Ciclo de mejora docente en la titulación de Ingeniería Mecánica: hacia un conocimiento real de las estructuras

La presente comunicación narra la experiencia del Ciclo de Mejora llevado a cabo en el área de Mecánica de Medios Continuos y Teoría de Estructuras sobre el tema del cálculo de deformaciones en diferentes tipologías de elementos estructurales. En la misma se detalla de manera estructurada el modelo metodológico utilizado y la secuencia de actividades llevadas a cabo, un breve diario de las sesiones y un estudio final de la evolución del aprendizaje de los estudiantes durante el ciclo. Las sesiones han sido grabadas para su análisis dentro del Proyecto de Excelencia del Plan Estatal 2013-2016 titulado “La Formación Docente del Profesorado Universitario. Progresos y Obstáculos de los Participantes en un Programa Basado en Ciclos de Mejora de su Práctica”

Criterios generales de intervención en monumentos de piedra

La piedra ha sido utilizada desde antiguo como material de construcción por su durabilidad y resistencia. En la actualidad, la contaminación ha producido graves alteraciones en la misma, poniendo en peligro la integridad de nuestro patrimonio histórico-artístico. El proceso de intervención deberá incluir los tratamientos adecuados que devuelvan al material su resistencia original y la cohesión entre sus partículas teniendo en cuenta que cada obra presenta una problemática diferente, sin olvidar la importancia de un adecuado y continuo mantenimiento.Stone has been used since remote ages as a construction material due to its durability and resistance. Nowadays, pollution is introducing severe damage in stone works and is al so harming the artistic legacy of our cities. This paper proposes a restoration process that includes adequate treatment to restore the original resistance and cohesion of the material. It al so stresses the importance of an adequate maintenance process

Definición de un modelo de comportamiento plástico durante la estricción para los aceros corrugados de alta ductilidad

El factor más influyente en la reducción de la rigidez de las estructuras de hormigón armado se encuentra en la capacidad de deformación anelástica de los aceros utilizados en las armaduras, es decir, en su ductilidad. En esta tesis se aborda el análisis del comportamiento plástico de varios tipos de acero corrugado hasta rotura, estudiando en profundidad las dos fases claramente diferenciadas que experimenta un acero sometido a tracción, evidenciado a nivel de deformaciones, con una primera etapa en la que éstas se traducen en un alargamiento uniforme de la probeta asociado a un estado de tensiones uniaxial, y una segunda en la que dichas deformaciones se concentran en la zona del cuello, pasándose a un complejo estado tensional triaxial. El conocimiento del comportamiento real de estos aceros hasta su agotamiento resulta de gran interés para un aprovechamiento más óptimo de las estructuras, especialmente en zonas de alto riesgo sísmico. Así mismo, resulta de gran utilidad a la hora de abordar el análisis de patologías estructurales, permitiendo conocer la capacidad de deformación del material antes del colapso y sus tensiones asociadas.The most influential factor in the reduction of the rigidity of reinforced concrete structures is the capacity of plastic strain of steels used in the armor. This thesis deals with the analysis of the plastic behavior of various types of corrugated steel to break, studying in depth the two distinct phases experienced by a steel in tensile test, evidenced at the level of strain, with a first phase in which they translate into a uniform elongation of the specimen associated with a uniaxial state of stress, and a second in which such deformations are concentrated in the area of the neck, passing to a triaxial stress state complex. Knowledge of the actual behavior of these steels until their exhaustion is of great interest for a more optimal use of structures, especially in areas of high seismic risk. Likewise, it is very useful in dealing with the analysis of structural pathologies, allowing to know the deformation capacity of the material before the collapse and its associated tensions

Analysis of the State of Stresses and Plastic Strains during the Necking Process in Ductile Steels

In steel, the knowledge beyond the yield strength elastic is of the utmost importance because of the large plastic strain that take place both at the time of the breakage and multiple conformation processes involving a stretch of material, such as rolling or extrusion. Beyond the manufacturing process, the trend nowadays is to the use of more ductile steels for concrete every time, that improve the behavior of structures due to loads limits such as those produced by seismic events. In this investigation, based on breakage testing tensile, we present a detailed analysis of the behavior of ductile steels, manufactured by hot rolling, defining plastic behavior of these laws to breaking, focusing primarily on the phenomenon of the formation of the neck

Elasto-plastic hardening models adjustment to ferritic, austenitic and austenoferritic Rebar

The elastoplastic behaviour of steel used for structural member fabrication has received attention to facilitate a mechanical-resistant design. New Zealand and South African standards have adopted various theoreti-cal approaches to describe such behaviour in stainless steels. With respect to the building industry, describing the tensile behaviour of steel rebar used to produce reinforced concrete structures is of interest. Differences compared with the homogenous material described in the above mentioned standards and related literatures are discussed in this paper. Specifically, the presence of ribs and the TEMPCORE® technology used to produce carbon steel rebar may alter the elastoplastic model. Carbon steel rebar is shown to fit a Hollomon model giving hardening exponent values on the order of 0.17. Austenitic stainless steel rebar behaviour is better described using a modified Rasmussen model with a free fitted exponent of 6. Duplex stainless steel shows a poor fit to any previous model.Ajuste de los aceros corrugados ferríticos, austeníticos y austenoferríticos a los modelos de endureci-miento elastoplástico por deformación. Uno de los principales factores tenidos en cuenta en la fabricación de aceros estructurales es su comportamiento durante la fase elastoplástica o de endurecimiento por deformación. Normas neozelandesas y sudafricanas plantean diversas aproximaciones teóricas para describir dicho comportamiento en el caso de los aceros inoxidables. En el campo de la construcción resulta de interés la descripción del comporta-miento tenso-deformacional de los aceros corrugados utilizados en las estructuras de hormigón armado. En este artículo se discuten los modelos planteados en las normas citadas anteriormente así como los existentes en la litera-tura tanto para los aceros corrugados inoxidables como para los aceros al carbono fabricados mediante el proceso denominado TEMPCORE® Los aceros TEMPCORE® analizados arrojan un valor del exponente de endureci-miento por deformación según el modelo de Hollomon de 0.17. Los aceros inoxidables austeníticos se ajustan mejor al modelo de Rasmussen presentando un exponente de valor 6 realizando un ajuste libre de la función correspondiente. Para los aceros inoxidables Dúplex se obtienen muy bajos ajustes para los dos modelos citados

Characterization of the mechanical behaviour of Tempcore 500C rebar steel during tensile test necking: Experimentation and simulation

The calculation of the true stress and strain values during the tensile test necking phase of smooth ductile metals specimens has been extensively pursued by several authors. A symmetrical neck profile, which leads to axial-symmetrical behaviour, is usually considered. In this study, the neck geometry of Temp-core ribbed bars, the most commonly used steel in reinforced concrete today, is analysed. Knowledge of the true stress and strain values up to failure of this steel is vital since these describe the real behaviour of the steel under extreme conditions. Due to the limited effectiveness of the previously reported theories, an experimental methodology is proposed in order to analyze ribbed bar neck 3D geometry. The results obtained are compared to those of smooth bars of similar steel, both of which are then validated through Finite Element analysis. As a result, the influence of ribbed geometry is found to involve a reduction of true strain values on failure, due to stress concentration occurring in proximity to the root of the transverse ribs affected by necking.El cálculo de los valores de tensión y deformación verdaderos en probetas cilíndricas de metales dúctiles durante la estricción ha sido ampliamente estudiado por diversos autores partiendo, en todos los casos, de una geometría simétrica del cuello. En este estudio se analiza la evolución del perfil del cuello en las barras corrugadas de los aceros Tempcore, proponiendo una metodología experimental mediante análisis en 3D. Conocer el verdadero comportamiento hasta rotura de este acero es de vital importancia para describir su respuesta ante situaciones límites. Los resultados experimentales obtenidos son comparados con los de barras cilíndricas de acero similar, siendo ambos validados mediante análisis por Elementos Finitos. Dicha comparativa permite comprobar que la existencia de corrugas implica una reducción de la deformación en rotura debido a la concentración de tensiones que se origina en zonas próximas al arranque de las mismas

Influence of rebar design on mechanical behaviour of Tempcore steel

22nd European Conference on Fracture, ECF 2018; Metropol Palace Belgrade; Serbia; 25 August 2018 through 26 August 2018; Code 145523Tensile behaviour of metals beyond the ultimate tensile strength (UTS) must be considered to calculate toughness or absorbed energy till fracture. Structural steels, designed to withstand earthquakes, are the typical material where post necking behaviour can be of paramount importance. This paper deals with the tensile stress-strain behaviour of Tempcore Rebar, a specifically shaped structural steel. Helical, short ribs, formed by rolling, protrude from the cylindrical basic shape of the Rebar. This help in increasing concrete/steel adherence in reinforced structures. On the other hand, those ribs make it difficult to assess strain distribution in the necking area, according to well-known theories describing neck profile. New or modified experimental methods, along with new theoretical approaches must be developed to help in studying neck profile evolution and corresponding stresses in rebars. Advances in such methods and theories are presented in this paper along with comparison with Tempcore cylindrical bars necking behaviour. The effect of ribs is clearly identified

Determinación del modelo de comportamiento hasta rotura de los aceros corrugados tempcore mediante modelado 3D

El estudio del comportamiento real hasta rotura de los metales resulta de gran interés en la industria ya que permite determinar la tenacidad o energía absorbida durante el proceso de deformación y rotura. En cuanto a los aceros estructurales, existe el interés añadido de conocer su respuesta real ante cargas asociadas a situaciones límites como son los movimientos sísmicos. En este trabajo se aborda el comportamiento tenso-deformacional de los aceros corrugados Tempcore. La peculiar geometría de estas barras, diseñadas a tal efecto para aumentar la adherencia acero-hormigón, dificulta el análisis de la fase de estricción desde la metodología que tradicionalmente se sigue para probetas cilíndricas, basada en diversas hipótesis de partida que no se cumplen en probetas corrugadas. Por tanto, se hace necesario el planteamiento de nuevos principios y, por ende, de nuevos procesos que permitan abordar su estudio. En este trabajo se presentan algunos de los avances realizados referentes a la evolución del perfil del cuello y a las deformaciones sufridas por las diferentes secciones transversales del mismo para estas barras.The real tensile behavior of metals beyond the UTS must be considered to calculate toughness or absorbed energy till fracture. Structural steels, designed to withstand earthquakes, are the typical material where post necking behavior can be of paramount importance. This paper deals with the tensile stress-strain behavior of TEMPCORE Rebar, a specifically shaped structural steel. Helical, short ribs, formed by rolling, protrude from the cylindrical basic shape of the Rebar. This help in increasing concrete/steel adherence in reinforced structures. On the other hand, those ribs make it difficult to assess strain distribution in the necking area, according to wellknown theories describing neck shape. New or modified experimental methods, along with new theoretical approaches must be developed to help in studying neck shape evolution and corresponding stresses in Rebar. Advances in such methods and theories are presented in this paper

Analysis of the main aspects affecting bonding in stainless steel rebars embedded in a hydraulic medium

The use of stainless steel rebars to reinforce masonry structures has become established as an eminently efficient methodology. From among the numerous techniques available, bed-joint structural repointing and superficial reinforcement with rebars or meshes attached to surfaces have become widespread, thanks to the excellent results they have produced in recent decades. Both techniques imply the use of diameters less than 6 mm and thin coverings. This article deals with the characterization of the bonding behavior of the rebar under these special circumstances. To this end, several finite element analyses have been carried out to identify the possible relationships between pull-out forces in various situations. These models allow certain conclusions to be drawn regarding the influence of the thickness of covering, boundary conditions, and geometrical aspects of the rebars in bonding. Certain mathematical expressions that relate the various conclusions from this research are finally laid out

Influence of bar thermal hardening via tempcore method on their properties after stretching

Mechanical properties after stretching testings were calcu-lated and experimentally determined via Tempcore method for bar core, bar surface and whole bar cross section. It was displayed on the base of experiments and imitating simulation that deformation in core and surface areas of a bar are equal and therefore influence of structural parameters in the core area is principally decisive for initiating of neck forming in the surface area. The results showed that resistance to destruction of martensite surface layer has rather less effect on bar properties in general in comparison with previous investigations. It is concluded that improvement of core structure quality can help to lower brittleness of the whole bar. It was also proved that used techniques provide good concordance between the obtained results and experimental data. Therefore, the additivity rule for structural components can be used successfully for determination of whole bar parameters, taking into account thickness of surface layer that can be measured easily using hardness sensor. It will simplify practically quality control of products