BRJ – Volume 60, Number 1–2, 2012 (with fulltext)
Turbulences in artificial boundary layer of photovoltaic power plants . . . . . . . . . . . . . 15-30 (fulltext)
Robert Šoltys, Michal Tomko and Stanislav Kmeť:
Study of local turbulent wind characteristics and wind velocity simulations . . . . . . . . 31-50 (fulltext)
P. M. Pradhan, R. K. Maskey and P. L. Pradhan:
Composite behavior of masonry partially infilled reinforced concrete frames . . . . . . . . 51-60 (fulltext)
Jan Jerga and Ľudovit Krajči:
Properties of concrete manifested in the stress-volumetric strain diagram . . . . . . . . . . 61-80 (fulltext)
P. Senthilkumar and S. Kandaswamy:
Performance of sound transmission on coconut fiber impregnated cavity ferrocement panels
with and without absorptive material using statistical energy analysis . . . . . . . . . . . . . 81-88 (fulltext)
Matúš Holúbek and Peter Matiašovský:
Determination of liquid water diffusivity of building materials using TDR method . . . . 89-108 (fulltext)
Dynamic factor of underpass structure using experimentally calibrated numerical model
Milan Sokol and Lenka Konečna
The paper deals with verification of eigen frequencies and determination of a dynamic factor of the underpass structure under railway platform which has already been realized. Eigen frequencies and eigen modes were verified by means of tests which have been made on the real structure and also by created computing frame model of the structure. Results obtained from tests were used for setting a numerical model. Subsequently, this model was used for determination of a dynamic ratio of the underpass structure depending on varied train speeds (from 1 km/h to 160 km/h). Description of the underpass structure, dynamic load, measurement equipment used during the tests, way of evaluation of the results from tests, creating computing frame model of the structure, creating and setting numerical model are also mentioned here. Resultant eigen frequencies, eigen modes and dynamic ratios are listed in this paper.
Keywords: dynamic test, dynamic ratio, moving load, numerical model
Turbulences in artificial boundary layer of photovoltaic power plants
The aeroelastic assessment of turbulences appearing in artificial boundary layer of photovoltaic power plants is treated in the present paper. The approach suggested takes into account multiple functions in the analysis of skew flat plates of solar panels subjected to laminar and turbulent wind forcing. Analysis and experimental assessments in the aerodynamic tunnel are presented. Some results obtained are discussed.
Keywords: aerodynamic tunnel, aeroelasticity, artificial boundary layer, photovoltaic power plant, mechanics of turbulent wind motion, skew flat plate, solar panel, turbulences, wave propagation
Study of local turbulent wind characteristics and wind velocity simulations
Robert Šoltys, Michal Tomko and Stanislav Kmeť
Results of the analyses of in situ measured wind records with a sampling frequency of 20 Hz and with the duration of 1 year are presented in the paper. Wind speed records were measured at Bily Kriz station in Beskydy by the Institute of Systems Biology and Ecology at the Academy of Sciences of the Czech Republic. Because a high measurement frequency for research applications was needed, wind velocity was measured according to the propagation speed of ultrasound signals. Records were performed by a GILL R3-100 ultrasonic anemometer positioned 18 m above the height of the terrain (approximately 5 m above the pine trees). From the annual record of wind velocities the measurement with the duration of 17.5 h was selected for further statistical processing. This measurement consists of 35 records of 30 min intervals. For selected data set statistical characteristics and power spectral density functions of the measured wind velocity components in the longitudinal, lateral and vertical direction are calculated. On the basis of the experimentally measured records of turbulent wind velocities the simulations of the wind field histories in the individual directions were generated using the Shinozuka method and developed WindSimul program. The evaluation of their statistical and frequency properties was performed. The physical importance of the mathematical approach and the functionality of the developed program were demonstrated and proved. Obtained statistical and frequency properties of the longitudinal, lateral and vertical component of the measured turbulent wind can find a wider use in the dynamic analysis and design of structures in similar areas.
Keywords: turbulent wind, fluctuating velocity components, in situ measurement, statistical characteristics, frequency characteristics, power spectral density functions, wind velocity simulation
Composite behavior of masonry partially infilled reinforced concrete frames
P. M. Pradhan, R. K. Maskey and P. L. Pradhan
Partially infilled reinforced concrete frames are susceptible to short-column effect. Past earthquakes have often damaged a large number of structures, which included masonry partially infilled concrete frames. This study is conducted to quantify the shear force developed within the columns having masonry partial infills using equivalent diagonal strut model. Similarly, the study is done for stiffness behaviors and fundamental period of vibration for partially infilled frames. The partially infilled frames were found most vulnerable to damage when the masonry infills were about 40 % filled.
Keywords: Flexural model, masonry partially infilled frames, short column effect
Properties of concrete manifested in the stress-volumetric strain diagram
Jan Jerga and Ľudovit Krajči
The unknown load history of structures in service does not allow determining the long-term compressive strength, critical for their reliability, from short-term tests of drilled concrete cylinders by the use of relationships derived on specimens without previous overloading. The extent of damage of the material must be taken into account when the residual strength should be estimated correctly. The existing knowledge of the microcracks in concrete, their origin and growth during loading, as well as their impact on the degradation of the long-term strength is dealt in the article. In this context, the possibility of the application of nonlinear acoustic methods is briefly pointed out. The main attention is paid to the stress-volumetric strain diagram. Based on experimental measurements, its ability to indicate the mechanical properties of concrete is studied.
Keywords: concrete, residual strength, combined microcracks, stress-volumetric strain diagram, environmental Factors
Performance of sound transmission on coconut fiber impregnated cavity ferrocement panels with and without absorptive material using statistical energy analysis
P. Senthilkumar and S. Kandaswamy
Lightweight building materials like ferrocement are used in a low cost and cost effective construction in the developing countries. Sound transmission studies were conducted on the ferrocement panel system with different types of reinforcement fibers. In this work sound reduction index and transmission behavior studies were conducted on cavity fiber impregnated ferrocement panels with and without absorptive material in the cavity. The panels were erected as slabs and lifted and placed in the opening provided between source and receiver rooms. Sound transmission studies were conducted on panels in the transmission loss suite which was specially constructed for this set of measurements. Two coconut shell fiber impregnated ferrocement panels with the cavity thickness of 50 mm between them were cast. Fiber glass wool of 50 mm thickness and density of 48 kg/m3 was used inside the cavity of the ferrocement panels. It has been found that the mass increase of ferrocement panels by providing cavity and absorptive material between two panels with the same thickness of 20 mm gives 10 dB difference in Sound Reduction Index (SRI). The results were then compared with the theoretical data using Statistical Energy Analysis (SEA).
Keywords: sound transmission, coconut shell fiber impregnated ferrocement panels, sound reduction index, statistical energy analysis
Determination of liquid water diffusivity of building materials using TDR method
Matúš Holúbek and Peter Matiašovský
The objective of this study is an application of time domain reflectometry (TDR) in determination of liquid water diffusivity of porous building materials. We chose the lime-cement perlite plaster to study the applicability of TDR method for continuous measurements of non-stationary water transport processes. The study includes determination of the relation between the equilibrium moisture content and the relative permittivity of a material (calibration curve) and its comparison to physical, empirical and mixing effective permittivity models. Depending on various probe placement techniques different calibration curves were obtained. Their comparison enabled the evaluation of the quality of contact between probe and material. The moisture profiles measured during water uptake experiment provided a basis for the determination of the moisture diffusivity. Boltzmann transformation was used to obtain the diffusivity function. Taking the error analysis of TDR method into account the proper methodology for determination of the diffusivity was proposed.
Keywords: diffusivity, moisture content profiles, time domain reflectometry, uncertainty