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Uso combinato di Tecniche diagnostiche strutturali ND per gli edifici storici
Full text linkL'analisi strutturale delle costruzioni storiche o dei monumenti rappresenta un importante campo di ricerca sia dal punto di vista analitico che sperimentale, poiché questi edifici presentano caratteri di vulnerabilità complessi. Il problema della conoscenza e della tutela del patrimonio culturale è un tema articolato che richiede la collaborazione di diverse figure professionali quali l’architetto, l’ingegnere ed il restauratore. La finalità comune è la formulazione di ipotesi sulla stabilità delle costruzioni in muratura e la stima della sicurezza nella fruizione dell’edificio, oltre alla conservazione dell’edificio stesso. Per questo motivo è sempre più necessario saper identificare tempestivamente i segnali di danno ed essere in grado di determinarne le cause. I test di diagnostica non distruttiva sono applicabili alla maggior parte del patrimonio esistente, grazie alla loro natura non invasiva e sono in grado di fornire informazioni sullo stato di conservazione di specifici materiali, della struttura stessa o di elementi di essa, rispettandone l’integrità. Questi tipi di test si basano sulla correlazione tra alcuni parametri fisici come la densità, la propagazione delle onde elastiche nei solidi o l’impedenza elettrica. Le indagini ND svolte in situ tendono spesso a considerare i risultati ottenuti da diverse tecniche separatamente. Tuttavia, specialmente dopo i terremoti o in presenza di importanti danni osservabili, l’interpretazione combinata dei risultati derivanti da distribuite tecniche ND può aggiungere valore alle indagini.
La seguente tesi di dottorato si pone in questo contesto articolato, con la proposta di combinare in modo innovativo due tecniche di diagnostica ND consolidate, basate sulla propagazione delle onde elastiche nei solidi e sulle vibrazioni ambientali, proponendone un’analisi finale critica. La risposta alle vibrazioni in un caso è stata ottenuta attraverso l’ausilio di test sonici, mentre le vibrazioni naturali sono state studiate con l’ausilio di un tromografo portatile. Generalmente la potenziale integrazione di queste due tecniche può risultare difficoltosa perché le prove soniche forniscono risultati locali mentre le vibrazioni ambientali risultati globali. Inoltre, l’eccitazione in un caso è indotta da un martello, mentre nel secondo caso la sorgente del rumore è il microtremore ambientale o il rumore antropico. Tuttavia, un potenziale punto comune di queste tecniche potrebbe essere l'identificazione dei danni, risentendo entrambi gli strumenti della rigidezza del sistema. Più specificamente, le frequenze naturali e le forme modali lungo una direzione principale, fornite dalle AVMs, possono essere messe in relazione con la velocità dell'onda sonica di attraversamento in porzioni di edificio danneggiate e non danneggiate lungo la stessa direzione. Il campo di applicazione delle indagini, proposto nella tesi, si concentra su un’unità strutturale tipo caratterizzata dalla presenza di muratura portante con un’apertura di tipo porta o finestra. Questa unità strutturale è facilmente identificabile in ogni edificio storico di ogni differente cultura e in questo lavoro vengono presentati i risultati di indagini condotte su murature Veneziane, Cubane e Nepalesi con caratteristiche geometriche comparabili.
Entrambi gli strumenti di diagnostica ND utilizzati per le analisi sono dotati di accelerometri ed il loro principio di funzionamento si basa sull’acquisizioni di segnali in velocità o accelerazione. Ai fini di validare la tesi iniziale, i segnali dei test sonici sono stati processati con le medesime modalità tipicamente adottate nell’analisi dei segnali ottenuti mediamente lo strumento Tromino®. I segnali registrati nel dominio del tempo sono stati elaborati attraverso la trasformata veloce di Fourier per ottenere analisi spettrali in dominio di frequenza, ottenendo così uniformità tra le grandezze rilevate dalle due strumentazioni
Damage assessment of Nepal heritage through ambient vibration analysis and visual inspection
No full textThe aim of this paper is to identify, both through microtremor analysis and visual inspection, the collapse mechanisms of the Nepalese wood-masonry monuments damaged by the 2015 seismic event that struck Kathmandu and its valley. The research analyses two case studies as the "Radha Krishna" temple located in Teku, a district in Kathmandu, and the "Pancha Deval complex" in Pashupati area. More specifically, after a careful anamnesis based on visual inspection and hypotheses on the temple's structural behaviour, global nondestructive testing (microtremor) was carried out for qualitative characterization of the structural system. The visual damage survey allowed to identify the recurring collapse mechanisms in the two case studies with the identification of typical Nepali expected damage. The case of Radha Krishna temple denotes a Nepali collapse mechanism typical in the corner of temples made of timber masonry, in which the mechanical contribution of the timber is manifested through columns and windows. The ambient vibration analysis carried out by tromograph device and microtremor evaluation allowed to dynamically characterize the two bases by identifying the peak frequencies both for Radha Krishna and for Pancha Deval complex. With the same device, the two historic constructions have been also studied in evaluating local modes and frequency. In the Pancha Deval complex, a relationship between damage, frequencies, and the amplification of the base was observed. In detail, the five buildings have similar damage and similar first frequencies (2.72-2.9 Hz). The most damaged sides are those with the frequencies close to the base (2.05-2.38 Hz)
Dynamic characterization of Nepali Masonry Temples hit by 2015 Earthquake
No full textThe objective of this work is present the results of ambient vibration measurements obtained in two different Nepal missions (October 2016 and October-December 2017). The object of the research is the comparison of the dynamic behavior, through the measurement of the ambient micro tremor, of two monumental Hindu masonry buildings (Jagannath Temple and Pancha Deval complex) damaged by the 2015 Gorkha earthquake. The methodology used involves a meticulous study of the building through visual inspection and the use of a tromograph for the survey of structures in elevation. The results obtained show, in the case of Jagannath temple, a relationship between the high level of damage and the asymmetrical disposition of the roof beams. In the case of Pancha Deval complex, the AVMs show an interaction between the structure and the ground
Surveys on the Jagannath Temple's seismic response in Kathmandu
No full textThe objective of this paper is to identify the mechanisms of collapse of the Nepalese wood-masonry monuments damaged by the 2015 seismic event that struck Kathmandu and its valley. The research analyzes the case study "Jagannath Temple" located on Durbar Square in Kathmandu. After a careful anamnesis based on visual inspection and hypotheses on the temple's structural behavior local non-destructive testing (sonic, endoscopic, rebound hammer) was carried out for qualitative characterization of the structural system. These tests have been aimed at a qualitative characterization of the structural structure prior to the study of the collapse mechanisms that characterize the response to the earthquake of these monuments. Specifically, the modal analysis has allowed to characterize the soil-structure restraint while the linear dynamic analysis has highlighted the main criticalities, which characterize the historic construction
Non-destructive techniques for structural characterization of cultural heritage: A pilot case study
Full text linkThis work describes an approach for combining local and global non-destructive techniques for the structural characterization and conservation assessment of cultural heritage buildings. An experimental investigation program was conducted on the south vault of St. Mark's Basilica in Venice, involving historical investigations, a damage survey, sonic tests, and ambient vibration measurements. Recorded data were employed to assess the material and structural properties of the vault and to characterize the observed damage pattern. The study of the correlation between results of sonic tests and ambient vibration measurements has shown how, in complex structural typologies, the information provided by both these two kinds of tests are necessary in order to effectively characterize the structural behaviour, which is strongly influenced by the complexity of geometry and restraint condition. Experimental results have been used for the validation of a numerical model adopting a non-conventional approach. The procedure is based on comparing numerical simulation of ambient vibration response in terms of the frequency content of acceleration signals. This approach can be performed using only a limited number of measured acceleration signals, proving to be useful and cost-effective. The work aims to provide helpful insights into the combined use of non-destructive tests for the efficient structural characterization and safety assessment of heritage structures
Detection of 2009 L'Aquila Earthquake Effects on Collemaggio Church through Experimental Surveys
No full textTen years after the earthquake that affected central Italy in 2009, noninvasive investigations were carried out in L’Aquila on the Basilica of Santa Maria di Collemaggio. These were conducted to characterize the ground from a site-response point of view. The study consisted of 11 ambient noise recordings using the Nakamura technique and distributed along two profiles: one longitudinal to the central nave and one transverse. Analyzing the results, it was possible to determine the frequency of the vibration of the ground. After comparison with data from previous literature, it was possible to graph the contrasting sections of the impedance of the subsoil up to about 300 m depth (bedrock) drawing on a passive seismic survey from the single station. Furthermore, sonic tests were performed on the 14 octagonal columns of the central nave. The data were compared with those collected 10 years earlier (post earthquake) and with postearthquake structural restorations. The new tests show an increase of velocity in the resistant sections of the pillars subjected to the structural consolidation
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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