Browsing by Author "Garcea, Giovanni"

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Advanced linear beam models to be exploited in the implicit corotational framework and FEM implementation
(2012-10-29) Genoese, Alessandra; Bartolino, Roberto; Casciaro, Raffaele; Garcea, Giovanni; Bilotta, Antonio
Università degli Studi della Calabria
The implicit corotational method: general theory and FEM implementation
(2014-03-12) Madeo, Antonio; Garcea, Giovanni; Casciaro, Raffaele; Aristodemo, Maurizio
Koiter's asymptotic numerical methods for shell structures using a corotational formulation
(2009-11-30) Zagari, Giuseppe; Aristodemo, Maurizio; Casciaro, Raffaele; Garcea, Giovanni
Optimal design and numerical modelling of imperfection sensitive shell structures
(Università della Calabria, 2020-02-24) Liguori, Francesco Salvatore; Garcea, Giovanni; Bartolino, Roberto
A brand-new design philosophy tends to harness the load-carrying capacity hidden beyond the onset of buckling phenomena in shell structures. However, when designing in the postbuckling range, among other effects, attention should be given at imperfection sensitivity which may generate catastrophic and unexpected consequences on the optimised structures. Therefore, what would be necessary is an optimisation strategy able to deal with the complex geometries of full-scale structures and, meanwhile, efficiently gather the complexity of their postbuckling response. The aim of this work is to meet this demand by proposing numerical methods that face the problem from different sides, namely the geometrically nonlinear description of the shell, the solution algorithm and the optimisation strategy. As a starting point, a convenient format to describe geometrically nonlinear shell structures is identified in the solid-shell model. On the basis of this model, a discretised environment is constructed using isogeometric analysis (IGA) that, by taking advantage from the high continuity of the interpolation functions, leads to a reduced number of variables with respect to standard finite elements. Afterwards, an IGA-based multimodal Koiter’s method is proposed to solve the geometrically nonlinear problem. This method meets the aforementioned requirements of efficiency, accuracy and is capable of providing information on the worst-case imperfection with no extra computational cost with respect to the analysis of a perfect structure. Additionally, a new strategy for improving the accuracy of the standard version of Koiter’s algorithm in the presence of geometrical imperfections is devised. The last part of the thesis concerns the optimal design of full-scale structures undergoing buckling phenomena. In particular, the design focuses on variable angle tow laminates, namely multi-layered composites in which fibre tows can describe curvilinear paths, thereby providing great stiffness-tailoring capacity. Two optimisation strategies are proposed, both based on the use of Koiter’s method to evaluate the postbuckling response. The first one makes use of a fibre path parameterisation and stochastic Monte Carlo random search as a global optimiser. The second one is based on direct stiffness modelling using lamination parameters as intermediate optimisation variables that lead to a reduction of the nonlinearity of the optimisation problem and remove the direct dependence from the number of layers.
Solid-shell finite element and isogeometric models for nonlinear analysis and design of elastic shells using Newton, Koiter and Koiter-Newton solution strategies
(2018-04-16) Magisano, Domenico; Carbone, Vincenzo; Garcea, Giovanni; Leonetti, Leonardo
This thesis aims at developing a reliable and efficient numerical framework for the analysis and the design of slender elastic shells, in particular when composite materials are adopted, taking account of the geometrically nonlinear behaviour. Different aspects of this challenging topic are tackled: discretisation techniques, numerical solution strategies and optimal design. The first chapter, after a short summary of the Riks and Koiter methods, discusses the important advantages of using a mixed (stress-displacement) solid model for analysing shell structures over traditional shell models and the implications of this on the performances of the solution strategies. The second chapter introduces a mixed solid-shell model and reformulates the Koiter method to obtain an effective tool for analysing imperfection sensitive structures. This approach is the starting point of the third chapter, which proposes a stochastic optimisation strategy for the layup of composite shells, able to take account of the worst geometrical imperfection. The fourth chapter extends the benefits of the mixed formulation in the Newton iterative scheme to any displacement-based finite element model by means of a novel strategy, called Mixed Integration Point. The fifth chapter illustrates an efficient implementation of the novel Koiter-Newton method, able to recover the equilibrium path of a structure accurately with a few Newton iterations, combining an accurate Koiter predictor with the reduced iterative effort due to a mixed formulation. The solid-shell discrete model is reformulated in the sixth chapter, following the isogeometric concept, by using NURBS functions to interpolate geometry and displacement field on the middle surface of the shell in order to take advantage of their high continuity and of the exact geometry description. The approach is made accurate and efficient in large deformation problems by combining the Mixed Integration Point strategy with a suitable patch-wise reduced integration. The resulting discrete model proves to be much more convenient than low order finite elements, especially in the analysis of curved shells undergoing buckling. This is shown in the seventh chapter, which proposes an efficient isogeometric Koiter analysis.
Use of seismic metamaterials as innovative concept for the design of earthquake-resistant structures
(Università della Calabria, 2022-04-01) Fiore, Stefania; Cipparrone, Gabriella; Garcea, Giovanni; Carbone, Vincenzo
La progettazione di edi ci sismo-resistenti è nalizzata a proteggere gli edi ci dall'impatto dei terremoti che rappresentano ancora oggi uno degli eventi più pericolosi in quanto causano ingenti danni e perdita di vita umane. Le attuali strategie di protezione sismica si basano o su un dimensionamento strutturale tale da permettere all'edi cio di danneggiarsi durante il terremoto evitando in ogni caso il meccanismo di collasso oppure nella riduzione degli e etti del sisma mediante sistemi di isolamento alla base o ai dissipatori sismici. Una nuova opportunità per migliorare le prestazioni anti-sismiche degli edi ci è l'impiego di metamateriali sismici che permettano di ottenere un e etto di scudo alla propagazione delle onde sismiche. Questo e etto può essere ottenuto grazie a una architettura periodica che tipicamente caratterizza i metamateriali e anche grazie alla presenza di elementi localmente risonanti. In questo lavoro sono studiate le performance di una metafondazione, chiamata METACOMF, progettata per mitigare gli e etti del sisma alle frequenze più basse. In primo luogo è stato studiato lo stato dell'arte nel campo dei metamateriali sismici e gli strumenti teorici per la modellazione di essi. Sono state implementate procedure numeriche per lo studio della propagazione delle onde in sistemi periodici armonici e anarmonici. Sono state inoltre implementate analisi di risposta sismica locale del terreno in presenza di metamateriale e, in ne, è stata condotta una campagna di simulazioni di edi ci a telaio multipiano isolati con la metafondazione al ne di evidenziarne il funzionamento. Inoltre, per quanto concerne il rischio sismico per gli edi ci esistenti, è stata proposta una metodologia basata su approccio meccanico a nalizzata alla costruzione di curve di fragilità per la valutazione di vulnerabilità sismica degli edi ci in muratura Abstract The design of earthquake-resistant buildings is aimed to protect buildings from the impact of earthquakes which represent one of the most dangerous events and still cause signi cant damage and loss of human life today. The current seismic protection strategies are based either on structural sizing that allows damages in the building when an earthquake occurs, avoiding in any case, collapse mechanism yet or in reducing the e ects of the earthquake through base isolation systems or seismic dissipators. A new opportunity for increasing the anti-seismic performance of the buildings is represented by the use of seismic metamaterials which introduce a shield e ect against the seismic waves propagation. This is achieved through a periodic architecture, which is typical in metamaterials, and locally resonances elements. In this work, the performance of a metafondation, called METACOMF, designed to mitigate the e ects of the system at lower frequencies, is studied. Firstly, the state of the art in seismic metamaterials is given. Furthermore, the theoretical tools for modelling them are described. Then, numerical procedures developed to study wave propagation in harmonic and anharmonic periodic systems are described. The local seismic response analysis of the soil in the presence of a metamaterial is also studied. Then, an extensive campaign of simulations of multi-storey frame buildings isolated with metafondation is carried out in order to highlight their operating. Finally, regarding the seismic risk for existing buildings, a methodology is proposed to assess the seismic vulnerability of masonry buildings. This is based on a mechanical approach and aims to obtains fragility curves.