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Influence of ice accretion at bridge rope on Strouhal number
Pospíšil, Stanislav; Gorski, P.; Kuznetsov, Sergeii
2015 - English
The paper is concerned with the method and results of wind tunnel investigations of the/nStrouhal number (St) of a stationary iced cable model of cable-supported bridges with/nrespect to different angles of wind attack. The methodology leading to the experimental/nicing of the inclined cable model was prepared in a climatic section of the laboratory./nThe St values were determined within the range of the Reynolds number (Re) between/n2.4·104 and 16.5·104, based on the dominant vortex shedding frequencies measured in/nthe wake of the model.
Keywords:
bridge cable; ice accretion; Strouhal number; angle of attack; vortex shedding frequency
Fulltext is available at external website.
Influence of ice accretion at bridge rope on Strouhal number
The paper is concerned with the method and results of wind tunnel investigations of the/nStrouhal number (St) of a stationary iced cable model of cable-supported bridges with/nrespect to different ...
The numerical assessment of a full-scale truss reconstructed employing a traditional all-wooden joints
Milch, J.; Tippner, J.; Sebera, V.; Kunecký, Jiří; Kloiber, Michal; Navrátil, M.
2015 - English
The assessment of mechanical behaviour of all-wooden joints used in historical timber structures such as churches, castles etc. is currently paid a big attention in the Czech Republic, and Central Europe as a whole. The reasons are (a) a high number of such structures; (b) their significance to the national cultural heritage and maintenance for preserving their cultural value; and (c) missing information about global mechanical behaviour of joints and whole truss structures when loaded. Generally, valuable historical monuments need to be evaluated as regards the structure and safety of all timber elements in the structure for their future preservation [1]. The present paper shows a novel methodology for virtual assessment of mechanical behaviour used in a historically valuable gothic truss structure of St. James's Church in Brno, which is very valuable from both structural and architectural points of view. The church was constructed between1220 and 1724, the used styles including the Romanesque, the Gothic and the Neogothic. Also carpentry master Anton Ebenberger participated [2]. The aim of this paper was to describe the real loading of a joint that corresponds to the real function of a joint in the truss structure during the loading owing to new positions of replacement joints in the truss. Currently, the truss of St. James’s church shows large defects including decayed members; therefore, renovation is needed. The restoration of the truss should be carefully implemented in the structure and analyzed beforehand. Therefore, the numerical approaches based on FEM were used to evaluate the mechanical behaviour of the beam truss with a detailed 3D solid joint.
Keywords:
timber structures; all-wooden joints; mechanical behaviour
Fulltext is available at external website.
The numerical assessment of a full-scale truss reconstructed employing a traditional all-wooden joints
The assessment of mechanical behaviour of all-wooden joints used in historical timber structures such as churches, castles etc. is currently paid a big attention in the Czech Republic, and Central ...
Strengthening of weak historic renders with traditional and innovated consolidation treatment
Slížková, Zuzana; Frankeová, Dita
2015 - English
The presented study was aimed to proof consolidation effects of different families of consolidants: inorganic agents (lime -based or silica-based solutions or sols), organic agents (silicic acid ester based consolidant) and their combination on the characteristics of weak mortars prepared in laboratory with different types of aggregates. Besides exploring consolidant-substrate interaction also the pozzolanic activity of the aggregate and the binder mortar component after reaction with lime (calcium hydroxide solution) was investigated in order to understand and describe the strengthening mechanism into consolidated mortars. As the study was based on experimental research, the production of mortar test specimens represented an important preliminary work. Different mortar components (various types of sand in terms of phase composition, clay, lime) and the same ratio of the aggregate and the binder were used in various mortar mixtures. Various mineralogical types of aggregate were used with the same grain size distribution (600 pieces of tubes of 40 mm in outer diameter, of the height of 40 mm and depth of 4 mm were prepared for testing the compressive strength, for the tension tests 550 thin plates of dimensions 40 mm x 100 mm x 4 mm were cast and 600 beams 20 x 20 x100mm were made for testing the flexural strength and other characteristics of reference and consolidated mortars). The sand used for mortar specimens was characterized by microscopic examination of thin section and also by X-ray diffraction, X-ray fluorescence spectroscopy and thermal analysis. The pozzolanic activity of the sands (reactivity with calcium hydroxide) was determined by means of the thermal analysis and supplemented by wet silicate analysis. The amount of the effective matter in the consolidant was the same for all agents per the square unit for all mortar types and specimen shape. One set of specimens was prepared as the reference set the second set was used for the evaluation.
Keywords:
lime mortar; lime render; consolidating products; lime water; nanolime; consolidation; strengthening
Available in a digital repository NRGL
Strengthening of weak historic renders with traditional and innovated consolidation treatment
The presented study was aimed to proof consolidation effects of different families of consolidants: inorganic agents (lime -based or silica-based solutions or sols), organic agents (silicic acid ester ...
O navrhování v geotechnice podle residuální smykové pevnosti
Koudelka, Petr
2015 - Czech
Příspěvek hodnotí možnosti a efektivitu nové koncepce navrhování na základě reziduální smykové pevnosti. Koncepce návrhů podle reziduální nebo kritické smykové pevnosti není vyzkoušená. K tomu, aby mohla být vyzkoušena a používána, je třeba znalost hodnot residuální smykové pevnosti. V současné době se residuální ani kritické hodnoty v běžné praxi téměř nevyšetřují, i když\njejich znalost může přispět ke spolehlivosti a hospodárnosti návrhů a všeobecně jsou\nprojekčním přínosem. Při návrhu svahů podle residuálních hodnot smykové pevnost, které jsou nejspolehlivější, bude možné stupeň bezpečnosti/součinitele odporu podstatně snížit oproti jeho hodnotám používaným při uvažování vrcholových/efektivních hodnotách. Doporučení jsou součástí tohoto příspěvku. The paper consider on possibility and effectivity of a new concept of ULS design on residual shear strength based. Values of residual shear strength are the most reliable and in opposite, applied peak values of shear strength are the most favorable and applicable for states of small deformations only. The paper presents results of a prior analysis of slope stability and compares designs applying values of residual shear strength and peak shear strength. Some recommendations are included.
Keywords:
residual shear strength; slope stability; peak shear strength
Fulltext is available at external website.
O navrhování v geotechnice podle residuální smykové pevnosti
Příspěvek hodnotí možnosti a efektivitu nové koncepce navrhování na základě reziduální smykové pevnosti. Koncepce návrhů podle reziduální nebo kritické smykové pevnosti není vyzkoušená. K tomu, aby ...
Numerical modelling of a bridge subjected to simultaneous effect of a moving load and a vertical seismic ground excitation
Fischer, Cyril; Fischer, Ondřej; Frýba, Ladislav
2015 - English
A simple beam subjected to a row of regularly distributed moving forces and simultaneous vertical motions of its supports is described using a simplied theoretical model and a nite dierences approach. Several levels of simplication of the structure and input data are supposed. Numerical results conrm legitimacy of the assumptions.
Keywords:
numerical modelling; seismic excitation; moving load
Available in digital repository of the ASCR
Numerical modelling of a bridge subjected to simultaneous effect of a moving load and a vertical seismic ground excitation
A simple beam subjected to a row of regularly distributed moving forces and simultaneous vertical motions of its supports is described using a simplied theoretical model and a nite dierences ...
Changes in dislocation substructure of S235JR steel during fatigue loading
Jandová, D.; Gajdoš, Lubomír; Šperl, Martin; Kaiser, J.
2014 - English
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and corresponding mean life Nf = 17,950 cycles. The microstructure of the steel consisted of ferrite with a small amount of pearlite. The substructure was observed in as received condition and after application of various relative numbers of cycles n/Nf, these being 0.25, 0.50 and 0.75. An irregular dislocation net occurred in the virgin specimen, however, during cyclic loading the dislocations started to accumulate gradually in slip bands and to form a cell substructure in grains of favourable crystallographic orientations. Total dislocation density, dislocation density in slip bands and inter-band distance were measured using transmission electron microscopy (TEM). The total dislocation density was found to slightly decrease and the density in slip bands to increase with increasing number of cycles. The results concerning the dislocation density were compared with changes in the microplastic limit (MPL) which were determined by the measurement of the inductance of the “specimen - coil” system. They consisted in a rapid initial decrease at the first stage of the fatigue process and in a gradual increase during the major part of the life. These changes can be interpreted on the basis of changes in dislocation density as was verified independently by X-ray diffraction and nanoindentation tests. On the basis of the measurement of dislocation density by TEM it appears that changes in MPL can be connected with the dislocation density in slip bands rather than with the total dislocation density.
Keywords:
carbon steel; cyclic loading; transmission electron microscopy; dislocation; inductance
Fulltext is available at external website.
Changes in dislocation substructure of S235JR steel during fatigue loading
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and ...
Assessment of damage propagation in carbon-fibre composite under cyclic loading
Šleichrt, J.; Fíla, T.; Šperl, Martin; Kytýř, Daniel
2014 - English
Carbon-fibre composite is very popular material in aircraft industry. Application of this material is limited by low fragility and low impact resistance. In flight airplane can be initialy damaged by hailstorm or bird strikes. Vibrations of the engine and turbulence during flight may cause propagation of this damage. This study describes the of laser profilometry to investigate post damage under cycling loading.
Keywords:
carbon-fibre composite; damage propagation; laser profilometry
Fulltext is available at external website.
Assessment of damage propagation in carbon-fibre composite under cyclic loading
Carbon-fibre composite is very popular material in aircraft industry. Application of this material is limited by low fragility and low impact resistance. In flight airplane can be initialy damaged ...
On the X-ray micro-tomography measurements of biological samples under compressive loading
Fíla, T.; Kumpová, Ivana; Zlámal, Petr; Kytýř, Daniel; Koudelka_ml., Petr; Doktor, Tomáš; Jiroušek, Ondřej
2014 - English
In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several deformation steps and micro-CT scanning was carried out in each step. Reconstructed three-dimensional data of intact bone sample were used to develop 3D model of the specimen. Data from each deformation step were processed by DVC method for identification of displacement and strain fields and thus for evaluation of deformation response of human trabecular bone sample.
Keywords:
micro-tomography; trabecular bone; compressive test; medical imaging; finite element modelling
Fulltext is available at external website.
On the X-ray micro-tomography measurements of biological samples under compressive loading
In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several ...
Calibration of an image processing tool for analysis of fibre orientation in fibre reinforced composites
Hos, J.; Doktor, T.; Petráňová, Veronika; Kytýř, Daniel
2014 - English
This paper deals with calculation of fibre orientation distribution (FOD) in fibre reinforced composite. The calculation was based on image analysis algorithm applied on image acquired by scanning electron microscope. A composite with oriented fibres was selected to be enable calibration of the algorithm by comparison of the obtained results with FOD declared by the manufacturer.
Keywords:
C/PPS; fibre orientation; SEM; composite
Fulltext is available at external website.
Calibration of an image processing tool for analysis of fibre orientation in fibre reinforced composites
This paper deals with calculation of fibre orientation distribution (FOD) in fibre reinforced composite. The calculation was based on image analysis algorithm applied on image acquired by scanning ...
New devices for diagnostics of historical structures
Hasníková, Hana; Kloiber, Michal; Zíma, Pavel
2014 - English
Two new devices developed at ITAM AS CR for non-destructive testing of materials, especially from historical structures, are presented below. So called microtube is a semi-automatic portable tool for water absorption measurements. The natural stones, mortars and other porous materials can be measured and it is very useful to assess the efficiency of various hydrophobic treatments used within the restoration also. The diagnostic device for in-situ assessment of timber enables direct determination of conventional compressive strength and modulus of deformation in arbitrary depth along timber profile. The semi-destructive method causes a very gentle damage on the structural members.
Keywords:
historical structures; water absorption measurement; timber assessment
Fulltext is available at external website.
New devices for diagnostics of historical structures
Two new devices developed at ITAM AS CR for non-destructive testing of materials, especially from historical structures, are presented below. So called microtube is a semi-automatic portable tool for ...
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