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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 ...
Microscopic features of cement paste modified by fine perlite
Hrbek, V.; Koudelková, Veronika; Padevět, P.; Šašek, Petr
2017 - English
The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight aggregate enhancing the insulating performance of concrete. This paper focuses on integration of fine perlite into the cement matrix and possible replacement of the cement binder in the composition of the material. The macromechanical performance of the modified paste is tested on specimens with 5, 10, 15 and 20% fine perlite substitution and pure cement sample. To distinguish the effect of the perlite on the microstructural level, pure cement material and specimen containing 10% of fine perlite are investigated by the electron microscopy. Furthermore, the mechanical properties of individual phases are examined and compared on same samples by instrumented indentation. The presented results enabled estimation of fine perlite impact on the macro and microscopic performance of the material..
Keywords:
perlite; SEM; nanoindentation; mechanical properties
Available at various institutes of the ASCR
Microscopic features of cement paste modified by fine perlite
The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight ...
Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level
Krčmářová, Nela; Šleichrt, J.; Doktor, T.; Kytýř, Daniel; Jiroušek, O.
2017 - English
Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose. In this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465 HV1.019 and average Vickers hardness of ALCORAS was 36.585 HV1.019..
Keywords:
metal foam; Vickers hardness; cell-wall; indentation under low loads
Available at various institutes of the ASCR
Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level
Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict ...
A concept for testing and monitoring of building structures – theoretical case study
Bayer, Jan
2017 - English
A mere comparison of measured and analytical deformations, natural frequencies and mode\nshapes provides us with just a small part of the information contained in the data, especially when component- level damage prevention is needed. The presented analysis studies in detail a few criteria for evaluation of measured data, with the example of simulated plane trusses in respect to the ultimate limit state. It demonstrates the high potential of a systematic approach, while combining several criteria, particularly when using simultaneous strain and deformation measurements, as it documents the proposed Relative Mode Difference (RMD) criterion. On the other hand, the study points out the major limitation of practical applications that is caused by unknown inherent uncertainties of various kinds, providing us with the incentive for further experimental research.
Keywords:
testing; monitoring; building structures; ultimate limit state; mode shapes; strains
Available at various institutes of the ASCR
A concept for testing and monitoring of building structures – theoretical case study
A mere comparison of measured and analytical deformations, natural frequencies and mode\nshapes provides us with just a small part of the information contained in the data, especially when component- ...
Numerical assessment of stability of the ball vibration absorber
Fischer, Cyril; Náprstek, Jiří
2017 - English
The ball vibration absorber (BVA) is in principle a heavy ball rolling inside a semi-spherical cavity. It is a convenient alternative to the usual pendulum-based dampers. The dynamics of the real ball absorber is significantly more complicated in comparison to the pendulum one. However, the numerical examination of the non-linear model of the BVA indicates that its resonance behaviour is similar to the spherical pendulum. Despite the theoretical differences, the resonance curves in both cases form similar patterns. It seems that detailed study of both separate cases can provide complementary results, whose parallels appear in the other model.
Keywords:
ball vibration absorber (BVA); non-linear model; resonance
Available at various institutes of the ASCR
Numerical assessment of stability of the ball vibration absorber
The ball vibration absorber (BVA) is in principle a heavy ball rolling inside a semi-spherical cavity. It is a convenient alternative to the usual pendulum-based dampers. The dynamics of the real ...
Grid indentation and statistic deconvolution: limitations and accuracy
Hrbek, V.; Koudelková, Veronika
2017 - English
The evaluation of heterogeneous materials used in civil engineering on the microscopic level has become important aspect in proper understanding of the macroscopic behavior of the material. This contribution aims at advantages and problems related to the technique of grid indentation and at the evaluation of mechanical properties.
Keywords:
indentation; microstructure; phase; heterogeneity; grid indentation; scanning electron microscopy
Available at various institutes of the ASCR
Grid indentation and statistic deconvolution: limitations and accuracy
The evaluation of heterogeneous materials used in civil engineering on the microscopic level has become important aspect in proper understanding of the macroscopic behavior of the material. This ...
Experimental study of horizontal forces of pedestrian dynamics
Urushadze, Shota; Pirner, Miroš
2017 - English
At present similar detailed examination of pedestrian dynamics has been brought about chiefly by the requirements of determining the loads on footbridges. In their case – contrary to bridges – the magnitude of dynamic response is more important than that of static response, as it determines also the serviceability of the footbridge with reference to pedestrian comfort. The forces frequencies of step or strides for different walking velocities is the most important for the further analysis and analysis of the mechanisms.s.
Keywords:
pedestrian dynamics; dynamic response of footbridge; stride strength; stride frequency; step frequency; dynamic coefficient; effects of striding velocity
Available at various institutes of the ASCR
Experimental study of horizontal forces of pedestrian dynamics
At present similar detailed examination of pedestrian dynamics has been brought about chiefly by the requirements of determining the loads on footbridges. In their case – contrary to bridges – the ...
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