Multiphysical failure processes in concrete: a consistent multiscale homogenization procedure

Durability and strength capabilities of concrete materials are vastly affected by the combined action of temperature and mechanical loading, which give rise to multiphysical failure processes. Such a phenomenon involves complex cracking, degradation and transport mechanisms on different scale lengths of concrete mixtures which, in turn, depend on the particular properties of the different constituents. Thus, the macroscopic observation of relevant concrete mechanical features such as strength, ductility and durability are the result of several different properties, processes and mechanisms which are not only coupled but moreover, depend on multiple scales. Particularly, regarding the pore pressure and thermal actions, most of the degradation processes in concrete are controlled by the heterogeneities of the microscopic scale. In the case of the mechanical actions both the micro and mesoscales play a relevant role. In this context, multiphysical failure processes in cementitious material-based mixtures like concrete can only and fully be understood and accurately described when considering its multiscale and multiconstituent features. In the realm of the theoretical and computational solid mechanics many relevant proposals were made to model the complex and coupled thermo-hydromechanical response behavior of concrete. Most of them are related to macroscopic formulations which account for the different mechanisms and transport phenomena through empirical, dissipative, poromechanical theories. Moreover, although relevant progress was made regarding the formulation of multiscale theories and approaches, none of the existing proposals deal with multiphysical failure processes in concrete. It should be said in this sense that, among the different multiscale approaches for material modeling proposed so far, those based on computational homogenization methods have demonstrated to be the most effective ones due to the involved versatility and accuracy. In this work a thermodynamically consistent semi-concurrent multiscale approach is formulated for modeling the thermo-poro-plastic failure behavior of concrete materials. A discrete approach is considered to represent the RVE material response. After formulating the fundamental equations describing the proposed homogenizations of the thermodynamical variables, the constitutive models for both the skeleton and porous phases are described. Then, numerical analyses are presented to demonstrate the predictive capabilities of the proposed thermodynamically consistent multiscale homogenization procedure for thermo-mechanical failure processes in concrete mixtures

Social Tragedy in Amma Darko’S Faceless: The Plight of Street Children

In every household, children are ‘the joys of motherhood’ and families. However, children cannot grow normally and decently without the care and the protection of their parents/family/society and government. In many African countries, homeless/street children roam about the street to beg for food and money and become easy preys for the sadistic and unscrupulous predators.This article examines through Amma Darko’s Faceless (2003) street children phenomenon, their plight and the irresponsibility of the adults be parents/family members and community. The causes of this phenomenon, the violence that it nurtures and the misfortunes street children are facing in the hands of the ‘street lords’ are also highlighted.  Most of the time, street children are forced into prostitution and are sexually active before their teens with its subsequent consequences. Keywords: street children, child abuse and prostitution, violence, irresponsibility, poverty

Inter-media agenda-setting effects in Ghana: newspaper vs. online and state vs. private

The influx of the worldwide web has brought about dynamism in the way news is formulated and reported. Over the years scholars have debated the key ingredients that influence news selection. At the bottom of this discussion rests the question: what is considered newsworthy? But an even more evolving question is: who sets the media agenda? This study argues that the news worthiness of print and online media or state and private media is based on inter-media agenda setting. It examines the inter-media agenda setting effects of four publications in Ghana-the Daily Graphic-a government controlled newspaper which has both print and online versions, the Daily Guide which is privately owned newspaper with print and online versions, the Ghana News Agency (GNA) which is a government controlled solely online publication and Ghanaweb which is a privately owned solely online website.;Traditional cross-lagged correlations, rank ordering, the Rozelle-Campbell baseline and chi-square tests are used in this research. The results show that there was limited inter-media agenda setting for Ghana News Agency, Daily Graphic and Daily Guide since they produced 80% of their own stories. There was however strong evidence of inter-media agenda setting for Ghanaweb from GNA and some level of inter-media agenda setting from the Daily Graphic and Daily Guide. Results from the cross-lagged topic agenda correlations showed that the GNA\u27s agenda at Time 1 was highly correlated with that of the other three publications at Time 2. Ghanaweb\u27s rank order for Time 1 was not significant for GNA and the Daily Guide even though there was some influence for the Daily Graphic. The two print newspapers Daily Guide and Daily Graphic influenced each other and both influenced the private online publication, Ghanaweb

Constitutive formulation and numerical validation of mechanical behavior of unsaturated soils

En este trabajo se presenta un modelo constitutivo elastoplástico para suelos parcialmente saturados. El modelo se formula en el marco general de la teoría de medios porosos y de la teoría del flujo de la plasticidad. La formulación constitutiva se basa en el conocido modelo de MRS Lade en el que se incorpora la succión como componente adicional independiente del estado de tensiones. Consecuentemente, las superficies de fluencia de cono y capa del modelo asi como la evolución de las variables internas de endurecimiento y ablandamiento muestran dependencias con el valor de la succión. Para el proceso de integración numérica de tensiones del modelo se propone el método de proyección al punto más cercano que es extendido en esta formulación para el caso de cuatro invariantes tensionales. Los resultados numéricos demuestran la capacidad de predicción del Modelo Extendido de MRS Lade para simular el comportamiento de los suelos parcialmente saturados tanto en régimen de prepico como en pospico bajo distintos niveles de saturación. Para la validación del modelo constitutivo formulado se realiza la simulación numérica de ensayos experimentales edométricos con succión controlada experimentales publicados por Gens et al 1 y ensayos de compresión triaxial convencional con succión controlada publicados por Macari et al 2.Peer Reviewe

Formulación elastoplástica para el análisis computacional de pórticos planos de hormigón armado

Se presenta una formulación de endurecimiento-ablandamiento en términos de resultantes de tensiones y desplazamientos para aplicar la teoría de elastoplasticidad a elementos de barra. Los factores se calibran con respecto a relaciones momento-curvatura de las secciones, obtenidas a partir de ecuaciones constitutivas realistas del hormigón y del acero. Ejemplos muestran la capacidad del modelo y la importancia del ablandamiento en la respuesta estructural hasta los estados límites considerados.A formulation of hardening and softening is presented in terms of stress resultants and displacements to apply the elastic-plastic theory to bar elements. The factors are adjusted with regard to moment-curvature relations of sections, obtained from realistic constitutive equations of confined concrete and steel. Examples shown the model capacity and the importance of softening in the structural response up to the limit states considered.Peer Reviewe

Las estrategias de diseño gráfico, marketing y comunicación en una campaña antitabaco dirigida a adolescentes de Buenos Aires

En Buenos Aires se crean y difunden campañas destinadas a adolescentes sobre diversas problemáticas tales como el cuidado del medio ambiente, las enfermedades sexuales, el consumo de drogas ilegales, el reciclado, entre otras. Sin embargo, la concientización en torno al tabaco es escasa ya que la existencia de campañas anti tabaco dirigidas a los adolescentes en la presente ciudad es reducida en comparación con el 22% de los menores de edad entre 13 a 15 años que fuman (Encuesta Mundial de Tabaquismo en Jóvenes, 2012). A su vez, no obstante la Ley Nº 3718 promulgada en Buenos Aires en 2010 con respecto a espacios 100% Libres de Humo, en el presente año (2015) se continúa fumando en lugares públicos o privados de acceso público del conurbano, como ser discotecas, colectivos, bares y universidades. Al mismo tiempo, en el año 2012 se extendió la prohibición a las salas de juego y se declaró a la Provincia 100% Libre de Humo pero como la ley nunca se reglamentó aún se fuma en bingos, a través de salas disfrazadas de “clubes de fumadores”. En este contexto, según una encuesta realizada por la Fundación Interamericana del Corazón Argentina (en adelante FIC Argentina), en territorio bonaerense el 41% de las personas siguen expuestas al humo de tabaco ajeno en sus lugares de trabajo y el 61% lo padece en lugares públicos cerrados. En consecuencia, se refleja una problemática con respecto al tabaco que abarca múltiples incumplimientos en torno a la legislación existente en la presente provincia. A partir de lo anteriormente planteado, la presente investigación cuestiona a partir de cuáles estrategias de diseño gráfico, marketing y comunicación se encuentra compuesta una campaña anti tabaco dirigida a adolescentes menores de edad y que, a su vez, se encuentre adecuada a las exigencias, necesidades y perfil en general del target. En este contexto, la selección de la provincia de Buenos Aires se encuentra fundamentada, en primer lugar, en función de sus factores demográficos e industriales ya que al ser la capital de Argentina contiene un alto nivel de desarrollo industrial, comercial y económico, lo que lleva a un mayor mercado para el consumo del cigarro. A su vez, su población (15.625.084, según el Censo Nacional del año 2012), es el más elevado de todo el país, implicando una muestra representativa amplia. Por otro lado, el actor social seleccionado para la presente investigación consiste en el adolescente, principalmente porque es uno de los principales target de las industrias tabacaleras. En la revista La rentabilidad a Costa de la Gente - Actividades de la industria tabacalera para comercializar tabacos en América Latina y el Caribe y minar la salud pública, desarrollada por la Organización Panamericana de la Salud (2002) se declara que aunque los documentos de la industria tabacalera demuestren que sus planes de comercialización se elaboran para llegar a diversos grupos de edad, es evidente que el blanco más deseable para la industria era ,y sigue siendo, el grupo de los adolescentes. El segundo factor determinante para la selección del adolescente reside en que es un segmento de la sociedad argentina que se encuentra descuidado frente a la problemática del tabaco, teniendo en cuenta la cantidad de adolescentes menores de edad que fuman.&nbsp

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

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