1,720,958 research outputs found
Tecniche di model updating e soft computing per l'identificazione dei parametri meccanici e del danno di strutture
No full textNumerose strutture e infrastrutture si trovano in uno stato di degrado o danneggiamento causato, per esempio, da un evento sismico o dall’esposizione prolungata a condizioni ambientali sfavorevoli. Questa situazione può compromettere la funzionalità dell’opera o, in casi più gravi, portare al collasso della stessa. In questo contesto, il monitoraggio dello stato di salute delle strutture mediante prove dinamiche rappresenta un’attività in crescente diffusione. Le metodologie per l’identificazione del danno basate sui dati acquisti dal sistema di monitoraggio sono spesso supportate dalla definizione di modelli numerici che, opportunamente calibrati, permettono una migliore conoscenza della struttura, di ottenere risultati più affidabili in merito alla valutazione della sicurezza delle strutture e di rilevare possibili condizioni anomale dal confronto con il comportamento atteso. In caso di danno, permettono inoltre la localizzazione e la quantificazione del danno stesso.
Nel presente lavoro sono stati studiati e approfonditi diversi aspetti riguardanti tecniche per l’identificazione del danno con l’ausilio di modelli numerici.
L’approccio multi-obiettivo alla calibrazione di modelli numerici, tipicamente necessario in problemi di sicurezza strutturale, fornisce un insieme di soluzioni ottimali, chiamato frontiera di Pareto, all’interno della quale deve essere scelta la soluzione preferita. In questo contesto, l’autore propone una procedura che consente il calcolo diretto della soluzione preferita, senza la necessità di determinare la frontiera, attraverso l’ottimizzazione di un’unica funzione obiettivo definita sulla base del criterio della minima distanza dal punto di equilibrio. Tale procedura è stata validata su una serie di casi studio, compreso quello della Rocca di San Felice sul Panaro, una struttura storica severamente danneggiata dal sisma dell’Emilia del 2012.
L’approccio Bayesiano consente la modellazione stocastica dei parametri e degli errori in modo tale che il risultato della calibrazione possa essere espresso anche in termini di incertezza. Sul caso della Rocca di San Felice, i risultati, sia in termini di parametri che di pesi attribuiti a frequenze e forme modali, sono stati confrontati con quelli ottenuti tramite l’ottimizzazione bi-obiettivo e analizzando le incertezze associate. Sono inoltre presentate varianti alla metodologia, per cercare di ridurne l’onere computazionale, soprattutto per la valutazione delle incertezze dei parametri identificati.
Le metodologie di model updating applicate all’identificazione del danno risultano spesso computazionalmente onerose e non permettono l’identificazione in tempo reale del possibile stato di danneggiamento. Le reti neurali, invece, permettono una rapida identificazione del possibile danno, se vengono opportunamente calibrate prima dell’utilizzo tramite modelli numerici capaci di simulare condizioni ordinarie e scenari di danno. Con riferimento al caso di un ponte ferroviario in struttura mista acciaio-calcestruzzo, sono stati sviluppati due modelli che differiscono per grado di dettaglio e permettono di simulare il comportamento “reale” della struttura e quello “del modello”, definito a partire dai parametri modali identificati. Quest’ultimo modello, più semplice, viene usato per la generazione dei dati destinati all’addestramento della rete. Con il primo modello, più dettagliato, si simulano i dati sperimentali impiegati per il test della rete, i quali inevitabilmente si discostano da quelli del modello semplificato, nonostante sia esso calibrato. I risultati ottenuti evidenziano come, per avere previsioni accurate nella fase di test, gli errori residui ottenuti al termine della calibrazione devono essere utilizzati per correggere i dati forniti in input alla rete.A multitude of structures or infrastructures is damaged or degraded due to, for example, a seismic event or the protracted exposure to adverse environmental and atmospheric conditions. This situation may prevent the construction serviceability and, in even more serious cases, may determine its collapse. In this context, vibration-based structural health monitoring became very diffused for the strict relationship existing between dynamic properties and stiffness of the structure, that depends on its health state. Damage detection methods based on data registered by a monitoring system are often supported by the definition of numerical models. They allow, if properly calibrated, a better knowledge of the structure, to obtain more reliable results about the structure safety and to identify possible anomalies through the comparison with the expected behavior. In case of damage, they further enable localization and quantification of damage itself.
In the present work, several aspects related to damage detection techniques with the support of numerical models are studied and deepened.
Multi objective approach for model updating, typically necessary in problems of structural safety, provides a set of optimal solutions, called Pareto front. The preferred solution has to be selected within this front. In this framework, the author proposes a procedure for the direct computation of the preferred solution, without the need to determine the whole front, by means of the minimization of a single objective function defined according to the criterion of the minimum distance from the equilibrium point. This procedure is validated on several case studies, included the case of the San Felice sul Panaro Fortress, an historical structure strongly damaged by the Emilia-Romagna seism occurred in 2012.
Bayesian model updating involves the stochastic modelling of model parameters and errors so that the updating result can be expressed also in terms of uncertainty. About the case of the San Felice sul Panaro Fortress, results, both in terms of parameters and weights attributed to frequencies and mode shapes, are compared with those obtained through bi-objective optimization, analyzing the associated uncertainties. Variants of the classical methodology are presented with the aim of reducing the computational effort, especially for the computation of the updated parameter uncertainties.
Model updating methods for damage detection are usually time-consuming and does not enable the real-time identification of a damaged condition. Instead, artificial neural networks ensure a quick identification if they are appropriately calibrated before their use by means of numerical models able to simulate ordinary conditions and damage scenarios. With regard to the case of a concrete/steel mixed railway bridge, two models different for the detail level have been developed. They simulate the “real” structure behavior and that of “the model”, defined starting from the identified modal properties. The last model, simpler, is employed for the generation of the dataset finalized to the training phase. With the first model, more detailed, the experimental data used for the network test are simulated. They unavoidably differ from those of the simplified model, despite it was calibrated. Results show how, in order to have accurate network predictions in the test phase, the residual errors obtained at the end of the calibration must be used to correct the data given in input to the network
Dynamic monitoring and evaluation of bell ringing effects for the structural assessment of a masonry bell tower
No full textThe paper presents a rational procedure for the structural assessment of bell towers with respect to the dynamic actions induced by the bell ringing, based on structural monitoring and data processing. This methodology is tested on the bell tower of Saint Prospero (Reggio Emilia, Northern Italy), a masonry tower of great historical interest. The procedure includes an accurate geometrical survey for a deep knowledge of the structural geometry, which is the base for the structural modelling. A finite element model of the tower is calibrated with respect to the modal properties evaluated from the structural response measured in operational conditions. The structural response of the tower was also measured during a famous cultural event held in the city centre of Reggio Emilia, when skilled bell ringers played traditional melodies. The tower displacements are evaluated applying a double integration technique and a detrending procedure based on the empirical mode decomposition to the acquired accelerations. To simulate the structural response to the bell ringing, the tower and the bell are modelled as a single degree of freedom system and an unforced and undamped simple pendulum, respectively. For safety assessment purposes, the structural response of the tower is evaluated considering different oscillation angles in order to identify the one causing the maximum displacement. Finally, the stress pattern of the masonry caused by the bell-induced displacement is estimated thanks to the calibrated finite element model of the tower. Results show that the bell ringing causes a stress pattern lower than the allowable masonry strength for the serviceability conditions
A computationally efficient procedure for calibrating model parameters of multiple specimens
Full text linkModel calibration can be a very intensive and time-consuming task, especially when dealing with non-linear
and large finite element models. The computational effort further increases when multiple specimens have to
be calibrated. This is typical of laboratory experiments where several specimens made with the same and/or
different constituent materials are tested. This paper proposes a calibration procedure aimed at reducing
the computational effort of multiple specimen model calibration. The calibration procedure combines the
robustness of a surrogate-assisted evolutionary algorithm with the exploitation of a database collecting the
results of the previously calibrated specimens. In this research, the proposed procedure is applied to the
calibration of the parameters of a cohesive crack model for fiber-reinforced concrete specimens. The benefit
of the proposed procedure is shown by comparing the results with those obtained from the same calibration
method but without accounting for the previous results in the calibration of a new specimen
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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