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A novel 2D dissipative connection for the seismic retrofit of precast RC structures:conceptualization, prototyping, mechanical and numerical study
No full textLe strutture prefabbricate in c.a. e c.a.p. sono spesso adottate per la realizzazione di edifici industriali e commerciali. Tuttavia, strutture prefabbricate con uno scarso grado di connettività possiedono un significativo rischio sismico a causa dell’effetto combinato di elevata vulnerabilità sismica ed esposizione. Gli
obiettivi di questa tesi sono la concettualizzazione, prototipazione e definizione meccanica e numerica di una connessione dissipativa 2D, chiamata Bidirectional Rotational Friction Damper (BRFD), che adegua sismicamente le strutture prefabbricate in c.a. e c.a.p. Lo studio di concettualizzazione mira alla definizione
di un modello analitico semplificato del BRFD e alla valutazione della sua influenza sul comportamento di una struttura durante un evento sismico. I risultati mostrano che l’introduzione del BRFD migliora la risposta dinamica della struttura, riducendo i drift d’interpiano e il tagliante alla base senza danneggiare la struttura. Lo studio di prototipazione mira alla selezione dell’accoppiamento di materiali più adatto per sviluppare un coefficiente d’attrito (COF) affidabile e stabile per il BRFD attraverso l’esecuzione di test Pin-on-Disk calibrati per simularne le condizioni d’uso reali. I risultati principali evidenziano come l’interazione
tra acciaio e un metallo più morbido migliori la stabilità del COF senza danneggiare significativamente le superfici. Lo studio meccanico del BRFD è stato condotto attraverso due campagne sperimentali: una campagna preliminare focalizzata sulla valutazione delle interfacce attritive selezionate, ed una campagna bidirezionale focalizzata sulla valutazione del comportamento meccanico del BRFD e dell’interazione tra la componente longitudinale e trasversale. I risultati mostrano una comportamento promettente del BRFD, sia in termini di stabilità del ciclo d’isteresi, sia in termini di capacità dissipativa. Lo studio numerico mira alla validazione delle prove meccaniche con analisi FEM attraverso lo sviluppo di due modelli numerici che riproducano il comportamento complessivo del BRFD basati sull’attrito: un modello semplificato per una semplice implementazione all’interno di un telaio, ed un modello raffinato per essere usato come Virtual Lab e che riproduca gli elementi del BRFD. I risultati evidenziano come il modello raffinato riproduca fedelmente il comportamento del BRFD e l’interazione tra la componente longitudinale e trasversale. La presente tesi mira al prolungamento della vita utile e alla mitigazione delle perdite dovute al sisma di strutture prefabbricate in c.a. e c.a.p. progettate solo per carichi verticali e situate in aree a rischio sismico. Questo è un argomento particolarmente sensibile che permette di soddisfare gli obiettivi 11, 12 e 13 dell’agenda ONU 2023 per uno sviluppo sostenibile.Precast RC structures are widely used in industrial and commercial buildings. However, precast RC buildings with poor connections have a significant seismic risk caused by a combination of high seismic vulnerability and exposure. The objectives of this thesis are the conceptualization, prototyping, mechanical and
numerical definition of a 2D dissipative connection called Bidirectional Rotational Friction Damper (BRFD) for the seismic retrofit of precast RC structures. The conceptualisation study aims to define a simplified analytical BRFD model and evaluate its impact on a structure’s behaviour during a seismic event. Results show that introducing the BRFD improves the structural dynamic performance, reducing inter-storey drift and total base shear without damaging the structure. The prototyping study aims to identify proper coupling materials that develop a reliable and steady friction coefficient (COF) for the device by performing Pin-on-Disk (PoD) tests set to simulate its real use conditions. The main findings highlight that the interaction between steel and softer metals improves COF steadiness without significant surface damage. The mechanical study aims to assess the mechanical behaviour of the BRFD by performing two investigations: a preliminary one that focuses on the assessment of the selected friction interfaces, and a bidirectional one that focuses on the assessment of the BRFD and the interaction between its longitudinal and transversal components. The results show the promising bidirectional behaviour of the BRFD, both in terms of hysteresis steadiness and good damping capacity. The numerical study aims to validate the mechanical experimental results with FEM analysis by developing two friction-based numerical models that simulate the BRFD behaviour: a simple model for an easy implementation inside a frame structure, and a more refined model to be used as a Virtual Lab tool and that simulates the BRFD elements. The results highlight that the refined model well reproduces the overall behaviour of the BRFD and the interaction between its longitudinal and transversal components. The present study aims to prolong the service life and mitigate the seismic losses of precast RC structures designed for gravity loads only and located in earthquake-prone areas. This is a particularly sensitive topic that allows the pursuit of goals 11, 12 and 13 of the UN 2030 Agenda for Sustainable Development
Dispositivo di collegamento dissipativo
No full textDispositivo di collegamento dissipativo comprendente: una pluralità di prime piastre parallele e affacciate tra loro; una pluralità di seconde piastre parallele e affacciate tra loro; ed almeno una terza piastra interposta tra due prime piastre adiacenti e tra due seconde piastre adiacenti in modo da poter ruotare rispetto a tali prime e seconde piastre; un primo elemento di
articolazione per attraversare e collegare tra loro le prime piastre; un secondo elemento di articolazione per attraversare e collegare tra loro le seconde piastre; e mezzi di guida per guidare il dispositivo di collegamento dissipativo durante il movimento rotatorio relativo delle sopracitate prime e seconde piastre rispetto alla terza piastra in modo da mantenere gli elementi di articolazione allineati tra loro e ad un baricentro della terza piastra
Preliminary experimental tests of a novel friction damper for seismic retrofit of RC precast structures
No full textPrecast RC structures have been widely adopted for industrial and commercial buildings since the ’60 s in the most developed countries. For his structural typology, connections between structural elements set a crucial point in the presence of lateral loads, such as earthquakes, since the deficiency, or lacking, of connection elements is the main responsible for heir structural collapse. This paper shows the preliminary mechanical testing of an innovative damping device conceived to be installed in beam-to-column joints of precast RC structures, with a bidirectional dissipative potential due to its geometry. This new Bidirectional Rotation Friction Damper (BRFD) has
been designed and optimised after a tribological campaign, which led to the selection of the two different friction interfaces investigated in this work. The mechanical tests have been performed considering the guidelines of EN15129 and the previous tribological investigation findings, showing the influence of sliding frequency and bolt torque increment on the steadiness of
the BRFD hysteresis cycle
Tribological investigation on metal mating surfaces to explore real use conditions of a novel friction damper for seismic applications
No full textThe seismic rehabilitation of existing buildings is a strategic goal for many countries located in high seismic risk areas of the globe. Retrofit techniques based on energy dissipation by implementing additional mechanical dampers into the structure have proved to be very efficient. Among the others, friction-based dampers have revealed to be particularly simple and cheap; nonetheless, for this kind of device, the selection of mating surfaces
set a crucial point. This paper shows the experimental investigation performed for the development of a novel Friction Damper (FD) using Pin-on-Disk (PoD) tests and highlights the main tribological aspects useful for the
full-scale tests. PoD tests have been set to simulate the real use condition of the device in development under the action of subsequent earthquakes. Sliding surface’s material and machining processes have been selected taking
into account the S355JR steel main body of the device in development, and the need of reducing the friction’s abrasive component and the particle formation during sliding. The experimental campaign has been addressed to highlight the influence of surface roughness, machining processes, additional treatment, and different coupling materials on Coefficient of Friction (COF) mean value and its statistical dispersion
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
A novel bidirectional friction damper for retrofitting of RC precast structures: Experimental and numerical assessment
No full textPrecast RC structures, commonly used since the '60 s for industrial and commercial buildings, often feature poor connections among the main structural elements and between structural and non-structural components due to sub-standard old building codes. Such a high vulnerability, in combination with the considerable exposed value, leads to a disproportionate seismic risk. To address this, a novel Bidirectional Rotation Friction Damper (BRFD) for RC precast structures is introduced. This easy-to-install, low-cost, and reusable damper simultaneously behaves as a beam-to-column joint and a damper with bidirectional dissipative capacity, improving seismic performance and preventing brittle failures. The BRFD's bidirectional capacity requires a unique testing methodology, validated through experimental and numerical analysis. An ad hoc setup with two orthogonal actuators was used to test the damper's behavior, measuring forces, displacements, and temperatures at varying levels. The experimental results are validated with FEM analysis in the Opensees environment by developing a refined numerical model that reproduces the behaviour of all the BRFD elements. Results show the promising bidirectional behaviour of the BRFD, both in terms of hysteresis steadiness and good damping capacity
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