1,721,012 research outputs found
A linear-elastic heuristic-molecular modelling for plane isotropic micropolar and auxetic materials
Full text linkA discrete Lagrangian approach is the basis for modelling the macroscale elastic response of a solid material, which can be homogeneous as well as a periodic composite. The basic topology is a square “heuristic molecule” that is an assemblage of four rigid bodies with a definite shape bonded by elastic springs. This is the minimum unit cell, UC, that contains all the macroscopic mechanical properties of the solid material, object of study. The paper presents 4 unit cells, in progression from a basic molecule bonded by 2 types of central forces, to a refined “Cosserat-auxetic” molecule that is connected by 4 types of shear and central bond-springs. The emphasis is given to the isotropic response in relation to the value of the macroscopic Poisson ratio, and the four examples of UC topologies are presented showing their relationship to different materials at the macro-scale: from a “rari-constant” continuum, through a standard isotropic Cauchy continuum, up to an isotropic centre-symmetric auxetic Cosserat solid
Nonlinear analysis of out-of-plane masonry façades: Full dynamic versus pushover methods by rigid body and spring model
No full textThe paper proposes a systematic comparison between two methods of analysis that are well established in the field of earthquake engineering: nonlinear dynamic analysis and nonlinear static procedure (NSP), applied to the out-of-plane seismic response of two masonry façades representative of many ancient Italian churches. The comparison is based on extensive numerical analyses, which focus on the flexural and torsional mechanisms, while the in-plane damage mechanisms and the possible detachment between the façade and the lateral walls because of a poor connection have been presently disregarded. The computations, both in the static and in the dynamic field, are based on a rigid body and spring model specifically implemented for this issue, computationally efficient and equipped with a realistic model of damage and hysteresis at the mesoscale. An innovative aspect of this study is the heuristic modelling of three-wythe masonry, to include some typical texture effects on the macroscale nonlinear response. For each façade, two different masonry textures were considered, performing extensive dynamic analyses that offered a detailed overview about the performance under earthquakes of different intensities. In parallel, NSP and the classical N2-based seismic assessment were applied. A critical discussion and comparison of the results of the two methods is presented to rationally appraise limits and opportunities. In particular, flexural and twisting out-of-plane mechanisms were clearly appraised in the dynamic field, whereas NSPs were not always able to describe the collapse, because they missed the partial failures determined by higher vibration modes, as could be expected
Full dynamic and pushover analyses of out-of-plane masonry facades: application and comparisons by RBSM
No full textThe paper is focused on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse
mode for the façade of buildings such as churches or basilicas. A full Nonlinear Dynamic (ND) modelling of the seismic
response is performed by adopting a specific rigid body and spring model (RBSM), where damage is ascribed to the
out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is
provided in the definition of the constitutive prescriptions, including hysteretic and degrading material behaviour. Then,
a comparison is made with a non linear static pushover (NSP) analysis, which is performed by means of the same
specific RBSM under quasi-static loading, incrementally applied. The seismic response in terms of generalized
force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic
displacement demand, expressed in terms of spectral coordinates. The two different approaches are compared by
considering as a case study the church of Rosario, in Guastalla, which was damaged by Emilia Romagna Earthquake
(1987). A number of analyses have been performed, investigating a variety of different aspects concerning the
accelerogram records and their correlation with the damage indicators of the non-linear models
A full orthotropic micropolar peridynamic formulation for linearly elastic solids
Full text linkAn original full orthotropic model for in-plane linear elasticity is proposed in the micropolar peridynamic analysis framework. The analytical formulation is derived from the definition of a specific microelastic energy function for micropolar nonlocal lattices which allows to obtain, for the first time, an orthotropic bond-based model characterized by four independent elastic moduli. An important feature of the model is that the bond properties, i.e. the elastic constants, are continuous functions of the bond orientation in the principal material axes. The introduction of the bond shear stiffness and the definition of a bond shear deformation measure which accounts for particle's rotation, on one hand eliminates the restriction of two independent constants that affects other bond-based orthotropic peridynamic formulations, and on the other makes the model suitable in predicting the mechanical behavior of a wide variety of Cauchy orthotropic materials undergoing homogeneous and non-homogeneous deformations. The accuracy of the proposed model in linear elasticity has been verified through simulating uniaxial extension test of a composite lamina with a central circular hole and natural frequency analyses considering different orientations of the principal material reference system
Out–of–plane seismic response of masonry façades: a comparison among full dynamic and pushover analyses
No full textStochastic discrete approaches for glass strength estimation
No full textA numerical investigation on the load carrying capacity of a glass beam modelled as a material with a random strength distribution is presented. The strength values were distributed randomly within the beam by a Monte Carlo simulation, according to statistical distributions calibrated on experimental results obtained from literature. The elastic-plastic problem has been solved using two different computational discrete approaches implemented in two inhouse computer codes: a Rigid Body-Spring Model (RBSM) and a mesh-free numerical method arising from lattice-based Peridynamics. Being discrete approaches directly based on algebraic governing equations, they are suitable in problems involving brittle failure, because cracks are not viewed as a pathology of the displacement field. By providing an appropraiate mathematical and computational framework, the differences and analogies of these models are discussed and then the variability of the load capacity of the structural element is evaluated as a function of the statistics of the strength related to the size of the defects. The results obtained show that both RBSM and Peridynamics seem to be powerful tools for modelling the failure of brittle materials with heterogeneous strength properties
Non-Linear Dynamic Analysis of Masonry Towers under Natural Accelerograms Accounting for Soil-Structure Interaction
No full textThe object of the paper is the influence of the soil-structure interaction on the dynamic response of masonry towers, for which a high level of stress is involved already in the static field. The relevant deformations and displacements at the base of the tower suggest that a significant volume of ground is engaged into the overall dynamic response, both as a participating mass and as a potential carrier of energy dissipation. In order to investigate this aspect and assess the sensitivity of the dynamic response of the soil-structure system to different soil characteristics, the non linear dynamic response of a case study is analysed, by including in the model a significant volume of foundation soil and considering two different ground types. The numerical model is based on a specific Rigid Body and Springs approach, in which the structure is idealized as a mechanism made of rigid elements connected each to the other by axial and shear springs. The nonlinear behaviour is lumped into the springs assigning proper constitutive laws able to model the significant inelastic aspects of the constitutive behaviour and the meso-scale damage mechanisms with a moderate computational effort. Two types of foundation soil have been considered in order to perform the dynamical analysis accounting for the soil-structure interaction: rock and deposits of compact gravel. For both models, non-linear dynamic analyses have been performed adopting natural records having different characteristics (with regard to the frequency content; distance from the epicentre and type of soil). Some interesting considerations are derived from this comparative study about a problem that is very actual for those who deal with non linear dynamics of structures, but yet is not much explore
Analisi sismica non lineare statica e dinamica di torri campanarie:applicazioni e confronti
No full textLa memoria riguarda la valutazione della vulnerabilità sismica dei campanili in muratura in Italia, che viene eseguita confrontando due metodi non lineari di analisi: analisi dinamica al passo e analisi pushover. Viene considerato un caso di studio ideale, al fine di confrontare la risposta strutturale prevista dai due metodi e valutarne le prestazioni. Il problema è semplificato, usando uno schema 2D piano, ed un modello specifico a masse rigide e molle per descrivere la dinamica nel piano. Le leggi costitutive sono state assegnate seguendo un approccio euristico semplificato, in cui sono contemplati i più significativi meccanismi di danno presenti alla meso-scala: i) resistenza a trazione molto bassa; ii) rilevante ortotropia ed effetti di tessitura in fase post-elastica; iii) diverse regole di danneggiamento assiale e a taglio; iv ) diversa resistenza a taglio a seconda della giacitura considerata (verticale o orizzontale); v) dissipazione isteretica dell’energia indotta dai carichi ciclici. Pur utilizzando una mesh abbastanza rada, il modello risulta
abbastanza ed efficiente, ed è in grado di cogliere anche gli effetti dei modi di vibrare superiori con un ragionevole sforzo computazionale. Analisi statiche non lineari sono state eseguite utilizzando il modello RBSM, ottenendo la curva di capacità e la valutazione della domanda sismica. Un confronto tra i due approcci, si propone, al fine di valutare la differenza di risultati (con particolare attenzione agli effetti danno indotto da modi di vibrazione più elevata) e di valutare la qualità e significatività dei risultati in termini di inconvenienti operativi e riduzione dei tempi di calcolo.The paper concerns the seismic vulnerability assessment of masonry bell towers in Italy, by comparing full non-linear dynamic and non-linear static analysis. An idealized case study is considered, in order to assess some basic and common features of the seismic structural response and to appraise the performance of the proposed approaches. The problem is simplified by using a plane 2D scheme. A specific Rigid Body and Spring Model is adopted to describe the in-plane dynamics. Constitutive laws were assigned following a simplified heuristic approach including the main meso–scale damage mechanisms: i) very low tensile strength; ii) significant post-elastic orthotropy plus texture effects; iii) different rules for post-elastic axial and shear damage; iv) different dependence of the shear strength on the vertical and horizontal axial stress component; v) hysteretic energy dissipation due to cyclic loading. Even using a quite coarse mesh, the model is capable to describe the higher vibration modes with a reasonable computational effort and using realistic accelerograms. Non linear static analysis was performed, by using the RBSM model, obtaining the capacity curve and assessing the seismic demand. A comparison between the two approaches is proposed, in order to appraise the difference in the results and to evaluate quality and significance of results in terms of operational drawbacks and reduction of computational times. Particular attention is devoted to the fact that static non-linear analyses tends to neglect the damage effects induced by higher vibration modes, as well as the influence of the shear response on the global damage
Caratterizzazione sintetica degli accelerogrammi e stima del danno strutturale atteso tramite un modello di strutture in muratura geometricamente regolari
No full textUn modello a parametri degradabili per lo studio della dinamica sismica delle torri in muratura
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