1,721,010 research outputs found
Un modello di danno anisotropo per il calcestruzzo soggetto a carichi ciclici pluriassiali: formulazione teorica e validazione sperimentale
No full textAn anisotropic damage model for concrete is proposed which is capable of describing the material behaviour both under static and cyclic uni- and triaxial load histories. The model is featured by two independent damage tensors which separately account for damage induced by tensile or compressive strains. This proposal is furtherly extended to simulate cumulation of damage and permanent strains during fatigue tests. Comparison between model response and available experimental results is encouraging. Finally, possible future extensions are outlined
A damage model for triaxial fatigue of concrete: theoretical formulation and parametric investigation
No full textA theoretical model for the description of the behaviour of concrete submitted to uni- and triaxial fatigue tests has been developed. It is based on damage mechanics and can be seen as extension of models formulated by other authors for static or quasi-static load histories. Special attention is devoted to the influence of the parameters defining the damage evolution law on the material fatigue life. In particular, some of the parameters are found to play a negligible role, at least in the range of values usually encountered for concrete. In the case of triaxial tests on cylinders, the effect of lateral confinement is carefully examined. The results obtained are discussed and possible further improvements are foreseen. The presented model also gives indications about the type of experimental information needed to forecast the fatigue lire of concrete under general load histories
Un modello viscoplastico con danneggiamento per il calcestruzzo soggetto a prolungati sforzi elevati
No full textA viscoplastic model with damage was developed to describe the mechanical behaviour of plain concrete subjected to sustained multiaxial stresses of high intensity. The model is characterized by inelastic strains due to plasticity and damage and by a second-order damage tensor. The evolution laws for these variables are based on the proposals by other authors for metals and rocksalt. The reliability of the model, presented here in the uniaxial case, was assessed through comparisons with available test results
Un modello per il calcestruzzo applicato all’interpretazione di prove cicliche
No full textIn the framework of damage mechanics, a model is presented for the description of the behaviour of concrete samples submitted to uni- and triaxial fatigue tests. This model is successfully applied to the interpretation of experimental results. The problem of identifying the model parameters is discussed. A first attempt to relating these parameters with the test conditions is made
A non-rotating anisotropic damage model for brittle materials
No full textA theoretical model is presented suitable for the description of the damaging process in brittle materials. Damage is defined by a second-order symmetric tensor and activates at different orientations to the principal strain directions, according to the sign of the principal strain which attains a damage threshold. The capabilities of the model in describing the mechanical response of material elements subjected to non-proportional stresses are illustrated
Prediction of the evolution of damage in ancient masonry towers
No full textIn this work, the results of numerical analyses carried out on a masonry tower are presented, with the aim of investigating the effects of creep-induced damage on the evolution of the global behaviour of the structure in time. These analyses were performed by implementing, into a commercial finite element code with user-oriented interface, a damage model recently developed by the authors to predict the creep behaviour of rock-like materials under constant stress and up to failure. The basic idea of this model is to describe primary creep through the Kelvin element of the Burger's rheological model, whereas the Maxwell's element consists of a spring and a dashpot in series where damage effects take place. The decrease in strength and stiffness associated with the occurrence of damage induces a stress redistribution throughout the structure. The numerical results show that the predicted zones of damage localization match the estimated failure mechanism of the tower, according to the morphology of the ruins
A visco-damage model for brittle materials under non-proportional monotonic and sustained stresses
No full textA theoretical model is proposed to describe the evolution of damage in brittle materials, such as concrete and masonry, subjected to increasing or sustained stresses of relatively high intensity. The model is based on the introduction of suitable damage variables in a rheological model. In this way, it is possible to describe the material behaviour under stresses either increasing or constant in time. The capabilities of the model in describing the mechanical response of material elements subjected to different stress histories are illustrated. Some correlations with experimental data from tests performed on masonry and concrete specimens are presented, to assess the reliability of the theoretical predictions. The results of some numerical applications to non--proportional stress paths are also illustrated. Finally, the limitations of the proposal are discussed and possible further improvements are envisaged
Creep modelling of masonry historic towers
No full textThis work illustrates a theoretical model developed to reproduce the behaviour of ancient masonry subjected to sustained stresses. Starting from a model recently proposed by the authors, two damage tensors have been introduced into a rheological model: the components of these tensors change both according to the intensity of the applied stress and, in case of sustained stress, to the duration of the load history. Evolution laws found in the literature for brittle materials have been employed. The principal directions of damage are meant to represent the directions of the experimental cracks; accordingly, when any damage direction is activated, it remains unchanged throughout the subsequent load history. The presence of second-order damage tensors makes it possible to describe the damage-induced anisotropy of the microcracked material. Also, since the possible increase of damage in time is accounted for, the model is able to describe creep failure and to predict the creep time to failure of the material under given stresses. The model parameters can be obtained through uniaxial creep tests on masonry samples at increasing stress levels and up to failure. The model was implemented into a finite element code, and structural analyses were carried out to assess the safety of middle-age masonry towers. The results obtained for one of these towers are briefly described and discussed
Modellazione del danneggiamento nelle murature in presenza di carichi non proporzionali
No full textIn questo lavoro viene presentato un modello sviluppato per riprodurre il comportamento di strutture murarie antiche soggette a carichi costanti e non proporzionali. Partendo da un modello proposto recentemente dagli autori, sono introdotti due tensori di danno le cui componenti evolvono in funzione sia dell’intensità degli sforzi applicati sia della loro durata. Si considera che ogni direzione principale di danno sia associata con la normale ad una microfessura che si forma e cresce in un punto qualsiasi del solido: pertanto quando una direzione è attivata rimane fissa qualunque sia l’evoluzione successiva dello sforzo e della deformazione. La presenza di tensori di danno del secondo ordine consente di descrivere l’anisotropia indotta dal danneggiamento e di predire la rottura per creep del materiale. Il modello è stato implementato in un codice di calcolo ad Elementi Finiti. I risultati delle analisi condotte sulla torre civica di Pavia e sulla torre del Duomo di Monza evidenziano la capacità del modello di cogliere i meccanismi di collasso riscontrabili sperimentalmente
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