1,720,984 research outputs found
Refining the masonry shear modulus in masonry towers via Bayesian model updating
Get PDFThe assessment of the structural behavior of masonry towers often involves developing and identifying computational models to be used to perform static and/or time-history nonlinear analyses. Such models are frequently developed assuming isotropic masonry behavior, with model identification carried out - based on available experimental data - through deterministic tuning of a limited set of representative parameters. However, masonry exhibits complex structural textures that often deviate significantly from the commonly made assumption of isotropic behaviour. This paper investigates the effects of this assumption by focusing on the masonry shear modulus. A two-dimensional rigid body–spring model is adopted as computational approach, as its fully discrete formulation allows overcoming the limitations of the Cauchy continuum while maintaining a reduced computational cost. A Bayesian updating framework based on dynamic experimental data is employed to account for multiple sources of uncertainty, including parameter uncertainty, model inadequacy, and observation errors. Three masonry towers with different slenderness ratios are considered as representative case studies. The adopted Bayesian model updating approach allows for the estimation of their shear modulus while accounting for uncertainties, and the results show that the common assumption of isotropic behaviour in masonry numerical modelling does not hold. Using a fully discrete computational approach in combination with experimental frequency data, this behaviour has been observed for squat masonry towers
Comparison between Bayesian updating and approximate Bayesian computation for model identification of masonry towers through dynamic data
Get PDFModel updating procedures based on experimental data are commonly used in case of historic buildings to identify numerical models that are subsequently employed to assess their structural behaviour. The reliability of these models is closely related to their ability to account for all the uncertainties that are involved in the knowledge process. In this regard, to handle these uncertainties and quantify their propagation, Bayesian inference is frequently employed being able to deal with the effects of parameter uncertainty, observation errors and model inadequacy. The computation of the posterior distribution through Bayesian inference needs–however–the evaluation of the likelihood function, which requires solving complex multi-dimensional integration problems. To bridge this shortcoming, the paper compares two Bayesian inference approaches to show how different approximations affect the results of simulated inference: a discrete approach for the likelihood computation in the Bayesian Model Updating (BMU) and a Monte Carlo likelihood-free method known as Approximate Bayesian Computation (ABC) are reported. As reference, the typology of historic masonry towers was considered by using their natural frequencies as experimental data for model updating. The two procedures provide very similar results supporting the validity of both methods despite ABC turns out to be a more flexible approach
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Zur Rolle der Bewertung der seismischen Gefährdung von historischen Türmen aus Mauerwerk
Get PDFThe research activity developed in the present work achieved both technical and scientific results on the seismic risk assessment of masonry towers. It provided semi empirical formulations for the main frequency estimation based on a wide database of historic masonry towers and a novel framework for the seismic risk assessment starting from the Bayesian model updating using dynamic experimental data.
The recent Italian earthquakes have dramatically highlighted the vulnerability of historic masonry constructions and the need to improve the knowledge on their seismic response. Due to this fact, the challenging issue of obtaining a reliable structural model has become increasingly relevant to the scientific community, promoting the employment of sophisticated tools of analysis and the need of numerical models to be set up. However, the significant lack of knowledge on historical structures (e.g., material properties, geometry, construction techniques, boundary conditions), still makes their numerical modelling difficult. The knowledge of the seismic response of this structural typology, taking into account uncertain parameters, represents a critical issue and the main scientific question to which this work aimed to answer.
The framework proposed in this research started with the Finite Element (FE) model updating of masonry towers through Bayesian approach; the prior distribution of relevant uncertain model parameters was converted into the posterior one by using experimental dynamic data. Nonlinear static analyses were employed to estimate the uncertainties in the seismic response of masonry towers. Taking into account both the modelling and the measurement uncertainties, fragility curves were defined related to different towers damage levels. Eventually, the seismic hazard was considered thus leading to the seismic risk assessment of masonry towers.
The idea of this work started from the necessity of obtaining a better awareness of the uncertainties involved in the seismic capacity prediction of historic constructions, and their effect on the overall reliability.
Although the proposed results are based on the application to a real case study, the procedure may be used for other similar structures and may represent an effective and alternative tool for the seismic risk quantification of historic masonry towers.Die vorliegende Doktorarbeit stellt teilempirische Formulierungen zur Verfügung, die mittels einer umfangreichen Datenbasis von historischen Türmen aus Mauerwerk und einer neuen auf dem Modell von Bayes basierenden Methode das Erbebenrisikos unter Nutzung der dynamischen Messwerte bewertet.
Der Bedarf nach einer solchen verbesserten Bewertung der Gefährdung von historischen Mauerwerkstürmen zeigte sich insbesondere nach den jüngsten seismischen Ereignisse Italiens bei der Frage der Beurteilung der Gefährdung der Türme der Toskana, z.B. in San Gimignano. Die wissenschaftliche Aufgabe besteht darin, das in vorhandenen Datenbanken vorhandene, aber in technischer Hinsicht begrenzte Wissen zum Strukturverhalten der Türme mit Hilfe eines Modells für eine möglichst zuverlässige Vorhersage der Strukturantwort zu verwenden. Der noch große Mangel an Kenntnissen über historische Baustrukturen, ihrer baustofflichen Eigenschaften, Geometrie, Bautechniken und Randbedingungen ermöglicht bisher keine ausreichende Beurteilung.
Die Erforschung der seismischen Reaktion dieser Strukturtypologie unter Berücksichtigung der unbestimmten Parameter stellt das entscheidende Thema und die hauptwissenschaftliche Frage dar, welche diese Arbeit beantworten möchte.
Das in dieser Forschungsarbeit vorgestellte Framework beruht auf einem Finite Element Modell (FEM) der Türme aus Mauerwerk, dessen Parameter durch die Bayes’sche Methode an Datenbankangaben kalibriert werden. Aus einer auf statischen Überlegungen basierenden Priori- Verteilung von wesentlichen unbestimmten Modell-Parametern wird dabei unter Verwendung von experimentell ermittelten Daten eine Posteriori- Verteilung ermittelt. Die Unsicherheit der daraus folgenden Berechnungsergebnisse der Erdbebenantwort wurde mit Hilfe nichtlinearer statischer Auswertung bewertet. Aus den ermittelten Unsicherheiten sowohl der Modellierungsparameter als auch der zugrunde liegenden Messungen wurden „fragility curves“ bezüglich der verschiedenen Schadenniveaus von Türmen definiert. Mit der Hilfe dieser Kurven wurde schließlich die Erdbebengefährdung für Türme aus Mauerwerk beurteilt.
Die in dieser Arbeit vorgestellte Methode verbessert die Beurteilung von seismischer Gefährdungseinschätzung, da eine Bewertung der in die Einschätzung einfließenden Unsicherheiten für die Ergebnisse möglich ist. Auch wenn die Methode am Beispiel der historischen Mauerwerkstürme durchgeführt wurde, ist sie für andere Bauwerke in gleichem Maße anwendbar
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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