This paper aims at investigating the matrix-to-textile stress transfer in a fabric reinforced cem... more This paper aims at investigating the matrix-to-textile stress transfer in a fabric reinforced cementitious matrix FRCM system, not bonded to any substrate, under shear loads. To this end, direct shear tests are performed on a basalt FRCM specimen introduced into an innovative properly designed four-hinge frame loaded by a universal testing machine. The role of the single components in the global shear behavior of the FRCM is experimentally analyzed. Digital image correlation (DIC) is adopted for evaluating both the displacement and strain fields as well as for detecting the damage. Furthermore, the shear response of the tested FRCM material is reproduced via an effective numerical approach that considers the nonlinear behavior of the mortar and the possible micro-mechanisms that arise between the textile and the matrix, introducing suitable interfaces joining the FRCM constituent layers, i.e. textile and mortar layers. Experimental outcomes highlighted the non-negligible influence of the matrix in the shear response of the composite, both in strength and stiffness. The proven DIC technique demonstrated to be suitable also for this novel test type, since it allows to obtain shear strains, location and amplitude of cracks with satisfying accuracy, such as to make direct shear tests results a benchmark to be used for numerical simulations. Numerical analyses are performed in order to verify the efficiency of the proposed model in reproducing the mechanical behavior of FRCM composites under shear loads and in describing the damage patterns during the loading process.
Aim of this paper is to proposed a micro-scale numerical approach for the evaluation of the mecha... more Aim of this paper is to proposed a micro-scale numerical approach for the evaluation of the mechanical behavior of Fiber Reinforced Cementitious Mortar (FRCM) composites. As a matter of fact, the FRCM constitutive behavior is affected by micro-mechanisms, such as the cracking of the mortar and the slippage of the fibers within the mortar. The repetitive structural geometry of the FRCMs, due to the presence of the mesh grid, allows to identify a representative unit cell. This element is made by different constituent materials, i.e. fiber and mortar, and composed by three layers, i.e. two external layers of mortar and one inner layer made with fibers and mortar. In the framework of 2D plane stress state, the numerical approach consists in modeling the constituents as linear elastic materials and accounting for the material non-linearities through the implementation of suitable interface elements. In the interface model, the damage, the friction effects and the unilateral contact are taken into account. This numerical approach is used for reproducing the tensile behavior of the FRCM composites. It is successfully validated with available experimental results and a parameter sensitivity analysis is performed.
Fabric Reinforced Cementitious Matrix (FRCM) composites represent an innovative and effective ret... more Fabric Reinforced Cementitious Matrix (FRCM) composites represent an innovative and effective retrofitting solution for masonry structures. The use of FRCMs as an external retrofitting technique requires an insight knowledge of their mechanical behavior, failure modes and masonry-to-FRCM bond properties. A Round Robin Test (RRT) programme was launched by twelve Italian Universities, aimed at evaluating the effect of the shear test setup parameters and at assessing the test variability. The experimental tests were performed on systems made of glass and steel fibers/cords applied onto masonry substrates. The results were carefully analyzed discussing failure modes, bond capacity, and slip statistical dispersion. Differences in the setup , including the clamping method, textile impregnation, and instrumentation used for measuring the slip during the tests, were discussed in detail providing useful considerations and suggestions for reducing experimental scattering and obtaining reliable results. The analysis showed that the considered parameters have an influence on the structural behavior of the FRCM samples demonstrating that an accurate setup standardization is needed.
The influence of mortars joints in masonry substrate reinforced with FRP is investigated from the... more The influence of mortars joints in masonry substrate reinforced with FRP is investigated from the numerical point of view. The analysis has been conducted by means of a new interface model specifically developed to reproduce the debonding process occurring between an elastic thin body in adhesion with a cohesive support material. The model accounts for mode I and mode II of failure, considering the effect of the in-plane deformation of the interface, i.e. the possible elongation or confinement of the material constituting the interface. Numerical results are compared with experimental evidences showing good performances of the proposed model in investigating the transferring phenomena and in studying the influence of the presence of mortar joints in the masonry texture in the debonding process.
Abstract A novel two-scale modeling approach, linking different structural models at macro and mi... more Abstract A novel two-scale modeling approach, linking different structural models at macro and microscale, is proposed to describe response of masonry walls with periodic texture. At the higher macroscopic scale, the real heterogeneous material is modeled as a homogenized medium, considering the classical Mindlin-Reissner theory for flat shells. At the lower microscopic scale, a representative masonry Unit Cell (UC), accounting for the actual geometry, arrangement and nonlinear behavior of constituent materials, is analyzed in detail by resorting to a three-dimensional Cauchy model. The UC is modeled as the assembly of elastic bricks and nonlinear zero-thickness interfaces, in which the sliding frictional and damaging mechanisms are concentrated. To perform the macro–micro information transition a proper kinematic map is defined, whereas the upscaling process is performed via a homogenization procedure based on the Transformation Field Analysis (TFA), properly extended to the case of interfaces. The developed homogenization procedure invokes a generalized Hill-Mandel principle and requires to satisfy ‘non-standard’ constraints at the microlevel, for which the perturbed Lagrangian method is employed. Numerical applications are performed to prove the model efficiency in describing the response of a running bond UC subjected to in-plane and out-of-plane loads. Special attention is devoted to the analysis of shell bending and shear behavior, comparing the results obtained with the proposed model with those recovered by detailed micromechanical analyses.
Masonry arches are amongst the most fascinating structures of the World's historical and arch... more Masonry arches are amongst the most fascinating structures of the World's historical and architectural heritage. Their vulnerability to earthquakes pointed out the necessity of their preservation. Fiber Reinforced Cementitious Mortar (FRCM) composites have been recently used as a more sustainable alternative to FRPs in the strengthening of masonry structures, since they can overcome the limits FRP show as strengthening systems: poor behavior to high temperature, delamination with significant loss of material at the bonded surface, lack of vapor permeability, impossibility of application on humid surfaces, incompatibility of resins with masonry, high cost and reduced reversibility of the installation. These aspects have a critical relevance in the case of historical structures, whose features have to be preserved, and motivate researches about the use of FRCM on masonry structures, from both experimental and analytical points of view. In this paper, the results of numerical analy...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Aim of the present paper is to develop an efficient multiscale procedure for studying the mechani... more Aim of the present paper is to develop an efficient multiscale procedure for studying the mechanical response of structural elements made of elastoplastic or viscoplastic composite materials. The micro and the macro scales are considered separated. At the microscale a PieceWise Uniform Transformation Field Analysis (PWUTFA) homogenization technique is adopted to derive the overall response of a periodic composite. Thus, a Unit Cell (UC) containing all the properties of the heterogeneous material is analyzed and divided in subsets; in each one the inelastic strain is considered uniform, i.e. constant, and represents the history variable of the analysis. Elastoplastic and elasto-viscoplastic models with isotropic hardening are adopted in order to describe the nonlinear response of the constituents. A new numerical procedure is developed in order to solve the evolutive problem in all the subsets simultaneously adopting a predictor-corrector technique. The corrector phase is solved by means of a modified Newton-Raphson iterative procedure. Furthermore, the tangent consistent with the algorithm is computed and adopted in the multiscale computations. Numerical applications are carried out in order to assess the efficiency of the proposed multiscale approach.
Aim of the present study is to propose an enhanced method for the domain decomposition (clusterin... more Aim of the present study is to propose an enhanced method for the domain decomposition (clustering) of the representative volume element (RVE) of composite materials to be used with homogenization techniques, based on the PieceWise Uniform Transformation Field Analysis (PWUTFA). With PWUTFA, both constitutive and evolutive equations for the constituents of the composite material are written in terms of averages in each cluster; moreover, it is not required to solve via FEM the nonlinear micro-mechanical problem, allowing to drastically reduce the number of internal variables. PWUTFA is founded on the idea that it is possible to divide the RVE into large subdomains (clusters) that should group together finite elements having, under any applied loading condition, the most similar values of strain. Accordingly, in this study a multi-objective optimization-based approach is proposed with the aim to simultaneously reduce both the error in the approximation of the strain fields and the number of clusters in which the domain is decomposed. Different clustering solutions, obtained through the proposed optimization approach are analyzed, and the corresponding mechanical responses are compared with the ones obtained by the finite element analysis and by uniform transformation field analysis.
The present study deals with the determination of the nonlinear response of the masonry regarded ... more The present study deals with the determination of the nonlinear response of the masonry regarded as a regular, i.e. periodic, composite material made of bricks and mortar. A homogenization procedure is applied deriving the masonry overall mechanical response on the basis of the study of a single unit cell. An enriched plane state kinematic model including the effect of the transversal strains of the masonry is presented. This is a simplified form of the full threedimensional approach. Different cohesive constitutive models are introduced for the brick and mortar; in particular, the frictional effect, playing an important role in the masonry response, is accounted for in the mortar joints. Two main issues are addressed: (a) different structural models are considered at macro-and micro-scale: the macro-model is formulated in the two-dimensional plane state context, while the enriched plane state kinematic approach is adopted at the microlevel; (b) a nonlocal integral strain technique, able to overcome the classical localization drawbacks due to the softening response of the masonry constituents, is developed for the case of periodic media. Numerical applications are presented to assess the effectiveness of the proposed modeling approach.
Experimental investigations on superelastic shape-memory alloy wires show a significant dependenc... more Experimental investigations on superelastic shape-memory alloy wires show a significant dependency of the load-displacement response on the loading-unloading rate, coupled with a non-negligible oscillation of the wire temperature. Motivated by these observations, the present work proposes a thermo-mechanical model, suitable to study the wire response under cyclic stretching-bending loadings. The proposed model is based on the kinematical assumptions that plain sections remain plain and that the wire shear deformation is negligible. As a consequence, we need to in- troduce only a one-dimensional constitutive stress-strain equation. Accordingly, the whole model is thermo-mechanically coupled, due to the presence of internal heat sources (in the form of phase-transition latent heat and of mechanical dissipation) as well as due to possible convection phenomena between the wire and the surrounding. The paper addresses a numerical scheme for the model time-integration and the solution of ...
This paper aims at investigating the matrix-to-textile stress transfer in a fabric reinforced cem... more This paper aims at investigating the matrix-to-textile stress transfer in a fabric reinforced cementitious matrix FRCM system, not bonded to any substrate, under shear loads. To this end, direct shear tests are performed on a basalt FRCM specimen introduced into an innovative properly designed four-hinge frame loaded by a universal testing machine. The role of the single components in the global shear behavior of the FRCM is experimentally analyzed. Digital image correlation (DIC) is adopted for evaluating both the displacement and strain fields as well as for detecting the damage. Furthermore, the shear response of the tested FRCM material is reproduced via an effective numerical approach that considers the nonlinear behavior of the mortar and the possible micro-mechanisms that arise between the textile and the matrix, introducing suitable interfaces joining the FRCM constituent layers, i.e. textile and mortar layers. Experimental outcomes highlighted the non-negligible influence of the matrix in the shear response of the composite, both in strength and stiffness. The proven DIC technique demonstrated to be suitable also for this novel test type, since it allows to obtain shear strains, location and amplitude of cracks with satisfying accuracy, such as to make direct shear tests results a benchmark to be used for numerical simulations. Numerical analyses are performed in order to verify the efficiency of the proposed model in reproducing the mechanical behavior of FRCM composites under shear loads and in describing the damage patterns during the loading process.
Aim of this paper is to proposed a micro-scale numerical approach for the evaluation of the mecha... more Aim of this paper is to proposed a micro-scale numerical approach for the evaluation of the mechanical behavior of Fiber Reinforced Cementitious Mortar (FRCM) composites. As a matter of fact, the FRCM constitutive behavior is affected by micro-mechanisms, such as the cracking of the mortar and the slippage of the fibers within the mortar. The repetitive structural geometry of the FRCMs, due to the presence of the mesh grid, allows to identify a representative unit cell. This element is made by different constituent materials, i.e. fiber and mortar, and composed by three layers, i.e. two external layers of mortar and one inner layer made with fibers and mortar. In the framework of 2D plane stress state, the numerical approach consists in modeling the constituents as linear elastic materials and accounting for the material non-linearities through the implementation of suitable interface elements. In the interface model, the damage, the friction effects and the unilateral contact are taken into account. This numerical approach is used for reproducing the tensile behavior of the FRCM composites. It is successfully validated with available experimental results and a parameter sensitivity analysis is performed.
Fabric Reinforced Cementitious Matrix (FRCM) composites represent an innovative and effective ret... more Fabric Reinforced Cementitious Matrix (FRCM) composites represent an innovative and effective retrofitting solution for masonry structures. The use of FRCMs as an external retrofitting technique requires an insight knowledge of their mechanical behavior, failure modes and masonry-to-FRCM bond properties. A Round Robin Test (RRT) programme was launched by twelve Italian Universities, aimed at evaluating the effect of the shear test setup parameters and at assessing the test variability. The experimental tests were performed on systems made of glass and steel fibers/cords applied onto masonry substrates. The results were carefully analyzed discussing failure modes, bond capacity, and slip statistical dispersion. Differences in the setup , including the clamping method, textile impregnation, and instrumentation used for measuring the slip during the tests, were discussed in detail providing useful considerations and suggestions for reducing experimental scattering and obtaining reliable results. The analysis showed that the considered parameters have an influence on the structural behavior of the FRCM samples demonstrating that an accurate setup standardization is needed.
The influence of mortars joints in masonry substrate reinforced with FRP is investigated from the... more The influence of mortars joints in masonry substrate reinforced with FRP is investigated from the numerical point of view. The analysis has been conducted by means of a new interface model specifically developed to reproduce the debonding process occurring between an elastic thin body in adhesion with a cohesive support material. The model accounts for mode I and mode II of failure, considering the effect of the in-plane deformation of the interface, i.e. the possible elongation or confinement of the material constituting the interface. Numerical results are compared with experimental evidences showing good performances of the proposed model in investigating the transferring phenomena and in studying the influence of the presence of mortar joints in the masonry texture in the debonding process.
Abstract A novel two-scale modeling approach, linking different structural models at macro and mi... more Abstract A novel two-scale modeling approach, linking different structural models at macro and microscale, is proposed to describe response of masonry walls with periodic texture. At the higher macroscopic scale, the real heterogeneous material is modeled as a homogenized medium, considering the classical Mindlin-Reissner theory for flat shells. At the lower microscopic scale, a representative masonry Unit Cell (UC), accounting for the actual geometry, arrangement and nonlinear behavior of constituent materials, is analyzed in detail by resorting to a three-dimensional Cauchy model. The UC is modeled as the assembly of elastic bricks and nonlinear zero-thickness interfaces, in which the sliding frictional and damaging mechanisms are concentrated. To perform the macro–micro information transition a proper kinematic map is defined, whereas the upscaling process is performed via a homogenization procedure based on the Transformation Field Analysis (TFA), properly extended to the case of interfaces. The developed homogenization procedure invokes a generalized Hill-Mandel principle and requires to satisfy ‘non-standard’ constraints at the microlevel, for which the perturbed Lagrangian method is employed. Numerical applications are performed to prove the model efficiency in describing the response of a running bond UC subjected to in-plane and out-of-plane loads. Special attention is devoted to the analysis of shell bending and shear behavior, comparing the results obtained with the proposed model with those recovered by detailed micromechanical analyses.
Masonry arches are amongst the most fascinating structures of the World's historical and arch... more Masonry arches are amongst the most fascinating structures of the World's historical and architectural heritage. Their vulnerability to earthquakes pointed out the necessity of their preservation. Fiber Reinforced Cementitious Mortar (FRCM) composites have been recently used as a more sustainable alternative to FRPs in the strengthening of masonry structures, since they can overcome the limits FRP show as strengthening systems: poor behavior to high temperature, delamination with significant loss of material at the bonded surface, lack of vapor permeability, impossibility of application on humid surfaces, incompatibility of resins with masonry, high cost and reduced reversibility of the installation. These aspects have a critical relevance in the case of historical structures, whose features have to be preserved, and motivate researches about the use of FRCM on masonry structures, from both experimental and analytical points of view. In this paper, the results of numerical analy...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Aim of the present paper is to develop an efficient multiscale procedure for studying the mechani... more Aim of the present paper is to develop an efficient multiscale procedure for studying the mechanical response of structural elements made of elastoplastic or viscoplastic composite materials. The micro and the macro scales are considered separated. At the microscale a PieceWise Uniform Transformation Field Analysis (PWUTFA) homogenization technique is adopted to derive the overall response of a periodic composite. Thus, a Unit Cell (UC) containing all the properties of the heterogeneous material is analyzed and divided in subsets; in each one the inelastic strain is considered uniform, i.e. constant, and represents the history variable of the analysis. Elastoplastic and elasto-viscoplastic models with isotropic hardening are adopted in order to describe the nonlinear response of the constituents. A new numerical procedure is developed in order to solve the evolutive problem in all the subsets simultaneously adopting a predictor-corrector technique. The corrector phase is solved by means of a modified Newton-Raphson iterative procedure. Furthermore, the tangent consistent with the algorithm is computed and adopted in the multiscale computations. Numerical applications are carried out in order to assess the efficiency of the proposed multiscale approach.
Aim of the present study is to propose an enhanced method for the domain decomposition (clusterin... more Aim of the present study is to propose an enhanced method for the domain decomposition (clustering) of the representative volume element (RVE) of composite materials to be used with homogenization techniques, based on the PieceWise Uniform Transformation Field Analysis (PWUTFA). With PWUTFA, both constitutive and evolutive equations for the constituents of the composite material are written in terms of averages in each cluster; moreover, it is not required to solve via FEM the nonlinear micro-mechanical problem, allowing to drastically reduce the number of internal variables. PWUTFA is founded on the idea that it is possible to divide the RVE into large subdomains (clusters) that should group together finite elements having, under any applied loading condition, the most similar values of strain. Accordingly, in this study a multi-objective optimization-based approach is proposed with the aim to simultaneously reduce both the error in the approximation of the strain fields and the number of clusters in which the domain is decomposed. Different clustering solutions, obtained through the proposed optimization approach are analyzed, and the corresponding mechanical responses are compared with the ones obtained by the finite element analysis and by uniform transformation field analysis.
The present study deals with the determination of the nonlinear response of the masonry regarded ... more The present study deals with the determination of the nonlinear response of the masonry regarded as a regular, i.e. periodic, composite material made of bricks and mortar. A homogenization procedure is applied deriving the masonry overall mechanical response on the basis of the study of a single unit cell. An enriched plane state kinematic model including the effect of the transversal strains of the masonry is presented. This is a simplified form of the full threedimensional approach. Different cohesive constitutive models are introduced for the brick and mortar; in particular, the frictional effect, playing an important role in the masonry response, is accounted for in the mortar joints. Two main issues are addressed: (a) different structural models are considered at macro-and micro-scale: the macro-model is formulated in the two-dimensional plane state context, while the enriched plane state kinematic approach is adopted at the microlevel; (b) a nonlocal integral strain technique, able to overcome the classical localization drawbacks due to the softening response of the masonry constituents, is developed for the case of periodic media. Numerical applications are presented to assess the effectiveness of the proposed modeling approach.
Experimental investigations on superelastic shape-memory alloy wires show a significant dependenc... more Experimental investigations on superelastic shape-memory alloy wires show a significant dependency of the load-displacement response on the loading-unloading rate, coupled with a non-negligible oscillation of the wire temperature. Motivated by these observations, the present work proposes a thermo-mechanical model, suitable to study the wire response under cyclic stretching-bending loadings. The proposed model is based on the kinematical assumptions that plain sections remain plain and that the wire shear deformation is negligible. As a consequence, we need to in- troduce only a one-dimensional constitutive stress-strain equation. Accordingly, the whole model is thermo-mechanically coupled, due to the presence of internal heat sources (in the form of phase-transition latent heat and of mechanical dissipation) as well as due to possible convection phenomena between the wire and the surrounding. The paper addresses a numerical scheme for the model time-integration and the solution of ...
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