Continuum large cracking in a rate-dependent plastic-damage model for cyclic-loaded concrete structures (original) (raw)
Related papers
Earthquake response of concrete arch dams: a plastic-damage approach
Earthquake Engineering & Structural Dynamics, 2013
There are several alternatives to evaluate seismic damage-cracking behavior of concrete arch dams, among which damage theory is the most popular. A more recent option introduced for this purpose is plasticdamage (PD) approach. In this study, a special finite element program coded in 3-D space is developed on the basis of a well-established PD model successfully applied to gravity dams in 2-D plane stress state. The model originally proposed by Lee and Fenves in 1998 relies on isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity to capture inelastic behaviors of concrete in cyclic or dynamic loadings. The present implementation is based on the rate-dependent version of the model, including large crack opening/closing possibilities. Moreover, with utilizing the Hilber-Hughes-Taylor time integration scheme, an incremental-iterative solution strategy is detailed for the coupled dam-reservoir equations while the damage-dependent damping stress is included. The program is initially validated, and then, it is employed for the main analyses of the Koyna gravity dam in a 3-D modeling as well as a typical concrete arch dam. The former is a major verification for the further examination on the arch dam. The application of the PD model to an arch dam is more challenging because the governing stress condition is multiaxial, causing shear damage to become more important than uniaxial states dominated in gravity dams. In fact, the softening and strength loss in compression for the damaged regions under multiaxial cyclic loadings affect its seismic safety.
Cracking Development Prediction in Concrete Gravity Dams Using Concrete Damage Plasticity Model
2014
As it is well known, many dams around the world are placed in seismic zones. Because of this, it should be check if they can resist dynamic loads typically associated with earthquake occurrences. According to USACE manual (ER 1110-2-2200), modal techniques can be used for dynamic stress analyses in gravity dams, including a simplified response spectrum method and Finite Element Method (FEM), using a response spectrum or acceleration-time record for dynamic input. In this paper the damage configuration of a concrete gravity dam has been studied. In order to identify the possible crack formation zones a nonlinear model which considers the concrete plastic behavior, was employed to simulate crack propagation within the dam body. The model was numerically implemented in ABAQUS, a FEM analyses code. The model referred is known as Concrete Damaged Plasticity. It assumes that the main two failure mechanisms are tensile cracking and compressive crushing of the concrete material. The evoluti...
Engineering Fracture Mechanics, 2010
A coupled plasticity-damage model for plain concrete is presented in this paper. Based on continuum damage mechanics (CDM), an isotropic and anisotropic damage model coupled with a plasticity model is proposed in order to effectively predict and simulate plain concrete fracture. Two different damage evolution laws for both tension and compression are formulated for a more accurate prediction of the plain concrete behavior. In order to derive the constitutive equations and for the easiness in the numerical implementation, in the CDM framework the strain equivalence hypothesis is adopted such that the strain in the effective (undamaged) configuration is equivalent to the strain in the nominal (damaged) configuration. The proposed constitutive model has been shown to satisfy the thermodynamics requirements. Detailed numerical algorithms are developed for the finite element implementation of the proposed coupled plasticity-damage model. The numerical algorithm is coded using the user subroutine UMAT and then implemented in the commercial finite element analysis program Abaqus. Special emphasis is placed on identifying the plasticity and damage model material parameters from loading–unloading uniaxial test results. The overall performance of the proposed model is verified by comparing the model predictions to various experimental data, such as monotonic uniaxial tension and compression tests, monotonic biaxial compression test, loading–unloading uniaxial tensile and compressive tests, and mixed-mode fracture tests.
Cracked concrete structures under cyclic load
2004
The safety of cracked concrete dams is fundamentally affected by their mechanical behaviour under seismic excitation. Such a load is far from being harmonic and is characterized by intermittent spikes. Therefore the sequence effect is analysed. Two widely accepted non-linear methods were used: the Cohesive Crack Model to analyse the evolution of the process zone and the Continuous Function Model (CFM) to analyse the local hysteresis loop. In its original formulation, CFM predicts that a higher preloading arrests the fatigue crack growth at a subsequent lower load level. This unrealistic and unconservative behaviour is due to the fact that the above mentioned model neglects the damage occurring during the so-called inner-loops. In other words the CFM assumes that inner loops are mere loading loops and not fatigue loops. This assumption causes an incorrect prediction of the sequence effect. For the same reason the CFM predicts an endurance limit which is higher than attested by experimental evidence. In order to obtain more realistic results, in the present paper the CFM was enhanced, introducing a damage mechanism for the inner loops too. In the new model proposed, as well as in the original CFM, the endurance limit is seen to be almost constant relative to structural size.
Seismic cracking of concrete gravity dams by plastic–damage model using different damping mechanisms
Finite Elements in Analysis and Design, 2013
Utilizing two different damping mechanisms, seismic cracking response of concrete gravity dams is examined by a plastic-damage model implemented in three-dimensional space. The material constitutive law employed herein is based on the one proposed by Lee and Fenves for the 2-D plane stress case. This plastic-damage model basically intended for cyclic or dynamic loading was founded on the combination of non-associated multi-hardening plasticity and isotropic damage theory to simulate the irreversible damages occurring in fracturing process of concrete. In this study, considering the HHT scheme as an implicit operator, the time integration procedure to iteratively solve the governing nonlinear equations is presented. Further, seismic fracture responses of gravity dams due to constant and damage-dependent damping mechanisms are compared. In order to assess the validity of the proposed model, several simple examples are solved and their results are presented first. Subsequently, Koyna gravity dam, which is a benchmark problem for the seismic fracture researches, is analyzed. It is concluded that employing the damage-dependent damping mechanism leads to more extensive damages and also predicts more reliable crack patterns in comparison with the constant damping mechanism in seismic analysis of concrete dams. Furthermore, including dam-water interaction intensifies the existing differences between the results of the two damping mechanisms.
Dynamic fracture of concrete – compact tension specimen
International Journal of Solids and Structures, 2011
The behavior of concrete structures is strongly influenced by the loading rate. Compared to quasi-static loading concrete loaded by impact loading acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia forces activated. Both influences are clearly demonstrated in experiments. Moreover, for concrete structures, which exhibit damage and fracture phenomena, the failure mode and cracking pattern depend on loading rate. In general, there is a tendency that with the increase of loading rate the failure mode changes from mode-I to mixed mode. Furthermore, theoretical and experimental investigations indicate that after the crack reaches critical speed of propagation there is crack branching. The present paper focuses on 3D finite-element study of the crack propagation of the concrete compact tension specimen. The rate sensitive microplane model is used as a constitutive law for concrete. The strain-rate influence is captured by the activation energy theory. Inertia forces are implicitly accounted for through dynamic finite element analysis. The results of the study show that the fracture of the specimen strongly depends on the loading rate. For relatively low loading rates there is a single crack due to the mode-I fracture. However, with the increase of loading rate crack branching is observed. Up to certain threshold (critical) loading rate the maximal crack velocity increases with increase of loading rate, however, for higher loading rates maximal velocity of the crack propagation becomes independent of the loading rate. The critical crack velocity at the onset of crack branching is found to be approximately 500 m/s.
Seismic cracking and energy dissipation in concrete gravity dams
Earthquake engineering & …, 1993
A finite element method for seismic fracture analysis of concrete gravity dams is presented. The proposed smeared crack analysis model is based on the non-linear fracture behaviour of concrete. The following features have been considered in the development of the model: (i) the strain softening of concrete due to microcracking; (ii) the rotation of the fracture band with the progressive evolution of microcrack damage in finite elements; (iii) the conservation of fracture energy; (iv) the strain-rate sensitivity of concrete fracture parameters; (v) the softening initiation criterion under biaxial loading conditions; (vi) the closing-reopening of cracks under cyclic loading conditions. The seismic fracture and energy response of dams and the significance of viscous damping models to take account of non-cracking structural energy dissipation mechanisms are discussed. The influences of global or local degradation of the material fracture resistance on the seismic cracking response of concrete dams were also studied. Two-dimensional seismic response analyses of Koyna Dam were performed to demonstrate the application of the proposed non-linear fracture mechanics model.