Elena Ferretti | Università di Bologna (original) (raw)

Papers by Elena Ferretti

Journal of Achievements in Materials and Manufacturing Engineering, 2022

According to ASTM, additive manufacturing is an assembly process of material printed layer by lay... more According to ASTM, additive manufacturing is an assembly process of material printed layer by layer to make objects from 3D model, the building in 3D printed started to make evolution with many start-ups and other companies. WASP ‒ World’s Advanced Saving Project ‒ is a company founded in 2012 in Massa Lombarda, Italy, inspired by the ”mason wasp”, which builds its own nest with materials collected from the surrounding environment, the company designs and produces 3D printers, GAIA is the first 3D printed ecological house in 2018, and TECLA is the new eco-habitat project created with recyclable and biodegradable materials [8]. The study of stability for a 3D printed structure presents a great challenge because the structure is printed without columns and beams. This article presents a new technique which helps improve stability and print other floors.

Buildings, 2023

Among all the active confinement techniques, the use of pre-tensioned stainless steel straps has ... more Among all the active confinement techniques, the use of pre-tensioned stainless steel straps has recently gained much attention. The flexibility of the stainless steel straps allows us to bend and pass them through the thickness of the masonry, thus creating a three-dimensional strengthening system between the two opposite facings. The use of the same perforation for the passage of several straps closed in a loop generates a continuous strengthening system that prevents parts of the structure from falling and injuring the occupants during seismic events. However, the perforations can nullify the in-plane strengthening, as they act as cylindrical hinges and make the reinforcement system labile for certain strap arrangements. Diagonal compression tests on square masonry panels performed in the present study show that the straps improve neither strength nor ductility when running along the mortar head and bed joints, arranged in square meshes. Conversely, they improve both strength and ductility when the straps make angles of ±45 with the mortar joints. Furthermore, the experimental results show that the straps exert an anisotropic effect that decreases the apparent in-plane Poisson ratio. They also provide new insights into the diagonal compression test and allow formulating a new proposal for the pseudo-ductility factor.

Buildings, 2024

This paper is the continuation of a previous study, which highlighted some inconsistencies in the... more This paper is the continuation of a previous study, which highlighted some inconsistencies in the RILEM guidelines for the interpretation of the diagonal compression test. Although improved compared to the ASTM guidelines, in fact, the RILEM guidelines underestimate the state of hydrostatic stress induced by the diagonal compression test at the center of the wallette. The new interpretation of the diagonal compression test proposed in this article shows that the RILEM guidelines actually underestimate both the hydrostatic and the deviatoric stress states at the center of the wallette. The new formulation complies with the linear elastic theory and allows us to use the diagonal compression test to identify the three elastic coefficients of masonry. In particular, it allows the identification of the Poisson ratio, which instead takes on a conventional value in the RILEM and ASTM guidelines. The difference of one order of magnitude between the conventional and proposed Poisson's ratio is in agreement with the experimental results on another brittle material, namely concrete. Finally, the new proposal fills the gap between the results provided by the two tests usually performed to identify the shear behavior of masonry: the diagonal compression test and the shear-compression test.

Two topics will be discussed here, which usually are not put in direct relationship: nonlocal app... more Two topics will be discussed here, which usually are not put in direct relationship: nonlocal approaches and the existence of strain-softening. It will be shown how some of the expedients used for treating strain-softening by avoiding the numerical instability associated with a material tangent stiffness matrix that ceases to be positive definite are equivalent to introducing a scale separation between the load-displacement and stress-strain laws. That is, they are equivalent to employing a relationship between effective stress and effective strain that is, not necessarily, softening. The identification procedure of the effective law is based just on the assumption that we must separate the material (stress-strain) from the structure (load-displacement) scale, since strain-softening is not a real material property but the result of inhomogeneous deformation caused by the experimental technique. This procedure provides the first experimental evidence against the existence of strain-softening in concrete and identifies a monotone strictly nondecreasing effective law. However, we could argue that this law is not interesting from the numerical point of view, since, being a local law, it is not suitable for modelling problems in which the size-effect is involved. As far as nonlocality is concerned, it will be argued that there is no evident physical justification for incorporating a length scale into the constitutive relationships. This need is due to the limit process on the basis of any differential formulation and may be avoided by using a discrete formulation. The Cell Method (CM) is the only formulation that is truly discrete, at present. This method allows us to express the governing equations in discrete form directly. Several numerical results will be provided here, which allows us to conclude that it is possible to perform a nonlocal analysis by means of the CM and the effective law, without any need to incorporate nonlocal effects in the constitutive equations

ABSTRACT The Cell Method (CM) is a computational tool that maintains critical multi-dimensional a... more ABSTRACT The Cell Method (CM) is a computational tool that maintains critical multi-dimensional attributes of physical phenomena in analysis. This information is neglected in the differential formulations of the classical approaches of finite element, boundary element, finite volume, and finite difference analysis, often leading to numerical instabilities and spurious results. This book highlights the central theoretical concepts of the CM that preserve a more accurate and precise representation of the geometric and topological features of variables for practical problem solving. Important applications occur in fields such as electromagnetics, electrodynamics, solid mechanics and fluids. CM addresses non-locality in continuum mechanics, an especially important circumstance in modeling heterogeneous materials. Professional engineers and scientists, as well as graduate students, are offered • A general overview of physics and its mathematical descriptions; • Guidance on how to build direct, discrete formulations; • Coverage of the governing equations of the CM, including non-locality; • Explanations of the use of Tonti diagrams; and • References for further reading.

International Journal of Fracture, Apr 1, 2004

La definizione di un modello meccanico adeguato allo studio del comportamento strutturale di una ... more La definizione di un modello meccanico adeguato allo studio del comportamento strutturale di una costruzione in muratura \ue8 tanto pi\uf9 difficoltosa quanto pi\uf9 piccola \ue8 la scala dimensionale dei fenomeni che si vuole cogliere. La costruzione del modello e la valutazione quantitativa dei parametri descrittivi del comportamento costitutivo non possono che essere il frutto di una procedura di identificazione parametrica stocastica. Nel recente passato, in tema di rappresentazione qualitativa e quantitativa del comportamento strutturale macroscopico, si \ue8 operato con modelli strutturali elementari. La ragione di questo approccio \ue8 in buona parte motivata dalla necessit\ue0 di contenere gli oneri computazionali e dalla impossibilit\ue0 pratica di definire la scala dimensionale del materiale. La descrizione di volumi danneggiati, la formazione e la propagazione di fessure, il comportamento isteretico di solidi murari sono oggetto del presente programma di ricerca. Il risultato di questa analisi costituisce la base di partenza utile alla stima di parametri strutturali, con valutazione dell'effetto scala. L'operazione di identificazione parametrica stocastica verte sulla definizione del comportamento costitutivo e si attiva su risultati sperimentali statici e/o dinamici di un organismo strutturale. Per l'aspetto metodologico ci si propone di operare nell'ambito delle teorie fisiche, introducendo un legame tra i valori efficaci degli sforzi e delle deformazioni. Il legame proposto non ha una formulazione meramente analitica, ma riassume i risultati di un'estesa campagna sperimentale sul comportamento in compressione dei materiali fragili, incentrata su una tecnica innovativa per la stima in tempo reale dello sviluppo del danno durante il processo di carico. Questa tecnica prevede anche una stima dei valori efficaci, che si configurano quindi come valori efficaci di derivazione sperimentale. L'obiettivo \ue8 quello di sanare su base sperimentale l'apparente divario tra le leggi medie acquisite sperimentalmente e le leggi efficaci multiparametriche che da almeno un ventennio vengono calibrate con precisione via via crescente per la modellazione dei principali fenomeni associati al comportamento strutturale dei materiali fragili. Uno sforzo successivo \ue8 quello di definire un modello strutturale che non necessiti della consueta calibrazione delle leggi efficaci multiparametriche per contenere gli effetti scala. Quest'ultimo impegno operativo \ue8 peraltro necessario ove si voglia pervenire alla modellazione di un comportamento strutturale sperimentalmente stabilito. Agli effetti computazionali, si intende utilizzare tanto il metodo delle celle, quanto il metodo degli elementi finiti, in modo da poter mettere a confronto l'efficienza computazionale dai due metodi, oltre che alcuni aspetti pi\uf9 prettamente teorici. Il metodo delle celle, ancora poco diffuso in ambito accademico e scientifico, fornisce una formulazione discreta diretta delle equazioni che reggono il problema in esame, senza dover ricorrere ad integrazioni sul campo di equazioni differenziali. Il vantaggio connesso all'uso di questo metodo \ue8 duplice. Infatti, la formulazione discreta diretta permette, da una parte, di abbattere notevolmente i tempi computazionali e, dall'altra, di costruire modelli intrinsecamente non-locali. Questo secondo aspetto va a tutto vantaggio delle leggi costitutive da impiegare nei modelli che, non dovendo pi\uf9 comprendere necessariamente gli effetti non-locali, possono assumere formulazioni notevolmente semplificate. Contrariamente a quanto accade con i modelli agli elementi finiti, quindi, l'adozione di un codice al metodo delle celle permette di scindere il concetto di non-localit\ue0 dal comportamento costitutivo, fornendo un notevole contributo all'analisi non-locale della meccanica della frattura, attualmente uno dei temi di maggior rilievo in ambito scientifico internazionale. Merito personale dei membri dell'Unit\ue0 di ricerca \ue8 l'aver messo in luce pe..

ABSTRACT Infinitesimal analysis has without doubt played a major role in the mathematical treatme... more ABSTRACT Infinitesimal analysis has without doubt played a major role in the mathematical treatment of physics in the past, and will continue to do so in the future, but we must also be aware that several important aspects of the phenomenon being described, such as its geometrical and topological features, remain hidden, in using the differential formulation. This is a consequence not of performing the limit, in itself, but rather of the numerical technique used for finding the limit. In this paper, we analyze and compare the two most known techniques, the iterative technique and the application of the Cancelation Rule for limits. It is shown how the first technique, leading to the approximate solution of the algebraic formulation, preserves information on the trend of the function in the neighbourhood of the estimation point, while the second technique, leading to the exact solution of the differential formulation, does not. Under the topological point of view, this means that the algebraic formulation preserves information on the length scales associated with the solution, while the differential formulation does not. This new interpretation of the Cancelation Rule for limits is also discussed in the light of the findings of non-standard calculus, the modern application of infinitesimals, in the sense of non-standard analysis, to differential and integral calculus.

European Journal of Engineering and Formal Sciences, Dec 29, 2018

SUMMARY. In this study, the results of an in-situ experimental program on the performance of conc... more SUMMARY. In this study, the results of an in-situ experimental program on the performance of concrete taxiways are presented. The experimental program has been undertaken at the Guglielmo Marconi airport of Bologna (Italy). It concerns two portions of the taxiway, one ...

Materials, 2022

This study provides a contribution to the research field of 3D-printed earthen buildings, focusin... more This study provides a contribution to the research field of 3D-printed earthen buildings, focusing, for the first time, on the load-bearing capacity of these structures. The study involves the entire production and testing process of the earthen elements, from the design, to the preparation of the mixture and the 3D printing, up to the uniaxial compression test on a wall segment. The results indicate that 3D-printed earthen elements have a compressive strength of 2.32 MPa, comparable to that of rammed earth structures. The experimental data also made it possible to draw conclusions on the action of the infill, which seems to have the function of stopping the propagation of cracks. This has a positive effect on the overall behavior of 3D-printed earthen elements, since it avoids the onset of dilative behavior in the final stages of the load test and maintains ultimate load values higher than 50% of the maximum load.

In this study, the Cell Method (CM) is applied in order to investigate the failure mechanisms of ... more In this study, the Cell Method (CM) is applied in order to investigate the failure mechanisms of masonry walls under shear force. The direction of propagation is computed step-wise by the code, and the domain is updated by means of a propagation technique of intra-element nodal relaxation with re-meshing. The crack extension condition is studied in the Mohr/Coulomb plane, using the criterion of Leon. The main advantage of using the CM for numerical analyses of masonry is that the mortar, the bricks and the interfaces between mortar and bricks can be modeled without any need to use homogenization techniques, simply providing each of them with their own constitutive properties. The capability of the CM to handle domains with more than one material is exploited to capture how the propagation direction changes when the crack overcome the joints or passes from the brick to the interface and to the mortar. Also, the principal stresses and principal directions of stress are mapped for the ...

This paper addresses the study of the stress field in composites continua with the multiscale app... more This paper addresses the study of the stress field in composites continua with the multiscale approach of the DECM (Discrete Element modeling with the Cell Method). The analysis focuses on composites consisting of a matrix with inclusions of various shapes, to investigate whether and how the shape of the inclusions changes the stress field. The purpose is to provide a numerical explanation for some of the main failure mechanisms of concrete, which is precisely a composite consisting of a cement-based matrix and aggregates of various shapes. Actually, while extensive experimental campaigns detailed the shape effect of concrete aggregates in the past, so far it has not been possible to model the stress field within the inclusions and on the interfaces accurately. The reason for this lies in the limits of the differential formulation, which is the basis of the most commonly used numerical methods. The Cell Method (CM), on the contrary, is an algebraic method that provides descriptions ...

Journal of Achievements in Materials and Manufacturing Engineering, 2022

Buildings, 2023

Buildings, 2024

International Journal of Fracture, Apr 1, 2004

European Journal of Engineering and Formal Sciences, Dec 29, 2018

Materials, 2022

Procedia Structural Integrity, 2020

As is well known, the main contribution of the FRP strips to the strength of load-bearing walls i... more As is well known, the main contribution of the FRP strips to the strength of load-bearing walls is an improvement in the in-plane strength. This paper deals with the possibility of applying the FRP strips in way to modify the strengthening mechanism of the FRP reinforcing system, from an in-plane to an out-of-plane strengthening mechanism. In order to achieve this goal, a second reinforcement system-derived from the CAM system (Active Confinement of Masonry)-provides connections between the FRP strips placed on the opposite sides of the wall. This new strengthening technique-called the straps/strips technique-establishes a stiffness constraint that forces the opposing FRP strips to behave like two flanges of an FRP I-beam embedded in the wall. Consequently, the use of FRP strips also improves the flexural strength of the wall. The present paper briefly summarizes the results obtained in previous works with the straps/strips technique and proposes an improvement of this strengthening technique, based on some weak-points emerged in the early experimentations. The paper also shows the results of a further experimental test, performed with the improved straps/strips technique. Finally, the similarity between FRP strips with transversal connection and concrete wythes of a sandwich panel with flexible connectors leads to interpret the behavior of the ideal I-beam in terms of composite action established between the FRP strips. This paves the way for analytical modeling of the straps/strips technique.

4th International Conference on Engineering and Formal Sciences, 2018

Proceedings RRRTEA, International Conference of Restoration, Recycling and Rejuvenation Technology for Engineering and Architecture Application, 2004

The Cell Method (CM) code with automatic remeshing for crack propagation analysis [6] is here use... more The Cell Method (CM) code with automatic remeshing for crack propagation analysis [6] is here used for modelling the pullout test. Particular emphasis is given to the analysis in the Mohr-Coulomb plane, since previous numerical models were not decisive in describing failure mechanism in pullout tests. The interpretations of experimental and analytical studies vary widely, and none of the existing explanations offer a complete description of the progressive failure of the concrete medium [21]. Nor do most existing interpretations appear to be totally compatible with the experimental evidence. Analysis of the failure mechanism for the pullout test requires a failure criterion accurately describing crack initiation in tension loading. The Mohr-Coulomb criterion of the first code [6] has therefore been abandoned in favour of a more realistic criterion for the tensile state of stress, the Leon criterion. The failure analysis has been performed for several ratios between the counterpres-sure diameter and the stem length (Fig. 1). Moreover, the complete crack path has been obtained for the geometry of the Lok-test. The evolving state of stress-strain for the Lok-test is also provided. The identification of the directions of principal stress completes the stress analysis. Modelling is performed both on the concrete specimen and on the steel insert, showing how the CM can easily handle domains with several materials.

Proceedings IGF 17, XVII National Conference Italian Group of Fracture, 2004

Short abstract: One of the main research fields in past years concerns the modeling of heterogene... more Short abstract: One of the main research fields in past years concerns the modeling of heterogeneous materials. For these materials, the use of the classical local continuum concept does not seem to be adequate. The classical local continuum concept leads to constitutive models falling within the category of simple nonpolar materials (Noll 1972). For these materials, the stress at a given point uniquely depends on the current values, and possibly also the previous history, of deformation and temperature at that point only (Bažant and Jirásek 2002). Beginning with Krumhansl (1965), Rogula (1965), Eringen (1966), Kunin (1966), and Kröner (1968), the idea was promulgated that heterogeneous materials should properly be modeled by some type of nonlocal continuum. Some preliminary ideas on nonlocal elasticity can be traced back to the late 19 th century (Duhem 1893). Nonlocal continua are continua in which the stress at a certain point is not a function of the strain at the same point, but a function of the strain distribution over a certain representative volume of the material centered at that point (Bažant and Chang 1984). Thus, nonlocality is tantamount to an abandonment of the principle of the local action of classical continuum mechanics (Bažant and Jirásek 2002). Local constitutive relations between stress and strain tensors are not adequate for describing the mechanical behavior of solids in the classical differential formulation, since no material is an ideal continuum, decomposable into a set of infinitesimal material volumes, each of which can be described independently. All materials, natural and man-made, are characterized by microstructural details whose size ranges over many order of magnitude (Bažant and Jirásek 2002). In constructing a material model, one must select a certain resolution level below which the microstructural details are not explicitly visible. Instead of refining the explicit resolution level, it is often more effective to use various forms of generalized continuum formulation, dealing with material that are nonsimple or polar, or both. A list of enriched continuum models is provided in Bažant and Jirásek (2002). Among these, a great variety of nonlocal models was developed. The aim of the present study is to show that nonlocal constitutive relations between stress and strain tensors are not strictly needed to construct a material model. They are required only if a differential formulation is used for modeling nonlocality, since differential operators are local. The physical well-posedness of nonlocality is discussed with regard to the differential and discrete formulations. Nonlocality was found to be a concept not attaining to the description of the material, but of the phenomenon. This made it possible to discuss the opportunity of using nonlocality in order to give respectability to strain-softening damage models. The mathematical and physical well-posedness and the existence of strain-softening are also discussed. When using the differential formulation, a length scale must be introduced into the material description of a strain-softening modeling. This need has been here justified on the basis of the geometrical information which has been lost in performing the limit process. It was shown how, avoiding the limit process, a length scale is intrinsically taken into account into a discrete formulation. Thus, the discrete formulation turns out to be more appealing than the differential formulation with nonlocal approach, from the physical point of view.

16th AIMETA Congress of Theoretical and Applied Mechanics, 2003

The Cell Method (CM) code with automatic remeshing for crack propagation analysis is here used fo... more The Cell Method (CM) code with automatic remeshing for crack propagation analysis is here used for modeling the pullout test. The interpretations of experimental and analytical studies on the pullout test vary widely, and none of the existing explanations offer a complete description of the progressive failure of the concrete medium. Here, failure analysis has been performed for several ratios between the counter-pressure diameter and the stem length. Moreover, the complete crack path has been obtained for the geometry of the Lok-test. The evolving state of stress-strain for the Lok-test is also provided. The identification of the directions of principal stress completes the stress analysis.

International Conference on Computational & Experimental Engineering and Sciences ICCES'13, 2013

This study deals with structural modeling of composite structures by using Generalized Differenti... more This study deals with structural modeling of composite structures by using Generalized Differential Quadrature Finite Element Method (GDQFEM), compared with Cell Method (CM) and Finite Element Method (FEM). In particular, results on stress and strain at fiber/matrix interface of the composite material are here provided. The GDQFEM is based on the classic Generalized Differential Quadrature (GDQ) technique applied to simple geometries [1]. A GDQ rule is applied upon each sub-domain, or element, in which the problem domain is divided. When the problem domain is not regular, the mapping technique is used to transform the fundamental system of equations, the compatibility conditions of the adjacent sub-domains and the boundary conditions defined on the physical sub-domain, into the regular master element in the computational domain. Pursuing the following GDQFEM, a differential problem can be turned into an algebraic system. With respect to the very well-known Finite Element Method (FEM), the GDQFEM is based on a different approach: the direct derivative calculation is performed by using the GDQ rule. The imposition of the compatibility conditions between two boundaries are also used in the CM for solving contact problems [4,5]. Since the GDQFEM is an higher-order tool connected with the resolution of the strong form, the compatibility conditions must be applied at each disconnection in order to capture the discontinuity between two boundaries, without losing accuracy. A comparison between GDQFEM, CM and FEM is presented and very good agreement is observed.

International Conference on Computational & Experimental Engineering and Sciences ICCES'13, 2013

The aim of this work is to study the static behavior of 2D soft core plane state structures, whic... more The aim of this work is to study the static behavior of 2D soft core plane state structures, which are very common in many engineering fields. Deflections and inter-laminar stresses caused by forces can have serious consequences for strength and safety of these structures. Therefore, an accurate identification of the variables in hand is of considerable importance for their technical design. In particular, it will be shown how a soft core structure can be tailored as a function of the stress profile of the two constituent materials. It is obvious that, since a complex plane structure is under consideration, there is no analytical solution which can be used to solve the physical system problem. Only numerical procedures can be considered to solve a two-material system subjected to generic static loads. In this study two advanced numerical technique will be used: the Generalized Differential Quadrature Finite Element Method (GDQFEM) procedure and the Cell Method (CM). The first is a numerical technique based on the classic Generalized Differential Quadrature (GDQ) rule [1,2,3] and it operates differently from the well-known Finite Element Method (FEM). In fact, compatibility conditions are enforced between the element boundaries, such as in the CM contact problems [4,5]. In order to capture the discontinuity between two boundaries, the compatibility conditions have to be applied at each disconnection, when the GDQFEM is used. New results are presented to illustrate comparisons between GDQFEM, CM and FEM.

GIMC XVI, 2006

The Cell Method (CM) is applied here in order to investigate the failure mechanisms of masonry wa... more The Cell Method (CM) is applied here in order to investigate the failure mechanisms of masonry walls under shear force. The direction of propagation is computed step by step by the code, and the domain is updated by means of a propagation technique of nodal relaxation intraelement with re-meshing. The crack extension condition is studied in the Mohr/Coulomb plane, using the criterion of Leon. The direction of propagation is computed as the slope of the line joining the Mohr’s pole to the point tangent to the Leon limit surface.

AIMETA 2011, 2011

In this study, the results of an in-situ experimental program on the performance of concrete taxi... more In this study, the results of an in-situ experimental program on the performance of concrete taxiways are presented. The experimental program has been undertaken at the Guglielmo Marconi airport of Bologna (Italy). It concerns two portions of the taxiway, one realized in plain concrete and one realized in rubberized concrete. Each portion has been instrumented with strain gauges for the acquisition of vertical strains inside concrete.

WCCM VII 7th World Congress on Computational Mechanics, 2006

The Cell Method (CM) is applied in order to investigate the failure mechanisms of masonry walls u... more The Cell Method (CM) is applied in order to investigate the failure mechanisms of masonry walls under shear force. The direction of propagation is computed step-wise by the code, and the domain is updated by means of a propagation technique of intra-element nodal relaxation with re-meshing. The crack extension condition is studied in the Mohr/Coulomb plane, using the criterion of Leon. The main advantage of using the CM for numerical analyses of masonry is that the mortar, the bricks and the interfaces between mortar and bricks can be modeled without any need to use homogenization techniques, simply providing each of them with their own constitutive properties. The capability of CM to handle domains with more than one material is exploited to capture how the propagation direction changes when the crack overcome the joints or passes from the brick to the interface and to the mortar. Also the principal stresses and the principal directions of stress are mapped for the bricks, the interfaces and the mortar.

International Conference on Computational & Experimental Engineering and Sciences ICCES'13 , 2013

In the present paper the Generalized Differential Quadrature Finite Element Method (GDQFEM) is ap... more In the present paper the Generalized Differential Quadrature Finite Element
Method (GDQFEM) is applied to solve plane state structures with generic discontinuities,
such as linear cracks and holes of various shapes. The GDQFEM is an extension of the
Generalized Differential Quadrature developed by Shu [1]. The static analysis of the
structures at issue is investigated. In particular, the results in terms of stresses and
displacements for classical and advanced plane stress problems with discontinuities are
compared to the Cell Method (CM) [2, 3, 4] and the Finite Element Method (FEM).

Abstract In the present paper fracture criteria for predicting crack initiation angles in an orth... more Abstract In the present paper fracture criteria for predicting crack initiation angles in an orthotropic homogeneous plate, with an inclined crack and subjected at infinity to a biaxial uniform load, are studied. The crack initiation angle θ0 can be calculated as a function of crack geometry and external loading applied at infinity. The numerical analysis is performed for a wide range of anisotropic material properties and applied loads.

Proceedings ICF XI, 11th International Conference on Fracture, 2005

Nonlocal approaches are discussed with regard to the differential and discrete formulations. Nonl... more Nonlocal approaches are discussed with regard to the differential and discrete formulations. Nonlocality was found to be a concept non attaining to the description of the material, but of the physical phenomenon. When using the differential formulation for modeling heterogeneous materials, a length scale must be introduced into the material description. This need has been here justified on the basis of the geometrical information which has been lost in performing the limit process. It was shown how, avoiding the limit process, a length scale is intrinsically taken into account into a discrete formulation. This made it possible to discuss the opportunity of using nonlocality in order to give respectability to strain-softening damage models.

International Conference on Computational & Experimental Engineering and Sciences ICCES'13, 2013

One of the hottest trends in floor tile marketplace is the emergence of thin tiles. Made of porce... more One of the hottest trends in floor tile marketplace is the emergence of thin tiles. Made of porcelain, they start at thicknesses of about 2.5 mm for walls up to about 6 mm thick for floors, while, until recently, floor tiles have been 8 to 12 mm thick and tiles less than 7.5 mm were not intended for floors. Manufacturers benefit a range of advantages from tiles engineered to be thinner, including installation over existing floor or wall coverings, eliminating the need for ripping out existing finishing materials in renovation projects, saving time and money in labor costs. Thin tiles are strong and lightweight, reduce material consumption – which benefits the environment – and take fewer resources to manufacture and ship. They can also be easily cut with a wet saw, and in some cases with a glass cutter.

Fifth World Congress on Computational Mechanics V, 2002

In this study, the problem of finding the complete trajectory of propagation in plates with inter... more In this study, the problem of finding the complete trajectory of propagation in plates with internal straight cracks is extended to the non-linear field. In particular, results concerning concrete plates in bi-axial tensile loading are shown.
The concrete constitutive law adopted for this purpose is monotonically non-decreasing, as following according to previous studies of the Authors on monotonic mono-axial loading. The analysis is performed in a discrete form, by means of the Cell Method (CM). The aim of this study is both to test the new concrete constitutive law in biaxial tensile load and to verify the applicability of the CM in crack propagation problems for bodies of non-linear material. The discrete analysis allows us to identify the crack initiation without using the stress intensity factors. Moreover, previous studies showed how the boundary conditions are no longer a problem with the CM. These two circumstances involve computational simplifications in cracked solids of finite dimensions. An example of computation in finite solids, the skew-symmetric four-point bending beam, is provided.

ASEM, Pusan (Korea), 2002

In this study, the problem of finding the limiting load in infinite plates with internal cracks i... more In this study, the problem of finding the limiting load in infinite plates with internal cracks is extended to the non-linear field. In particular, results concerning concrete plates in bi-axial loading are shown. The analysis is performed in discrete form, by means of the Cell Method. The discrete analysis allows us to identify the crack initiation without using the stress intensity factors. This simplifies the computation in cracked solids of finite dimensions. An example of computation in finite solids, the skew-symmetric four-point bending beam, is provided.

Proceedings of XVI Convegno Italiano di Meccanica Computazionale, GIMC, 2006

In this paper an exact solution methodology, based on the coupling of the dynamic stiffness matri... more In this paper an exact solution methodology, based on the coupling of the dynamic stiffness matrix and the line-spring, enabling one to analyze the coupled bending-torsion free vibration of Timoshenko beams weakened by multiple non-propagating part-through surface cracks is presented. The changes introduced by the presence of three transverse open cracks, regarding the modal response, are investigated. A parametric study has been carried out for various crack parameters such as crack depth and location.

Atti del Convegno AIMETA, 1999

The results of a numerical simulation of the macroscopic behavior in axial compression of concret... more The results of a numerical simulation of the macroscopic behavior in axial compression of concrete cylindrical specimens were presented. According with the results of previous works [1, 2, 3, 4], the introduced constitutive law was a monotonically increasing one. Stresses and displacements fields were evaluated by discrete formulation of the elastic equilibrium problem. When the Mohr/Coulomb cracking criterion was verified, the cylinder geometry was modified with the introduction of new free surfaces due to crack propagation. The macroscopic result in terms of load-displacement was affected by the decreasing of stiffness due to crack propagation. It was showed that the softening behavior is a macroscopic effect bonded to the structural behavior and that it doesn’t correspond to a material constitutive property.

Atti del Convegno AIAS, 1999

The results of a numerical simulation of the macroscopic behavior in axial compression of concret... more The results of a numerical simulation of the macroscopic behavior in axial compression of concrete cylindrical specimens are presented. According with the results of a previous work [1], the introduced constitutive law is a monotonically increasing one. Stress and displacements fields were evaluated by discrete formulation of the elastic equilibrium problem. When the Coulomb cracking criterion is verified, the cylinder geometry is modified with the introduction of new free surfaces due to the crack propagation. The macroscopic result in terms of load-displacement is affected by the decreasing of rigidity due to the crack propagation. We shown that the softening behavior is a macroscopic effect bonded to the structural mechanics and that it doesn’t correspond to a material constitutive property.

The Cell Method (CM) is a computational tool that maintains critical multidimensional attributes ... more The Cell Method (CM) is a computational tool that maintains critical
multidimensional attributes of physical phenomena in analysis. This
information is neglected in the differential formulations of the classical
approaches of finite element, boundary element, finite volume,
and finite difference analysis, often leading to numerical instabilities
and spurious results.
This book highlights the central theoretical concepts of the CM that
preserve a more accurate and precise representation of the geometric
and topological features of variables for practical problem solving.
Important applications occur in fields such as electromagnetics, electrodynamics,
solid mechanics, and fluids. CM addresses non-locality
in continuum mechanics, an especially important circumstance in
modeling heterogeneous materials. Professional engineers and scientists,
as well as graduate students, are offered:
• A general overview of physics and its mathematical descriptions;
• Guidance on how to build direct, discrete formulations;
• Coverage of the governing equations of the CM, including
non-locality;
• Explanations of the use of Tonti diagrams; and
• References for further reading.

Advanced in Fracture and Damage Mechanics II. Proc. Int. Conf. on Fracture and Damage Mechanics, 2001

A new procedure is proposed for identifying mono-axial stress-strain relationship and Poisson rat... more A new procedure is proposed for identifying mono-axial stress-strain relationship and Poisson ratio in compressed plain concrete. By considering the specimen as a structure, the procedure identifies effective properties from experimental data. This way of proceeding involves a modification of traditionally identified mono-axial stress-strain relationship and Poisson ratio. Results are presented for cylinders of various slendernesses.

Mathematics and Computers in Science and Engineering Series - Recent Advances in Applied Mathematics, Modelling and Simulation, 2014

The Cell Method (CM) associates any physical variable with the geometrical and topological featur... more The Cell Method (CM) associates any physical variable with the geometrical and topological features, usually neglected by the differential formulation. This goal is achieved by abandoning the habit to discretize the differential equations. The governing equations are then derived in algebraic manner directly, by means of the global variables. In the original formulation of the CM, the association between physical variables and geometry is made on the basis of physical considerations. In this paper, we analyze the same association under the mathematical point of view. This allows us to view the CM as a geometric algebra, which is an enrichment of the exterior algebra. The-space p elements and their inner and outer orientations are derived inductively. They are obtained from the outer product of the geometric algebra and the features of-vectors p. Space and time global variables are treated in a unified four-dimensional space/time cell complex, whose elementary cell is the tesseract. Moreover, the configuration variables with their topological equations, on the one hand, and the source variables with their topological equations, on the other hand, are viewed as a bialgebra and its dual algebra.

Proceedings RRRTEA, International Conference of Restoration, Recycling and Rejuvenation Technology for Engineering and Architecture Application, 2004

Rapporto Biennale CINECA, 2000

A numerical code for modeling crack propagation using the Cell Method (CM) has been implemented. ... more A numerical code for modeling crack propagation using the Cell Method (CM) has been implemented. The crack geometry is updated with an intra-element propagation technique. Automatic remeshing is activated after each update. The code was implemented in Matlab on EIDOS. Results for Mixed Mode crack propagation are presented.

Research and Applications in Structural Engineering, Mechanics and Computation - Proceedings of the 5th International Conference on Structural Engineering, Mechanics and Computation, SEMC, 2013

In this document, we have proposed a second order solution to Boussinesq's problem (Boussinesq 18... more In this document, we have proposed a second order solution to Boussinesq's problem (Boussinesq 1885), which allows us to account for the new experimental evidence (Ferretti & Bignozzi 2012, Ferretti 2012b) on the stress field induced by aircraft traffic in concrete pavements. In particular, the second order solution is able to describe the tensile state of stress acquired in the proximity of the contact area and not accounted for in the classical solution of Boussinesq's problem for a homogeneous linear-elastic and isotropic half-space. The second order solution also allows us to evaluate the effect of the elastic constants on the stress field, improving the solution of Boussinesq in this second case also.

Problems in Structural Identification and Diagnostics: General Aspects and Applications: MURST Project n. MM08342598—COFIN 2000, 2003

A numerical code for modeling crack propagation using the Cell Method is proposed. The Leon failu... more A numerical code for modeling crack propagation using the Cell Method is proposed. The Leon failure surface is used to compute the direction of crack propagation, and the new crack geometry is realized by an intra-element propagation technique. Automatic remeshing is then activated. Applications in Mode I, Mode II and Mixed Mode are presented to illustrate the robustness of the implementation.

Problems in Structural Identification and Diagnostics: General Aspects and Applications: MURST Project n. MM08342598—COFIN 2000, 2003

The present study is part of an identifying programme for constitutive parameters in damaged mate... more The present study is part of an identifying programme for constitutive
parameters in damaged materials, termed the “effective parameters”. The programme
starting point is that the experimental response depends not only on constitutive
parameters, but also on structural mechanics and interaction with the
test-machine. It is showed how the load-displacement diagram of compressed concrete
cylinders is affected by crack propagation, through the resistant structure
modification. Moreover, it is analytically demonstrated that the effective stress
(σeff )-effective strain (²eff ) curve exhibits a strictly positive derivative at the point
corresponding to the average stress (σ)-average strain (ε) curve peak. Finally, it
is proposed a new identification procedure which provided satisfactory results, giving
monotone strictly non-decreasing, size-effect insensitive and failure mechanism
insensitive σeff − εeff curves.

Mathematics and Computers in Science and Engineering Series - Proceedings ICACM '14 - 3rd International Conference on Applied and Computational Mathematics, 2014

Infinitesimal analysis has without doubt played a major role in the mathematical treatment of phy... more Infinitesimal analysis has without doubt played a major role in the mathematical treatment of physics in the past, and will continue to do so in the future, but we must also be aware that several important aspects of the phenomenon being described, such as its geometrical and topological features, remain hidden, in using the differential formulation. This is a consequence not of performing the limit, in itself, but rather of the numerical technique used for finding the limit. In this paper, we analyze and compare the two most known techniques, the iterative technique and the application of the Cancelation Rule for limits. It is shown how the first technique, leading to the approximate solution of the algebraic formulation, preserves information on the trend of the function in the neighbourhood of the estimation point, while the second technique, leading to the exact solution of the differential formulation, does not. Under the topological point of view, this means that the algebraic formulation preserves information on the length scales associated with the solution, while the differential formulation does not. This new interpretation of the Cancelation Rule for limits is also discussed in the light of the findings of non-standard calculus, the modern application of infinitesimals, in the sense of non-standard analysis, to differential and integral calculus.

Nota Tecnica N° 55, 2001

A numerical code for modeling crack propagation using the cell method is proposed. The Mohr-Coulo... more A numerical code for modeling crack propagation using the cell method is proposed. The Mohr-Coulomb criterion is used to compute the direction of crack propagation, and the new crack geometry is realized by an intra-element propagation technique. Automatic remeshing is then activated. Applications in Mode I and Mixed Mode are presented to illustrate the robustness of the implementation.

Nota Tecnica N° 67, 2002

In this study, the problem of finding the limiting load in infinite plates with internal cracks i... more In this study, the problem of finding the limiting load in infinite plates with internal cracks is
extended to the non-linear field. In particular, results concerning concrete plates in bi-axial
loading are shown. The analysis is performed in discrete form, by means of the Cell Method.
The discrete analysis allows us to identify the crack initiation without using the stress intensity
factors. This simplifies the computation in cracked solids of finite dimensions. An example of
computation in finite solids, the skew-symmetric four-point bending beam, is provided.

Nota Tecnica N° 68, 2002

In this study, the problem of finding the complete trajectory of propagation in plates with inter... more In this study, the problem of finding the complete trajectory of propagation in plates with internal
straight cracks is extended to the non-linear field. In particular, results concerning concrete plates in
bi-axial tensile loading are shown.
The concrete constitutive law adopted for this purpose is monotonically non-decreasing, as following
according to previous studies of the Authors on monotonic mono-axial loading.
The analysis is performed in a discrete form, by means of the Cell Method (CM).
The aim of this study is both to test the new concrete constitutive law in biaxial tensile load and to
verify the applicability of the CM in crack propagation problems for bodies of non-linear material.
The discrete analysis allows us to identify the crack initiation without using the stress intensity factors.
Moreover, previous studies showed how the boundary conditions are no longer a problem with the
CM. These two circumstances involve computational simplifications in cracked solids of finite
dimensions. An example of computation in finite solids, the skew-symmetric four-point bending beam,
is provided.

Nota Tecnica N° 146, 2004

La risposta sismica di un oggetto d’arte può essere valutata assimilandolo ad un blocco rigido. L... more La risposta sismica di un oggetto d’arte può essere valutata assimilandolo ad un blocco rigido. L’indagine verrà condotta con riferimento al modello di Housner [1] utilizzando però il regime di grandi spostamenti. L’oggetto d’arte si pensa investito direttamente da un accelerogramma al piede che può provocarne il ribaltamento e la seguente rottura da impatto. Per evitare tale fenomeno che potrebbe, alcune volte, portare alla perdita di un capolavoro di inestimabile valore, si è eseguita una indagine della loro vulnerabilità alle azioni sismiche. Le equazioni del moto che governano il fenomeno delle oscillazione forzate, del manufatto artistico, sono state ricavate attraverso le equazioni di Lagrange generalizzate ed integrate numericamente, visto la loro elevata non linearità. La caratterizzazione dello specifico oggetto d’arte è stata eseguita tramite il suo rapporto geometrico, il fattore di scala e un parametro di inerzia rotazionale. Inoltre, sono state distinte quattro modalità di comportamento dinamico del blocco a seguito dell’eccitazione sismica: pieno contatto, oscillazione con rientro in stick, oscillazione, ribaltamento. Inizialmente, si è pensato di studiare il comportamento dinamico di una statua, rappresentante una figura umana di circa due metri, con accelerazione al piede pari a quella del terremoto di El Centro (1940). Si è fatta un’analisi variando la snellezza e tenendo costante il fattore di scala, riportando in un grafico il tempo di ribaltamento in funzione della snellezza dell’oggetto. Successivamente, si è vista l’influenza del fattore di scala sul comportamento della statua, incrementandolo e mantenendo costante il rapporto geometrico. Per avere una visone d’insieme, si è calcolato il tempo di uscita dalla fase di stick e il tempo di ribaltamento, variando entrambi i paramenti contemporaneamente. Quindi si è elaborato una mappa di vulnerabilità sismica e un diagramma del fattore di rischio che consentono di distinguere immediatamente i manufatti artistici più stabili. Per testare la sensibilità della risposta dinamica al variare dell’oggetto d’arte, sono state compiute le stesse analisi partendo da un vaso vuoto alto circa 1.00 m. Per poter confrontare i diversi risultati ottenuti per la statua e per il vaso si sono rappresentate le tipologie di risposta dinamica, sopra descritte, in forma percentuale. Al fine di comprendere l’influenza del livello di eccitazione sismica sul comportamento dinamico degli oggetti d’arte, è stata analizzata la classe di statue soggette all’accelerogramma di Kobe. Per stimare la bontà dei risultati è stato riportato il confronto tra la frequenza linearizzata della classe di blocchi e la trasformata di Fourier del terremoto. In seguito si sono creati degli accelerogrammi artificiali partendo da quello di Kobe, moltiplicandolo per un’onda sinusoidale selezionando ampiezza, frequenza e fase. Lo scopo è quello di mantenere la PGA del nuovo terremoto circa costante. Si è analizzato, quindi, il comportamento dinamico di una classe di manufatti artistici soggetti a questi accelerogrammi artificiali, stilando sempre una mappa di vulnerabilità e una mappa si stabilità per ogni caso. Inoltre, per riassumere le differenti risposte ottenute, sono state rappresentate in forma probabilistica in un unico diagramma. Infine è stato eseguito uno studio della classe di statue soggette allo stesso accelerogramma di Kobe per diversi fattori di scala, per capire come l’incremento della PGA, a parità di spettro di frequenze dell’eccitazione, influisca sulla risposta del sistema.

Nota Tecnica N° 54, 2001

Problems in Structural Identification and Diagnostics: General Aspects and Applications: MURST Project n. MM08342598—COFIN 2000, 2003

The present study is part of an identifying programme for constitutive parameters in damaged mate... more The present study is part of an identifying programme for constitutive parameters in damaged materials, termed the " effective parameters ". The programme starting point is that the experimental response depends not only on con-stitutive parameters, but also on structural mechanics and interaction with the test-machine. It is showed how the load-displacement diagram of compressed concrete cylinders is affected by crack propagation, through the resistant structure modification. Moreover, it is analytically demonstrated that the effective stress (σ ef f)-effective strain (² ef f) curve exhibits a strictly positive derivative at the point corresponding to the average stress (σ)-average strain (ε) curve peak. Finally, it is proposed a new identification procedure which provided satisfactory results, giving monotone strictly non-decreasing, size-effect insensitive and failure mechanism insensitive σ ef f − ε ef f curves.

Problems in Structural Identification and Diagnostics: General Aspects and Applications: MURST Project n. MM08342598—COFIN 2000, 2003

Atti del Congresso su “La Sicurezza delle Strutture in Calcestruzzo ad Alte Prestazioni, 1999

Atti delle Giornate di Studio su" La Sicurezza delle Strutture in Calcestruzzo ad Alte Prestazioni, 1999

La ricerca si riferisce ad un'applicazione dei metodi di analisi basati sulla propagazione di ond... more La ricerca si riferisce ad un'applicazione dei metodi di analisi basati sulla propagazione di onde elastiche di vibrazione, finalizzata a valutare l’insorgenza e la propagazione di fessure durante prove di compressione su cilindri in calcestruzzo ad alta resistenza. La metodologia di indagine si basa sull’impiego simultaneo di un elevato numero di trasduttori piezoelettrici e sull’elaborazione dei risultati per ottenere immagini tomografiche, a partire da determinazioni di valori di velocità di propagazione e di attenuazione.

Materials, 2022

This paper is part of a study of earthen mixtures for 3D printing of buildings. To meet the ever-... more This paper is part of a study of earthen mixtures for 3D printing of buildings. To meet the ever-growing environmental needs, the focus of the paper is on a particular type of bio-composite for the stabilization of earthen mixtures – the rice husk-lime bio-composite – and on how to enhance its effect on the long-term mechanical properties of the hardened product. Having assumed that the shredding of the vegetable fiber is precisely one of the possible ways to improve the mechanical properties, we compared the results of uniaxial compression tests performed on cubic specimens made with both shredded and raw vegetable fiber, for three curing periods. The results showed that the hardened earthen mixture is not a brittle material in the strict sense, because it exhibits some peculiar behaviors, anomalous for a brittle material. However, being a “designable” material, its properties can be varied with a certain flexibility to get as close as possible to the desired ones. One of the pecul...

The construction field uses up over one-third of the global energy consumption and contribute to ... more The construction field uses up over one-third of the global energy consumption and contribute to 40% of CO2 emissions according to the International Energy Agency (IEA) and the 2020 annual reporter of United Nation, Goal 11 (Make cities inclusive, safe, resilient and sustainable) which discusses sustainable, safe and efficient buildings. Therefore, Morocco has a commitment to this program by publishing the law 47-09 of energy efficiency. This work aims to study the energy efficiency of two types of building, a conventional and a natural building. Conventional building is constructed using concrete, while the natural one uses sand clay and straws. As for the technique of making the natural building, it perpetually follows the same approach accustomed in rural zones of Atlas Mountains in Morocco. In this research we also simulate, temperature and humidity variation inside these buildings using TRNSYS software. Sketch Up software was employed to design these houses. The weather databas...