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Application of FMEA method for assessment of reliability of structures
Full text linkIn the last years several methods have been proposed, aimed to explore the theme of degradation and reliability of building components, with the main purpose of preventing
performance deficits in general, and especially from sudden and unforeseen faults. This topic is an element of strong competitiveness in the world of professionals and business, and fits with the trend clearly demonstrated by the regulatory framework, particularly in the field of structures.
One of the methods that can be used to assess the suitability of a component to its performance specifications, and which belongs to the field of Risk Management, is FMEA, (Failure Modes and Effects Analysis). This methodology analyzes a project from the point of view of its reliability before it is carried out and realized.To allow this verification the components are firstly verified in the form of drawings, technical specifications, flow-charts, information, standards, etc. that are all the elements that make up the documentation of the work to be performed and the knowledge that is available on the subject. There have been many applications of FMEA on building components, and it is of particular interest - considering
the recrudescence of seismic events of the last decade, but also the emergence of structural defects, even of a certain gravity – for the use in the field of structures.
This is of a considerable relevance in a period when there are issues about the possibility of adaptation of the real estate to earthquakes, but it also raises the argument of the modalities and the criteria leading the inevitable reconstruction of what no longer exists. In this article an example of application to a reinforced concrete structure is shown, from which it is possible to notice the most critical items and the modalities for preventing negative events
Influenza degli elementi di rivestimento sulla carbonatazione del calcestruzzo
Full text linkLa valutazione della durata dei componenti edilizi rappresenta da ormai alcuni decenni un argomento di significativo interesse per la comunità scientifica internazionale, ma è diventato di notevole rilevanza anche per il settore della produzione edilizia, anche a seguito di un quadro normativo che chiama alcuni degli stakeholders del processo edilizio a proporre stime sul ciclo di vita: basti pensare al piano di manutenzione dell’opera e delle sue parti introdotto dalla legge 109/94, al piano di manutenzione delle strutture introdotto dalle N.T.C. 2008, al Life Cycle Costing introdotto dal D. Lgs. 50/2016, ma anche da analisi Life Cycle Assessment che hanno negli ultimi anni assunto un ruolo molto importante, evidentemente sotto la spinta che deriva dai temi della sostenibilità e dell’economia circolare, che campeggiano a pieno titolo nei focus del Piano Nazionale di Industria 4.0.
La necessità di procedere alla determinazione della durata dei componenti edilizi necessita di un attento studio delle variabili che influiscono sul loro comportamento nel tempo. Lo sviluppo e la continua immissione sul mercato di materiali e di tecnologie esecutive di nuova concezione, determinano, in particolare, l’esigenza di apprezzarne le aspettative di durata nel tempo. Gli studi effettuati in questo settore di ricerca hanno finora affrontato la questione in maniera compiuta relativamente ad un vasto panorama di componenti edilizi e di sistemi, primi fra i quali quelli strutturali, ed in particolare il calcestruzzo.
L’evoluzione del fenomeno della carbonatazione e gli effetti connessi alla variazione del pH sono probabilmente fra gli aspetti di maggiore interesse nello studio del degrado di questo materiale.
Dall’analisi dello stato dell’arte, con specifica attenzione a tale fenomeno, emerge che è opportuno, in particolare, approfondire gli studi relativi alla durabilità degli elementi strutturali in calcestruzzo armato sottoposti a interventi di consolidamento con tecnologie e materiali innovativi, quali ad esempio l’incamiciatura con calcestruzzo autocompattante (conosciuto anche con l’acronimo inglese SCC), stante la carenza di studi scientifici mirati a questo particolare aspetto.
Nel panorama degli studi e delle sperimentazioni condotte, poi, molte volte sono state proposte trattazioni del comportamento del tempo di calcestruzzi protetti da strati di pittura, ma tale soluzione non è certamente quella che si riscontra nella maggior parte degli edifici (soprattutto quelli realizzati nel periodo fra il dopoguerra e gli anni ’70), che invece presentano uno strato di intonaco fra l’elemento strutturale e quello di finitura.
È possibile individuare se esiste un contributo degli strati di rivestimento alla durabilità del calcestruzzo, e – in caso affermativo – quali sono le soluzioni tecniche che garantiscono il miglior risultato?
L’approccio che si è adottato per fornire risposta alle problematiche evidenziate è stato quello di proporre una valutazione comparativa – condotta mediante sperimentazioni di laboratorio – fra le diverse soluzioni che una indagine preliminare ha rivelato essere le più diffuse su una certa parte del territorio (la città di Napoli), non trascurando i dovuti approfondimenti sulle specifiche caratteristiche dei materiali.
La fase di realizzazione delle prove di laboratorio, preceduta dalla definizione dei modelli di simulazione e dalle caratteristiche dei provini, nonché dalla definizione delle sollecitazioni a cui sottoporli, è consistito in cicli di carbonatazione accelerata, completati dalle necessarie prove per la lettura e per l’analisi dei risultati ottenuti
Performance characterization of the concrete subjected to fire in terms of sustainability
Full text linkThe research, in a context of a sustainability of the building process, that should consider adequately the problem of building waste disposal, has the objective of determining the performance characteristics of concrete under the effect of fire, in order to evaluate the possibility of reutilization, and in positive case, what could the best uses be, considering the current regulations.
The experimentation, carried out on cubic samples with a side of 15 cm (according to UNI EN 12390, using aggregates with Dmax= 30 mm), with Portland cement of mixture 42,5 in two types (one with Pozzolana CEM II/B-P 42.5 and one with limestone CEM II/A-LL 42.5), with class of resistance C25/30, is based on the following parameters: increase of temperature, nature of fire, heating speed, time of exposition. The tests that have been carried out were both destructive (sclerometric, ultrasounds, Sonreb) and non-destructive (crushing and thermogravimetric), and the experimental results obtained also show that:
- the concretes present a remaining mechanical resistance that is lower than 50% of the initial one, after they have been subjected to the full cycle of temperature increase;
- between 200°C and 600°C, there is a significant decomposition of the binding component (hydrated cement), while that of limestone is predictable for temperatures higher than 700°C;
- the phenomenon of the “explosive spalling” – verified on two samples – has far more devastating consequences than the simple decay of the mechanical characteristics as, considered in a structural element, it causes a reduction of the resisting section, with a consequential increase of tensions in the remaining part, and direct exposition of the reinforcement without protection, situations which can cause the structural collapse of the element.
Some uses in the field of transport have been hypothesized, also basing on the indications of the current regulations and on the detected statistics of the current uses
Rapporto tra catene alfa e beta globiniche in ovini caratterizzati da diversi arrangiamenti alfa genici
No full textMULTICRITERIA ANALYSIS FOR CHOOSING MAINTENANCE STRATEGIES
Full text linkThe life cycle of building components can be managed according to different maintenance strategies, which mainly differ in performance and economic terms.
What is the most convenient among the possible scenarios? It has been shown in the past that the typology of maintenance interventions and the consequent periodicity are closely related to performance decay, and can lead to choices that, however, generally concern the purely economic sphere.
In this sense, it seems interesting to know the modalities of the performance decay, which may allow – even though for many components the "measurement" of its values is problematic - the construction of performance / time curves.
This result was possible, in other experiments conducted in the past, for one of the components to be considered most critical for the whole building (the plaster), thanks to a study that sampled 53 buildings with homogeneous characteristics (both from the technological point of view and from the era of realization), observed within 20 years.
This paper highlights that the only economic evaluation is not enough to identify the ideal solution, because – inter alia - there is a more suitable solution depending on the context framework in which the decision maker is operating. Commitment, budget, component typology, time span to consider, are the main factors influencing the choice, not ignoring design issues.
A Topsis multicriteria analysis is proposed, the results of which are an interesting starting point for define maintenance plans characterized by greater reliability, not only technical but also economical
Circuit-based electrothermal simulation of multicellular sic power MOSFETs using FANTASTIC
Full text linkThis paper discusses the benefits of an advanced highly-efficient approach to static and dynamic electrothermal simulations of multicellular silicon carbide (SiC) power MOSFETs. The strategy is based on a fully circuital representation of the device, which is discretized into an assigned number of individual cells, high enough to analyze temperature and current nonuniformities over the active area. The cells are described with subcircuits implementing a simple transistor model that accounts for the utmost influence of the traps at the SiC/SiO2 interface. The power-temperature feedback is emulated with an equivalent network corresponding to a compact thermal model automatically generated by the FANTASTIC tool from an accurate 3D mesh of the component under test. The resulting macrocircuit can be solved by any SPICE-like simulation program with low computational burden and rare occurrence of convergence issues
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
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