Thermodynamic Framework of Multiscale Homogenization Schemes for Dissipative Materials

The prediction of failure processes in composite, heterogeneous materials require multiscale analysis to account for the complex mechanisms and features taking place. Between the different multiscale schemes the more commonly used are those based on homogenization procedures, due to their versatility. In this work a thermodynamically consistent homogenisation based multiscale approach is formulated for modelling thermo-plastic materials. The proposal is valid for arbitrary multiscale procedures, including local or nonlocal methods, and continuum or discontinuum methods in either scale. The necessary and sufficient conditions for fulfilling the thermodynamic consistency are defined. It is demonstrated that the Hill-Mandel variational criterion for homogenization scheme is a necessary, but not a sufficient condition when dissipative material responses are involved at any scale. On this point, the additional condition that needs to be fulfilled is established. The general case of temperature-dependent, higher order elastoplasticity is considered as theoretical framework to account for the material dissipation at micro and macro scales of observation. Additionally, it is shown that the thermodynamic consistency enforces the homogenization of the nonlocal terms of the micro scale’s free energy density; however, this does not necessarily lead to nonlocal effects on the macro scale. Finally, the particular cases of local isothermal elastoplasticity and continuum damage are considered for the purpose of the proposed approach for multiscale homogenizations.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí

Algunos aspectos del reglamento aci 562-19 relativo a la evaluación de estructuras de hormigón existentes

El ACI (American Concrete Institute) cuenta con una serie de comités que elaboran reportes y recomendaciones relacionados con múltiples aspectos de las estructuras de hormigón. Hasta hace unos años, el único de estos trabajos con el carácter de reglamento, era el ACI 318, “Requisitos reglamentarios para hormigón estructural”. Sin embargo, desde hace unos pocos años, se ha sumado un nuevo documento con carácter reglamentario: el ACI 562, titulado “Código de requerimientos para la evaluación, reparación y rehabilitación de estructuras de hormigón existentes” que establece lineamientos para encarar trabajos de ingeniería estructural relacionados con estructuras de hormigón existentes. Especialmente, se centra en el caso de estructuras que presentan patologías o que, debido a algún cambio en las condiciones originales, es necesario realizar una evaluación para luego decidir cómo proceder. El objetivo del presente trabajo es difundir la existencia del ACI 562-19, mostrar los aspectos fundamentales del mismo y discutir cómo encaja dentro de la reglamentación local.Fil: Folino, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Ripani, Marianela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina26° Jornadas Argentinas de Ingeniería EstructuralCiudad Autónoma de Buenos AiresArgentinaAsociación de Ingenieros Estructurale

Thermodynamic Framework of Multiscale Homogenization Schemes for Dissipative Materials

The prediction of failure processes in composite, heterogeneous materials require multiscale analysis to account for the complex mechanisms and features taking place. Between the different multiscale schemes the more commonly used are those based on homogenization procedures, due to their versatility. In this work a thermodynamically consistent homogenisation based multiscale approach is formulated for modelling thermo-plastic materials. The proposal is valid for arbitrary multiscale procedures, including local or nonlocal methods, and continuum or discontinuum methods in either scale. The necessary and sufficient conditions for fulfilling the thermodynamic consistency are defined. It is demonstrated that the Hill-Mandel variational criterion for homogenization scheme is a necessary, but not a sufficient condition when dissipative material responses are involved at any scale. On this point, the additional condition that needs to be fulfilled is established. The general case of temperature-dependent, higher order elastoplasticity is considered as theoretical framework to account for the material dissipation at micro and macro scales of observation. Additionally, it is shown that the thermodynamic consistency enforces the homogenization of the nonlocal terms of the micro scale’s free energy density; however, this does not necessarily lead to nonlocal effects on the macro scale. Finally, the particular cases of local isothermal elastoplasticity and continuum damage are considered for the purpose of the proposed approach for multiscale homogenizations.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí

Resistencia a fuego en estructuras de acero y hormigón armado. disposiciones reglamentarias

La respuesta estructural frente a un incendio constituye un aspecto critico que debiese tenerse en cuenta en el diseño de toda obra de ingeniería civil. En el caso de un siniestro, se debe procurar la estabilidad de la estructura durante un periodo de tiempo razonable, en el que pueda llevarse a cabo la evacuación de las personas. Existen diversos métodos para el análisis de las estructuras en situación de incendio, cuya complejidad va desde la aplicación de curvas de fuego estándar en simples elementos estructurales, hasta la modelación numérica de estructuras reales por medio de herramientas computacionales capaces de resolver el problema de la dinámica de los fluidos. En cuanto a reglamentaciones, existen diversas normas europeas y americanas dedicadas al respecto. Tal es el caso particular del Eurocodigo, que presenta un enfoque más orientado al desempeño estructural, y el ACI en conjunto con la AISC que tienen una orientación más prescriptiva del diseño frente a fuego. En este trabajo se presentan los aspectos principales de las normas citadas, comparándose, además, con aquellas disposiciones presentadas por el CIRSOC 2005.Fil: Ripani, Marianela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Folino, Paula. Universidad de Buenos Aires. Facultad de Ingeniería. Laboratorio de Métodos Numéricos en Ingeniería; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Construcciones y Estructuras. Laboratorio de Materiales y Estructuras; ArgentinaFil: Xargay, Hernan Daniel. Universidad de Buenos Aires. Facultad de Ingeniería. Laboratorio de Métodos Numéricos en Ingeniería; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Construcciones y Estructuras. Laboratorio de Materiales y Estructuras; Argentina26° Jornadas Argentinas de Ingeniería EstructuralCiudad Autónoma de Buenos AiresArgentinaAsociación de Ingenieros Estructurale

Uso de materiales reciclados en compuestos cementicios

Context: Concrete production is characterized by a significant demand for energy and raw materials, and by emitting large amounts of greenhouse gases (GHG). Moreover, the processes of construction, maintenance, and demolition of buildings generate huge quantities of waste that require costly and environmentally sensitive disposal procedures. Therefore, several solutions are being investigated to reduce the environmental impact of the processes associated with the life cycle of concrete. Methodology: Through experimental tests, the physical and mechanical properties of three sustainable concrete mixtures were studied (concrete with recycled aggregates, concrete with partial replacement of Portland cement by fly ash, and cementitious composites reinforced with recycled fibers). Results: The use of coarse recycled aggregates degraded the mechanical characteristics of the concrete due to their greater porosity and water absorption capacity. However, the mixture made out of recycled aggregates and fly ash showed a synergistic effect, mitigating the adverse consequences mentioned. The post-cracking response of concrete reinforced with recycled steel fibers was characterized by a lower tenacity and ductility compared to composites with industrial fibers. Specifically, mixtures with recycled fibers showed a more pronounced softening stage. This revealed a lower efficiency of recycled fibers compared to industrial fibers. Conclusions: The experimental results showed that the incorporation of recycled materials led to a deterioration in the physical and mechanical behavior of the analyzed composites. However, the resulting properties exceeded the recommended minimum values required for their application as structural materials.Contexto: La producción de hormigón se caracteriza por una importante demanda de energía y materias primas, emitiendo grandes cantidades de gases de efecto invernadero (GEI). Asimismo, la construcción, mantenimiento y demolición de edificios genera enormes cantidades de residuos que requieren costosos y ambientalmente sensibles procedimientos de disposición final. Por tanto, en la actualidad se están investigando diversas soluciones para reducir el impacto ambiental de los procesos asociados al ciclo de vida del hormigón. Metodología: Se estudiaron, mediante ensayos experimentales, las propiedades físicas y mecánicas de los siguientes materiales sustentables: hormigón con agregados reciclados, hormigón con reemplazo parcial de cemento Portland por cenizas volantes y compuestos cementicios reforzados con fibras recicladas. Resultados: El uso de agregados gruesos reciclados degradó las características mecánicas del hormigón debido a su mayor porosidad y capacidad de absorción de agua. Sin embargo, su combinación con cenizas volantes mostró un efecto sinérgico, mitigando las consecuencias adversas mencionadas. La respuesta posfisuración del hormigón reforzado con fibras de acero recicladas se caracterizó por una menor tenacidad y ductilidad respecto a los compuestos con fibras industriales. Específicamente, las mezclas con fibras recicladas mostraron una etapa de ablandamiento más pronunciada. Esto reveló una eficiencia menor de las fibras recicladas con respecto a las industriales. Conclusiones: Los resultados experimentales demostraron que la incorporación de materiales reciclados condujo a un deterioro en el comportamiento físico y mecánico-resistente de los compuestos analizados. No obstante, las propiedades resultantes superaron los valores mínimos recomendados para su aplicación como materiales estructurales

Il Progetto EnCoRe : una iniziativa sovranazionale per promuovere il concetto di sostenibilità del calcestruzzo e dei materiali cementizi

Environmental issues are getting more and more relevant in several fields of human activities and the building industry is fully concerned by these concerns. Recycled concrete aggregates (RCA) can be produced by existing concrete members resulting by either industrial processes (i.e., precast structures) or demolitions of existing structures as a whole. Moreover, waste resulting from industrial processes other than the building industry (i.e., production of steel, management of glass, powders resulting from other depuration processes) could be efficiently disposed as concrete aggregates or employed as reinforcement for Fiber-Reinforced Concretes (FRC). The use of natural fibres can also result into an environmentally-friendly and cost-effective solution, especially in developing countries, because of the local availability of raw materials. In order to promote the use of concretes with recycled and/or natural constituents as construction materials, the compatibility between the non conventional constituents and the concrete matrix have to be deeply investigated and correlated to the resulting mechanical and durability properties of the composite. This is the main goal of the EnCoRe Project (www.encore-fp7.unisa.it), a EU-funded initiative, whose activities and main findings will be summarized in this paper

The encore project: sustainable solutions for cementitious materials

Since concrete is the most widely utilized construction material, several solutions are currently being developed and investigated for enhancing the sustainability of cementitious materials. One of these solutions is based on producing Recycled Concrete Aggregates (RCA) from existing concrete members resulting by either industrial processes or demolitions of existing structures as a whole. Moreover, waste resulting from industrial processes other than the building construction (i.e., tire recycling, production of steel, powders resulting from other depuration processes) are also being considered as possible low-impact constituents for producing structural concrete and Fiber-Reinforced Cementitious Composites (FRCC). Furthermore, the use of natural fibers is another option for producing environmentally-friendly and cost-effective materials, depending on the local availability of raw materials. To promote the use of concretes partially composed of recycled constituents, their influence on the mechanical and durability performance of these concretes have to be deeply investigated and correlated. This was the main goal of the EnCoRe Project (www.encore-fp7.unisa.it), a EU-funded initiative, whose activities and main findings are summarized in this paper.The authors wish to acknowledge the support to the networking activities provided by "EnCoRe" project (www.encore-fp7.unisa.it) (FP7-PEOPLE-2011-IRSES, n. 295283) funded by the European Union as part of the 7th Framework Programme for Research and Innovation

Thermal Action on Normal and High Strength Cement Mortars

High temperature effect on cement-based composites, such as concrete or mortars, represents one of the most important damaging process that may drastically affect the mechanical and durability characteristics of structures. In this paper, the results of an experimental campaign on cement mortars submitted to high temperatures are reported and discussed. Particularly, two mixtures (i.e., Normal (MNS) and High Strength Mortar (MHS)) having different water-to-binder ratios were designed and evaluated in order to investigate the incidence of both the mortar composition and the effects of thermal treatments on their physical and mechanical properties. Mortar specimens were thermally treated in an electrical furnace, being submitted to the action of temperatures ranging from 100 to 600 °C. After that and for each mortar quality and considered temperature, including the room temperature case of 20 °C, water absorption was measured by following a capillary water absorption test. Furthermore, uniaxial compression, splitting tensile and three-points bending tests were performed under residual conditions. A comparative analysis of the progressive damage caused by temperature on physical and mechanical properties of the considered mortars types is presented. On one hand, increasing temperatures produced increasing water absorption coefficients, evidencing the effect of thermal damages which may cause an increase in the mortars accessible porosity. However, under these circumstances, the internal porosity structure of lower w/b ratio mixtures results much more thermally-damaged than those of MNS. On the other hand, strengths suffered a progressive degradation due to temperature rises. While at low to medium temperatures, strength loss resulted similar for both mortar types, at higher temperature, MNS presented a relatively greater strength loss than that of MHS. The action of temperature also caused in all cases a decrease of Young’s Modulus and an increase in the strain corresponding to peak load. However, MHS showed a much more brittle behavior in comparison with that of MNS, for all temperature cases. Finally, the obtained results demonstrated that mortar quality cannot be neglected when the action of temperature is considered, being the final material performance dependent on the physical properties which, in turn, mainly depend on the mixture proportioning

Performance dependent model for normal and high strength concretes

A new constitutive formulation, the so-called Performance Dependent Model valid for normal and high strength concretes is presented. The distinctive aspect of the proposed model is the consideration of relevant properties of concrete mix components in the evaluation of the involved material performance or quality at the macroscopic stand point. In this way, the composite features of concrete are appropriately taken into account.The model maximum strength surface is defined by means of the Performance Dependent Failure Criterion proposed by the authors in previous works. Concrete behaviors in pre and post peak regimes are modeled with a non uniform hardening law and an isotropic softening rule, respectively. To realistically reproduce the concrete ductility in pre and post peak regimes under different load scenarios, the hardening and softening laws are dened in terms of the acting conning pressure. Concrete dilatancy behavior is approached by means of a volumetric non associative fow rule. The softening law is embedded in fracture energy concepts for mode I and II types of failure. The model considers two main input material parameters: the uniaxial compressive strength and the performance parameter, a quality index defined in the context of the Performance Dependent Failure Criterion.The proposed constitutive model is able to capture the substantial differences in the failure behavior of normal and high strength concretes as well as of concretes with the same compressive strength but different mix components. The predictive capabilities of the model are demonstrated in the numerical analyses included in this paper where the numerical predictions are compared with experimental results related to concrete specimens of different qualities and subjected to stress histories under both compressive and tensile regimes.Fil: Folino, Paula. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Etse, Jose Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Centro de Métodos Numéricos y Computacionales en Ingeniería; Argentin

Validation of Performance-Dependent Failure Criterion for Concretes

This paper focuses on the reformulation of the internal functions of the performance-dependent failure criterion (PDFC) for concrete, proposed by the authors, and its validation for different concrete qualities and stress states. The PDFC predicts the maximum strengths of plain concretes characterized by uniaxial compressive strengths in the range of 20 to 120 MPa (2901 to 17,405 psi). Concrete performance in this criterion is defined in terms of four material features. Supported on an extensive experimental database, they are reformulated in this work as a function of the two parameters that most effectively describe the involved concrete quality: fc′ and the so-called concrete performance parameter. The objective definition of the involved concrete quality by means of these two fundamental material parameters is also demonstrated. The numerical validation analysis in this paper illustrates the capabilities of the PDFC—when the internal functions as described in this work are considered—to predict the maximum strength properties of concretes of different qualities. Moreover, as the experimental data considered in this analysis include biaxial and triaxial test results on concrete specimens that involve a wide spectrum of confining pressures and stress meridians, the results in this work not only demonstrate the accuracy of the PDFC dependent functions on all three stress invariants, but also their variations with the involved quality.Fil: Folino, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Etse, Jose Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Centro de Métodos Numéricos y Computacionales en Ingeniería; Argentin