1,720,959 research outputs found
A design method for the prediction of load distribution in hollow-core floors
No full textA general design method is provided to predict the load distribution at serviceability condition in hollow-core floors formed by precast units linked together through cast in place reinforced concrete joints. Each panel forming the floor is schematized as a Saint-Venant beam connected to the others by means of rotational hinges. In this way, the only unknowns of the solving system, characterized by an exponential dichotomy, are represented by shear forces transmitted along joints. The model is first validated through comparisons with significant experimental results available in the literature, and subsequently applied to the construction of design charts to be used in current practice. These latter are also compared with the provisions on load distribution effects suggested by European Standard UNI EN 1168, pointing out some limitations of current design procedures and suggesting possible improvements
Numerical simulation of RC beams reinforced with FRCM
No full textFRCM (Fibre Reinforced Cementitious Matrix) system consists in two or more layers of cementitious mortar, in which a dry grid of fibres is disposed. This strengthening technique overcomes some of the limits of traditional systems, like FRP. Indeed, the presence of the mortar assures a better compatibility with the surface of the structural element, which could be either concrete or masonry. Moreover, FRCM can resist at higher temperatures and it can lead to a more ductile failure of the reinforced element. In this work, the attention is focused on the analysis of reinforced concrete (RC) beams retrofitted by FRCM. To this aim, both the behaviour of RC beams and of FRCM composite material is modelled through proper non-linear models implemented into a Finite Element (FE) code. The proposed approach is subsequently validated through significant experimental data relative to strengthened RC beams, available in technical literatur
A non-linear constitutive relation for the analysis of FRCM elements
No full textAbstractNowadays, the strengthening of existing buildings represents one of the most innovative fields within current research in civil engineering. Among the developed techniques, a recent solution consists in the use of FRCM composites (Fabric Reinforced Cementitious Matrix), which are obtained by placing a dry grid of fibers inside a cement-based material (mortar). In comparison with traditional systems, the use of FRCM seems to provide some advantages; however, a full understanding of the mechanical properties of each component (mortar and fibers) and of their interaction, as well as their effect on the strengthened structure, still represents an open research topic. This work aims to be a first attempt to numerically simulate the global behavior of FRCM composites through the development of a macroscopic constitutive model subsequently implemented into a Non-Linear Finite Element (NLFE) procedure. The effectiveness of the proposed procedure is verified through comparisons with significant experimental results available in technical literature, relative to FRCM tension ties. The influence exerted by the adoption of different materials (such as Poliparafenilenbenzobisoxazolo (PBO) and carbon) for the internal fiber grid on the global behavior is also analyzed and discussed
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
Experimental and numerical study on cement-based composites (FRCM) for the strengthening of RC structural members
No full textIl presente elaborato di tesi verte sullo studio di sistemi di rinforzo a matrice cementizia addizionata con fibre inorganiche, conosciuti come FRCM (Fiber-Reinforced Cementitious Matrix). Il materiale investigato, impiegato per il rinforzo di elementi strutturali in cemento armato e muratura, è stato solo recentemente introdotto sul mercato, non è ancora normato in tutti i paesi ed è pertanto oggetto di numerosi studi e ricerche al fine di caratterizzarne in modo approfondito il comportamento meccanico e l’interazione col supporto.
In relazione a ciò, la ricerca è stata condotta seguendo due filoni principali. Il primo filone è stato rivolto alla modellazione e simulazione numerica del comportamento meccanico del materiale e degli elementi rinforzati con questa tecnica, mentre il secondo ha riguardato l’esecuzione di una serie di prove sperimentali volte alla determinazione delle proprietà meccaniche del composito e dei suoi componenti, in particolare della malta cementizia.
Dopo aver analizzato la letteratura tecnico-scientifica relativa sia ai sistemi di rinforzo più tradizionali che agli FRCM, si è proceduto allo sviluppo di un legame costitutivo per lo studio del materiale composito. In particolare, si è adottato un approccio continuo in cui, nei diversi stadi del materiale (prima e dopo la comparsa della fessurazione), i contributi irrigidenti legati alla matrice e alla rete sono valutati separatamente e poi combinati tra loro in modo da formare la matrice di rigidezza del materiale, implementata in un codice di calcolo ad elementi finiti. Nello stadio non fessurato si è assunta l’ipotesi di perfetta aderenza tra la malta e la rete di rinforzo, considerando un comportamento elastico-lineare per entrambi i materiali. Nella fase fessurata, la deformazione totale è assunta pari alla somma della deformazione del materiale tra le fessure e di quella della fessura.
L’efficacia del modello è stata quindi verificata effettuando dei confronti con numerosi risultati sperimentali reperiti in letteratura scientifica, relativi sia a tiranti in FRCM, che a travi in c.a. rinforzate a flessione. Tali confronti hanno messo in luce un ottimo accordo tra i risultati numerici e sperimentali.
Al fine di meglio indagare alcuni parametri utili per la messa a punto di idonei legami costitutivi presenti nel modello meccanico proposto, è stato deciso di effettuare una campagna di prove sperimentali rivolta alla caratterizzazione meccanica della malta, nonché dell’intero composito FRCM. Nello specifico, si sono eseguite prove a flessione su prismi di sola malta per la determinazione della resistenza a trazione per flessione e per ottenere l’energia specifica di frattura. Al fine di integrare i dati ottenuti e per avere una correlazione analitica tra la resistenza a trazione diretta e quella flessionale apposita per il materiale in questione, si è proceduto ad eseguire ulteriori prove di trazione diretta su provini a “osso di cane” di sola malta. Oltre a ciò, si è studiato il comportamento dell’intero composito, eseguendo delle prove a trazione diretta su provini prismatici in FRCM. Le prove sono state eseguite nel laboratorio di “Prove materiali e strutture” dell’Università di Parma e le rielaborazioni sono state eseguite anche mediante l’uso della DIC (Digital Image Correlation). Dalla campagna sperimentale si è ottenuta una serie di dati utili per una corretta calibrazione del legame costitutivo. Tra questi si annoverano, per la malta cementizia, il coefficiente di Poisson e il modulo di elasticità normale, nonché l’energia specifica di frattura. Per quanto concerne l’intero composito FRCM, si sono ottenute informazioni utili in termini di carico-spostamento e soprattutto una conoscenza della distanza e dell’apertura di fessura che sono dati difficilmente reperibili in letteratura.This work aims to study a new strengthening material, which is formed by a cement-based mortar enriched by inorganic fibers, known as FRCM (Fiber- Reinforced Cementitious Matrix). The investigated material, which is used to strengthen structural elements made of reinforced concrete and masonry, has been only recently launched on the market consequently, it is not yet regulated in all the countries and, it is still object of several studies and research works, in order to deeply characterize its mechanical behaviour and its interaction with the support.
In relation to this, the research carried out in this work was structured into two main branches. The first one was the modeling and the numerical simulation of the material and of the elements strengthened with this technique, while the second one was relative to the execution of a series of experimental tests for the determination of the mechanical properties of both the composite and its components.
After the analysis of the technical literature relative to both traditional reinforcing techniques and to FRCMs, a constitutive model was developed to study the nonlinear behavior of the composite material. In more detail, a continuous approach was adopted. Both in the uncracked and cracked stages, the stiffening contributions related to the mortar and to the fiber grid were separately evaluated, and then combined to each other in order to build the material stiffness matrix, implemented into a finite elements code. In the uncracked stage, perfect bond between the mortar and the fiber grid was assumed, hypothesizing a linear-elastic behavior for both the constituent materials. In the cracked stage, the total strain was assumed as the sum of the strain of the material between the cracks, and that in the crack.
The effectiveness of the proposed model was then verified by carrying out several comparisons with experimental results from the technical literature, relative to both FRCM tension ties, and RC beams retrofitted in bending. These comparisons showed an excellent agreement between numerical and experimental results.
However, in order to better investigate some parameters required for the calibration of the constitutive models adopted in the proposed mechanical model, it was decided to perform an experimental campaign, devoted to the mechanical characterization of the cement-based mortar and of the whole FRCM composite.
In more detail, flexural tests on prismatic specimens of mortar were first made so as to determine the flexural strength and the material fracture energy. These latter allowed to complete the obtained data on the mortar and to find an analytical correlation between the tensile and the flexural strength of the material. Further tensile tests on “dog bone” specimen of mortar were also made.
In addition to this, the behavior of the whole composite was studied, by performing tensile tests on prismatic FRCM specimens. All the tests were carried out at the “Testing Laboratory of Materials and Structures” of the University of Parma. The post-processing was made by also using the DIC technique (Digital Image Correlation). As already stated, the experimental campaign allowed to obtained several data required for the correct calibration of the constitutive model. Among these, the Poisson’s coefficient, the normal elastic modulus and the fracture energy for the mortar were calculated. As regards the entire FRCM composite, useful information in terms of load-displacement behavior and, above all, the knowledge of the cracking distances and openings, hardly available in the literature, were obtained
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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