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## Publications

Publications (68)

Avalanches are natural events that can have consequences such as silvicultural losses, infrastructural damages, fatalities. In this paper, the attention is given to glide avalanches starting by a glide crack, a tensile crack that propagates at the crown – the upper release limit – due to the internal stress variation. However, the presence of a gli...

The shear properties are key characteristics for evaluating masonry elements under in-plane horizontal actions. Historical structures may need the evaluation of these properties in order to perform safety evaluations, diagnoses, retrofitting, etc. These properties are often difficult to estimate and may be measured using Destructive Testing (DT) me...

The EQuivalent Polynomials library, EQP, herein provided is a powerful tool for the numerical integration, with classical quadrature rules (e.g. Gauss–Legendre), of a function given by the product of an arbitrary polynomial times a Heaviside step function. The library can handle a multiplicity of shapes for the integration domain in one, two and th...

The shear properties of unreinforced masonry are key parameters used in order to understand the behaviour of these structures under horizontal actions. These characteristics are usually determined using Destructive Testing (DT) methods. However, this typology of tests is not always suitable due to both their high impact and cost. The present work a...

The paper illustrates the development and the application of an active monitoring system, and analyzes the investigated dynamic behaviour of the structure where the system is applied. The system is installed on a 250 m suspended arch steel bridge that has been instrumented with sensors of different type. This work focuses on the employed methodolog...

An innovative approach, defined by the term “Active Monitoring”, has been designed and implemented by the Company ARCOS Engineering for a steel suspended arch bridge, starting from its design phases, for the sake of structural control and maintenance operations. The structure has a span of 250 m with a central arch that supports the runway through...

IIn the present study, Acoustic Emission (AE) monitoring technique is applied in order to characterize the brick masonry of two important military buildings located in Northern Italy: the barracks of Alessandria and Boves. The internal brick masonry walls of the two barracks object of the study are tested by two double flat-jack systems, in order t...

We consider the problem of laser scanners are increasingly being employed as surveyinginstruments for numerous applications. In this paper we have constructed a system for monitoringdangerous parts of archaeological sites or buildings. In order to the fragile parts of an archaeologicalsite or building are protected without human intervention, the s...

In the present paper, a new d⁺/d⁻ damage model apt for quasi-brittle materials is described and its validation is carried out considering unreinforced concrete, reinforced concrete and masonry elements.Two independent scalar damage variables, d⁺ and d⁻ , in combination with the split of the reversible strain tensor into its positive and negative co...

Bordas thanks funding provided by the European Research Council Starting Independent Research Grant (ERC Stg grant agreement No. 279578)“RealTCut towards real time multiscale simulation of cutting in non-linear materials with applications to surgical simulation and computer guided surgery”. Stéphane Bordas also thanks the financial support of the F...

A stable extended finite element method (XFEM) is combined to a three dimensional version of the vector level set method (Ventura et al., Int. J. Numer. Methods Eng. 58(10):1571–1592, 2003) to solve non-planar three-dimensional (3D) crack propagation problems. The proposed XFEM variant is based on an extension of the degree of freedom gathering tec...

In the present paper, a constitutive nonlocal damage model is proposed for the non-linear incremental finite element analysis of masonry structures. The mechanical model is based on the assumptions of linear elasticity under compression and softening behaviour under tension, described by the adoption of a unique strain-driven nonlocal damage variab...

One of the drawbacks of the eXtended Finite Element Method and similar approaches, like the Generalized Finite Element Method, is the problem of ill-conditioning of the related systems of equations at the solution stage. This occurs for example in Heaviside function enrichments when the discontinuity is close to discretisation nodes but also for no...

This book gathers selected contributions on emerging research work presented at the International Conference eXtended Discretization MethodS (X-DMS), held in Ferrara in September 2015. It highlights the most relevant advances made at the international level in the context of expanding classical discretization methods, like finite elements, to the n...

In computational mechanics, the quadrature of discontinuous and singular functions is often required. To avoid specialized quadrature procedures, discontinuous and singular fields can be regularized. However, regularization changes the algebraic structure of the solving equations, and this can lead to high errors. We show how to acquire accurate an...

One of the advantages of partition-of-unity FEMs, like the extended FEM, is the ability of modeling discontinuities independent of the mesh structure. The enrichment of the element functional space with discontinuous or non-differentiable functions requires, when the element stiffness is computed, partitioning into subdomains for quadrature. Howeve...

We propose an eXtended Finite Element Method convergent to the asymptotic solution of a thin interface problem for both planar and curved imperfect interfaces in three dimensions. The main advantage over standard cohesive-zone models is the bulk-mesh size independence. With respect to standard eXtended Finite Element Method, in the proposed procedu...

In this paper, recent contributions to the modelling of coated inclusions by means of an eXtended Finite Element Method are presented. The matrix particle interface is modelled as a finite thickness, imperfect interface. Two approaches are considered: a variational approach inspired to Suquet's work on asymptotic analysis of thin layers, and an app...

The analysis of fibre-reinforced concrete taking into account the nonlinear behaviour of the material in tension and compression is addressed by a numerical approach based on the Cohesive–Overlapping Crack Model, in order to reveal the influence of fibre content in the flexural behavior of beams. The results of a numerical analysis and of an experi...

Reinforced concrete beams in flexure exhibit three different collapse mechanisms by varying the mechanical and geometrical parameters. The limit cases are: tensile failure for low steel percentages and/or small and slender beams, and crushing failure for high steel percentages and/or large and stocky beams. The intermediate collapse mechanism, and,...

Regularized Heaviside and Dirac delta function are used in several fields of computational physics and mechanics. Hence the issue of the quadrature of integrals of discontinuous and singular functions arises. In order to avoid ad-hoc quadrature procedures, regularization of the discontinuous and the singular fields is often carried out. In particul...

A size-effect theory is herein introduced to investigate the average expansion of concrete containing free lime (CaO) and impurities. By drawing an analogy with the structural size-effect, the phenomenon of CaO hydration shows a characteristic length, whose dimension remains constant at all scales. If a grain of free lime is assumed to be a sphere,...

Limit Analysis provides a conceptually simple and robust method to estimate the safety of structures and has been long applied to the analysis of the ultimate collapse state of two-dimensional masonry structures or structural elements. In revolving symmetric domes, the three-dimensional problem can be reduced to the two-dimensional case under appro...

A new method for modeling discontinuities, such as cracks, in the element free Galerkin method is presented. A jump function
is used for the displacement discontinuity along the crack faces and the Westergard’s solution enrichment near the crack tip.
These enrichments, being extrinsic, can be limited only to the nodes surrounding the crack. The met...

The bridged crack model is an efficient theoretical and numerical tool for investigating the behavior of structural reinforced concrete (RC) elements in bending. The model is based on linear elastic
fracture mechanics concepts and equilibrium and compatibility equations are applied to a Mode I cracked beam segment. The model is herein extended to i...

This paper presents the results of an experimental research program validating a recently developed mechanical model connecting failure modes with cracking processes in reinforced concrete (RC) beams. In the analysis of the experimental results, special emphasis is given to the shape, extension, and initial location of the main tensile or shear cra...

The extended and generalized flnite element methods are reviewed with an emphasis on their applications to problems in material science: (1) fracture (2) dislocations (3) grain boundaries and (4) phases interfaces. These methods facilitate the modeling of complicated geometries and the evolution of such geometries, particularly when combined with l...

Two issues in the extended finite element method (XFEM) are addressed: efficient numerical integration of the weak form when the enrichment function is self-equilibrating and blending of the enrichment. The integration is based on transforming the domain integrals in the weak form into equivalent contour integrals. It is shown that the contour form...

There exists a wide literature on reinforced concrete beams models involving separately the three possible failure mechanisms: flexure, shear and crushing. However, the study of the transition between these mechanisms inside a consistent theoretical framework is still an open question, in particular with reference to the experimentally known size e...

This work focuses on the modelling through the extended finite element method of structural problems characterized by discontinuous displacement. As a model problem, an elastic isotropic domain characterized by a displacement discontinuity across a surface is studied. A regularization of the displacement field is introduced depending on a scalar pa...

The two main properties making the extended finite element method one of the most promising finite element technologies are
the possibility for the mesh not to conform to discontinuities and the introduction of arbitrary enrichment functions able
to effectively describe the features of the problem being solved. However, non polynomial bases inside...

The problem of the assessment of minimum reinforcement in concrete members has been examined both theoretically and experimentally
by the bridged crack model. The model has been demonstrated to be an efficient numerical tool for investigating the behavior
of structural elements in bending, and allowed to show the minimum reinforcement percentage de...

The bridged crack model has been developed for modelling the flexural behaviour of reinforced concrete beams and related size effects explaining brittle-ductile-brittle failure mode transitions. In the present paper the model is extended to analyse shear cracks, introducing a given shape for the hypothetical crack trajectory and determining the ini...

A new technique for the modelling of multiple dislocations based on introducing interior discontinuities is presented. In contrast to existing methods, the superposition of infinite domain solutions is avoided; interior discontinuities are specified on the dislocation slip surfaces and the resulting boundary value problem is solved by a finite elem...

The problem of the evaluation of the stiffness matrix for finite elements enriched by discontinuous/non-linear functions is
investigated. If the introduction of discontinuities inside the elements through enrichment functions is nowadays well established
by local partition of unity techniques, the evaluation of the element stiffness requires splitt...

The bridged crack model has been developed for modelling the flexural behaviour of reinforced concrete beams and related size effects explaining brittle-ductile-brittle failure mode transitions. In the present paper the model is extended to analyze shear cracks and concrete crushing, introducing a given shape for the hypothetical crack trajectory a...

This contribution deals with regularized extended finite element approximations of strong embedded discontinuities. The discontinuous enrichment displacement func-tion is here replaced by suitable regularized versions. This regularized approach make it possible the elimination of quadrature subcells for discontinuous functions in the eXtended Finit...

The introduction of discontinuous/non-differentiable functions in the eXtended Finite-Element Method allows to model discontinuities independent of the mesh structure. However, to compute the stiffness matrix of the elements intersected by the discontinuity, a subdivision of the elements into quadrature subcells aligned with the discontinuity line...

The purely nodal discretization, typical of meshless methods, turns out in the necessity of properly defining both the external
boundary and the material interfaces which may be present in the analysis of mechanical problems. Each material domain is
dicretized independently, and interface conditions are imposed into the variational formulation by t...

A new finite element method for accurately modelling the displacement and stress fields produced by a dislocation is proposed. The methodology is based on a local enrichment of the finite element space by closed form solutions for dislocations in infinite media via local partitions of unity. This allows the treatment of both arbitrary boundary cond...

A new level set method is developed for describing surfaces that are frozen behind a moving front, such as cracks. In this formulation, the level set is described in two dimensions by a three-tuple: the sign of the level set function and the components of the closest point projection to the surface. The vector level set method provides a very simpl...

The main subject of the paper is the investigation of Augmented Lagrangian algorithms and update formulas in the solution of elastoplastic problems. A stress rate formulation for elastoplastic models with internal variables and its finite increment form is employed to state the mechanical problem. In this formulation the Augmented Lagrangian is use...

The properties of new generation concretes for structural applications allow for larger steel percentages, while the increased brittleness may be reduced by adding steel fibers in the matrix. Nonetheless, coded procedures for the design of structural members where these new properties are accurately accounted for are still missing for a variety of...

The bridged crack model has been demonstrated to be an efficient numerical tool for investigating the behaviour of structural elements in bending. In the model, Linear Elastic Fracture Mechanics concepts are used to determine the equilibrium and the compatibility equations of a beam segment subjected to bending in presence of a mode I crack. Recent...

A new level set method is developed for describing surfaces that are frozen behind a moving front, such as cracks. In this formulation, the level set is described in two dimensions by a three-tuple: the sign of the level set function and the components of the closest point projection to the surface. The update of the level set is constructed by geo...

One of the most promising application of element-free methods is the ability of analyzing crack propagation problems without the necessity of remeshing the model as the crack advances. Moreover the possibility of enriching the classical polynomial basis, introducing some integrals of the Westergaard’s solution, make the near crack tip solution accu...

A dimensionless formulation of the bridged and of the cohesive crack model for reproducing the constitutive flexural response of a reinforced concrete element with a nonlinear matrix is proposed. The nonlinearity of the matrix is modelled by considering a distribution of closing forces onto the crack faces which increases the fracture toughness of...

A general procedure for the determination of the explicit expression of the Green's function of an ordinary differential operator is described in the paper, that requires only the knowledge of the null spaces of the operator and its adjoint. Although the main results concerning the structure of the Green's function are known in the literature, the...

A new algorithm has been developed for smoothing the surfaces in finite element formulations of contact-impact. A key feature of this method is that the smoothing is done implicitly by constructing smooth signed distance functions for the bodies. These functions are then employed for the computation of the gap and other variables needed for impleme...

In dealing with mesh-free formulations a major problem is connected to the computation of the quadratures appearing in the variational principle related to the differential boundary value problem. These integrals require, in the standard approach, the introduction of background quadrature subcells which somehow make these methods not ‘truly meshles...

A new vector level set method for modelling propagating cracks in the element-free Galerkin (EFG) method is presented. With this approach only nodal data are used to describe the crack; no geometrical entity is introduced for the crack trajectory, and no partial differential equations need to be solved to update the level sets. The nodal descriptio...

The problem of boundary conditions enforcement in meshless methods has been solved in the literature by several approaches. In the present paper, the moving least-squares (MLS) approximation is introduced in the total potential energy functional for the elastic solid problem and an augmented Lagrangian term is added to satisfy essential boundary co...

High-performance and fiber-reinforced concretes are receiving growing attention because of their physical and mechanical properties. The appropriate mix of cementitious matrix, additives and fibers create a very large class of materials, requiring a careful design for each particular application. Typical applications of these materials include conc...

A new meshless formulation for numerical analysis in fracture mechanics is presented. The formulation is based on the construction of shape functions by a moving least-squares approximation (MLSA). The peculiarity of the present approach lies in the definition of an augmented Lagrangian total potential energy functional. With this technique, called...

One of the most promising application of element-free methods is the ability of analyzing crack propagation problems without the necessity of remeshing the model as the crack advances. Moreover the possibility of enriching the classical polynomial basis, introducing some integrals of the Westergaard's solution, make the near crack tip solution accu...

In the present work a complementary energy formulation for the solution of the static equilibrium problem of no-tension solids is presented. The main feature of the work is systematic use of the augmented Lagrangian approach for the regularisation of the nonsmooth and nondifferentiable anelastic deformation potential. The proposed formulation is ap...

A stress formulation for frictionless contact problems between deformable bodies is proposed. Linear compatibility equations are assumed, while the constitutive relations are supposed nonlinear, yet Reversible, i.e., ruled by a convex strain potential. The relevant contact rules are formulated in terms of concave conjugated potentials, whose superd...

Object of the paper is a class of structural problems that will be abstractly defined by the following three sets of equations:
the compatibility equation C(u) = ε, where the operator C:u —>D is assumed linear (and so is its dual C’ that relates the internal stress a to the external actions f ∈ u’);
the constitutive equation f (ε) = σ, assumed to b...

The main purpose of this mini symposium is to bring together the experts in the field of numerical modelling and experimental validation in reinforced concrete. Concrete is a composite material that exhibits a heterogeneous internal structure and the study of its damage mechanisms is complex. When reinforced with steel bars, modelling the failure m...

The size effects in compression on drilled cylindrical concrete specimens obtained from a unique concrete block over a large scale range (1:19) are analyzed. The experimental results show scale effects on dissipated energy density rather than on the compressive strength. A theoretical explanation for such a phenomenon is presented, assuming a nonin...

The Bridged Crack Model has been developed for modelling the flexural behaviour of reinforced concrete beams and related size effects explaining brittle-ductile-brittle failures modes transitions. In the present paper the model is extended to shear failure modelling, introducing a given shape for the hypothetical crack path and determining the load...

Keywords: vector level sets, discontinuity representation, extended/generalized finite element method. SUMMARY. The ability of the extended and generalized finite element methods of modeling dis-continuities independent of mesh alignment requires a suitable representation for the discontinuity surfaces. In the present paper a method for constructin...