Wyniki wyszukiwania - BazTech

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Zastosowanie techniki dzielonego pręta Hopkinsona do badania wpływu skrępowania bezwładnościowego na dynamiczną odpowiedź mechaniczną betonu

Pająk Małgorzata, Janiszewski Jacek, Baranowski Paweł, Pytlik Mateusz

Inżynieria i Budownictwo

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2023

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R. 79, nr 9-10

547--551

PL

W pracy przedstawiono wyniki dynamicznych badań wytrzymałościowych próbek betonowych skrępowanych tuleją ołowianą z wykorzystaniem techniki dzielonego pręta Hopkinsona. Przeanalizowany zakres dużych szybkości odkształcenia wynosił od 80 s-1 do 194 s-1. Wykazano przyrost wytrzymałości betonu wynikający nie tylko z wrażliwości badanego betonu na szybkość odkształcenia, ale także ze skrępowania, które w warunkach dynamicznego obciążenia wywołuje dodatkowe efekty bezwładnościowe.

EN

In the paper, the results from the SHPB tests of concrete specimens confined with the lead covers are presented. The analysed high strain rate was from 80 s-1 to 194 s-1. The increase of the compressive strength was noted due to strain rate sensitivity of concrete but also to confinement which caused additional inertial effects.

2

Behavior of RC columns strengthened with steel jacket under static axial load

Ghoneim Abd Rahman Mujahid Ahmed, Mohamed Mohamed Mahmoud Ahmed, Haridy Kader, Ahmed Hazem, Pyram Mohmmad, Khalf Abdu

Archives of Civil Engineering

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2023

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Vol. 69, nr 2

367--379

EN

The column is one of the most significant structural elements, which is designed to support mainly the compressive load. Strengthening of existing reinforced concrete columns is required to enhance ductility and increase load capacity to sustain the overload as sometimes there may be a change in use. Ten rectangular concrete columns were constructed and tested. H/b ratio was kept constant and equals 6 for all columns. The aim of this work is to study the behaviour and efficiency of RC columns strengthened with steel jackets subjected to axial load. An experimental study of the behaviour of ten strengthened concrete columns with slenderness ratio (H/b) equals 6 was carried out. Variables such as aspect ratio (t/b), the volume of steel batten plates, and spacing of steel batten plates at centres (S) were considered. The results showed that using this method of strengthening is very effective and an increase in the axial load capacity of the strengthened columns is obtained.

3

Sejsmiczność górotworu w rejonach przygranicznych kopalń węgla kamiennego na tle lokalnych uwarunkowań geologiczno-górniczych

Dzik Grażyna, Chlebowski Dariusz

Bezpieczeństwo Pracy i Ochrona Środowiska w Górnictwie

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2020

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nr 11

11--17

PL

Doświadczenia kopalń Górnośląskiego Zagłębia Węglowego wskazują, że elementem sprzyjającym generowaniu ponadprzeciętnej aktywności sejsmicznej są zaszłości eksploatacyjne, a wysoki stopień skrępowania wynikający z ich istnienia dotyczy wielu obszarów przygranicznych. Na przykładzie trzech rejonów eksploatacyjnych w sąsiedztwie granic obszarów górniczych dokonano w artykule analizy zagrożenia sejsmicznego towarzyszącego prowadzeniu dziewięciu ścian. W ramach próby powiązania poziomu aktywności sejsmicznej z lokalnymi warunkami geologiczno-górniczymi jako kryterium wykorzystano zmienność takich jej parametrów, jak: ogólna liczba i energia zjawisk, jednostkowy wskaźnik wydatku energetycznego, średnia energia i liczba zdarzeń przypadających na 1 m.b. postępu oraz średnia energia pojedynczego zjawiska sejsmicznego.

EN

The element conductive to generation of above-average seismic activity are issues related to past exploitation, and the high degree of restraint stemming from their existence concerns many border areas. Using 3 mining zones located in the vicinity of extraction area borders as an example, the article analyses the seismic hazard related to exploitation of nine longwalls. Substantive discussion is preceded by a generał description of geological and mining conditions and properties of the rock mass in the mining zones as well as components of the extraction system. The criterion used in the attempt to link the level of seismic activity with the local geological and engineering conditions was the variability of such parameters of seismic activity as: total number and energy of events, unit energy expenditure, mean energy and the number of events per linear metre of advancement as well as mean energy of a single seismic event. The erected boundary pillars are characterised by a highly irregular geometry and course, which complicates the process of designing and conducting of mining activities in their vicinity, especially with respect to seams located above and below. An additional problem for conducting excavations in such zones is the varied, but high, seismic activity in areas with boundary pillars, as evidenced by the obtained results, on the basis of which it is possible to conclude that the probable causes of that seismic activity were: the advancement of mining works in conjunction with successive narrowing of the face belt along the border of the extraction area, approaching of the excavation to the immediate vicinity of abandoned workings, the length of excavated longwalls as well as geological and engineering properties.

4

Stress-strain model for confined fiber-reinforced concrete under axial compression

Sabariman B., Soehardjono A., Wisnumurti, Wibowo A., Tavio

Archives of Civil Engineering

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2020

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Vol. 66, nr 2

119--133

EN

Confinement in concrete can improve the descending branch of the stress-strain relationship of concrete. The addition of steel fiber in concrete can also improve the descending branch of the stress-strain relationship of concrete. The combination of the use of both can double the impact significantly on the post-peak response. It can be seen from the trend of the post-peak response that the values of both 0.85fccf and 0.5fccf can be well predicted. The study involved an experimental investigation on the effect of confinement on square column specimens reinforced with steel fiber. From the experimental program, it is proven that the use of combination of confining steel and steel fiber works very well which is indicated by the better improvement on the post-peak response. The proposed equations can predict the actual stress-strain curves quite accurately which include the effects of confinement parameters (Zm) and steel fiber volumetric parameter (Vf).

5

The molecular dynamics of nematic liquid crystal confined in porous membranes treated by different surfactants

Różański Stanisław Andrzej

Opto-Electronics Review

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2019

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Vol. 27, No. 4

339--344

EN

The molecular dynamics of the well-known nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl geometrically restricted in Anopore and Synpor porous membranes with various pore structure and treated by different surfactants (namely decanoic acid and lecithin) is compared. In the Anopore membrane the chosen surfactants induce the homeotropic orientation of the molecules on the walls of the cylindrical pores and observed corresponding relaxation processes (librational modes) are practically the same. The dielectric measurements of lecithin treated Synpor membranes reveals the reorientation of the molecules from planar to homeotropic on the complex multilayer structure present in their volume. The dielectric strengths of the observed two molecular processes (δ-process and librational mode) are inversed in the ratio compared to the untreated membranes. The observed differences in molecular dynamics results from the orientation of the liquid crystal molecules in untreated and treated membranes and the structure of the membranes themselves.

6

Możliwości zupełnego wykorzystania właściwości betonu komórkowego

Drobiec Łukasz, Jasiński Radosław

Cement Wapno Beton

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2019

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R. 22/84, nr 5

383--399

PL

Przeprowadzony duży program badawczy posłużył głównie do lepszego poznania właściwości murów z autoklawizowanego betonu komórkowego oraz wpływu różnych czynników, które powinny być uwzględniane lub pomijane na etapie projektowym. Jak wykazano ważny okazał się wpływ wilgotności ABK, który w normach jest arbitralnie ustalony. Równie ważny jest wpływ rodzaju zaprawy oraz technologii układania zbrojenia, w spoinach wspornych. Wyniki uzyskiwane na elementach dużych i średnich wymiarów wykazały wpływ zbrojenia, który w normach jest zupełnie pomijany. Dalsze prace będą służyć wykorzystaniu uzyskanych wyników do analitycznych modeli nośności ścian ściskanych i ścian usztywniających ścinanych, z uwzględnieniem możliwości najlepszego stosowania ABK. Na wstępie wykorzystane zostaną zalecenia Eurokodu PN-EN 1990, dopuszczającego zastosowanie metod projektowania, wspomaganego badaniami, w celu weryfikacji zaproponowanych modeli.

EN

The extensive research programme was mainly used to learn details about properties of AAC masonry and the effect of various factors, which should be included or neglected at the design phase. Moisture content of AAC was found to have a significant effect, arbitrary defined in standards. The type of used mortar and technology of reinforcement embedding in bed joints is also very important. Results obtained for large and middle-size units indicated the significance of reinforcement, which is completely neglected in standards. Further works will focus on employing the obtained results in analytical models of load-bearing capacity of compressed walls and shear stiffening walls, taking into account the best possible use of AAC. At first, recommendations of Eurocode PN-EN 1990 which allows for design methods based on tests to verify the proposed models.

7

Experimental and analytical investigation on strengthening of heat damaged concrete by textile reinforced concrete (TRC)

Esmaeili J., Sharifi I., Kasaei J., Nourizadeh M., Emamieh A. Ebrahim

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1468--1483

EN

Composites fabricated of textile as reinforcement and a fine-grained concrete as matrix are referred to textile reinforced concrete (TRC) which provides the opportunity to build thin and shell constructions and to repair and strengthen concrete and masonry structures. This paper aimed to exploit the repair potential of TRC through confinement of heat-damaged concrete columns. For this purpose, a two-phase approach was conducted, in the first phase of which the effect of elevated temperature on mechanical properties of concrete was examined. The main objective of the second phase, however, was to assess the efficiency of glass textile reinforced concrete (GTRC) in the confinement of heat-damaged concrete. This phase commenced with selecting a candidate mortar among commonly used TRC mortars to confine heat-damaged specimens. Experimental results revealed that the adopted confinement system is an efficient solution to enhance the load bearing capacity of even seriously heat-damaged specimens. Eventually, experimental results were compared with available prediction models from the literature for both of the load-bearing capacity and also the compressive strength of confined concrete. Then an analytical confinement model was proposed based on best-fit analysis exclusive to heat-damaged concrete confined by GTRC.

8

Behavior of eccentrically loaded rcc columns confined with frp sheets

Chakrabarti A., Bhargava P.

International Journal of Applied Mechanics and Engineering

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2011

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Vol. 16, no 4

943-958

EN

A nonlinear finite element model is developed for the analysis of an RCC (reinforced concrete column) confined by FRP (fiber - reinforced polymers) sheets and subjected to eccentric loading. A practical design of FRP confined concrete columns requires an accurate estimate of the performance enhancement due to the confinement mechanism under eccentric loading. Therefore, a confinement model is developed which relates the confined concrete strength with the unconfined concrete strength. In the present study, a 3-D finite element model is developed using the finite element software, ANSYS for the analysis of an FRP confined reinforced concrete circular column under axial and eccentric loading. The effects of four important parameters are studied in the present work: namely, the unconfined concrete strength, FRP thickness with different layer orientation, orthotropic properties of FRP and orientation of FRP fibers. The study focused on some interesting effects of these parameters on the confinement effectiveness of eccentrically loaded reinforced concrete columns. Many new results are generated which should be useful for future references.

9

Phase transitions in confined lamellar phases

Ciach A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2007

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Vol. 55, nr 2

179-186

EN

Effects of confinement on mechanical, structural and thermodynamic properties of uniform fluids are very well understood. In contrast, a general theory based on statistical thermodynamics for confined nonuniform and non-isotropic phases, such as the lamellar phase, is in its infancy. In this review we focus on the lamellar phase confined in a slit or in a pipe in order to illustrate various effects of confinement. We limit ourselves to the results obtained by M. Tasinkevych, V. Babin and the author for lamellar phases in oil-water-surfactant mixtures within a generic semi-microscopic model, using a mean-field approximation. We show that compared to isotropic fluids the excess grand potential contains additional terms associated with structural deformations. These terms depend on the type of the confining walls, the shape of the container and on the thickness of the lamella. As a result of the dependence of the structure of the confined lamellar phase on the shape of the container, capillary lamellarization and capillary delamellarization is found in slits and in pipes respectively.

10

Material modeling of concrete subjected to multiaxial loading: application to pull-out analyses

Pivonka P., Lackner R., Mang H. A.

Archives of Mechanics

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2001

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Vol. 53, nr 4-5

487-499

EN

This paper deals with the application of 3D-constitutive models for concrete to simulations of pull-out experiments [1]. Two different models are considered: The first material model is formulated within the framework of multi-surface plasticity. It consists of three Rankine yield surfaces for the simulation of cracking and a Drucker-Prager yield surface for the description of compressive failure of concrete. The Drucker-Prager surface is reformulated in order to account for the influence of confinement on the compressive strength and the ductility of concrete. The formulation of the second model, the Extended Leon Model (ELM) [4], is based on one yield function for description of compressive and tensile failure of concrete. It accounts for the influence of the Lode angle on the material strength. The simulation of ductile behavior of concrete is controlled by means of a pressure-dependent ductility function. The predictive capability of the models is demonstrated by means of a finite element (FE) analysis of a pull-out test [1]. The influence of confinement on the peak load and the failure mode is investigated.

11

Effect of confinement to porous glass on structure and optical properties of alkylcyanobiphenyls.

Bezrodnaya T., Gavrilko T., Gnatyuk I., Yaroshchuk O., Puchkovskaya G., Baran J., Ratajczak H., Kukielski J.I.

Optica Applicata

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2000

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Vol. 30, nr 4

585-590

EN

The 4-n-alkyl-4'-cyanobiphenyls (nCB, n is the number of carbon atoms in alkyl radical n=5, 8) confined to porous glasses with four different mean pore sizes (2, 4, 54 and 90 nm) have been studied. Using FT MIR and NIR spectroscopy methods we have investigated the interaction of nC8 molecules with the pore surface. It has been shown that the interaction is accompanied by the formation of hydrogen bonds between the SiOH group on the glass pore surface and the cyano-group of the nCB monomer. This is demonstrated by the change in the position and shape of CN stretching and Q(C identical to N)+Q(C=C) combination bands in the vibrational spectra of confined nCB depending on pore size and the length of the alkyl tail. To the contrary, in the case of benzophenone confined to PG, weak pi ...OH-Si hydrogen bonds are formed.