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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 ...
Creep behavior of oak pegs under tension in dry and wet conditions
Kunecký, Jiří; Kloiber, Michal; Hasníková, Hana; Hrivnák, Jaroslav; Sebera, V.; Tippner, J.; Milch, J.
2017 - English
Carpentry joints equipped with oak pegs are well suited for applications where increased moisture is not a significant factor. However, for the use in outside conditions, e.g. in the repairs of historical timber bridges, the pegs connecting the two halves of the joint may deform and change their original shape. This happens especially during long-term loading and can be augmented significantly by environmental changes. Creep behavior can play a crucial role for some types of carpentry joints, especially when precise contacts of faces in the joint are required. The paper deals with experimental testing of creep behavior of 16 mm oak pegs under dry and wet conditions loaded by the combination of shear and bending between two planks made of spruce in the direction parallel to grain. The results show that the decrease of theoretical stiffness values over time plays a significant role in the force redistribution in the joint especially due to moisture effects (drop 50-70% of the original stiffness).
Keywords:
creep; oak; pegs; dowels; tension
Available at various institutes of the ASCR
Creep behavior of oak pegs under tension in dry and wet conditions
Carpentry joints equipped with oak pegs are well suited for applications where increased moisture is not a significant factor. However, for the use in outside conditions, e.g. in the repairs of ...
Research report 2013-11-08 Calcite_S12
Kumpová, Ivana; Vopálenský, Michal; Vavřík, Daniel
2017 - English
Porosity was measured on a irregular sample of calcite, designated Calcite_S12, using the TORATOM device in the Centre of Excellence Telč.
Keywords:
calcite; TORATOM; measuring
Available at various institutes of the ASCR
Research report 2013-11-08 Calcite_S12
Porosity was measured on a irregular sample of calcite, designated Calcite_S12, using the TORATOM device in the Centre of Excellence Telč.
Stochastic stability of the generalized van der Pol system under random additive excitation
Náprstek, Jiří; Fischer, Cyril
2017 - English
The paper is motivated by a series of wind tunnel experiments investigating aeroelastic SDOF and TDOF section models of various shape and aeroelastic properties. It reveals that most of them can be theoretically modeled by the van der Pol – Duffing type equations or their combination adjusting degree of individual nonlinear terms or their coefficients. It should be emphasized that this character of the system response is very stable and is obvious in linear as well as in weakly nonlinear domain when the post-critical effect emerges. Moreover, many special effects identified by an experimental way evoke properties recognized in the pure theory of differential equations.
Keywords:
wind tunnel experiment; random excitation; stochastic stability
Available at various institutes of the ASCR
Stochastic stability of the generalized van der Pol system under random additive excitation
The paper is motivated by a series of wind tunnel experiments investigating aeroelastic SDOF and TDOF section models of various shape and aeroelastic properties. It reveals that most of them can be ...
Using homogenization and nanoindentation for microfibril angle determination of spruce
Kucíková, L.; Hrbek, Vladimír; Vorel, J.; Šejnoha, M.
2017 - English
This paper is concerned with the evaluation of microfibril angle of spruce. The microfibril angle is defined as an inclination of microfibrils from the longitudinal axis, the direction of lumens. It is well known and further supported by the present study that the microfibril angle has a great influence on the final mechanical properties of wood. This angle could be measured either directly using, e.g. polarisation microscopy, X-ray diffraction, infrared spectroscopy, or indirectly, as used in this study, by employing the nanoindentation measurements. Therein, the measured indentation modulus is compared with that obtained numerically using the anisotropic theory of indentation. The latter one depends on the entire stiffness matrix derived through homogenization and the searched microfibril angle. In view of the cell wall microstructure, the effective cell properties were found using the two-step micromechanical homogenization adopting both the Self-consistent and Mori-Tanaka methods.
Keywords:
spruce; nanoindentation; microfibril angle; homogenization
Available at various institutes of the ASCR
Using homogenization and nanoindentation for microfibril angle determination of spruce
This paper is concerned with the evaluation of microfibril angle of spruce. The microfibril angle is defined as an inclination of microfibrils from the longitudinal axis, the direction of lumens. It ...
Early stage microstructure development of cement paste modified by crystalline admixture
Hrbek, V.; Petráňová, Veronika; Němeček, J.
2017 - English
This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on reference specimens consisting of pure cement. Samples of pure CA and cement modified by 1% of CA with the same w/c ratio were examined and compared in this paper. By investigation of these materials on the micro-scale, it is possible to identify the development of the microstructure of each and determine the impact of the modification. For this purpose, backscattered electrons microscopy (BSE) with energy-dispersive X-ray spectroscopy (EDX) was used for phase analysis as well as instrumental nano-indentation to obtain micro-mechanical properties. Presented results show the evolution of mechanical properties and microstructure in time and the impact of the crystalline admixture on modified cement.
Keywords:
cement; crystalline admixture; microstructure; nanoindentation; phase; SEM
Available at various institutes of the ASCR
Early stage microstructure development of cement paste modified by crystalline admixture
This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on ...
The Cloak Bridge in Český Krumlov – measuring of mechanical properties
Kloiber, Michal; Sebera, V.; Hrivnák, Jaroslav; Tippner, J.; Kunecký, Jiří
2017 - English
Timber bridges are often exposed to harsh conditions of the environment. The exposure of the timber structure often leads to its deterioration. Standard test procedures to determine typical properties of wood cannot be used as there is the requirement of the minimum interference with the structure. Several non-destructive testing (NDT) methods for the determination of timber condition have been developed and are used. However, the results of NDT can be used to predict mechanical properties of timber elements only to a limited degree. Semi-destructive testing (SDT) methods are a compromise. In the paper a functional model of a device that allows for the measurement of conventional strength and modulus of deformation of timber in compression parallel to the grain is presented. The device is inserted to a bored hole and pushes the jaws apart with a small test jack loading the bore walls. This paper presents possible use of the device for surveys of timber bridges.
Keywords:
model of device; mechanical properties
Available at various institutes of the ASCR
The Cloak Bridge in Český Krumlov – measuring of mechanical properties
Timber bridges are often exposed to harsh conditions of the environment. The exposure of the timber structure often leads to its deterioration. Standard test procedures to determine typical properties ...
Investigation of Strouhal number of ice-accreted bridge cables at moderate flow turbulence
Górski, P.; Tatara, M.; Pospíšil, Stanislav; Kuznetsov, Sergeii
2017 - English
This paper is concerned with the investigation of the Strouhal number (St) for a stationary iced cable model of cable-supported bridges using wind tunnel tests with respect to three principal angles of wind attack. The investigations were carried out in the Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telč. The St values were determined at the flow turbulence intensity of the order of 12%, within the range of the Reynolds number from 2.4·10^4 to 12.9·10^4, based on the dominant vortex shedding frequencies measured in the wake of the model. The obtained experimental St values of the iced cable of a cable-supported bridge will allow to determine the critical wind velocity as well as will be helpful for prediction of the cable response due to the vortex excitation phenomenon at moderate flow turbulence condition.
Keywords:
Strouhal number; climatic wind tunnel; vortex excitation phenomenon; cable-supported bridge
Available at various institutes of the ASCR
Investigation of Strouhal number of ice-accreted bridge cables at moderate flow turbulence
This paper is concerned with the investigation of the Strouhal number (St) for a stationary iced cable model of cable-supported bridges using wind tunnel tests with respect to three principal angles ...
Measurements of dynamic wind pressures on gable roofs – comparison with ČSN EN 1991-1-4
Pospíšil, Stanislav; Macháček, Michael; Hračov, Stanislav; Kuznetsov, Sergeii; Trush, Arsenii
2017 - English
The contribution is dealing with the wind tunnel measurements of dynamic pressures on the canopy roofs. It compares experimentally determined pressure coefficients Cp with the values in ČSN EN 1991-1-4 and former code ČSN 73 0035 as well. The pressures are expressed by the dynamic values. Thus, the averaged values are presented together with the fluctuating part, which significantly contributes to the overall loading. The measurement is carried out at two roof models, two basic directions, and two turbulence intensities.
Keywords:
wind tunnel experiments; dynamic pressures on roofs; wind loads; wind load codes; gable roof; atmospheric boundary layer
Available at various institutes of the ASCR
Measurements of dynamic wind pressures on gable roofs – comparison with ČSN EN 1991-1-4
The contribution is dealing with the wind tunnel measurements of dynamic pressures on the canopy roofs. It compares experimentally determined pressure coefficients Cp with the values in ČSN EN ...
Chemical and microstructural characterization of the render, sampled from the Garden wall of 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 Garden wall (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 the Garden wall of the US Embassy in Prague 1
The aim of the work was to analyze the mortar taken from the Garden wall (US Embassy, Prague 1). Analyzes were performed for the binder and filler characterization and the sample was also dissolved in ...
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