Controllo e sindacati azionari nelle società quotate italiane

Lo studio propone un indagine empirica sugli assetti proprietari delle società quotate italiane, per individuare situazioni di controllo individuale o congiunto, messi in relazione alla dimensione a-ziendale delle società, onde verificare l’interazione tra la struttura del controllo societario e le potenzialità economiche dell’impresa. L’indagine si soffermerà sui sindacati azionari, per valutarne la ri-levanza nel contesto delle società quotate: analizzando il contenuto del-le pattuizioni, si cercherà di mettere a fuoco l’incidenza di tali patti su-gli assetti di controllo delle società stesse. L’analisi delle situazioni di controllo congiunto da sindacato azionario potrà fornire ulteriori indica-zioni sulla correlazione tra controllo e dimensione economica. La ricerca intende sperimentare un nuovo approccio nello studio dei problemi applicativi del diritto societario, e avviare la necessaria rifles-sione sulla relativa impostazione metodologica

New soft rock pillar strength formula derived through parametric FEA using a critical state plasticity model

Many abandoned room and pillar mines have been excavated not far from the surface of large areas of important European cities. In Rome, these excavations took place at shallow depths (3-15 m below the ground surface) in weak pyroclastic soft rocks. Many of these cavities have collapsed; others appear to be in a stable condition, although an appreciable percentage of their structural components (pillars, roofs, etc.) have shown increasing signs of distress from both the morphological and mechanical points of view. In this study, the stress-strain behaviour of soft rock pillars sustaining systems of cavities under vertical loads was numerically simulated, starting from the in situ initial conditions due to excavation of the cavities. The mechanical behaviour of the constituent material of the pillar was modelled according to the Modified Cam-Clay constitutive law (elastoplastic with strain hardening). The influence of the pillar geometry (cross-section area, shape, and height) and mechanical parameters of the soft rock on the ultimate compressive strength of the pillar as a whole was parametrically investigated first. Based on the numerical results, an original relationship for pillar strength assessment was developed. Finally, the estimated pillar strengths according to the proposed formula and well-known formulations in the literature were compared

Bi-Dissipative Thick Level Set (TLS) Damage Model for Quasi-Brittle Materials

The Thick Level Set (TLS) approach applied to damage models allows for a nonlocal treatment that prevents from spurious localization problems. In previous works, isotropic damage models with a single scalar parameter were adopted. Under these conditions, a single level set was used to separate the undamaged zone from the damaged zone, and damage growth was expressed as a level set propagation. Schematically, in the damaged zone, the damage variable directly depended on the level set through an explicit function. Beyond a critical length, material was assumed as fully damaged, thus allowing for a natural transition from damage to localized cracking (i.e., strain localization). In this paper, a first step toward the extension of the TLS approach to “bi-dissipative” isotropic damage models is presented. In the adopted formulation, degradation of material properties under prevailing compressive/tensile loading conditions is separately treated. Two distinct damage variables and activation criteria are used. This allows taking into account the degradation of material properties in tension due to compressive damage (for the moment, no unilateral effect is accounted for). In the article, the local damage model and its mathematical properties are discussed first. A strategy for dealing with bi-dissipative damage in the framework of a TLS approach is then presented

Analytical strain localization analysis of isotropic and anisotropic damage models for quasi-brittle materials

Strain and damage localization are usually precursors of rupture. We present a three-dimensional method dedicated to quasi-brittle materials based on the works of Bigoni & Hueckel, and Jirásek and coworkers, aiming at simplifying the analysis of the localization properties of continuous damage models of a general form, and possibly anisotropic. The method reformulates the localization problem as a two-variable polynomial maximization problem, a strategy commonly used in softening plasticity models, but not so much in Continuum Damage mechanics. The quasi-brittle hypothesis is exploited to render the problem solvable in a fully analytical way, and a post-analysis criterion for the validity of the analysis is also exhibited. In this work, the method is fully established from a theoretical viewpoint, and examples illustrating its use are provided. Multiaxial calculations are performed for four continuous damage models (two isotropic and two anisotropic ones). The method applies to induced anisotropy and constitutive models representing isotropic linear elasticity before damage growth, and remains accurate when models display immediate softening after the elastic limit (and thus to multiaxial tensile cases). The analytical method is, however, entirely general and allows for the calculation of (i) the orientation of a potential localization plane, (ii) the mode angle of the weak discontinuity, and (iii) the validity domain of such a simplified analysis

Preconditioning strategies for vectorial finite element linear systems arising from phase-field models for fracture mechanics

International audiencePhase-field models are frequently adopted to simulate fracture mechanics problems in the context of the finite element method. To depict fracture, this method involves solving a coupled set of Helmholtz-like damage-field equation and augmented linear momentum balance equation. Solutions to these coupled equations are then used as descriptions of crack propagation phenomena within solids. However, this method imposes a constrain of using extremely fine meshing for properly predicting cracks. For practical problems of interest, this very often leads to linear systems with large sizes that have to be repetitively assembled and solved. As such, iterative solution procedures such as the Krylov subspace based methods for solving these large linear systems within the framework of serial/parallel computing environments become mandatory toobtain results in a feasible time. In this work, the vectorial finite discretization for a hybrid phase-field formulation — a monolithic solving scheme — is presented. The underlying nonlinearity present in the coupled set of equations of the the hybrid phase-field model is dealt through Picard iteration that helps to preservethe symmetry of the linearized system to solve. Due to the symmetric positive definite nature of the finite element linear systems obtained for this problem, the conjugate gradient method makes a standard choice of iterative solution algorithm. Within this article, to improve convergence rates, consequently time to solution, of the conjugate gradient method applied to crack propagation problems, different preconditioning strategies are analyzed, tuned, and discussed. Brittle fracture benchmarks are used to measure the performance of preconditioners which are then applied to massively parallel simulations with millions of unknowns. A series of numerical experiments show that the algebraic multigrid preconditioner is well suited for solving the phase-field model for fracture, being superior to the Jacobi and the block Jacobi preconditioning in allregards: ease of solving the problem, iterations to converge, time to solution, and parallel scaling on more than a thousand processes

Controllo e sindacati azionari nelle società quotate italiane

Lo studio propone un indagine empirica sugli assetti proprietari delle società quotate italiane, per individuare situazioni di controllo individuale o congiunto, messi in relazione alla dimensione a-ziendale delle società, onde verificare l’interazione tra la struttura del controllo societario e le potenzialità economiche dell’impresa. L’indagine si soffermerà sui sindacati azionari, per valutarne la ri-levanza nel contesto delle società quotate: analizzando il contenuto del-le pattuizioni, si cercherà di mettere a fuoco l’incidenza di tali patti su-gli assetti di controllo delle società stesse. L’analisi delle situazioni di controllo congiunto da sindacato azionario potrà fornire ulteriori indica-zioni sulla correlazione tra controllo e dimensione economica. La ricerca intende sperimentare un nuovo approccio nello studio dei problemi applicativi del diritto societario, e avviare la necessaria rifles-sione sulla relativa impostazione metodologica

Analyse unidimensionnelle de la transition « endommagement non local eikonal-fissure cohésive »

International audienceCette contribution présente la transition d'un modèle d'endommagement Eikonal Non Local (ENL) vers un modèle à discontinuité forte dans un cas unidimensionnel. En introduisant la formation d'une fissure cohésive dans les zones où l'endommagement est proche de l'unité, cette nouvelle formulation cherche à résoudre les problèmes d'objectivité des résultats par rapport au maillage des méthode de régularisation avec évolution des interactions non locales (e.g. la méthode ENL) à la localisation de l'endommagement dans un seul élément fini