Browsing by Author "Olivito, Renato S."

Now showing 1 - 20 of 20

Analisi teorico-sperimentale di pareti murarie caricate fuori dal piano
(2006-11-20) Zuccarello, Francesca Anna; Bruno, Domenico; Olivito, Renato S.
Comportamento a taglio di elementi murari rinforzati con compositi FRCM in fibre naturali
(2011) Venneri, Assunta; Olivito, Renato S.
Nel presente lavoro, svolto nell’ambito del dottorato di ricerca, si è affrontato l’argomento della progettazione strutturale sostenibile attraverso lo studio di un sistema di rinforzo costituito da materiali a basso impatto ambientale. È stata analizzata, in particolare, la possibilità di sviluppo di un nuovo composito a matrice cementizia da impiegare nel campo della riabilitazione strutturale e dell’adeguamento sismico come rinforzo esterno di elementi in muratura. La fase fibrosa è rappresentata anch’essa da materiali non convenzionali ed eco-sostenibili, composti da fibre naturali di canapa e di lino nella forma di nastri e tessuti uni e bi-direzionali. Riguardo l’uso dei sistemi FRCM (Fiber Reinforced Cementitious Matrix), costituiti da leganti inorganici idraulici in sostituzione delle resine epossidiche dei più tradizionali FRP (Fiber Reinforced Polymer), numerosi sono ormai gli studi sperimentali presenti nella letteratura scientifica che li vedono accoppiati a fibre di natura sintetica (vetro, carbonio, PBO, etc.). Tali indagini hanno dimostrato buone caratteristiche di adesione alla muratura, buona resistenza alle alte temperature e, con un’opportuna scelta della fase di rinforzo, buone caratteristiche meccaniche. Meno apprezzabile è risultata invece la compatibilità con le fibre. Prove sperimentali di delaminazione eseguite su murature e/o su elementi resistenti in laterizio/pietra rinforzati, hanno evidenziato, infatti, la frequenza di una modalità di crisi per perdita di aderenza tra la matrice e l’elemento di rinforzo. Il problema dello “scollamento” delle fibre dall’adesivo (debonding) è alla stregua del fenomeno del distacco del materiale composito dalla parte superficiale del supporto murario (peeling, tipico dei sistemi con FRP), poiché entrambe le tipologie di rottura si manifestano all’interfaccia tra gli strati impedendo al materiale di rinforzo di lavorare al massimo delle proprie prestazioni a trazione. Nell’ambito delineato, la scelta di impiegare fibre lunghe naturali (NF) in sostituzione delle fibre artificiali sintetiche comunemente impiegate nel campo dei rinforzi strutturali con compositi rappresenta un’innovazione assoluta. Si tratta di materiali con modeste caratteristiche meccaniche ed elastiche ma del tutto paragonabili alle fibre di vetro di medie prestazioni. L’attività sperimentale condotta per il presente studio ha avuto lo scopo di indagare preliminarmente la compatibilità di tali fibre con una matrice cementizia specifica per sistemi di consolidamento esterno e, successivamente, di valutare l’efficacia del materiale composito ottenuto (NFRCM) quando applicato a elementi in muratura di mattoni pieni sottoposti ad azioni di taglio nel piano. Più specificamente, dopo una prima fase di caratterizzazione a trazione dei nastri, affiancata a una campagna di prove di tipo pull-out su elementi in laterizio fibrorinforzati, si è proceduto a una serie di prove di compressione diagonale su campioni di muratura privi di rinforzo e su campioni rinforzati, consentendo di rilevare l’efficacia del rinforzo in termini di capacità resistente e rigidezza al taglio. Le strisce di materiale composito sono state applicate su ambo le superfici regolarizzate dei pannelli murari secondo le disposizioni geometriche in diagonale e a reticolo a maglie quadrate. Le prove di aderenza e quelle di taglio nel piano sono state ripetute utilizzando un tessuto in fibre di vetro immerso nella stessa matrice in cui sono state impregnate le fibre naturali, allo scopo di eseguire un confronto con i materiali di rinforzo comunemente impiegati nei sistemi FRCM. Alla campagna sperimentale, infine, è stata accostata un’analisi numerica atta a fornire dei modelli capaci di descrivere il comportamento sperimentale esibito dai provini murari durante le prove di laboratorio. In particolare, i pannelli sono stati discretizzati all’interno del codice di calcolo LMGC90 e le strisce di composito modellate tenendo conto solo della modalità di rottura a trazione delle fibre nell’ipotesi di perfetta aderenza al supporto murario. Il codice risulta essere particolarmente adatto alla modellazione della muratura, basandosi su un metodo agli elementi distinti (DEM) che adotta un algoritmo di risoluzione completamente implicito (Non Smooth Dynamic Contact method). In particolare, esso è utilizzato per modellare il comportamento globale di sistemi discreti considerando il comportamento dinamico proprio di ogni componente in interazione con gli altri elementi. Le analisi numeriche risultano in buon accordo con le risultanze sperimentali, mostrando la validità di questo primo approccio di modellazione numerica per la muratura rinforzata. Parole chiave: Muratura, Rinforzo, FRCM, Fibre naturali, Compressione diagonale,Modellazione
Dalla città compatta all'urbanizzazione diffusa: controurbanizzazione e sostenibilità delle forme insediative nella media val di Crati
(2011-11-29) Bonavita, Giuseppe; Parise, Federico; Olivito, Renato S.
Definizione di modelli di sviluppo nei processi di pianificazione delle aree sottoposte a vincolo
(2012) Scarpino, Antonio; Olivito, Renato S.; Francini, Mauro; Llop, Charles
Differenti criteri di intervento sui centri storici sotto l'effetto delle azioni di rigenerazione urbana
(2011-11-29) Ferrari, Myriam; Olivito, Renato S.; Francini, Mauro; Llop Torné, Carlos; Viapiana, M. F.
Fotogrammetria e fotomodellazione nel rilievo dell'architettura
(2012-11-29) Lio, Antonio; Olivito, Renato S.; De Sanctis, Aldo
Hot mix asphalt composition versus surface characteristics: optimization processes
(2012-11-29) Minani, Venant; Olivito, Renato S.; Vaiana, Rosolino
Il Paesaggio della strada
(2014-11-26) Chimento, Vincenzo; Olivito, Renato S.; Festa, Demetrio C.
Innovative methodologies for concept modelling of vehicle body structures
(2014-11-26) De Gaetano, Giovanni; Olivito, Renato S.; Mundo, Domenico; Maletta, Carmine
La cattedrale di Cosenza tra architettura e geometria
(2012-12-29) Guido, Angela; Olivito, Renato S.; Guenot, Jacques
La modellazione delle interazioni tra il sistema territoriale e il sistema dei trasporti
(2012-11-30) Forciniti, Carmen; Olivito, Renato S.; Mazzulla, Gabriella
Le qualità intrinseche delle infrastrutture di trasporto su gomma: studio di un modello di decadimento delle caratteristiche superficiali del piano di rotolamento
(2011) Iuele, Teresa; Olivito, Renato S.; Vaiana, Rosolino
Le tecniche ottichedi misura 3D nel rilevamento architettonico
(2011) Zappani, Antonio Agostino; De Sanctis, Aldo; Olivito, Renato S.
Mechanical performanceof naturalfiber-reinforced composites for the strengthening of ancient masonry
(2013-11-25) Codispoti, Rosamaria; Oliveira, Daniel V.; Olivito, Renato S.
Modelling the lateral pedestrian force on rigid and moving floors by a self-sustained oscillator
(2009-11-23) Trovato, Andrea; Olivito, Renato S.; Bruno, Domenico; Argoul, Pierre
For the serviceability analysis of civil engineering structures under human induced vibrations, a correct modelling of the pedestrian-structure interaction is needed. The proposed approach consists in thinking the human body as a Single Degree of Freedom oscillator: the force transmitted to the floor is the restoring force of this oscillator [1, 2]. In rigid floor conditions, such an oscillator must be able to reproduce two experimentally observed phenomena: (i) the time-history of lateral force can be approximated by a periodic signal with a “natural” frequency related with the single pedestrian characteristics; (ii) the motion of a pedestrian is self-sustained, in the sense that the pedestrian produces by itself the energy needed to walk. Accounting for these aspects, a modified Van der Pol (MVdP) oscillator is proposed here to represent the lateral pedestrian force. The suitable form of its nonlinear restoring force is inferred from experimental data concerning a sample of twelve pedestrians. The experimental and model lateral forces show an excellent agreement. For a laterally moving floor, the MVdP oscillator representing a pedestrian becomes non-autonomous. It is well-known that self-sustained oscillators in the non-autonomous regime are characterized by the so-called entrainment phenomenon. It means that under certain conditions, the vibration frequency switches from the ”natural” value to that of the external force: the response frequency is entrained by the excitation frequency. According to the physical interpretation considered here, the entrainment corresponds to the situation where the pedestrian changes its natural walking frequency and synchronizes with the floor oscillation frequency. The steady response of the MVdP oscillator subjected to a harmonic excitation is discussed in terms of non-dimensional amplitude response curves, obtained using the harmonic balance method truncated at the first harmonic. The model predictions are compared with some experimental results concerning pedestrians available in the literature and a good agreement is obtained. These topics are detailed in this thesis and also in the companion papers [3, 4] and in the report [5].
Multiscale approaches for failure analyses of composite materials
(2013-11-25) Leonetti, Lorenzo; Olivito, Renato S.; Greco, Fabrizio
Fiber-reinforced composite materials are being increasingly adopted in place of metallic elements in many structural applications of civil, automotive and aeronautical engineering, owing to their high stiffness-to-weight and strengthto- weight ratios, resistance to environmental deterioration and ability to form complex shapes. However, in many practical situations, composite materials experience different kinds of failure during their manufacturing processes and/or in-services, especially for laminate configurations, where damage phenomena are rather complex, involving both intralaminar mechanisms (e.g. matrix cracking, fiber splitting and interface debonding between fiber and matrix) and interlaminar mechanisms (e.g. delamination between plies). These damage mechanisms, which take place at the microscopic scale in conjunction with eventual contact interaction between crack faces, strongly influence the macroscopic structural behavior of composites, leading to a highly nonlinear post-peak response associated with a gradual loss of stiffness prior to failure. As a consequence, a proper failure analysis of a composite material subjected to such microstructural evolution should require a numerical model able to completely describe all its microscopic details; however fully microscopic models are not pursued in practice due to their large computational cost. To overcome this problem, homogenization techniques have increasingly gained in importance, based on either classical micromechanical or periodic homogenization approaches; if combined each other, these models are able to deal with both periodic and nonperiodic (e.g. random) composite microstructures. According to these approaches, also referred to as sequential multiscale methods, a “one-way” bottom-up coupling is established between the microscopic and macroscopic problems. As a consequence, such methods are efficient in determining the macroscopic behavior of composites in terms of stiffness and strength, but have a limited predictive capability for problems involving damage phenomena. To overcome these limitations, two classes of multiscale methods have been proposed in the literature: computational homogenization schemes and concurrent multilevel approaches. Computational homogenization approaches, also referred to as semiconcurrent approaches, are very efficient in many practical cases, also for only locally periodic composites, especially when implemented in a finite element setting, as in the FE2 method. The key idea of such approaches is to associate a microscopic boundary value problem with each integration point of the macroscopic boundary value problem, after discretizing the underlying microstructure. The macrostrain provides the boundary data for each microscopic problem (macro-to-micro transition or localization step). The set of all microscale problems is then solved and the results are passed back to the macroscopic problem in terms of overall stress field and tangent operator (micro-tomacro transition or homogenization step). Localization and homogenization steps are carried out within an incremental-iterative nested solution scheme, thus the two-scale coupling remains of a weak type. On the other hand, concurrent multiscale methods abandon the concept of scale transition in favor of the concept of scale embedding, according to which models at different scales coexist in adjacent regions of the domain. Such methods can be regarded as falling within the class of domain decomposition methods, since the numerical model describing the composite structure is decomposed into fine- and coarse-scale submodels, which are simultaneously solved, thus establishing a strong “two-way” coupling between different resolutions. The present thesis aims to develop a novel multiscale computational strategy for performing complete failure analyses of composite materials starting from crack initiation events, which usually occur at the microscopic level, up to the formation of macroscopic cracks, subjected to propagation and coalescence phenomena. To this end, two alternative models have been proposed, belonging to the classes of semiconcurrent and concurrent multiscale models, respectively. Firstly, a novel computational homogenization scheme is described, able to perform macroscopic failure analyses of fiber-reinforced composites incorporating the microstructural evolution effects due to crack initiation and subsequent crack propagation process. A two-scale approach is used, in which coupling between the two scales is obtained by using a unit cell model with evolving microstructure due to mixed-mode crack initiation and propagation at fiber/matrix interface. The method allows local failure quantities (fiber/matrix interfacial stresses, energy release and mode mixity for an interface crack) to be accurately obtained in an arbitrary cell from the results of the macroscale analysis, and, consequently, crack initiation and propagation at fiber/matrix interface to be predicted. Crack initiation at fiber/matrix interface is simulated by using a coupled stress and energy failure criterion, whereas crack propagation is analyzed by means of a mode mixity dependent fracture criterion taking advantage of a generalization of the J-integral technique in conjunction with a component separation method for computing energy release rate and mode mixity. The evolving homogenized constitutive response of the composite solid is determined in the context of deformation-driven microstructures, based on the crack length control scheme able to deal with unstable branches of the equilibrium path, such as snap-back and snap-through events; moreover, the micro-to-macro transition is performed by adopting periodic boundary conditions, based on the assumed local periodicity of the composite. The second approach proposed in this thesis consists in a novel concurrent multiscale model able to perform complete failure analyses of fiber-reinforced composite materials, by using a non-overlapping domain decomposition method in a finite element tearing and interconnecting (FETI) framework in combination with an adaptive strategy able to continuously update the finescale subdomain around a propagating macroscopic crack. The continuity at the micro-macro interface, characterized by nonmatching meshes, is enforced by means of Lagrange multipliers. When modeling fracture phenomena in composites, the competition between fiber/matrix interface debonding and kinking phenomena from and towards the matrix is accounted for, whereas continuous matrix cracking is described by using a shape optimization strategy, based on a novel moving mesh approach. A key point of the proposed approach is adaptivity, introduced into the numerical model by a heuristic zoom-in criterion, allowing to push the micro-macro interface far enough to avoid the strong influence of spurious effects due to interface nonmatching meshes on the structural response. It is worth noting that this heuristic zoomin criterion is uniquely based on geometric considerations. Numerical calculations have been performed by using both the proposed approaches, with reference to complete failure analyses of fiber-reinforced composite structures subjected to different global boundary conditions, involving both uniform and non-uniform macroscopic gradients. The validity of the proposed multiscale models has been assessed by comparing such numerical results with those obtained by means of a direct numerical simulation, considered as a reference solution. Numerical results have shown a good accuracy, especially for the proposed concurrent multiscale approach; moreover, this model has been proved to be more suitable for handling problems involving damage percolation in large composite structures and, at the same time, managing boundary layer effects
Pianificazione territoriale e politiche di rinnovo urbano: una sperimentazione nelle realtà meridionali
(2011-11-29) Cosimo, Vincenzo Alfonso; Olivito, Renato S.; Rossi, Franco
Studio teorico sperimentale del comportamento meccanico delle travi prefabbricate reticolari miste (PREM)
(2012-11-29) Sorrenti, Fabio; Olivito, Renato S.; Ombres, Luciano
Sustainable fabric-reiforced cementitious composites for the strengthening of masonry elements
(2014-11-30) Cevallos Velàsquez, Oscar Alfredo; Olivito, Renato S.
Uno studio sul comportamento statico non-lineare dei ponti di grande luce
(2012-11-29) Bianchi, Elisabetta; Olivito, Renato S.; Bruno, Domenico; Blasi, Paolo Nevone