Computational Models for Fracture and Degradation of Structures (original) (raw)
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A CONCURRENT TWO-SCALE APPROACH FOR HIGH STRENGTH CONCRETE
At the mesoscopic level, the fracture behaviour of high strength concrete (HSC) can differ significantly from the conventional strength concrete since the coarse aggregate may be the weakest phase of the composite. In this way, the influence of coarse aggregate type, size, and distribution can affect all the macroscopic mechanical responses, such as the ultimate tensile strength and fracture energy. The present work proposes a concurrent two-scale (macro and mesoscale) approach for HSC, in which (i) a linear elastic model with homogenized elastic properties is used for the macroscale and (ii) a three-phase material composed of coarse aggregate, mortar matrix and the interfacial transition zone (ITZ) with nonlinear behaviour models are assumed for the mesoscopic level. The coarse aggregates are randomly generated from a certain grading curve and placed in the mesoscale subdomain, using the "take-and-place" method. The mesh fragmentation technique is employed, as proposed by Manzoli et al. This technique is based on the use of interface finite elements with high aspect ratio, which along with the employment of a constitutive tensile damage model is able to represent the crack initiation, propagation and coalescence, considering the individual behaviour of each phase as well as their mutual interactions in the mesoscale HSC. The macroscopic and mesoscopic meshes are attached via coupling finite elements, which provide a rigid coupling between them. Three-point bending tests are simulated on beams with different aggregate size distribution. The numerical results are compared with those obtained by the experimental test results developed by Siregar et al.
Multi-scale (FE2) analysis of material failure in cement/ aggregate-type composite structures
Computational Modelling of Concrete Structures, 2014
The work propases a FP multiscale approach to computational modeling of material failure in concreteMlike structures, made of cement/aggregate-type composite materials. Keeping the approach in a classical homogenization setting, a multiscale model is proposed, which naturally provides a microscopic length-scale to be exported to the macrostructure. There, this length scale is used as regularization parameter in the context of the Continuum Strong Discontinuity Approach to material failure, and finite elements with embedded strong discontinuities (E~ FE M). The resulting technique allows robust modeling of crack propagation at the structural scale, accounting for the mesostructure morphology, supplies proper energy dissipation and solutions independent of the finite element and RVE sizes. Application toa number of examples, in the range from light-aggregate concrete to regular concrete, shows the potentiality of the method.
Modeling Framework for Fracture in Multiscale Cement-Based Material Structures
Materials (Basel, Switzerland), 2017
Multiscale modeling for cement-based materials, such as concrete, is a relatively young subject, but there are already a number of different approaches to study different aspects of these classical materials. In this paper, the parameter-passing multiscale modeling scheme is established and applied to address the multiscale modeling problem for the integrated system of cement paste, mortar, and concrete. The block-by-block technique is employed to solve the length scale overlap challenge between the mortar level (0.1-10 mm) and the concrete level (1-40 mm). The microstructures of cement paste are simulated by the HYMOSTRUC3D model, and the material structures of mortar and concrete are simulated by the Anm material model. Afterwards the 3D lattice fracture model is used to evaluate their mechanical performance by simulating a uniaxial tensile test. The simulated output properties at a lower scale are passed to the next higher scale to serve as input local properties. A three-level m...
International Journal for Numerical and Analytical Methods in Geomechanics, 2012
A new phenomenological macroscopic constitutive model for the numerical simulation of quasi-brittle fracture and ductile concrete behavior, under general triaxial stress conditions, is presented. The model is particularly addressed to simulate a wide range of confinement stress states, as also, to capture the strong influence of the mean stress value in the concrete failure mechanisms.
A multi-scale constitutive model of solidifying cementitious materials is presented based on a systematic knowledge coupling structural mechanics with chemo-physical phenomena. The model can reasonably simulate time-dependent deformations such as autogenous/drying shrinkage and basic/drying creep in laboratory tests under arbitrary environmental and loading conditions. Shrinkage induced cracking in an actual PRC bridge structure was examined by the analytical system, which reveals that large shrinkage of concrete and heavy reinforcement in the bridge led to plenty of cracks. In addition, the effect of aggregate on shrinkage was studied. Through sensitivity analyses and experimental verifications, the possible reasons to bring large shrinkage of concrete in the bridge are presented focusing on aggregate properties.
2011
Brittle or quasi-brittle materials such as concrete or rocks typically present localized failure modes due to cracking processes which usually start from internal material defects such as micro-cracks or non-homogeneous weak zones. Recently, several studies have been carried out on the fracture mechanical behavior of concrete materials by taking into account some aspects such as material strength, presence of reinforcing fibers, aggregate size effects, presence of nano-particles, etc. In this work both plain and fiber reinforced concrete composite (FRCC) are analyzed and modeled with two different approaches. On one hand, a continuum (smeared-crack) formulation based on nonlinear microplane theory is proposed. While on the other hand, a discontinuous constitutive theory is formulated to model the cracking response of fiber reinforced mortar-mortar interfaces. The well-known “Mixture Theory” is considered in both models to describe the fiber effects on the failure behavior of FRCC. T...
Modeling Material Failure in Concrete Structures
A constitutive model devised for the analysis of concrete structures, and suitable for generic two- or three-dimensional applications, is presented and validated. For plain concrete a tension-compression distinguishing stress split is performed, and two scalar damage variables account for the degradation induced by the tensile and compressive stress components. As outcomes the model reproduces the stiffness recovery upon load reversal, and it captures the strength enhancement under multiaxial compression. Besides, the simple formulation as well as the extremely reduced number of parameters involved in the concrete model makes it quite suitable for the analysis of real structures, and constitutes a useful design tool. As regards to the nonlinear performance of the steel reinforcement, the explicit Giuffrè–Menegotto–Pinto model is adopted. Efficiency of the global model is illustrated via two seismic applications: one concerning an arch dam, and the other a six-floor reinforced concrete wall. The latter application is presented for validation purposes.
2D Crack Propagation in High-Strength Concrete Using Multiscale Modeling
Multiscale Science and Engineering
In this work a concurrent multiscale (macro and mesoscale) approach for high-strength concrete (HSC) is proposed for seeking to better understand the influence of coarse aggregate type, shape, and size distribution as well as the interfacial transition zone (ITZ) effects on the fracture mechanical responses. A linear elastic model with homogenized elastic properties is used for the macroscale, while a three-phase material composed of coarse aggregates, mortar matrix and the ITZ equipped with nonlinear behavior models are assumed for the mesoscopic level. To geometrically represent and gain insights into effects of coarse aggregates, two polygonal shapes are assumed: irregular quadrilateral and regular octagonal forms, which are used separated and randomly generated from a given grading curve and placed in the mesoscale region using the "take-and-place" method. A mesh fragmentation technique is used to explicitly represent the crack propagation process by considering the individual behavior of each phase as well as their mutual interactions. The non-matching macro and mesoscopic meshes are attached based on the use of coupling finite elements in the context of the rigid coupling scheme to adequately guarantee the continuity of displacement between both scales. Numerical analyses of dog-bone shape specimens under tensile load and three-point bending beams were performed. The responses obtained numerically show a good agreement with experimental ones found in literature demonstrating how the proposed approach is efficient, robust and useful for modeling crack propagation in HSC.