this study, we investigated specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz, which are used to mimic the haptic feedback of physiologic and pathologic bone for more realistic surgery training. Specimens with two kinds of mineral filler material as well as different amounts of foaming agent were tested in an environmental in-situ loading stage developed by the ITAM CAS and scanned via X-ray micro-computed tomography. In this in-situ stage, specimens can be immersed in liquid and tested under temperature-controlled conditions. Consequently, a total amount of 12 specimens was subjected to compression loading, half of them immersed in water at 36.5 °C and half in dry condition. Results showed that there is no significant influence of liquid immersion to the compression outcome. However, foams with less amount of foaming agent appeared to have smaller pores resulting in higher compression strength.
Keywords:
x-ray micro-computed tomography; artificial bone foams; in-situ testing
Available at various institutes of the ASCR
In-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography
In this study, we investigated specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz, which are used to mimic the haptic feedback of physiologic ...
Lomové parametry AAAS kompozitů s keramickým střepem
Šimonová, H.; Rozsypalová, I.; Kumpová, Ivana; Trčka, T.; Frantík, P.; Rovnaníková, P.; Keršner, Z.
2019 - Czech
Příspěvek se zabývá alkalicky aktivovanými aluminosilikátovými kompozity na bázi keramických prekurzorů z hlediska charakterizace lomově-mechanickými parametry. Byly vyšetřovány tři kompozity, vyrobené z cihelného prachu jako prekurzoru a alkalického aktivátoru se silikátovým modulem Ms = 1,0, 1,2 a 1,4. Zkušební tělesa měla nominální rozměry 40 × 40 × 160 mm a byla po 28 dnech opatřena zářezy uprostřed rozpětí do 1/3 výšky těles. Z každého kompozitu bylo zkoušeno nejméně 6 vzorků. Tělesa byla podrobována testům v tříbodovém ohybu, při kterých byly zaznamenávány diagramy síla vs. průhyb uprostřed rozpětí a síla vs. otevření ústí trhliny. Po korekci těchto diagramů se s využitím modelu efektivní trhliny, metody lomové práce a modelu dvojí-K stanovily hodnoty statického modulu pružnosti, efektivní lomové houževnatosti (včetně její iniciační složky) a specifické lomové energie. Po lomových testech se vždy na jednom ze zlomků určovaly hodnoty informativní pevnosti v tlaku. Všechna vyhodnocení zahrnovala určení aritmetických průměrů a výběrových směrodatných odchylek. Pro získání informace o vnitřní struktuře kompozitů před mechanickým testováním a po něm bylo vybrané těleso zkoumáno pomocí mikro-tomografie. Tomografická měření a zpracování obrazu byla provedena pro kvalitativní a kvantitativní vyhodnocení změn vnitřní struktury s důrazem na výpočet porozimetrických parametrů a také vizualizace lomové procesní zóny. Byla stanovena fraktální dimenze objektů lomu. The paper deals with alkali-activated aluminosilicate composites based on ceramic precursors with respect to their characterization by fracture-mechanical parameters. Three composites made of brick dust as a precursor and alkaline activator with silicate modulus Ms = 1.0, 1.2 and 1.4 were investigated. After 28 days of maturation, specimens with nominal dimensions of 40 × 40 × 160 mm were provided by an initial notch to 1/3 of the body height in the middle of the span. At least 6 samples were tested from each composite. Specimens were subjected to three-point bending tests during which force vs. deflection at midspan (F–d) and force vs. crack mouth opening displacement (F–CMOD) diagrams were recorded. By processing these diagrams, the values of the static modulus of elasticity, the effective fracture toughness (including its initiating component) and the specific fracture energy were determined using the effective crack model, Work-of-Fracture method, and Double-K fracture model. After the fracture experiments had been performed, compressive strength values were determined for informational purposes from one part of each specimen that remained after testing. All evaluations included the determination of arithmetic means and standard deviations. To obtain information about the internal structure of composites before and after mechanical testing, the selected body was examined by micro-tomography. Tomographic measurements and image processing were performed for qualitative and quantitative evaluation of internal structure changes with an emphasis on the calculation of porosimetric parameters as well as visualization of the fracture process zone. The fractal dimension of fracture objects was determined.
Keywords:
alkali-activated aluminosilicate (AAAS); ceramic precursor; fracture test; force-displacement diagram; X-ray micro-tomography
Available at various institutes of the ASCR
Lomové parametry AAAS kompozitů s keramickým střepem
Příspěvek se zabývá alkalicky aktivovanými aluminosilikátovými kompozity na bázi keramických prekurzorů z hlediska charakterizace lomově-mechanickými parametry. Byly vyšetřovány tři kompozity, ...
Local stabilization of the quasiperiodic response of the generalized van der Pol oscillator
Fischer, Cyril; Náprstek, Jiří
2019 - English
The generalized van der Pol equation is often used for description of various effects originating in the aero-elasticity of large slender engineering structures. This applies mainly to the quasiperiodic beatings that can be encountered especially in lock-in regimes when the vortex frequency becomes close to the structure eigenfrequency with a small detuning. The current paper presents numerical analysis of influence of the subor superharmonic excitation on the character of the response of a generalized van der Pol oscillator. This way it complements two previous papers of the authors dealing with stability analysis of certain types of the stationary periodic or quasiperiodic response of the system under study.
Keywords:
generalized van der Pol equation; quasiperiodic response; sub- and superharmonic synchronization; beating effect; numerical simulation
Available at various institutes of the ASCR
Local stabilization of the quasiperiodic response of the generalized van der Pol oscillator
The generalized van der Pol equation is often used for description of various effects originating in the aero-elasticity of large slender engineering structures. This applies mainly to the ...
Celodřevěné spoje a jejich využití při opravách historických konstrukcí
Kunecký, Jiří
2019 - Czech
Nejčastější opravou při citlivých rekonstrukcích dřevěných konstrukcí je plátový spoj, který dovoluje nahradit pouze část poškozeného prvku protézou a zachovat tak maximální možné množství původního materiálu v konstrukci. Chybějící metodika pro navrhování těchto spojů byla vyvinuta v minulých čtyřech letech v rámci programu NAKI. Výsledky uvedené v metodice jsou založeny na experimentálních výsledcích, ale i na numerických a mechanických modelech. Je vhodná a srozumitelná pro statiky, tesaře i pracovníky památkových ústavů, je vhodnou referencí pro opravy cenných střešních konstrukcí památkových objektů. Obsahuje jak část návrhovou tak část prováděcí (technologickou). Most common issue when some moisture or insect- induced decay is present in historical timber structures is the use of lapped scarf joints. This technology keeps the look of the original construction, the decayed part is removed while keeping the healthy wood in the structure. The work presents the guidelines written for the purpose during four years of intensive research activities. The guidelines describe experimental results but also results of numerical and mechanical models. It is intended to be valuable for structural engineers, carpenters and workers of the cultural heritage institutes. The technology is suitable for repair of valuable historic timber structures.
Keywords:
timber; lapped scarf joints
Available at various institutes of the ASCR
Celodřevěné spoje a jejich využití při opravách historických konstrukcí
Nejčastější opravou při citlivých rekonstrukcích dřevěných konstrukcí je plátový spoj, který dovoluje nahradit pouze část poškozeného prvku protézou a zachovat tak maximální možné množství původního ...
Postupy používané při zjišťování stavu dřeva historických konstrukcí
Kloiber, Michal
2019 - Czech
V rámci přednášky byly představeny metody stavebně-technických průzkumů a jejich použití. Diskutována byla potřeba diagnostiky, její význam v projektové činnosti a různá podoba výstupů průzkumů, jakými jsou např. přesná identifikace dřeviny a druhu poškození, podrobné hodnocení obsahu vlhkosti ve dřevě, identifikace rozsahu biologického napadení a posouzení stupně poškození. Within the scope of the lecture, methods of structural and technical surveys and their use were presented. The need for this kind of diagnostics, its significance for design projects, and various forms of survey outcomes were discussed, such as identification of tree species, identification of damage type, a detailed evaluation of moisture content in wood, identification of biological damage scope, and evaluation of damage degree.
Keywords:
timber structures; diagnostic methods; structural and technical survey
Available at various institutes of the ASCR
Postupy používané při zjišťování stavu dřeva historických konstrukcí
V rámci přednášky byly představeny metody stavebně-technických průzkumů a jejich použití. Diskutována byla potřeba diagnostiky, její význam v projektové činnosti a různá podoba výstupů průzkumů, ...
Rapid research with computer algebra systems
Fischer, Cyril
2019 - English
Computer algebra systems (CAS) are gaining popularity not only among young students and scholars but also as a tool for serious work. These highly complicated software systems, which used to just be regarded as toys for computer enthusiasts, have reached maturity. Nowadays such systems are available on a variety of computer platforms, starting from freely-available on-line services up to complex and expensive software packages. The aim of this review paper is to show some selected capabilities of CAS and point out some problems with their usage from the point of view of 25 years of experience.
Keywords:
computer algebra system; methodology; Wolfram Mathematica
Available at various institutes of the ASCR
Rapid research with computer algebra systems
Computer algebra systems (CAS) are gaining popularity not only among young students and scholars but also as a tool for serious work. These highly complicated software systems, which used to just be ...
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