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Strong embedded discontinuities for simulating fracture in quasi-brittle materials
In this paper embedded strong discontinuities are used to model discrete cracking in materials like concrete. In the approach followed a discontinuous displacement field is considered and the deformation is localized at a surface of zero width. Both a damage law and a plasticity law are adopted to describe the constitutive relation between tractions and displacement jumps at the discontinuity surface. An algorithm is introduced to enforce the continuity of the crack path, permitting a clear identification of the discontinuities in the mesh. Both mode-I and mixed-mode cracking have been considered and the importance of the shear tractions on the global behaviour of a structure is assessed. With the formulation adopted it is concluded that: i) realistic crack patterns are obtained, similar to those found in experiments and ii) the dissipation of energy can be objectively found irrespective of the mesh that is used
Arbitrary bi-dimensional finite strain crack propagation
In the past two decades numerous numerical procedures for crack propagation have been developed. Lately,
enrichment methods (either local, such as SDA or global, such as XFEM) have been applied with success to simple
problems, typically involving some intersections. For arbitrary finite strain propagation, numerous difficulties are
encountered: modeling of intersection and coalescence, step size dependence and the presence of distorted finite
elements. In order to overcome these difficulties, an approach fully capable of dealing with multiple advancing
cracks and self-contact is presented (see Fig.1). This approach makes use of a coupled Arbitrary Lagrangian-Eulerian
method (ALE) and local tip remeshing. This is substantially less costly than a full remeshing while retaining its full
versatility. Compared to full remeshing, angle measures and crack paths are superior. A consistent continuationbased
linear control is used to force the critical tip to be exactly critical, while moving around the candidate set.
The critical crack front is identified and propagated when one of the following criteria reaches a material limiting
value: (i) the stress intensity factor; or (ii) the element-ahead tip stress. These are the control equations.
The ability to solve crack intersection and coalescence problems is shown. Additionally, the independence from
crack tip and step size and the absence of blade and dagger-shaped finite elements is observed. Classic benchmarks
are computed leading to excellent crack path and load-deflection results, where convergence rate is quadratic
The influence of load misalignment on frp-concrete bond behaviour, a numerical study
Various authors have used pure shear test models in order to describe the bond between FRP and concrete. However, considerable dispersion of the parameters which characterize the bond behaviour has been found. In pure shear models it is assumed that the load applied to the FRP is parallel to the axis of the concrete specimen and acts on the plane of symmetry. In this work, a numerical model is presented to analyse the influence of load misalignment on FRP-concrete bond behaviour
An embedded formulation with conforming
Use of strong discontinuities with satisfaction of compatibilit
O reforço de vigas de betão armado com chapas metálicas coladas com resina
Neste trabalho efectua-se a simulação do reforço com chapas metálicas coladas com resinas epoxy, em vigas de betão armado. Cada viga é inicialmente carregada à flexão e submetida a um elevado nível de dano. Posteriormente, sob carga constante, as fendas são reparadas com resina epoxy e aplica-se o reforço, colando a chapa metálica na face traccionada da viga. Conclui-se o teste aumentando a carga até se obter a rotura da viga reforçada. O nível de dano pré-reforço é modelado recorrendo a uma abordagem discreta com fendas embebidas e a ligação betão-resina-chapa é modelada em modo II de fractura através de elementos de interface com espessura inicial nula. Os resultados numéricos são comparados com os resultados obtidos em vigas ensaiadas experimentalmente de acordo com os procedimentos referidos
Modelling the behaviour of reinforced concrete beams strengthened with FRP
Comunicação apresentada em III European Conference on Computational Mechanics Solids, Structures and Coupled Problems in Engineering, Lisbon, 5–8 June 2006The strengthening of reinforced concrete structures with fiber reinforced polymers
(FRP) is particularly attractive due to their mechanical properties. The understanding of the premature failure modes is of great importance. Since rupture is frequently found to occur at the interface FRP concrete, there is a clear need to study the nature of the bonding so as to develop techniques to permit its design modeling. The stress distribution in shear test models
does not precisely match the one obtained in flexural reinforcement; in the latter, according to various authors [1, 2], in addition to the stresses tangential to the interface, normal stresses are also important. In this paper, a numerical model is presented to describe the behavior of reinforced concrete beams strengthened with FRP. This model is based on previous studies focused both on: i) the distribution of shear stresses at the interface FRP concrete and on ii) the stress concentration at the plate ends in flexural models. Furthermore, the importance of the flexural cracks in the premature rupture of the element is also analyzed. The behavior of reinforced c concrete beams strengthened with both FRP laminates and sheets is considered. The FRP epoxy concrete arrangement and the flexural cracks are modeled with interface elements with initial zero thickness, using a discrete approach and a localized damage
model. A softening behavior is adopted to simulate the stress transfer along the FRP-
-concrete interface. The importance of considering the mixed mode of fracture is discussed. Mention is also made to some of the main mathematical models found in the literature
Mixed-mode fracture and load misalignment on the assessment of FRP-concrete bond connections
Considerable dispersion is usually found in experimental data concerning the material properties of FRP-concrete bond connections. In pure shear models, the direction of FRP loading is assumed to be parallel to the axis of the concrete specimen. However, in practice, it is very difficult to prevent load misalignment. This fact can have important consequences on the derivation of material properties from experimental data. This is why a parametric study is herein undertaken to thoroughly identify the role of the load misalignment in the behaviour of the connection. It is concluded that the load capacity of the connection significantly decreases in the case of a misaligned load pointing outwards the reinforced surface. It is also found that this effect is less relevant for thick laminates when compared to thin FRP sheets.Australian Research Council Discovery Early Career Researcher Award (DE150101703); Faculty of Engineering & Information Technologie
Modelling the behaviour of steel fibre reinforced concrete using a discrete strong discontinuity approach
The use of Fibre Reinforced Concrete (FRC) is gradually wide-spreading due to the significant advantages relatively to Normal Concrete (NC). In the case of steel fibres, the quasi-brittle behaviour of plain concrete structures can be modified into an enhanced ductile behaviour as a direct result of this addition. Since the mechanical properties of both FRC and NC can be significantly different, this work aims at developing a finite element formulation to specifically address the simulation of the behaviour of FRC members up to failure. For this purpose, the Conforming Generalised Strong Discontinuity Approach (CGSDA) is adopted with steel fibres explicitly introduced in the finite element mesh. The resulting formulation has the following main characteristics: i) variational consistency; ii) fibre elements automatically considered regardless of the presence of cracks; and iii) no additional degrees of freedom are required. The proposed formulation is validated using experimental results from tests conducted with different dosages of steel fibres.FCOMP-01-0124-FEDER-020275, FCT PTDC/ECM/119214/2010, FCT SFRH/BD/85922/2012, ARC DE150101703
The influence of the mode II fracture energy on the behaviour of composite plate reinforced concrete
Comunicação apresentada em Fifth International Conference on Fracture Mechanics of Concrete and Concrete Structures, Vail, Colorado, USA, 2004In this paper, the finite element method is used to analyse the behaviour of concrete
externally strengthened by sheets of carbon fibre reinforced polymer (CFRP). The bond between concrete and CFRP is modelled by a discrete approach using interface elements. The mechanisms involved in the behaviour of externally reinforced concrete specimens are complex, the global strength of the specimen
being governed by the strength of each individual material as well as by the adhesion properties conferred by the epoxy. It is observed in experiments that, in most cases, failure occurs due to the loss of cohesion of a portion or lamina of concrete attached to the epoxy-fibres layers, the latter remaining intact. In this paper, the results of numerical simulations of bond tests are presented, aiming to contribute for a better understanding, in qualitative and quantitative terms, of mode II fracture energy in concrete and its influence on the behaviour of the interface concrete-FRP
Análise do comportamento de vigas de betão armado reforçadas à flexão simples com CFRP
Comunicação apresentada em Encontro Nacional Betão Estrutural, Porto, 2004O reforço de estruturas de betão armado com recurso a CFRP é actualmente uma prática
corrente. Este artigo tem como objectivo ilustrar a aplicação de um modelo numérico ao caso de uma viga simplesmente apoiada com quatro pontos de carga. Pretende-se aferir da
importância dos modos de rotura locais provenientes de tensões de corte ao nível da interface, no comportamento à rotura de um elemento à flexão simples
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