Examinando por Autor "Enfedaque, Alejandro"
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Ítem Fracture and Size Effect of PFRC Specimens Simulated by Using a Trilinear Softening Diagram: A Predictive Approach(MDPI, 2021-07) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; García-Alberti, Marcos; Enfedaque, AlejandroThe size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram cannot capture the material behaviour on elements with different sizes due to dependence of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be very convenient for reproducing fracture of polyolefin-fibre-reinforced concrete elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of polyolefin-fibre-reinforced concrete specimens of different sizes under three-point bending. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental points of these softening functions are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately.Ítem Modelling fracture on polyolefin fibre reinforced concrete specimens subjected to mixed-mode loading(Elsevier, 2019-02) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Enfedaque, Alejandro; García-Alberti, MarcosIn recent years, polyolefin fibres have proved a remarkable performance as reinforcement of concrete, which has inspired a number of studies involving, among others, the simulation of fracture on polyolefin fibre reinforced concrete (PFRC) specimens. Fracture has been successfully reproduced on PFRC specimens in the past by means of an embedded crack model with a trilinear softening function, but always using for comparison the classical three-point bending test, which employs a symmetrical setup and induces fracture under pure mode I conditions. In the present study, six sets of specimens tested under an alternative setup of the three-point bending test, which induces fracture under mixed-mode conditions (I and II), are simulated using the same numerical approach. The results not only prove that the use of a trilinear softening function together with an embedded cohesive crack approach can reproduce fracture under mixed-mode conditions, but also provide interesting insights on how the trilinear softening function may be designed for suiting the usage of different fibre lengths or varying the proportions of polyolefin fibres.Ítem Numerical modelling of fracture in polyolefin fibre reinforced concrete specimens under mixed-model loading (I+II)(2019-06) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Enfedaque, Alejandro; García-Alberti, MarcosIn the last decades, many researchers have focused their work on studying the behaviour of fibre-reinforced concrete (FRC). The appearance of specific recommendations in several Standards has boosted their usage and the interest in this technology. Apart from the traditional steel fibres, new materials are now studied as fibre-type reinforcement in structural concrete. This is the case of polyolefin, a polymer that has proved to be a suitable alternative that overcomes some of the drawbacks of steel, namely those related to corrosion processes, and keeps a good ductile behaviour providing structural strength to concrete against tensile stresses. Modelling fracture of FRC elements has also proved to be successful using trilinear softening functions, not only with polyolefin fibres, but also with steel and glass fibres. Nevertheless, these numerical models have been used to contrast only notched specimens under three-point bending symmetric loading. In this contribution, trilinear softening functions are used to model fracture in specimens in which crack initiates under a combination of modes I and II. Fracture is modelled by means of an embedded crack formulation based on the strong discontinuity approach. Two sets of experimental data are compared, one with specimens of the same size with different proportions of fibres and another one where, keeping the fibre proportion constant, the specimens are scaled up in order to analyse the size effect. In both sets of experimental results, the Load-CMOD diagrams fit reasonably well using trilinear softening functions, predicting with correction the maximum load and the shape of the diagram due to the influence of the fibres.Ítem Numerical Simulation of PFRC Fracture Subjected to High Temperature by Means of a Trilinear Softening Diagram(MDPI, 2023-09-03) Suárez-Guerra, Fernando; Enfedaque, Alejandro; García-Alberti, Marcos; Gálvez-Ruíz, Jaime CarlosFibre-reinforced concrete (FRC) has been used for decades in certain applications in the construction industry, such as tunnel linings and precast elements, but has experienced important progress in recent times, boosted by the inclusion of guidelines for its use in some national and international standards. Traditional steel fibres have been studied in depth and their performance is well-known, although in recent years new materials have been proposed as possible alternatives. Polyolefin macro-fibres, for instance, have been proven to enhance the mechanical properties of concrete and the parameters that define their behaviour (fibre length, fibre proportion or casting method, for instance) have been identified. These fibres overcome certain traditional problems related to steel fibres, such as corrosion or their interaction with magnetic fields, which can limit the use of steel in some applications. The behaviour of polyolefin fibre-reinforced concrete (PFRC) has been numerically reproduced with success through an embedded cohesive crack formulation that uses a trilinear softening diagram to describe the fracture behaviour of the material. Furthermore, concrete behaves well under high temperatures or fire events, especially when it is compared with other construction materials, but the behaviour of PFRC must be analysed if the use of these fibres is to be extended. To this end, the degradation of PFRC fracture properties has been recently experimentally analysed under a temperature range between 20 ◦ C and 200 ◦ C. As temperature increases, polyolefin fibres modify their mechanical properties and their shape, which reduce their performance as reinforcements of concrete. In this work, those experimental results, which include results of low (3 kg/m3 ) and high (10 kg/m3 ) proportion PFRC specimens, are used as reference to study the fracture behaviour of PFRC exposed to high temperatures from a numerical point of view. The experimental load-deflection diagrams are reproduced by modifying the trilinear diagram used in the cohesive model, which helps to understand how the trilinear diagram parameters are affected by high temperature exposure. Finally, some expressions are proposed to adapt the initial trilinear diagram (obtained with specimens not exposed to high temperature) in order to numerically reproduce the fracture behaviour of PFRC affected by high temperature exposure.Ítem Predictive approach of the size effect of PFRC simulated by using a softening function(2022-05) Gálvez-Ruíz, Jaime Carlos; Suárez-Guerra, Fernando; Enfedaque, Alejandro; García-Alberti, MarcosThe size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram cannot capture the material behaviour on elements with different sizes due to dependence of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be very convenient for reproducing fracture of polyolefin-fibre-reinforced concrete elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of polyolefin-fibre-reinforced concrete specimens of different sizes under three-point bending. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental points of these softening functions are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately.Ítem Simulation of fracture on PFRC specimens subjected to high temperature using a cohesive model(2022-05) Suárez-Guerra, Fernando; Enfedaque, Alejandro; García-Alberti, Marcos; Gálvez-Ruíz, Jaime CarlosConcrete has been traditionally reinforced with steel rebars that confer good tensile properties to this material. Nevertheless, concrete can also be reinforced with fibres, which have been traditionally made of steel, although in the last years new types of fibres have appeared, such as polypropylene fibres, glass fibres or polyolefin fibres. Their use widens the range of application of fibre-reinforced concrete (FRC) and has experienced an significant boost by national and international standards, which now include guidelines for their use in structures. More specifically, textured polyolefin macro-fibres have proved to provide very good tensile properties in concrete. The use of these fibres has significant advantages when compared with traditional steel fibres, since they reduce the tear and wear of devices involved in their production, avoid corrosion problems in concrete and have no influence on magnetic fields, which can be very important in some situations. Concrete properties, both in fresh and hardened states, have been extensively studied in the last years, proving to be a promising alternative to steel fibres. Fracture of FRC, and more specifically of PFRC, has been successfully reproduced using the finite element analysis by means of an embedded cohesive model with a trilinear softening function. On another note, concrete has a good behaviour when subjected to high temperatures and fire, especially when it is compared with other traditional construction materials, such as wood or steel. Nevertheless, concrete reinforcement is usually made of materials that are critically sensitive to these events and the behaviour of the composite material must be assessed to meet the requirements described in the structural standards. With regard to polyolefin-fibre reinforced concrete (PFRC), a recent study has analysed how the fracture properties of this material degrade when subjected to high-temperatures, ranging from 20oC to 200oC. As temperature increases, fibres modify their geometry and their mechanical properties, which leads to a reduction of their effectiveness. In this work, the fracture behaviour of PFRC specimens subjected to high temperatures is reproduced by using an embedded cohesive model that uses a trilinear softening function. The specific trilinear softening diagram that provides a good numerical simulation of fracture is obtained for each temperature increment. This helps to understand how the trilinear diagram must be adapted when PFRC is subjected to high temperatures and will allow the use of this model to a wider range of situations.Ítem Suitability of Constitutive Models of the Structural Concrete Codes When Applied to Polyolefin Fibre Reinforced Concrete(MDPI, 2022-03) Enfedaque, Alejandro; Suárez-Guerra, Fernando; García-Alberti, Marcos; Gálvez-Ruíz, Jaime CarlosThe use of fibres as structural reinforcement in concrete is included in standards, providing guidelines to reproduce their behaviour, which have been proven adequate when steel fibres are used. Nevertheless, in recent years new materials, such as polyolefin fibres, have undergone significant development as concrete reinforcement. This work gives insight on how suitable the constitutive models proposed by the Model Code 2010 (MC2010) are in the case of such polymer fibres. A set of numerical models has been carried out to reproduce the material behaviour proposed by the MC2010 and the approach based on the softening function proposed by the authors. The results show remarkable differences between the experimental results and the numerical simulations when the constitutive models described in the MC2010 are employed for different polyolefin fibre reinforced concrete mixes, while the material behaviour can be reproduced with greater accuracy if the softening function proposed by the authors is employed when this type of macro-polymer fibres is used. Moreover, the relatively complex behaviour of polyolefin fibre reinforced concrete may be reproduced by using such constitutive model.