1,720,963 research outputs found
Effect of hot and cold temperature on the mechanical behaviour of macro-synthetic fiber reinforced concretes
No full textFiber reinforced concretes (FRCs) are used in many civil engineering applications, i.e. industrial floors, tunnels, etc., given their ability of reducing concrete cracking. Besides their mechanical characteriza-tion, the effect of the environmental conditions, i.e. temperature, need to be properly understood.
The present paper presents results of experimental tests on the effects of hot and cold temperatures, from -30 °C to + 60 °C, on the mechanical performances of FRCs containing polypropylene fibers. The results show that the temperature affects the compressive, tensile and residual flexural strength of the material
Study of temperature variation effect on MSFRC long term behaviour
No full textThe long-term behaviour of Fiber Reinforced Concrete is a topic still under investigation. Apart from the conditions related to the serviceability states, environmental conditions affect the material behaviour. The present work is focused on macro-synthetic fibres used as reinforcement. In fact, polymers suffer from creep and temperature affects their mechanical characteristics. Therefore, it is important to understand and develop predictive models for these phenomena. The paper presents the results of an experimental campaign on cracked FRC cylinders in uniaxial tensions, under sustained loads at temperatures from 20°C to 40°C. Moreover, a first approach towards a numerical predictive model accounting these phenomena is described. / Il comportamento dif-ferito nel tempo di materiali compositi fibrorinforzati è un tema ancora oggetto d’indagine. Oltre alle condizioni di servizio, le con-dizioni ambientali influiscono sul comportamento del materiale. Il presente lavoro fa riferimento al comportamento di calcestruzzi rinforzati con fibre macro-sintetiche. I polimeri infatti presentano deformazioni viscose e le loro proprietà meccaniche sono influen-zate dalla temperatura. Risulta quindi importante comprendere e prevedere come questi fenomeni possano influenzare il comporta-mento di elementi strutturali e non strutturali. La memoria mostra i risultati di una campagna sperimentale su provini fessurati in cal-cestruzzo fibrorinforzato in regime di trazione, mantenuti sotto carico costante ed esposti a temperature crescenti tra 20 °C e 40° C. Inoltre, è descritto un primo approccio verso la calibrazione di un modello numerico predittivo dell’effetto di queste variabili sul comportamento del materiale
High Performance Fibre Reinforced Concrete: optimization of the concrete matrix with porcelain stoneware powder
No full textUHPFRCs feature high performance in terms of compressive strength (> 150 MPa – 21755 psi) and tensile
strength (> 5 MPa – 725 psi). Compared to normal concrete, their matrix is designed with lower water/cement ratios (
0.25), higher cement content and smaller aggregate size. Since their crack pattern is typically characterized by small
cracks, the use of short fibers to reinforce the matrix is more appropriate. In general, UHPFRC production requires plenty
of non-renewable natural raw materials with polluting emissions mainly related to the high dosage of cement. In this
framework, the presented work proposes the usage of porcelain stoneware waste powders from rectification, as part of
fine-grained components. The paper presents preliminary results of an experimental campaign aimed at optimizing the
flexural and compressive performances of concrete admixtures with porcelain stoneware waste materials, using design of
experiments. All the admixtures contained the same quantity of PVA fibers. The performances of the mixes were
evaluated by means of four point bending and compressive tests, performed after 28 and 60 days. Introducing stoneware
waste powders it was possible to obtain high strength materials with a reduced cement content
Lattice Discrete Particle Modeling of MSFRC material
No full textFiber Reinforced Concrete (FRC) is an innovative composite material whose important capabilities are currently investigated both experimentally and numerically. The development of a reliable predictive numerical model requires the careful consideration of concrete heterogeneity and random or oriented arrangement of fibres reinforcement. Among the most validated theories, the Lattice Particle Discrete Model (LDPM) effectively simulates the concrete composite behaviour derived from the interaction of aggregates: the meso-structure of the quasi-brittle material is designed with polyhedral particles reflecting the actual coarse aggregate distribution. The LDPM theory was previously extended to account for the fibers crack-bridging effect, typical of FRCs. In this first step of a larger study, the short-term capabilities of the model are studied before investigating the sustained load response. Experimental results from FRC with 8 kg/m3 of polypropylene (PP) macrofibres are used to calibrate the numerical model, presenting many considerations preliminary the model validation
Experimental investigation and numerical modelling of macro-synthetic fibre reinforced concrete materials
No full textFibre Reinforced Concretes are innovative composite materials covering a plenty of structural applica-tions. The mechanical behaviour of these materials has been studied by many researchers, and many official guidelines cover their usage. Nevertherless, many aspects are still under investigation above all its long term performance and time dependent phenomena. The whole research project is aimed at un-derstanding which ascpets, that could be represented by the material properties or external factors, could affect the mechanical behaviour. The investigation is carried on by means of experimental tests on FRCs characterized by different strengths of the matrix, different fibre dosages and different fibre types. The experimental part is the starting point for the elaboration of a numerical predictive model because the prediction of the cracking mechanisms evolution typical of FRCs is the key for the design with fibre reinforced concrete materials. On the other side, the time dependent phenomena affect the behaviour and the serviceability state of the material. The time and the environmental conditions play an important role in the deformations evolution over time. In a first step, the experimental investigation is carried analysing the effect of compressive, tensile and flexural load aimed at studying the separated contribu-tions. The hetereoneneity of the concrete mixed with the discontinuity of the reinforcement need to be accounted. For this reason, based on the experimental results achieved, a numerical predictive model is going to be elaborate. It is straightforward to think that the composite nature makes necessary the char-acterization of the fibrous reinforcement, concrete matrix and their mechanical bond interaction. The present work shows a part of the entire research project. In particular, it discusses the effect of macro-synthetic fibres in cementitious matrixes analysing their short term mechanical performance. Three concrete strength classes, from 33 MPa to 55 MPa are combined with 2 kg/m3 and 4 kg/m3 of fibre dosages. The experimental results are used to calibrate a numerical predictive model based on the Lat-tice Particle Discrete Model constitutive law
Calibration of the viscoelastic behavior of polypropylene fiber reinforced concrete with the extended Lattice Discrete Particle Model approach
No full textFiber reinforced concrete (FRC) is a composite material whose adoption is becoming widespread. The ability of exhibiting remarkable residual capacity after cracking of the cementitious matrix represents its characteristic feature.
At present, studies dealing with the mechanical characterization of this material are mainly focused on the analysis of the mechanical behavior under short-term conditions. On the other hand, a comprehensive identification of FRC performance requires also the investigation of the rheological properties and the long-term behavior. To this purpose, some researches are making first steps towards the standardization of the creep testing methodologies for FRCs, together with the study of the relevant aspects influencing their time-dependent behavior.
On the other side, the numerical simulation of the FRCs behavior is another challenging topic, due to the composite nature of the material. In particular, the reliability of the model is often driven by the method of introducing the concrete heterogeneity and the fiber distribution. Among the others, the extended lattice discrete particle model (LDPM-F) approach is able to describe the instantaneous composite material behavior through the inclusion of fibers and the simulation of the crack-bridging effect responsible for the FRCs residual strength. At the same time, conventional LPDM model can be coupled with the HTC model and the microprestress solidification theory to fully reproduces the concrete viscoelasticity and aging properties.
In the present paper, a new version of LPDM model has been proposed, where both a concrete viscosity and a fiber viscosity are utilize to describe the long-term behavior of FRC. In the case of plastic fibers (MS), the contribution of fibers to the creep deformation is remarkable. The numerical predictive model has been calibrated with respect to experimental results obtained from instantaneous and creep tests on macro-synthetic fiber reinforced concrete (MSFRC) with polypropylene fibers. In particular, fiber viscoelasticity has been calibrated against tensile creep tests for a single fiber. The validated model has been then used to predict the long-term elongation of pre-cracked notched MSFRC cylinders under the uniaxial tensile stress. Results show that the presented numerical scheme is able to capture this complex behavior
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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