1,720,956 research outputs found
A preliminary investigation on the failure of prestressed members under natural fires
No full textThe present work is aimed at investigating the behaviour of prestressed concrete members under the effects of natural fires, that are characterized by the presence of a cooling phase. To this aim, several numerical analyses were carried out on a typical P/C section in order to highlight the most significant parameters. The results show that the high insulating power of concrete, together with the rate of cooling, play a decisive role for the failure probability of P/C members in the cooling phase
Prestressed members under natural fires: a preliminary study on the residual behaviour
Full text linkThe present work is aimed at investigating the residual behaviour of prestressed concrete members exposed to natural fires, since experience has shown that substantial losses of the load bearing capacity may take place during the cooling phase. This topic is of great practical significance, because the knowledge of the residual response can help the engineers to decide whether a structure can be refurbished after being exposed to fire, with minor costs, or whether demolition is inevitable. Sequentially coupled thermo-mechanical analysis was performed on typical inverted T and double T-beam sections, subjected to heating and subsequent cooling. The results show that the residual deflection is primarily governed by the load level and the section shape and that the magnitude of the residual deflection can be even several times higher than the initial value
On the structural behavior of reinforced concrete walls exposed to fire
No full textThe present work deals with numerical simulations concerning the international benchmark "Vulcain tests on 3 Walls" regarding fire tests conducted in CSTB in Paris, France. To this aim, sequentially-coupled thermo-mechanical analyses have been performed on three reinforced concrete walls, characterized by different load levels and boundary conditions. The numerical results show that the imposed compressive load and boundary conditions significantly influence the magnitude of the displacements. In the case of simply supported walls, the wall with the lower load level exhibited a gradual and monotonic increase of the displacements at mid-height (both in the tests and in the numerical analyses), while the wall with the higher load level exhibited a displacement reversal due to second-order effects after approximately 60 minutes of fire exposure. This reversal, which was obtained in the analyses, was not observed in the test. Load bearing capacity of all the three specimen walls was maintained in such a way that the collapse did not take place during two hours of fire exposure
On the structural behaviour of prestressed concrete members subjected to heating and subsequent cooling
No full textLAUREA MAGISTRALEPrestressed concrete members are very popular solution in variety of structural applications. Naturally, their performance in fire became a popular topic, yet not completely investigated and not even to the same extent as reinforced concrete members.
Studying the thermo-mechanical response of prestressed members in fire implies the cooling phase to be taken into account, as real fires are characterized not only by an ascending branch, where the temperature is monotonically increasing until it reaches its maximum value, but also by a decay phase, where the temperature tends to go down, back to the ambient temperature. While the behaviour of P/C members at elevated temperatures was the main topic of few research studies, its behaviour during and after cooling still remains an open issue. Most of the engineering codes and common engineering practices do not explicitly take into account the residual material properties, which are certainly different from the, so-called “hot” properties. Lack of experimental data on the residual and post-fire properties makes it more difficult to build up a comprehensive and reliable numerical approach, but also to define material properties and constitutive laws which can accurately represent the behaviour of a material that is heated and subsequently cooled down.
Sequentially coupled thermo-mechanical sectional analysis was conducted on four prestressed concrete simply supported beam sections, aiming to study the mechanical response, caused by thermal gradients as well as externally applied loads, at elevated temperature but also during the subsequent cooling phase. For that purpose, Visual Basic codes were developed by the Author. The influence of different parameters was investigated, and the maximum temperature in the strands and the load level were recognized as the most important ones, in view of the accurate interpretation of the failure in the heating or cooling phase, as well as the residual behaviour
On the role of materials properties and structural context in reinforced concrete members exposed to natural fires
Full text linkIl fuoco è uno dei pericoli più gravi che una struttura può sperimentare durante la sua vita utile. Dato che la maggior parte delle strutture in calcestruzzo armato è in grado di resistere all’intera fase di riscaldamento-raffreddamento, investigare il comportamento residuo ed il danno subito durante l'incendio diventa la priorità.
Tuttavia, l'attuale pratica di progettazione si concentra solo sulla fase di riscaldamento, fornendo pochissime indicazioni sul comportamento durante il raffreddamento e nella fase residua. La maggior parte delle conoscenze sul comportamento strutturale di elementi in calcestruzzo armato al fuoco proviene da test standard; quindi la maggior parte degli studi disponibili in letteratura sono focalizzati sul comportamento strutturale nella fase di riscaldamento. Manca ancora una chiara base comune per eseguire analisi relative agli incendi che coinvolgono riscaldamento e raffreddamento. Questa tesi si occupa dell'analisi strutturale di travi e pilastri tipici in calcestruzzo armato e precompresso, sulla base di tre diversi approcci di modellazione: analisi sezionale, analisi agli elementi finiti tramite elementi di tipo trave e analisi agli elementi finiti tramite elementi 3D. Lo scopo di questa tesi è duplice: (a) studiare il ruolo delle proprietà dei materiali nella fase di raffreddamento sul comportamento strutturale; (b) fornire una panoramica sulle possibili strategie di modellazione, evidenziando gli aspetti specifici della fase di raffreddamento.Fire is one of the most severe hazards that a structure can experience during its service life. Given that the most of the RC structures are able to survive the full heating-cooling phase, investigating the residual behaviour and suffered damage during fire becomes the priority.
Still, the current design practice focuses only on the heating phase, giving very little indication on the behaviour during cooling and in the residual phase. Most of the knowledge on the structural behaviour of RC members in fire comes from standard testing; therefore most of the studies available in the literature are focused on the structural behaviour in the heating phase. A clear common background for performing analyses as regards fires involving heating and cooling is still missing.
This thesis deals with the structural analysis of typical reinforced and prestressed concrete beams and columns, on the basis of three different modeling approaches: sectional analysis, finite element analysis via beam elements and finite element analysis via 3D elements. The aim of this thesis is twofold: (a) to investigate the role of materials properties in the cooling phase on the structural behaviour; (b) to give an overview on the possible modeling strategies, highlighting the particular aspects of the cooling phase.DIPARTIMENTO DI INGEGNERIA CIVILE E AMBIENTALE31PANDOLFI, ANNA MARINAPEREGO, UMBERT
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
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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