Este trabalho apresenta uma estratégia numérica desenvolvida usando o método dos elementos finitos para simular o processo de falha de compósitos cimentícios reforçados com fibras de aço. O material é descrito como um compósito composto por três fases: matriz cimentícia (pasta, argamassa ou concreto), fibras descontínuas discretas, e interface fibra-matriz. Um novo esquema de acoplamento para malhas de elementos finitos não-conformes foi desenvolvido para acoplar as malhas geradas independentes, da matriz cimentícia e de uma nuvem de fibras de aço, baseado na utilização de novos elementos finitos desenvolvidos, denominados elementos finitos de acoplamento. Utilizando este esquema de acoplamento, um procedimento não-rígido é proposto para a modelagem do complexo comportamento não linear da interface fibra-matriz, utilizando um modelo constitutivo de dano apropriado para descrever a relação entre a tensão de cisalhamento (tensão de aderência) e deslizamento relativo entre a matriz e cada fibra de aço individualmente. Este esquema também foi adotado para considerar a presença de barras de aço para as análises de estruturas de concreto armado. As fibras de aço são modeladas usando elementos finitos lineares com dois nós (elementos de treliça) com modelo material elastoplástico. As fibras são posicionadas usando uma distribuição randômica uniforme isotrópica, considerando o efeito parede. Uma abordagem contínua e outra descontínua são investigadas para a modelagem do comportamento frágil da matriz cimentícia. Para a primeira, é utilizado um modelo de dano isotrópico com duas variáveis de dano para descrever o comportamento de dano à tração e à compressão. A segunda emprega uma técnica de fragmentação de malha que utiliza elementos finitos degenerados, posicionados entre todos os elementos finitos que formam a matriz cimentícia. Para esta técnica é proposto um modelo constitutivo à tração, compatível com a abordagem descontínua forte contínua, para prever a propagação de fissura. Para acelerar o cálculo e aumentar a robustez dos modelos de dano contínuos para simular o processamento de falhas, um esquema de integração implícito-explícito é utilizado. Exemplos numéricos são apresentados ao longo do desenvolvimento desta tese. Inicialmente, exemplos numéricos com um único reforço são apresentados para validar a técnica desenvolvida e para investigar à influência das propriedades geométricas 7 das fibras e sua posição em relação à superfície de falha. Posteriormente, exemplos mais complexos são considerados envolvendo uma nuvem de fibras. Nestes casos, atenção especial é dada à influência da distribuição das fibras no comportamento do compósito relacionado ao processo de fissuração. Comparações com resultados experimentais demonstram que a aplicação da ferramenta numérica para modelar o comportamento de compósitos cimentícios reforçados com fibras de aço é muito promissora e pode ser utilizada como uma importante ferramenta para melhor entender os efeitos dos diferentes aspectos envolvidos no processo de falha deste material. / This work presents a numerical strategy developed using the Finite Element Method (FEM) to simulate the failure process of Steel Fiber Reinforced Cementitious Composites (SFRCCs). The material is described as a composite made up by three phases: a cementitious matrix (paste, mortar or concrete), discrete discontinuous fibers, and a fiber-matrix interface. A novel coupling scheme for non-matching finite element meshes has been developed to couple the independent generated meshes of the bulk cementitious matrix and a cloud of discrete discontinuous fibers based on the use of special finite elements developed, termed Coupling Finite Elements (CFEs). Using this approach, a nonrigid coupling procedure is proposed for modeling the complex nonlinear behavior of the fiber-matrix interface by adopting an appropriate constitutive damage model to describe the relation between the shear stress (adherence stress) and the relative sliding between the matrix and each fiber individually. This scheme has also been adopted to account for the presence of regular reinforcing bars in the analysis of reinforced concrete structural elements. The steel fibers are modeled using two-node finite elements (truss elements) with a one-dimensional elastoplastic constitutive model. They are positioned using an isotropic uniform random distribution, considering the wall effect of the mold. Continuous and discontinuous approaches are developed to model the brittle behavior of the bulk cementitious matrix. For the former, an isotropic damage model including two independent scalar damage variables for describing the composite behavior under tension and compression is considered. The discontinuous approach is based on a mesh fragmentation technique that employs degenerated solid finite elements in between all regular (bulk) elements. In this case, a tensile damage constitutive model, compatible with the Continuum Strong Discontinuity Approach (CSDA), is proposed to predict crack propagation. To increase the computability and robustness of the continuum damage models used to simulate the failure processes in both of the strategies, an implicit-explicit integration scheme is used. Numerical analyses are performed throughout the presentation of the work. Initially, numerical examples with a single reinforcement are presented to validate the technique and to investigate the influence of the fibers geometrical properties and its position relative to the crack surface. Then, more complex examples involving a cloud of steel fibers are considered. In these cases, special attention is given to the analysis of the influence of the fiber distribution on the composite behavior relative to the cracking process. Comparisons with experimental results demonstrate that the application of the numerical tool for modeling the behavior of SFRCCs is very promising and may constitute an important tool for better understanding the effects of the different aspects involved in the failure process of this material.

Various anchorage systems including both cast-in-place and post-installed anchors have been developed for fastening both non-structural and structural components to concrete structures. The need for increased flexibility in the design of new structures and strengthening of existing concrete structures has led to increased use of various metallic anchors in practice. Although millions of fasteners are used each year in the construction industry around the world, knowledge of the fastening technology remains poor. In a sustainable society, buildings and structures must, from time to time, be adjusted to meet new demands. Loads on structures must, in general, be increased to comply with new demands, and the structural components and the structural connections must also be upgraded. From the structural connection point of view, the adequacy of the current fastenings for the intended increased load must be determined, and inadequate fastenings must either be replaced or upgraded. The current design models are generally believed to be conservative, although the extent of this behavior is not very clear. To address these issues, the current models must be refined to allow the design of new fastenings and also the assessment of current anchorage systems in practice. The research presented in this thesis consists of numerical and experimental studies of the load-carrying capacity of anchors in concrete structures. Two different types of anchors were studied: (I) cast-in-place headed anchors, and (II) post-installed adhesive anchors. This research focused particularly on the tensile load-carrying capacity of cast-in-place headed anchors and also on the sustained tension loading performance of post-installed adhesive anchors. The overall objective of this research was to provide knowledge for the development of improved methods of designing new fastening systems and assessing the current anchorage systems in practice. For the cast-in-place headed anchors (I), the influence of various parameters including the size of anchor head, thickness of concrete member, amount of orthogonal surface reinforcement, presence of concrete cracks, concrete compressive strength, and addition of steel fibers to concrete were studied. Among these parameters, the influence of the anchor head size, member thickness, surface reinforcement, and cracked concrete was initially evaluated via numerical analysis of headed anchors at various embedment depths. Although these parameters have considerable influence on the anchorage capacity and performance, this influence is not explicitly considered by the current design models. The numerical results showed that the tensile breakout capacity of headed anchors increases with increasing member thickness and/or increasing size of the anchor head or the use of orthogonal surface reinforcement. However, their capacity decreased considerably in cracked concrete. Based on the numerical results, the current theoretical model for the tensile breakout capacity of headed anchors was extended by incorporating several modification factors that take the influence of the investigated parameters into account. In addition, a supplementary experimental study was performed to verify the numerically obtained findings and the proposed refined model. The experimental results corresponded closely to the numerical results, both in terms of failure load and failure pattern, thereby confirming the validity of the proposed model. The validity of the model was further confirmed through experimental results reported in the literature. Additional experiments were performed to determine the influence of the concrete compressive strength and the addition of steel fiber to concrete on the anchorage capacity and performance. These experiments showed that the anchorage capacity and stiffness increase considerably with increasing concrete compressive strength, but the ductility of the anchor decreases. However, the anchorage capacity and ductility increased significantly with the addition of steel fibers to the concrete mixture. The test results also revealed that the tensile breakout capacity of headed anchors in steel fiber-reinforced concrete is significantly underestimated by the current design model. The long-term performance and creep behavior of the post-installed headed anchors (II) was evaluated from the results of long-time tests on adhesive anchors under sustained loads. In this experimental study, adhesive anchors of various sizes were subjected to various sustained load levels for up to 28 years. The anchors were also exposed to several in-service conditions including indoor temperature, variations in the outdoor temperature and humidity, wetness (i.e., water on the surface of concrete), and the presence of salt (setting accelerant) additives in the concrete. Among the tested in-service conditions, variations in the outdoor temperature and humidity had the most adverse effect on the long-term sustained loading performance of the anchors. Based on the test results, recommendations were proposed for maximum sustained load levels under various conditions. The anchors tested under indoor conditions could carry sustained loads of up to 47% of their mean ultimate short-term capacities. However, compared with these anchors, the anchors tested under outdoor conditions exhibited larger creep deformation and failure occurred at sustained loads higher than 23% of their mean ultimate short-term capacities. Salt additives in concrete and wet conditions had negligible influence on the long-term performance of the anchors, although the wet condition resulted in progressive corrosion of the steel. Based on the experimental results, the suitability of the current testing and approval provisions for qualifying adhesive anchors subjected to long-term sustained tensile loads was evaluated. The evaluations revealed that the current approval provisions are not necessarily reliable for qualifying adhesive anchors for long-term sustained loading applications. Recommendations were given for modifying the current provisions to ensure safe long-term performance of adhesive anchors under sustained loads.