Alberto Taliercio - Academia.edu (original) (raw)

Papers by Alberto Taliercio

The theory of homogenization applied to limit analysis allows to rigorously define the macroscopi... more The theory of homogenization applied to limit analysis allows to rigorously define the macroscopic strength properties of periodic multi-phase materials, such as composite materials reinforced by arrays of equally spaced fibers, embedded in a matrix. By means of this approach, the strength properties of composite laminae reinforced by long and parallel fibers have already been obtained by various authors. The theoretical results established for these materials showed excellent agreement with experimental findings. The aim of the present work is to extend the same procedure to composites reinforced by a tridirectional array of mutually orthogonal fibers, which are materials of recent development. Through a static approach of limit analysis applied to a representative volume element, lower bounds to the actual failure domain of the material is obtained. This allows the numerical computation of strength domains for the material subjected to complex states of stress. Furthermore, if the...

International Journal of Solids and Structures, 2015

ABSTRACT The problem of the optimal strengthening of concrete plates subjected to transverse load... more ABSTRACT The problem of the optimal strengthening of concrete plates subjected to transverse loads by unidirectional FRP layers is dealt with. A topology optimization (TO) procedure is proposed to define the layout of the layers that maximizes the elastic stiffness of the reinforced plate for a given maximum amount of reinforcing material. The anisotropy of the layers is taken into account, and local orientations of the fibers are included in the set of design variables. According to the SIMP model for TO problems, the mechanical properties of the reinforcing layers are assumed to depend locally on the densities of the material in the layers, which are additional design variables. Compressive stresses along the fibers are avoided by a suitable penalization technique. The possibility of cracking in the concrete core is also indirectly taken into account. The discretized version of the constrained minimization problem that gives the optimal solution is solved by mathematical programming, using the Method of Moving Asymptotes and the finite element method in its displacement-based formulation. Numerical investigations are presented to discuss the features of the computed optimal layouts, along with the possible application as preliminary design for the structural retrofitting of concrete plates. The reliability of the achieved layouts is also investigated comparing the distribution and orientation of the reinforcing fibers with the yield lines that characterize the collapse mechanisms of the analyzed concrete plates suggested by limit analysis theory. The good performances of the adopted numerical procedure are also pointed out. It follows that the proposed procedure is a robust and computationally effective tool for the preliminary design of the optimal reinforcement of concrete plates in bending.

Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, 2013

ABSTRACT A contribution toward the thermal insulation of masonry buildings is given in this paper... more ABSTRACT A contribution toward the thermal insulation of masonry buildings is given in this paper, assuming the heat flux across any wall to be uniform along its height and seeking the optimal geometry of the cross-section of any block forming the wall. The minimization of the thermal transmittance of the block is dealt with as a topology optimization problem. Constraints on the mechanical properties of the blocks are also prescribed, to allow for the presence of in-plane and out-of-plane loads. A parametric investigation is carried out to investigate the effects of the design constraints and the geometry of the boundary of the block on their optimal layout. The thermal efficiency of the optimized units is also compared with that of standard blocks, showing that topology optimization may be conveniently adopted to improve the thermomechanical performance of conventional layouts.

Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, 2013

ABSTRACT

International Journal of Solids and Structures, 2013

ABSTRACT The paper presents a numerical approach for the optimal design of any unidirectional fib... more ABSTRACT The paper presents a numerical approach for the optimal design of any unidirectional fiber-reinforcement to improve the structural performance of existing structural elements. A problem of topology optimization is formulated, simultaneously searching for the regions to be strengthened and the optimal pointwise inclination of the reinforcement. Aim of the formulation is the minimization of the maximum equivalent stress in the underlying material, for a prescribed amount of fiber-reinforcement. The Tsai–Wu failure criterion is implemented to detect highly tensile-stressed regions in the existing structural components, both in case of isotropic material (e.g. concrete) and orthotropic media (e.g. brickwork or reinforced concrete). A suitable set of relaxed stress constraints is dealt with, calling for a no-compression stress state in the fiber-reinforcement. The resulting multi-constrained min–max problem is solved by mathematical programming. Numerical examples are presented to discuss the features of the achieved optimal layouts, along with their possible application as preliminary design for structural retrofitting. Performances of the adopted computational procedure are investigated as well.

Computers & Structures, 2015

ABSTRACT The macroscopic strength domain of in-plane loaded masonry walls is derived using an app... more ABSTRACT The macroscopic strength domain of in-plane loaded masonry walls is derived using an approach based on the upper bound theorem of limit analysis within the framework of homogenization theory. Following an approach similar to the Method of Cells for fiber-reinforced composites, a typical representative volume of masonry is subdivided into a few sub-cells, and a strain-rate periodic, piecewise differentiable velocity field, depending on a limited number of degrees of freedom, is defined. The ensuing approximated macroscopic failure surface is found to match with fair accuracy both available experimental data and theoretical predictions obtained by other authors with more refined numerical approaches. The proposed model is also applied to the prediction of the bearing capacity of a deep masonry beam: for any joint thickness, the criterion is found to give results as accurate as other complex numerical models, which take the heterogeneous nature of masonry into account. The model thus combines computational efficiency and accuracy.

The Open Civil Engineering Journal, 2012

The seismic behaviour of Maniace Castle, built on the Ortigia island in Syracuse (Italy) during t... more The seismic behaviour of Maniace Castle, built on the Ortigia island in Syracuse (Italy) during the thirteenth century by Emperor Frederick II, was investigated by a numerical approach with the aim of comparing different strategies for structural reinforcement. The original building consisted of a square perimeter made by 4 m thick limestone masonry walls and round towers at the corners, embedding a large hypostyle hall. The roof of this main hall was supported by a system of arches, five on each side span. The current state of the castle is the result of subsequent interventions following the explosion that devastated the interior of the castle in 1704. Accordingly, at present the indoor hall consists of only 2/5 of the original covered area, and the primitive structural concept has greatly changed, since the double symmetry of the plant was substantially lost. Buttresses and transverse walls were added to improve the mechanical response to horizontal loads. Previous studies, both experimental and numerical, proved that the interior columns supporting the arches experience a level of vertical stress that is quite high in comparison to the actual strength. The situation is particular serious accounting for the seismicity of Syracuse, as a the significant increase in axial stress in the columns due to their flexural deformation might occur. In the present study, the behaviour of the castle is studied by means of a detailed full 3D FE model, both under vertical and lateral loads. The results of the analysis are used for a proposal of reconstruction of the hypostyle hall, bringing it back to the original geometrical configuration of the XIII century, by the use of modern building materials.

International Journal of Solids and Structures, 1995

ABSTRACT A homogenization technique applied in conjunction with limit analysis theory allows the ... more ABSTRACT A homogenization technique applied in conjunction with limit analysis theory allows the prediction of the macroscopic strength of fiber composites as a function of the strength properties of the phases (i.e. fiber, matrix and interface). Emphasis is placed here on the uniaxial strength, for which bounds based on static and kinematic approaches are proposed. Special attention is devoted to the influence of the matrix, which is presumed to be polymeric and complying with Drucker-Prager, Mohr-Coulomb or a parabolic type criterion. Also the limited strength of the fiber-matrix interface is accounted for through the introduction of a Mohr-Coulomb type strength criterion. Analytical equations describing the dependence of the macroscopic strength of the composite on the orientation of the applied stress with respect to the fibers are proposed. The parameters required to define the model are limited in number and possess a clear mechanical meaning. Comparisons with experimental data available in the literature prove quite satisfactory.

International Journal of Solids and Structures, 1999

ABSTRACT A numerical model is developed with the aim of describing the macroscopic mechanical res... more ABSTRACT A numerical model is developed with the aim of describing the macroscopic mechanical response of unidirectional brittle–matrix fiber-reinforced composites subjected to stresses acting in any plane transverse to the fibers. Finite element analyses of a representative unit cell are performed, with suitable boundary conditions ensuring continuity of the displacement field across adjacent cells and periodicity of the strain field over the cell. A strain–softening constitutive law is adopted for the matrix in tension to allow, for instance, for brittleness induced by possible defects in a polymeric matrix. The perfectly plastic case is also considered for sake of comparison. Results established for ductile composites are found to be inappropriate for brittle matrix composites: numerical analyses show that composites with softening matrix have transverse strength properties much poorer than perfectly plastic composites with matrix of equal strength, and even than the unreinforced matrix. An induced transverse anisotropy in the post-peak regime is also observed. A discussion on the proposed approach concludes the note.

Studies in Applied Mechanics, 1998

ABSTRACT A viscoplastic model with damage was developed to describe the mechanical behaviour of p... more ABSTRACT A viscoplastic model with damage was developed to describe the mechanical behaviour of plain concrete subjected to sustained multiaxial stresses of high intensity. The model is characterized by inelastic strains due to plasticity and damage and by a second-order damage tensor. The evolution laws for these variables are formulated by extending the proposal of other authors for metals and rocksalt. The procedure to obtain the main model parameters from experiments is also outlined. The reliability of the model was assessed through comparisons with available test results.

Structural Studies, Repairs and Maintenance of Heritage Architecture X, 2007

A theoretical model is presented suitable for the description of the damaging process in brittle ... more A theoretical model is presented suitable for the description of the damaging process in brittle materials. Damage is defined by a second-order symmetric tensor and activates at different orientations to the principal strain directions, according to the sign of the principal strain which attains a damage threshold. The capabilities of the model in describing the mechanical response of material elements subjected to non-proportional stresses are illustrated.

Key Engineering Materials, 2014

ABSTRACT The problem of finding the optimal layout of FRP strips to effectively retrofit masonry ... more ABSTRACT The problem of finding the optimal layout of FRP strips to effectively retrofit masonry walls undergoing transverse loads is dealt with, taking the presence of permanent vertical loads into account. An innovative topology optimization approach is proposed to define the minimum amount of reinforcement that keeps the stress within a given strength domain throughout the wall. The macroscopic strength properties of masonry are defined by means of a simplified limit analysis approach based on homogenization theory. The capabilities of the proposed procedure are illustrated through applications on a windowed panel subjected to out-of-plane actions and vertical loads.

Mechanics Research Communications, 1999

International Journal of Solids and Structures, 2013

ABSTRACT A novel approach for the rational positioning of fiber reinforcements on masonry structu... more ABSTRACT A novel approach for the rational positioning of fiber reinforcements on masonry structures based on topology optimization is presented. Due to the brittle behavior of masonry, the minimization of the strain energy cannot be implemented to generate truss-like layouts that may be interpreted as strut-and-tie models in the discontinuity regions of reinforced concrete structures. To cope with the brittleness of brickwork, the optimal problem can be conveniently reduced to the minimization of the amount of reinforcement required to keep tensile stresses in any masonry element below a prescribed threshold. A strength criterion recently proposed for masonry is employed, based on a lower bound limit analysis homogenization model (Milani, 2011) and relying upon a discretization of ¼ of any unit cell by six CST elements. Thanks to the limited number of variables involved, closed form solutions for the masonry macroscopic strength domain can be obtained. This criterion is implemented into the multi-constrained discrete formulation of the topology optimization algorithm, to locally control the stress field over the design domain. For comparison, the phenomenological Tsai–Wu strength criterion for anisotropic solids is also implemented.The contribution discusses three sets of numerical results, addressing the fiber-reinforcement of some benchmark masonry walls. The optimal reinforcement layouts are found to be affected by the choice of the masonry strength criterion only to a limited extent, as far as failure in the masonry element is mainly due to tensile stresses. Contrary to intuition, placing the reinforcing fibers along the direction of the principal tensile stresses in masonry is also found to be not necessarily the most effective solution, for certain geometries and load conditions.

Advanced Materials Research, 2010

ABSTRACT For safety assessment, a double curvature hollow bricks cloister vault with lunettes has... more ABSTRACT For safety assessment, a double curvature hollow bricks cloister vault with lunettes has been studied. Its geometry, constructive aspects, crack pattern have been surveyed and a 3D finite element analysis has been carried out, the numerical model exploiting the accurate survey of the vault geometry.

Structural and Multidisciplinary Optimization, 2012

ABSTRACT Aim of this work is the maximization of the fundamental eigenfrequency of 2D bodies made... more ABSTRACT Aim of this work is the maximization of the fundamental eigenfrequency of 2D bodies made of micropolar (or Cosserat) materials using a topology optimization approach. A classical SIMP–like model is used to approximate the constitutive parameters of the micropolar medium. A suitable penalization is introduced for both the linear and the spin inertia of the material, to avoid the occurrence of undesired local modes. The robustness of the proposed procedure is investigated through numerical examples; the influence of the material parameters on the optimal material layouts is also discussed. The optimal layouts for Cosserat solids may differ significantly from the truss–like solutions typical of Cauchy solids, as the intrinsic flexural stiffness of the material can lead to curved beam-like material distributions. The numerical simulations show that the results are quite sensitive to the material characteristic length and the spin inertia.

Meccanica, 1987

Sommario Vengono presentati alcuni criteri di rottura per materiali stratificati eterogenei, cara... more Sommario Vengono presentati alcuni criteri di rottura per materiali stratificati eterogenei, caratterizzati da regolare altenanza di due materiali omogenei. Tali criteri sono stati ottenuti mediante una procedura di omogeneizzazione, sulla base delle condizioni di rottura dei materiali che compongono il continuo stratiflcato. Sono stati considerati strati formati da materiali del tipo di Mohr-Coulomb (per i casi in cui i materiali

Materials and Structures, 1992

ABSTRACT An apparatus specifically designed for static and cyclic testing of concrete and rock cy... more ABSTRACT An apparatus specifically designed for static and cyclic testing of concrete and rock cylindrical samples is described. A particular characteristic of this equipment is the possibility of cyclic variation of the confining pressure, in addition to variation of the vertical load. The technical features of the apparatus are illustrated, as well as those of the instruments used for measuring and recording the variation of loads and displacements during the tests, up to the failure of the specimens. Comments are also presented on the devices controlling the variation of load with time and on the characteristics of the load histories adopted in an experimental research aimed at investigating the behaviour of concrete under repeated triaxial loads. On décrit un appareillage spécialement conçu pour l'essai statique et cyclique d'échantillons cylindriques de béton et de roches, qui permet d'appliquer des variations cycliques de la pression de confinement en plus de la variation de la charge verticale. On montre les caractéristiques techniques de l'équipement utilisé pour mesurer et enregistrer la variation des charges et des déplacements au cours des essais, jusqu'à rupture des éprouvettes. On se livre également à des observations sur les appareils de contrôle de la variation de la charge dans le temps, et sur les caractéristiques des charges sélectionnées pour une recherche expérimentale qui visait à examiner le comportement du béton sous charges triaxiales répétées.

Materials and Structures, 1998

A survey was performed to find in the literature theoretic;al models suitable to the description ... more A survey was performed to find in the literature theoretic;al models suitable to the description of the triaxial creep behaviour of plain concrete at high stresses. The considered models are based on the theory of elasto-viscoplasticity with damage and are mainly addressed to the domain of geotechnics. Application of these models to the simulation of experiments turned out to be satisfactory on the whole, although several features of the creep behaviour of the material are not reproduced. The suggestions given by this preliminary work will be taken into account in the development of a future model specifically conceived for concrete. On a conduit une recherche bibliographique pour rep~rer des modules math(matiques capables de d~crire le comportement de fluage du bdton ordinaire soumis ~ des contraintes triaxiales prolonge'es de haute intensitL Les modules considd-~z 9 , , / r~s se basent sur la th~orie de I elasto-vlscoplastzclte avec endommagement, et sont concus principalement pour des mat~riaux gdotechniques. Leur application h la simulation des expdriences s'est averse satisfaisante, bien que plusieurs aspects du comportement de.fluage du mat~riau ne soient pas reproduits. Les indications fournies par ce travail pr~liminaire seront prises en compte dans le d~veloppement d'un module confu sp~cifiquement pour le b~ton.

The theory of homogenization applied to limit analysis allows to rigorously define the macroscopi... more The theory of homogenization applied to limit analysis allows to rigorously define the macroscopic strength properties of periodic multi-phase materials, such as composite materials reinforced by arrays of equally spaced fibers, embedded in a matrix. By means of this approach, the strength properties of composite laminae reinforced by long and parallel fibers have already been obtained by various authors. The theoretical results established for these materials showed excellent agreement with experimental findings. The aim of the present work is to extend the same procedure to composites reinforced by a tridirectional array of mutually orthogonal fibers, which are materials of recent development. Through a static approach of limit analysis applied to a representative volume element, lower bounds to the actual failure domain of the material is obtained. This allows the numerical computation of strength domains for the material subjected to complex states of stress. Furthermore, if the...

International Journal of Solids and Structures, 2015

ABSTRACT The problem of the optimal strengthening of concrete plates subjected to transverse load... more ABSTRACT The problem of the optimal strengthening of concrete plates subjected to transverse loads by unidirectional FRP layers is dealt with. A topology optimization (TO) procedure is proposed to define the layout of the layers that maximizes the elastic stiffness of the reinforced plate for a given maximum amount of reinforcing material. The anisotropy of the layers is taken into account, and local orientations of the fibers are included in the set of design variables. According to the SIMP model for TO problems, the mechanical properties of the reinforcing layers are assumed to depend locally on the densities of the material in the layers, which are additional design variables. Compressive stresses along the fibers are avoided by a suitable penalization technique. The possibility of cracking in the concrete core is also indirectly taken into account. The discretized version of the constrained minimization problem that gives the optimal solution is solved by mathematical programming, using the Method of Moving Asymptotes and the finite element method in its displacement-based formulation. Numerical investigations are presented to discuss the features of the computed optimal layouts, along with the possible application as preliminary design for the structural retrofitting of concrete plates. The reliability of the achieved layouts is also investigated comparing the distribution and orientation of the reinforcing fibers with the yield lines that characterize the collapse mechanisms of the analyzed concrete plates suggested by limit analysis theory. The good performances of the adopted numerical procedure are also pointed out. It follows that the proposed procedure is a robust and computationally effective tool for the preliminary design of the optimal reinforcement of concrete plates in bending.

Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, 2013

ABSTRACT A contribution toward the thermal insulation of masonry buildings is given in this paper... more ABSTRACT A contribution toward the thermal insulation of masonry buildings is given in this paper, assuming the heat flux across any wall to be uniform along its height and seeking the optimal geometry of the cross-section of any block forming the wall. The minimization of the thermal transmittance of the block is dealt with as a topology optimization problem. Constraints on the mechanical properties of the blocks are also prescribed, to allow for the presence of in-plane and out-of-plane loads. A parametric investigation is carried out to investigate the effects of the design constraints and the geometry of the boundary of the block on their optimal layout. The thermal efficiency of the optimized units is also compared with that of standard blocks, showing that topology optimization may be conveniently adopted to improve the thermomechanical performance of conventional layouts.

Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, 2013

ABSTRACT

International Journal of Solids and Structures, 2013

ABSTRACT The paper presents a numerical approach for the optimal design of any unidirectional fib... more ABSTRACT The paper presents a numerical approach for the optimal design of any unidirectional fiber-reinforcement to improve the structural performance of existing structural elements. A problem of topology optimization is formulated, simultaneously searching for the regions to be strengthened and the optimal pointwise inclination of the reinforcement. Aim of the formulation is the minimization of the maximum equivalent stress in the underlying material, for a prescribed amount of fiber-reinforcement. The Tsai–Wu failure criterion is implemented to detect highly tensile-stressed regions in the existing structural components, both in case of isotropic material (e.g. concrete) and orthotropic media (e.g. brickwork or reinforced concrete). A suitable set of relaxed stress constraints is dealt with, calling for a no-compression stress state in the fiber-reinforcement. The resulting multi-constrained min–max problem is solved by mathematical programming. Numerical examples are presented to discuss the features of the achieved optimal layouts, along with their possible application as preliminary design for structural retrofitting. Performances of the adopted computational procedure are investigated as well.

Computers & Structures, 2015

ABSTRACT The macroscopic strength domain of in-plane loaded masonry walls is derived using an app... more ABSTRACT The macroscopic strength domain of in-plane loaded masonry walls is derived using an approach based on the upper bound theorem of limit analysis within the framework of homogenization theory. Following an approach similar to the Method of Cells for fiber-reinforced composites, a typical representative volume of masonry is subdivided into a few sub-cells, and a strain-rate periodic, piecewise differentiable velocity field, depending on a limited number of degrees of freedom, is defined. The ensuing approximated macroscopic failure surface is found to match with fair accuracy both available experimental data and theoretical predictions obtained by other authors with more refined numerical approaches. The proposed model is also applied to the prediction of the bearing capacity of a deep masonry beam: for any joint thickness, the criterion is found to give results as accurate as other complex numerical models, which take the heterogeneous nature of masonry into account. The model thus combines computational efficiency and accuracy.

The Open Civil Engineering Journal, 2012

The seismic behaviour of Maniace Castle, built on the Ortigia island in Syracuse (Italy) during t... more The seismic behaviour of Maniace Castle, built on the Ortigia island in Syracuse (Italy) during the thirteenth century by Emperor Frederick II, was investigated by a numerical approach with the aim of comparing different strategies for structural reinforcement. The original building consisted of a square perimeter made by 4 m thick limestone masonry walls and round towers at the corners, embedding a large hypostyle hall. The roof of this main hall was supported by a system of arches, five on each side span. The current state of the castle is the result of subsequent interventions following the explosion that devastated the interior of the castle in 1704. Accordingly, at present the indoor hall consists of only 2/5 of the original covered area, and the primitive structural concept has greatly changed, since the double symmetry of the plant was substantially lost. Buttresses and transverse walls were added to improve the mechanical response to horizontal loads. Previous studies, both experimental and numerical, proved that the interior columns supporting the arches experience a level of vertical stress that is quite high in comparison to the actual strength. The situation is particular serious accounting for the seismicity of Syracuse, as a the significant increase in axial stress in the columns due to their flexural deformation might occur. In the present study, the behaviour of the castle is studied by means of a detailed full 3D FE model, both under vertical and lateral loads. The results of the analysis are used for a proposal of reconstruction of the hypostyle hall, bringing it back to the original geometrical configuration of the XIII century, by the use of modern building materials.

International Journal of Solids and Structures, 1995

ABSTRACT A homogenization technique applied in conjunction with limit analysis theory allows the ... more ABSTRACT A homogenization technique applied in conjunction with limit analysis theory allows the prediction of the macroscopic strength of fiber composites as a function of the strength properties of the phases (i.e. fiber, matrix and interface). Emphasis is placed here on the uniaxial strength, for which bounds based on static and kinematic approaches are proposed. Special attention is devoted to the influence of the matrix, which is presumed to be polymeric and complying with Drucker-Prager, Mohr-Coulomb or a parabolic type criterion. Also the limited strength of the fiber-matrix interface is accounted for through the introduction of a Mohr-Coulomb type strength criterion. Analytical equations describing the dependence of the macroscopic strength of the composite on the orientation of the applied stress with respect to the fibers are proposed. The parameters required to define the model are limited in number and possess a clear mechanical meaning. Comparisons with experimental data available in the literature prove quite satisfactory.

International Journal of Solids and Structures, 1999

ABSTRACT A numerical model is developed with the aim of describing the macroscopic mechanical res... more ABSTRACT A numerical model is developed with the aim of describing the macroscopic mechanical response of unidirectional brittle–matrix fiber-reinforced composites subjected to stresses acting in any plane transverse to the fibers. Finite element analyses of a representative unit cell are performed, with suitable boundary conditions ensuring continuity of the displacement field across adjacent cells and periodicity of the strain field over the cell. A strain–softening constitutive law is adopted for the matrix in tension to allow, for instance, for brittleness induced by possible defects in a polymeric matrix. The perfectly plastic case is also considered for sake of comparison. Results established for ductile composites are found to be inappropriate for brittle matrix composites: numerical analyses show that composites with softening matrix have transverse strength properties much poorer than perfectly plastic composites with matrix of equal strength, and even than the unreinforced matrix. An induced transverse anisotropy in the post-peak regime is also observed. A discussion on the proposed approach concludes the note.

Studies in Applied Mechanics, 1998

ABSTRACT A viscoplastic model with damage was developed to describe the mechanical behaviour of p... more ABSTRACT A viscoplastic model with damage was developed to describe the mechanical behaviour of plain concrete subjected to sustained multiaxial stresses of high intensity. The model is characterized by inelastic strains due to plasticity and damage and by a second-order damage tensor. The evolution laws for these variables are formulated by extending the proposal of other authors for metals and rocksalt. The procedure to obtain the main model parameters from experiments is also outlined. The reliability of the model was assessed through comparisons with available test results.

Structural Studies, Repairs and Maintenance of Heritage Architecture X, 2007

A theoretical model is presented suitable for the description of the damaging process in brittle ... more A theoretical model is presented suitable for the description of the damaging process in brittle materials. Damage is defined by a second-order symmetric tensor and activates at different orientations to the principal strain directions, according to the sign of the principal strain which attains a damage threshold. The capabilities of the model in describing the mechanical response of material elements subjected to non-proportional stresses are illustrated.

Key Engineering Materials, 2014

ABSTRACT The problem of finding the optimal layout of FRP strips to effectively retrofit masonry ... more ABSTRACT The problem of finding the optimal layout of FRP strips to effectively retrofit masonry walls undergoing transverse loads is dealt with, taking the presence of permanent vertical loads into account. An innovative topology optimization approach is proposed to define the minimum amount of reinforcement that keeps the stress within a given strength domain throughout the wall. The macroscopic strength properties of masonry are defined by means of a simplified limit analysis approach based on homogenization theory. The capabilities of the proposed procedure are illustrated through applications on a windowed panel subjected to out-of-plane actions and vertical loads.

Mechanics Research Communications, 1999

International Journal of Solids and Structures, 2013

ABSTRACT A novel approach for the rational positioning of fiber reinforcements on masonry structu... more ABSTRACT A novel approach for the rational positioning of fiber reinforcements on masonry structures based on topology optimization is presented. Due to the brittle behavior of masonry, the minimization of the strain energy cannot be implemented to generate truss-like layouts that may be interpreted as strut-and-tie models in the discontinuity regions of reinforced concrete structures. To cope with the brittleness of brickwork, the optimal problem can be conveniently reduced to the minimization of the amount of reinforcement required to keep tensile stresses in any masonry element below a prescribed threshold. A strength criterion recently proposed for masonry is employed, based on a lower bound limit analysis homogenization model (Milani, 2011) and relying upon a discretization of ¼ of any unit cell by six CST elements. Thanks to the limited number of variables involved, closed form solutions for the masonry macroscopic strength domain can be obtained. This criterion is implemented into the multi-constrained discrete formulation of the topology optimization algorithm, to locally control the stress field over the design domain. For comparison, the phenomenological Tsai–Wu strength criterion for anisotropic solids is also implemented.The contribution discusses three sets of numerical results, addressing the fiber-reinforcement of some benchmark masonry walls. The optimal reinforcement layouts are found to be affected by the choice of the masonry strength criterion only to a limited extent, as far as failure in the masonry element is mainly due to tensile stresses. Contrary to intuition, placing the reinforcing fibers along the direction of the principal tensile stresses in masonry is also found to be not necessarily the most effective solution, for certain geometries and load conditions.

Advanced Materials Research, 2010

ABSTRACT For safety assessment, a double curvature hollow bricks cloister vault with lunettes has... more ABSTRACT For safety assessment, a double curvature hollow bricks cloister vault with lunettes has been studied. Its geometry, constructive aspects, crack pattern have been surveyed and a 3D finite element analysis has been carried out, the numerical model exploiting the accurate survey of the vault geometry.

Structural and Multidisciplinary Optimization, 2012

ABSTRACT Aim of this work is the maximization of the fundamental eigenfrequency of 2D bodies made... more ABSTRACT Aim of this work is the maximization of the fundamental eigenfrequency of 2D bodies made of micropolar (or Cosserat) materials using a topology optimization approach. A classical SIMP–like model is used to approximate the constitutive parameters of the micropolar medium. A suitable penalization is introduced for both the linear and the spin inertia of the material, to avoid the occurrence of undesired local modes. The robustness of the proposed procedure is investigated through numerical examples; the influence of the material parameters on the optimal material layouts is also discussed. The optimal layouts for Cosserat solids may differ significantly from the truss–like solutions typical of Cauchy solids, as the intrinsic flexural stiffness of the material can lead to curved beam-like material distributions. The numerical simulations show that the results are quite sensitive to the material characteristic length and the spin inertia.

Meccanica, 1987

Sommario Vengono presentati alcuni criteri di rottura per materiali stratificati eterogenei, cara... more Sommario Vengono presentati alcuni criteri di rottura per materiali stratificati eterogenei, caratterizzati da regolare altenanza di due materiali omogenei. Tali criteri sono stati ottenuti mediante una procedura di omogeneizzazione, sulla base delle condizioni di rottura dei materiali che compongono il continuo stratiflcato. Sono stati considerati strati formati da materiali del tipo di Mohr-Coulomb (per i casi in cui i materiali

Materials and Structures, 1992

ABSTRACT An apparatus specifically designed for static and cyclic testing of concrete and rock cy... more ABSTRACT An apparatus specifically designed for static and cyclic testing of concrete and rock cylindrical samples is described. A particular characteristic of this equipment is the possibility of cyclic variation of the confining pressure, in addition to variation of the vertical load. The technical features of the apparatus are illustrated, as well as those of the instruments used for measuring and recording the variation of loads and displacements during the tests, up to the failure of the specimens. Comments are also presented on the devices controlling the variation of load with time and on the characteristics of the load histories adopted in an experimental research aimed at investigating the behaviour of concrete under repeated triaxial loads. On décrit un appareillage spécialement conçu pour l'essai statique et cyclique d'échantillons cylindriques de béton et de roches, qui permet d'appliquer des variations cycliques de la pression de confinement en plus de la variation de la charge verticale. On montre les caractéristiques techniques de l'équipement utilisé pour mesurer et enregistrer la variation des charges et des déplacements au cours des essais, jusqu'à rupture des éprouvettes. On se livre également à des observations sur les appareils de contrôle de la variation de la charge dans le temps, et sur les caractéristiques des charges sélectionnées pour une recherche expérimentale qui visait à examiner le comportement du béton sous charges triaxiales répétées.

Materials and Structures, 1998

A survey was performed to find in the literature theoretic;al models suitable to the description ... more A survey was performed to find in the literature theoretic;al models suitable to the description of the triaxial creep behaviour of plain concrete at high stresses. The considered models are based on the theory of elasto-viscoplasticity with damage and are mainly addressed to the domain of geotechnics. Application of these models to the simulation of experiments turned out to be satisfactory on the whole, although several features of the creep behaviour of the material are not reproduced. The suggestions given by this preliminary work will be taken into account in the development of a future model specifically conceived for concrete. On a conduit une recherche bibliographique pour rep~rer des modules math(matiques capables de d~crire le comportement de fluage du bdton ordinaire soumis ~ des contraintes triaxiales prolonge'es de haute intensitL Les modules considd-~z 9 , , / r~s se basent sur la th~orie de I elasto-vlscoplastzclte avec endommagement, et sont concus principalement pour des mat~riaux gdotechniques. Leur application h la simulation des expdriences s'est averse satisfaisante, bien que plusieurs aspects du comportement de.fluage du mat~riau ne soient pas reproduits. Les indications fournies par ce travail pr~liminaire seront prises en compte dans le d~veloppement d'un module confu sp~cifiquement pour le b~ton.