DIMM-Artículos

URI permanente para esta colecciónhttps://hdl.handle.net/10953/243

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A material model to reproduce mixed-mode fracture in concrete
(Wiley, 2018-08) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón , David A.
This paper presents a material model to reproduce crack propagation in cement-based material specimens under mixed-mode loading. Its numerical formulation is based on the cohesive crack model, proposed by Hillerborg, and extended for the mixed-mode case. This model is inspired by former works by Gálvez et al but implemented for its use in a finite element code at a material level, that is to say, at an integration point level. Among its main features, the model is able to predict the crack orientation and can reproduce the fracture behaviour under mixed-mode fracture loading. In addition, several experimental results found in the literature are properly reproduced by the model.
A smeared crack formulation for simulating fracture of fibre-reinforced concrete by means of a trilinear softening diagram
(Elsevier, 2023-08) Suárez Guerra, Fernando
This study presents a smeared crack model for reproducing the fracture behaviour of FRC that is based on an embedded crack formulation used lately with this material. In both cases, a trilinear softening diagram allows reproducing the post-peak behaviour correctly. The model proposed here differs from the one on which it is inspired, since it is a smeared crack model based on the crack band concept where the material damage is isotropic and controlled by a damage factor ranging from 0 to 1, while the original model is an embedded crack model that allows fracture in three directions per element. This new formulation overcomes some limitations of the embedded crack model, that could only be used with triangular elements with an only integration point, since it can be used with triangular and quadrilateral elements with any number of integration points. Unlike previous models, developed for commercial codes, this model is developed in OOFEM, a free finite element code developed at the Czech Technical University in Prague (Czech Republic) and Chalmers University of Technology (Sweden), thus providing the general public with an advanced tool that allows reproducing fracture in structural elements made with fibre-reinforced concrete elements. This work shows that the proposed formulation provides similar results to those obtained with the model on which it is inspired under different situations: mode I fracture, size effect analysis and, finally, modes I and II mixed fracture.
Cumulative effects of cracking in monoblock multipurpose precast concrete sleepers on railway tracks
(Elsevier, 2025-03) Donaire-Ávila, Jesús; Fernández-Aceituno, Javier; Suárez-Guerra, Fernando
This work addresses the phenomenon of cracking in multipurpose precast monoblock concrete sleepers by examining the entire process from fabrication to final installation on railway tracks. This includes stages such as manufacturing, stockpiling, track installation for rail neutralization, and eventually fastening the rails to the sleepers. A nonlinear numerical model, which is experimentally validated, is used to analyze this effect. Also, thermal and mechanical actions are considered at each stage of the process. Accordingly, different types of polymeric dowels and concrete aggregates—siliceous and carbonate—are evaluated to assess their impact on cracking. The results indicate that the thermal expansion capacity and elastic stiffness of the dowels, as well as the outdoor temperatures during fabrication, stockpiling, and installation, play critical roles in the cracking process. Sleepers made with carbonate aggregate, stiff-expansive dowels, fabricated in cold environments, and installed in hot conditions are particularly prone to severe cracking. Consequently, these conditions should be avoided to minimize cracking in multipurpose sleepers.
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, Alejandro
The 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.
Macro Photography as an Alternative to the Stereoscopic Microscope in the Standard Test Method for Microscopical Characterisation of the Air-Void System in Hardened Concrete: Equipment and Methodology
(MDPI, 2018-08) Suárez Guerra, Fernando; Conchillo, José J.; Gálvez, Jaime C.; Casati, María J.
The determination of the parameters that characterize the air-void system in hardened concrete elements becomes crucial for structures under freezing and thawing cycles. The ASTM C457 standard describes some procedures to accomplish this task, but they are not easy to apply, require specialised equipment, such as a stereoscopic microscope, and result in highly tedious tasks to be performed. This paper describes an alternative procedure to the modified point-count method that is described in the Standard that makes use of macro photography. This alternative procedure uses macro-photographic images that can be obtained with a quite standard photo camera and it is successfully applied to a large set of samples and presents some advantages over the traditional method, since the required equipment is less expensive and provides a more comfortable and less tedious procedure for the operator.
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, Marcos
In 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.
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 Carlos
Fibre-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.
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 Carlos
The 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.

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