Behavior Of Concrete Dams Research Articles

Dynamic Damage Analysis for Seismic Responses of Arch Dam

The accuracy of the risk evaluation associated with existing dams as well as the efficient design of future dams is highly dependent on a proper understanding of their behavior due to earthquakes. This paper presents a 3D anisotropic damage model for arch dam under strong earthquakes. The modified effective Mohr–Coulomb criterion is adopted as the failure criteria of the dynamic damage evolution of concrete. From the simulation of the dynamic damage process, some process fields of the dynamic displacement, the dynamic stress, dynamic damage distribution and other necessary information for the safety evaluation are obtained. These results show that the seismic behavior of concrete dams can be satisfactorily predicted. This will provide a reasonable theoretical support on the safety evaluation of the capability for concrete arch dams against earthquake loading.

Thermo-structural monitoring of RCC dam in India through instrumentation

The knowledge of the behavior of any roller compacted concrete (RCC) dam and its foundation is gained by studying the service action of the dam and its foundation using measurements of an external and internal nature. The information by which a continuing assurance of structural safety of the RCC dam can be gauged is of primary importance. Similarly, the fact that the information on structural and thermal behavior and the properties of concrete that may be used to give added criteria for use in the design of future RCC dams is of secondary importance. Wide spread attention is now being given to the installation of more expensive instrumentation for studying the behavior of concrete dams and reservoirs and forecasting of any adverse trends. In view of this, the paper traces installation and need of the comprehensive instrumentation scheme implemented to monitor the structural and thermal behavior of 102.4 m high RCC dam constructed near Mumbai in India. An attempt is made in the present paper to emphasize the need to undertake an instrumentation program and evaluate their performance during construction and post construction stage of RCC structures. Few typical results, regarding the thermal and structural behavior of the dam, obtained through instrumentation installed at the dam site are presented and compared with the design considerations. The fair agreement is seen in the response observed through instrumentation with that governing the design criteria.

An improved 1D-model for computing the thermal behaviour of concrete dams during operation. Comparison with other approaches

Thermal effects are significant loads for assessing concrete dam behaviour during operation. A new methodology to estimate thermal loads on concrete dams taking into account processes which were previously unconsidered, such as: the evaporative cooling, the night radiating cooling or the shades, has been recently reported. The application of this novel approach in combination with a three-dimensional finite element method to solve the heat diffusion equation led to a precise characterization of the thermal field inside the dam. However, that approach may be computationally expensive. This paper proposes the use of a new one-dimensional model based on an explicit finite difference scheme which is improved by means of the reported methodology for computing the heat fluxes through the dam faces. The improved model has been applied to a case study where observations from 21 concrete thermometers and data of climatic variables were available. The results are compared with those from: (a) the original one-dimensional finite difference model, (b) the Stucky-Derron classical one-dimensional analytical solution, and (c) a three-dimensional finite element method. The results of the improved model match well with the observed temperatures, in addition they are similar to those obtained with (c) except in the vicinity of the abutments, although this later is a considerably more complex methodology. The improved model have a better performance than the models (a) and (b), whose results present larger error and bias when compared with the recorded data.

Damage–Rupture Process of Concrete Dams Under Strong Earthquakes

A new concept for establishing the damage model for high concrete dams under earthquakes based on damage mechanics is presented in this paper. Unlike the conventional approach of considering the residual deformation by means of plastic-damage coupling, the proposed approach relates the degraded apparent elastic moduli of loading and unloading directly to the material experimental data. As such, the nonlinear analysis of the seismic response of dam-foundation systems is simplified and more reasonable, with no recourse to plastic-damage coupling. To verify the proposed approach of damage–rupture process for high concrete dams, the seismic behaviors of the Koyna gravity dam in India and the Shapai RCC arch dam in China both subjected to strong earthquakes were examined. It is demonstrated that the proposed approach can be reliably used to study the damage–rupture behavior of concrete dams under strong earthquakes.

Comparison of different fracture modelling approaches to gravity dam failure

Purpose – There is not a unified modelling approach to finite element failure analysis of concrete dams. Different behaviours of a dam predicted by different fracture methods with various material constitutive models may significantly influence on the dam safety evaluation. The purpose of this paper is to present a general comparative investigation to examine whether the nonlinear responses of concrete dams obtained from different fracture modelling approaches are comparable in terms of crack propagation and failure modes. Design/methodology/approach – Three fracture modelling approaches, including the extended finite element method with a cohesive law (XFEM-COH), the crack band finite element method with a plastic-damage relation (FEPD), and the Drucker-Prager (DP) elasto-plastic model, are chosen to analyse damage and cracking behaviour of concrete gravity dams under overloading conditions. The failure process and loading capacity of a dam are compared. Findings – The numerical results indicate that the three approaches are all applicable to predict loading capacity and safety factors of gravity dams. However, both XFEM-COH and FEPD give more reasonable crack propagation and failure modes in comparison with DP. Therefore, when cracking patterns are the major concern for safety evaluation of concrete dams, it is recommended that XFEM-COH and FEPD rather than DP be used. Originality/value – The comparison of cracking behaviours of concrete dams obtained from different fracture modelling approaches is conducted. The applicability of the modelling approaches for failure analysis of concrete dams is discussed, and from the results presented in this work, it is significant to consider the suitability of the selected fracture modelling approach for dam safety evaluation.

A damage model for concrete under cyclic actions

Neither damage mechanics model nor elastoplastic constitutive law can solely describe the behavior of concrete satisfactorily. In fact, they both fail to represent proper unloading slopes during cyclic loading. To overcome the disadvantages of pure plastic models and pure damage approaches, a constitutive model devised for the analysis of concrete structures, and suitable for generic two- or three-dimensional applications, is presented and validated. Multiaxial damage failure criteria are introduced to be able to adequately describe the plastic and damage behavior of concrete. The multiaxial damage failure criteria can not only deal with failure from compressive damage, tensile damage degradation under related axes, but also consider anisotropic characteristic for damage. Several numerical examples of concrete modeling are shown with the experimental counterparts to demonstrate the effectiveness of the present plastic-damage approach.

Strain-based seismic failure evaluation of coupled dam-reservoir-foundation system

Generally, mass concrete structural behavior is governed by the strain components. However, relevant guidelines in dam engineering evaluate the structural behavior of concrete dams using stress-based criteria. In the present study, strain-based criteria are proposed for the first time in a professional manner and their applicability in seismic failure evaluation of an arch dam are investigated. Numerical model of the dam is provided using NSAD-DRI finite element code and the foundation is modeled to be massed using infinite elements at its far-end boundaries. The coupled dam-reservoir-foundation system is solved in Lagrangian-Eulerian domain using Newmark-<TEX>${\beta}$</TEX> time integration method. Seismic performance of the dam is investigated using parameters such as the demand-capacity ratio, the cumulative inelastic duration and the extension of the overstressed/overstrained areas. Real crack profile of the dam based on the damage mechanics approach is compared with those obtained from stress-based and strain-based approaches. It is found that using stress-based criteria leads to conservative results for arch action while seismic safety evaluation using the proposed strain-based criteria leads to conservative cantilever action.

Time–frequency analysis for concrete dam safety control: Correlation between the daily variation of structural response and air temperature

The purpose of this research work is to identify the effect of the daily variation of the air temperature on the structural response of a concrete dam. It is intended to obtain a better knowledge about structural behaviour of concrete dams. In current day to day activities, quantitative interpretation models are used for the assessment of structural dam behaviour of concrete dams. Most models ignore the temperature effect of a wave with a daily variation. However, in dams with automated data acquisition systems this daily effect can be used to anticipate the detection of abnormal behaviour.In this paper, the Short Time Fourier Transform analysis of the residuals is used, obtained by the quantitative interpretation models and measurement data, to identify the signature that the daily variation of the air temperature has on the structural behaviour of a concrete dam. A case study is presented based on the analysis of a horizontal displacement measured on a pendulum, in the Alto Lindoso concrete dam. As a result, the relation between magnitudes of daily variations of the horizontal displacement analysed and the air temperature was defined. The relation obtained can be used to assess if there is alterations or not in the dam response to short period loads corresponding to the daily variations analysed.

Numerical modeling of arch dam under blast loading

The damage of unallowable blast induced vibrations on the concrete structures results in a decrease in the safety of its structures. This paper develops a three dimensional anisotropic dynamic damage model for Dagangshan arch dam subjected to blast loading. The multiple damage failure criteria are adopted as the failure criteria of the dynamic damage evolution of concrete. From the simulation of the dynamic damage process in the arch dam due to the blast loading, some process fields of the dynamic displacement, the dynamic stress, dynamic damage distribution and other necessary information for the safety evaluation are obtained. The results obtained using the proposed model show that the nonlinear behavior of concrete dams can be satisfactorily predicted. This will provide a reasonable theoretical support on the safety evaluation of the capability of concrete arch dams against blast loading and useful information for further research in these areas.

Seismic Safety Evaluation of High Arch Dams Using Concrete Damage Theory

To reasonably evaluate the seismic behavior of high arch dams, a damage plasticity model is adopted to simulate the dynamic nonlinear behavior of dam concrete for a hydropower station. Combining with the viscous-spring boundary and compressibility reservoir model, the maximum principal stress on upstream and downstream surfaces is obtained. The results show that the effects of material nonlinearity damage on the dynamic response of the arch dam are significant under earthquake load.

A review of continuum damage modelling for dam analysis

ABSTRACT This article presents the different steps of a research process initiated in the field of dam engineering, through collaboration between EDF and ENS Cachan, following Jacky Mazars' pioneering work on the application of the damage concept to concrete structure modelling. Considering the importance of concrete swelling phenomena for the long-term behaviour of concrete dams, special efforts have been devoted to the development of a rheologic model in this field. This paper explains how the research performed contributed to the elaboration and the justification of the main equations included. An application to the Temple-sur-Lot dam is presented.

Gradient-enhanced Coupled Plasticity-anisotropic Damage Model for Concrete Fracture: Computational Aspects and Applications

It is widely studied that classical continuum damage theory for concrete fracture exhibits an extreme sensitivity to the spatial discretization in the finite element simulations. This sensitivity is caused by the fact that the mathematical description becomes ill-posed at a certain level of accumulated damage. A well-posed problem can be recovered by using a gradient-enhanced damage model in which a material length scale is introduced as a localization limiter. In this work, a nonlocal gradient-enhanced fully coupled plastic-damage constitutive model for plain concrete is developed. Anisotropic damage with a plasticity yield criterion and a damage criterion are introduced to be able to adequately describe the plastic and damage behavior of concrete. In order to account for different effects under tensile and compressive loadings, nonlocal damage variables that account for the progressive degradation of mechanical properties under stress states of prevailing tension and compression and two internal length scales, one for tension and the other for compression, are introduced as localization limiters. Therefore, two nonlocal damage criteria are used: one for compression and a second for tension such that the total stress is decomposed into tensile and compressive components. In order to solve the time step problem, a decoupled elastic predictor and plastic corrector steps are performed first in the effective configuration where damage is absent, and then a nonlocal damage corrector step is applied in order to update the final stress state. The algorithmic treatment of both tension and compression is presented in a unified way. A simple procedure to calculate the gradient of the tensile/compressive damage variables is described which can be used directly without the need of intensive numerical modifications of an existing finite element code. The effectiveness of the proposed local model has been demonstrated in both uniaxial and biaxial tension and compression problems and compared with experimental data. Numerical results obtained with the proposed nonlocal model are compared with experimental results concerning bending of three-point notched and four-point notched concrete beams. As the mesh is refined, convergence of numerical results is observed both in terms of damage patterns and of the global response.

Behavior of dam concrete under biaxial compression-tension and triaxial compression-compression-tension stresses

In order to meet the requirement for nonlinear analysis and design of mass concrete structures, the deformation behavior and strength of three-graded concrete specimens 250 mm × 250 mm × 400 mm with a maximum aggregate size of 80 mm and the corresponding wet-screened concrete specimens 150 mm × 150 mm × 300 mm with a maximum aggregate size of 40 mm were studied experimentally. Specimens subjected to biaxial compression-tension (C-T) and triaxial compression-compression-tension (C-C-T) stress states. Test data indicate that both the deformation and strength of the mass concrete specimens are lower than those of the corresponding wetscreened concrete small specimens, but the initial tangent modulus of the stress-strain curve of the former is greater than that of the latter. Test results show that the wetscreened effect and size effect of the specimens under complex stress states are obvious such that these should be considered in the design of mass concrete structures. In addition, respective failure criteria for mass concrete in principal stress space and octahedron stress space are proposed.

A plasticity and anisotropic damage model for plain concrete

A plastic-damage constitutive model for plain concrete is developed in this work. Anisotropic damage with a plasticity yield criterion and a damage criterion are introduced to be able to adequately describe the plastic and damage behavior of concrete. Moreover, in order to account for different effects under tensile and compressive loadings, two damage criteria are used: one for compression and a second for tension such that the total stress is decomposed into tensile and compressive components. Stiffness recovery caused by crack opening/closing is also incorporated. The strain equivalence hypothesis is used in deriving the constitutive equations such that the strains in the effective (undamaged) and damaged configurations are set equal. This leads to a decoupled algorithm for the effective stress computation and the damage evolution. It is also shown that the proposed constitutive relations comply with the laws of thermodynamics. A detailed numerical algorithm is coded using the user subroutine UMAT and then implemented in the advanced finite element program ABAQUS. The numerical simulations are shown for uniaxial and biaxial tension and compression. The results show very good correlation with the experimental data.

Earthquake safety assessment of concrete arch and gravity dams

Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessment of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrete subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range. Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods.

Finite element analysis of concrete swelling due to alkali-aggregate reactions in dams

Many concrete dams throughout the world are suffering from deteriorations induced by alkali-aggregate reaction (AAR) that impair the durability, serviceability, and might also affect, in the long term, the safety of the installation. AAR produces concrete expansion, and generally leads to a loss of strength, stiffness (cracking), and generates undesirable deformations and disturbances in the equilibrium of internal forces. This paper first presents a brief review of the physical processes that control the structural behaviour of concrete dams suffering from AAR. A methodology to distribute the observed concrete expansion in proportion to the compressive stress state, temperature, moisture, and reactivity of the constituents is then proposed for the numerical modelling of AAR concrete swelling in dams. A case study on a concrete spillway pier that is affected by AAR is presented to illustrate some features of the proposed methodology.

Numerical simulation of concrete expansion in concrete dams affected by alkali–aggregate reaction: state-of-the-art

Many concrete dams and other concrete structures in Canada, and throughout the world, are suffering from deteriorations induced by alkali–aggregate reaction (AAR) that impair the durability and serviceability, and might also affect, in the long term, the safety of the installation. Alkali–aggregate reaction produces concrete expansion, and generally leads to a loss of strength and stiffness (cracking), and generates undesirable deformations and disturbances in the equilibrium of internal forces. The expansion mechanisms in concrete affected by AAR are complex and influenced by a number of factors that are difficult to quantify. Nevertheless, advanced numerical simulation models are generally used in close conjunction with field monitoring of displacements to assist in the structural evaluation and rehabilitation of dams where AAR has been identified. A review of the physical processes that control the structural behaviour of concrete dams suffering from AAR, and numerical simulation procedures to represent AAR concrete expansion by the finite element method, is presented herein. The present state of knowledge to simulate the AAR expansion process has been found to be limited and not yet satisfactorily developed. A methodology to distribute the observed concrete expansion in proportion to the compressive stress state, temperature, moisture, and the reactivity of the concrete constituents is proposed in this paper as a first step to rationalize the numerical modelling of the AAR concrete swelling process in concrete dams. Key words: alkali–aggregate reaction, concrete dams, finite element method, dam safety.

Effect of opening of joints on the behavior of concrete dams during operation

1. Theoretical investigations confirmed considerable opening of the contact joint both in nonoverflow and especially in powerhouse sections of the Bratsk dam. Other conditions being equal, the length of the zone of opening of the contact joint in the powerhouse sections is 2–3 m greater than in the nonoverflow sections. 2. Opening of joints has a seasonal character. In the winter the zone of opening in the powerhouse sections reaches the grout curtain (9–10 m from the upstream face), in the summer it is about half as much. 3. Such opening of the contact joint together with the phenomenon of decompression of the foundation leads to an increase of the uplift pressure, increase of seepage discharges, and decrease of safety against shearing. In turn, an increase of uplift pressure can lead to an increase of the zone of opening of the joint by 1–2 m. 4. A decrease in the winter of the upper pool level from the NPL (402 m) to 398 m brings the contact zone into about the same state as in the summer at the NPL. 5. Calculations showed that the zone of opening of the contact joint can be followed by a closed joint zone with displaced surfaces (sliding zone) and only then does the remaining part of the joint have an undisturbed initial strength. The size of the sliding zone depends on many factors and requires further refinement, but in any event this zone can completely enter the second column. 6. In the future we must refine the state of the contact zone in various sections with a more accurate consideration of the characteristics of the contact joint (friction with the initial strength) and with consideration of decompression of the foundation or the formation of cracks in it, seepage in the foundation, and effect of opening of the column joints.

A note on spurious oscillations in FEM joint elements

A unified view of joint elements yields a rationale perspective of sometimes observed «erratic» behaviour. These elements appear not to be particularly fragile compared to those in other analysis problems of strong material non-linearity. However, noise in dynamic application can be obstinate, and more experience with velocity smoothing (local viscosity or transfer of momentum) is needed before definite recommendations can be given. The work on joint elements forms part of a project on the seismic behaviour of concrete dams

Advanced dam analysis

An overview is presented of the techniques used within ENEL (the Italian National Power Board) for the analysis of behaviour of concrete dams, outlining the outstanding problems on which research is going on. Among these, non-linear behaviour and development/stability of cracks are perceived as the subjects deserving a determined effort both on the experimental and the anaytical level. Ongoing investigations seem to indicate that as 1 ong as the process zone at the crack tip is small as compared with the dimensions of the structure, the LEFM approach could be used to appraise stability conditions of existing cracks. However, proper determination of concrete fracture toughness factors and accurate representation of actual stress pattern—which is heavily influenced by complex thermal loads—present difficulties which will have to be overcome if application to real situation is to be undertaken.