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Despite tremendous advances made in fracture mechanics of concrete in recent years, very little information has been available on the nature of fracture processes and on reliable test methods for determining parameters for the different models. Moreover, most texts on this topic discuss numerical modeling but fail to consider experimentation. This book fills these gaps and synthesizes progress in the field in a simple, straightforward manner geared to practical applications.
Despite tremendous advances made in fracture mechanics of concrete in recent years, very little information has been available on the nature of fracture processes and on reliable test methods for determining parameters for the different models. Moreover, most texts on this topic discuss numerical modeling but fail to consider experimentation. This book fills these gaps and synthesizes progress in the field in a simple, straightforward manner geared to practical applications.
Concrete has traditionally been known as a material used widely in the construction of roads, bridges and buildings. Since cost effectiveness has always been one of the more important aspects of design, concrete, when reinforced and/or prestressed, is finding more use in other areas of application such as floating marine structures, storage tanks, nuclear vessel containments and a host of other structures. Because of the demand for concrete to operate under different loading and environmen tal conditions, increasing attention has been paid to study concrete specimens and structure behavior. A subject of major concern is how the localized segregation of the constituents in concrete would affect its global behavior. The degree of nonhomogeneity due to material property and damage. by yielding and/or cracking depends on the size scale and loading rate under consideration. Segregation or clustering of aggregates at the macroscopic level will affect specimen behavior to a larger degree than it would to a large structure such as a dam. Hence, a knowledge of concrete behavior over a wide range of scale is desired. The parameters governing micro-and macro-cracking and the techniques for evaluating and observing the damage in concrete need to be better understood. This volume is intended to be an attempt in this direction. The application of Linear Elastic Fracture Mechanics to concrete is discussed in several of the chapters.
The book analyzes a quasi-static fracture process in concrete and reinforced concrete by means of constitutive models formulated within continuum mechanics. A continuous and discontinuous modelling approach was used. Using a continuous approach, numerical analyses were performed using a finite element method and four different enhanced continuum models: isotropic elasto-plastic, isotropic damage and anisotropic smeared crack one. The models were equipped with a characteristic length of micro-structure by means of a non-local and a second-gradient theory. So they could properly describe the formation of localized zones with a certain thickness and spacing and a related deterministic size effect. Using a discontinuous FE approach, numerical results of cracks using a cohesive crack model and XFEM were presented which were also properly regularized. Finite element analyses were performed with concrete elements under monotonic uniaxial compression, uniaxial tension, bending and shear-extension. Concrete beams under cyclic loading were also simulated using a coupled elasto-plastic-damage approach. Numerical simulations were performed at macro- and meso-level of concrete. A stochastic and deterministic size effect was carefully investigated. In the case of reinforced concrete specimens, FE calculations were carried out with bars, slender and short beams, columns, corbels and tanks. Tensile and shear failure mechanisms were studied. Numerical results were compared with results from corresponding own and known in the scientific literature laboratory and full-scale tests.
The combined finite discrete element method is a relatively new computational tool aimed at problems involving static and / or dynamic behaviour of systems involving a large number of solid deformable bodies. Such problems include fragmentation using explosives (e.g rock blasting), impacts, demolition (collapsing buildings), blast loads, digging and loading processes, and powder technology. The combined finite-discrete element method - a natural extension of both discrete and finite element methods - allows researchers to model problems involving the deformability of either one solid body, a large number of bodies, or a solid body which fragments (e.g. in rock blasting applications a more or less intact rock mass is transformed into a pile of solid rock fragments of different sizes, which interact with each other). The topic is gaining in importance, and is at the forefront of some of the current efforts in computational modeling of the failure of solids. * Accompanying source codes plus input and output files available on the Internet * Important applications such as mining engineering, rock blasting and petroleum engineering * Includes practical examples of applications areas Essential reading for postgraduates, researchers and software engineers working in mechanical engineering.
This conference is the first in a series of conferences dedicated to Fracture Mechanics of Concrete Structures. Due to the recent explosion of interest in research on fracture in concrete, the conference has brought together the world's leading researchers in fracture of concrete and this book contains the proceedings.
The main goal of this research is to implement recent advances in nonlinear fracture mechanics, most notably the introduction of the cohesive zone concept, in investigating the post-cracking behavior of concrete pavements, subjected to wheel load and curling. The cohesive zone is assumed to lie along a specified direction known a priori, and cohesive elements are inserted along this path. The study follows a step-by-step approach, beginning with fracture analysis of simply supported beams. In this initial step, experimental and numerical studies available in literature are reproduced and excellent agreement is observed. Furthermore, important fracture parameters and numerical challenges are identified, pertinent to the cohesive zone concept. It is observed that post-crack responses of the beams are sensitive to choices regarding the solution type, the concrete softening curve, and the uncracked region mesh sizes. Single slabs-on-grade under wheel loads located at the slab edge or interior are considered next. In this phase, it is observed that the increased size of the problem inhibits generating as refined mesh as for the beams, and consequently obtaining a convergent solution poses a significant challenge. This is resolved by using so-called viscous regularization, in which a small viscosity term is introduced. Accordingly, a small deviation of traction stresses beyond the pre-defined material softening curve can be tolerated. Once again, the simulation in this phase is verified by reproducing experimental and numerical results available in literature. The effects of concrete softening curve, cohesive zone mesh, solution method, fracture energy, and tensile strength on the fracture process are investigated. It is observed that the fracture energy is the major parameter that influences the responses. In a third phase of the study, a single slab-on-grade is subjected to wheel load and curling, individually or in combination. In both cases, it is observed that the diurnal temperature cycle and the shape of its profile through the slab thickness plays a significant role on the post-crack responses of the slab. When the slab top is warmer, unstable cracks form; in contrast, a warmer bottom results in stable cracks, thereby increasing the resistance of the slab and avoiding sudden failure. The final two phases of the research are devoted to the study of jointed concrete pavements, also subjected to wheel load and temperature variations: the fourth phase encompasses aggregate interlock joints and the fifth phase pertains to dowel bar joints. Linear and nonlinear aggregate interlock mechanisms are simulated and their repercussions on the fracture responses of the slabs are examined. Similarly, the effects of numerical idealization techniques for the dowel-slab interaction, joint size and dowel looseness on the fracture process are examined. It is concluded that the cohesive zone approach is a very promising tool in the ongoing exploration of fracture behavior in concrete pavements. The techniques can be extended to general loading situations that involve fatigue and crack branching. The results from this study will contribute to the development of a more mechanistic failure analysis of concrete pavements.