Behavior Of Concrete Gravity Dams Research Articles

Polynomial response surface-based transformation function for the performance improvement of low-fidelity models for concrete gravity dams

The behavior of concrete gravity dams under seismic loading is a complex engineering problem dependent on a wide range of variables. Probabilistic methods can be used to evaluate the capacity of an individual or a portfolio of dams to withstand seismic events. However, due to the high number of re-evaluations required by such methods, simplified models that may not fully capture the complexity of the problem are frequently adopted in the evaluations. For a portfolio of dams that requires geometric uncertainty to be included in the list of controlled variables, the number of re-evaluations increases even further. This is a common engineering problem, where the cost-performance trade-off must be evaluated for every project. To address this issue, this study proposes a machine learning-based transformation function that improves the results obtained with a simplified method by converting low-fidelity data into high-fidelity data. The proposed procedure is applied to analyze the seismic response of a dam-reservoir-foundation system considering three approaches for geometric uncertainty, with increasing complexity. The final function takes as input low-fidelity observations, as well as geometric, material and seismic parameters, and outputs improved observations, with accuracy levels comparable to those obtained with a high-fidelity model but at a much lower cost. The sliding factor of safety resulting from a pseudostatic analysis is taken as the low-fidelity observation, and the sliding displacement from a nonlinear finite element analysis is selected as the high-fidelity observation. The resulting transformation function is then used to generate fragility curves for a well-documented case study dam, and the results using the proposed methodology and from a traditional fragility analysis are compared. It is observed that the proposed methodology to generate transformation functions is capable of correlating methods with radically different hypotheses, precision levels and even different outputs.

Numerical Modeling of Early-age Effects on the Mechanical Behavior of Concrete Gravity Dams

The control of thermal cracks induced by the effect of early age are the main concerns in concrete dam during the construction stage. Despite its importance, detailed thermal analysis of concrete gravity dams during the construction period is relatively rarely in the literature, eventually because prediction the behavior of concrete gravity dam on early stage requires taking into account the several phenomena and interaction, demands a considerable computational effort. To overcome this drawback, the present paper proposes a numerical modeling strategy to predict the thermo-mechanical behavior of concrete gravity dams during construction periods considering the effect of early age and the construction schedule. The proposed strategy is also used to study the effect of pre-cooling methods on the thermal-mechanical fields on concrete gravity dam during construction process. For this purpose, a Chemo-Thermo-Mechanical model is developed for predicting the behavior of a gravity dam at early stages. Firstly, temperature field model was established and verified with the results reported in the literature. Furthermore, the thermo-mechanical behavior of a concrete gravity dam is performed for two configurations: Early age state with pre-cooling and early age without pre-cooling. Thermal stress analysis was also conducted and results showed that the greatest tensile stresses after construction are developed at the heel of dams and resumption of concreting interface due to the internal restraint imposed by the concrete. The numerical results showed that the pre-cooling methods is an effective way to reduce both the hydration temperature and tensile stress induced by the effect of early age.

Seismic Performance Evaluation of Concrete Gravity Dams Using an Efficient Finite Element Model

The effective numerical model that examines the seismic behavior of concrete gravity dams in the Laplace domain-Finite Element (FE) approach is presented. Further research on seismic performance of the dam body is done considering the simultaneous effect of horizontal (H) and vertical (V) components of six different earthquake loads. The time durations of the selected earthquakes vary from 10 to 80 s with the magnitude range from 6.5 to 7.62 Mw. The Lagrangian fluid finite elements are utilized to model the near-field water domain, while the fluid infinite elements are utilized to model the far-field water domain. The two-dimensional (2D) FE model is developed in FORTRAN 90 and MATLAB programming languages. The obtained results revealed that the longer length of significant earthquake duration leads to the high deformations, high stress excursions and high probability of damages in the dam body. 20.9% and 18.8% of the selected dam cross section experienced overstress condition under the H and H + V components of the Chi-Chi earthquake loads, respectively; this indicate the severe damages and even the dam failure. This study concludes that the seismic behavior of concrete gravity dam affects not only with the seismic severity; the length and significant time duration of the earthquake are also important factors should be considered in the seismic analysis and design of dams.

Earthquake Behavior of Concrete Gravity Dams During Ground Motions

Abstract The stability evaluation of the dams subjected to seismic excitations is really very complex as the earthquake response of the concrete gravity dam depends upon its connection joints with foundation rock. This study presents the seismic response of concrete gravity dams considering welded contact and friction contact and along dam-foundation rock interface. Friction contact is provided using contact elements. Two-dimensional finite element model of Oued Fodda concrete gravity dam, located in Chlef at the northwestern part of Algeria, is used for this purpose. Nonlinear analyses of dam-foundation rock system are performed using ANSYS software. The reservoir water is modeled as added mass using the Westergaard approach. The Druker-Prager model is employed in the nonlinear analysis for dam concrete. The surface-to-surface contact elements based on the Coulomb's friction law are used to describe the friction. These contact elements use a target surface and a contact surface to form a contact pair. According to this study, when the friction contact is considered in joints, sliding displacement of dam base occurs along the dam-foundation rock interface. The dam sliding along its foundation decreases the deformation response; principal stresses in the dam body and shear force at both the heel and toe of the dam.

Displacement behavior interpretation and prediction model of concrete gravity dams located in cold area

The measured displacement-driven structural health monitoring (SHM) model is a significant approach to interpreting the influencing mechanism of environmental loads on dam displacement and to predicting the future operating behavior. Considering the large ambient temperature difference in cold area and the insufficient interpretive performance of the hydrostatic-seasonal-time (HST) model on thermal displacement behavior caused by the short-term dynamic fluctuations of ambient temperature, a hydrostatic-thermal-time (HTT) model considering hysteresis effect of boundary temperature is proposed to quantitatively analyze the influencing mechanism of environmental loads on displacement behavior of concrete gravity dams in cold area. Meanwhile, to improve the predictive performance of the proposed HTT model, whale optimization algorithm (WOA)-optimized gated recurrent unit (GRU) network is employed to effectively excavate the complex nonlinear relationship between dam displacement and its explanatory variables. A roller compacted concrete (RCC) gravity dam in cold area is taken as an example, and the cause of the disharmonious horizontal displacement behavior of an overflow dam crest is explained via the proposed HTT model and numerical simulation method. The conclusion is conducive for better understanding the displacement behavior of concrete dams in cold area. Meanwhile, engineering examples show that the proposed HTT model can reasonably interpret the thermal displacement behavior caused by the ambient temperature variations, and the WOA-optimized GRU network-based HTT model exhibits excellent fitting and predicting capabilities. A novel technique is provided for the accurate prediction of dam displacement.

Study of the influence of the foundation and the reservoir on the dynamic response in a concrete gravity dam profile

abstract: This work aims to verify the influence of the foundation and the reservoir on the dynamic behavior of concrete gravity dams in terms of the natural frequencies, vibration modes for a free vibration analysis; and in terms of maximum displacements and maximum stresses at singular points of the structure for a seismic excitation. The dam-reservoir-foundation interaction was investigated through modal and transient analysis by the finite element method via ANSYS APDL software. For this study, we used a typical Brazilian dam profile and compatible data from a Brazilian earthquake for the seismic excitation. The results showed the influence of the reservoir and the foundation on the natural frequencies in the coupled system, as well as its repercussions on the response of the dam under seismic excitation.

Evaluation of the effect of reservoir length on seismic behavior of concrete gravity dams using Monte Carlo method

Evaluation of the effect of reservoir length on seismic behavior of concrete gravity dams using Monte Carlo method

Seismic Damage Behavior of Gravity Dams under the Effect of Concrete Inhomogeneity

ABSTRACT Dam concrete exhibits inhomogeneity due to its inherent material characteristic, construction-induced cracks/defects, and aging deterioration. The inhomogeneity may affect earthquake performance and seismic safety of concrete dams. In this work, a gravity dam-reservoir-foundation model, involving radiation damping, compressibility of reservoir water, and damage/cracking of concrete, is presented to investigate the influence of concrete inhomogeneity on seismic behavior of dams. The Weibull probabilistic distribution assumption is employed in the model to describe the heterogeneity of the dam concrete. A series of numerical analyses of the Koyna gravity dam, which is assigned with different heterogeneity indexes, is performed. The result demonstrates that the heterogeneity of concrete has significant influence on the seismic damage behavior of concrete gravity dams. A more heterogeneous material generally results in a larger dynamic displacement, a more severe damage pattern, and a greater damage level of the dam, indicating that an increase in homogeneity of concrete would be of benefit to seismic capability of concrete gravity dams.

Response study of concrete gravity dam against aircraft crash

Concrete gravity dam is considered as acritically important mega structure and lifeline of countries with rich water resources. Its failure due to natural and manmade hazard may cause a huge loss of human life and economy. The recent terror attacks involving intentionally crash of aircrafts have raised the safety concern of these critical structures. In the present study, a finite element analysis has been carried out to analyse the behaviour of concrete gravity dams against possible aircraft crash. Reaction-time curve of fighter jet Phantom F4 has been applied on the crest of the dam from upstream face. The Concrete Damaged Plasticity model has been incorporated to predict the behaviour of concrete under high strain loading. It has been found that at a crash speed of Mach 1, fighter jet had caused severe damage to dam. Although the penetration will be small on the loading face of the dam due to massiveness of structure, however, the concrete around crest and neck will fail in tension. Further, redistribution of moments will cause failure of the structure. Maximum deformation has been found to be 8.8 mm. Stresses are quite high at the impact face, however it diminishes at a depth of 8 m from the impact face.

Investigation of to the Effect of Bedrock Stiffness on Seismic Behaviour of Roller Compacted Concrete Dam

In this research, the effect of bedrock stiffness on seismic performance of roller compacted concrete (RCC) dam is evaluated using probabilistic analysis. Due to the geometry and behavior of RCC dams, a two-dimensional modeling was selected for system. Ansys software is used for modeling and analysis of dam-reservoir- foundation system. Newmark implicit time integration scheme is developed to solve the time-discretized equations which are an unconditionally stable method. The Watana dam, due to San Fernando earthquake has been selected as a case study. In order to propagate the parametric sensitivity to the seismic performance of the system, Monte Carlo simulation with Latin hypercube sampling (LHS) method is used as a probabilistic method and uncertainty analysis. The sensitivity of responses under seismic loading is reliably examined utilizing different values of ratio of bedrock stiffness to body concrete stiffness as random inputs. Consider to obtained results, it is revealed that the bedrock stiffness how can effect on seismic behavior of concrete gravity dams due to earthquake. Regarding the safety of dams due to compressive stresses, various ways have been assessed to investigate the induced tensile stress in the heel and the results have been investigated. Finally, appropriate range of the ratio of bedrock stiffness to concrete stiffness of dam body is presented to assess the safety design.

Seismic behavior of concrete gravity dams

Dams play a vital role in the development and sustainment in a country. Failure of dams leads to the catastrophic event with sudden release of water and is of great concern. Hence earthquake-resistant design of dams is of prime importance. The present study involves static, modal and transient analyses of dam-reservoir-foundation system using finite element software ANSYS 15. The dam and the foundation are modeled with 2D plane strain element PLANE 42 and the reservoir by fluid acoustic element FLUID 29 with proper consideration of fluid-structure interaction. An expression for the fundamental period of concrete dams is developed based on modal analysis. Seismic response of gravity dams subjected to earthquake acceleration is evaluated in terms of peak displacement and stress.

Investigation of the effect of reservoir bottom absorption on seismic performance of concrete gravity dams using sensitivity analysis

In this research, probabilistic analysis of the seismic performance of gravity dams is presented considering interaction effects to quantify the sensitivity of seismic response to reservoir bottom absorption. The maximum value of horizontal displacement of dam crest, hydrodynamic pressure, 1st principle stress at heel and 3rd principle stress at toe of dam, during earthquake excitations, are considered random variables in the probabilistic analysis of base-case model. In order to propagate the parametric sensitivity to the seismic performance of the system, Monte Carlo simulation with Latin hypercube sampling is used as a probabilistic simulation method. Sensitivity of responses under seismic loading is reliably examined utilizing different values of bottom absorption as random inputs. Computational procedure for two-dimensional finite-element analysis of the base-case model is carried out in time domain considering the dynamic excitation and dam-reservoir interaction. Considering the obtained results, that the manner through which the bottom absorption can affect the seismic behavior of concrete gravity dams due to earthquake is determined. To estimate the structural performance under seismic loads, a suite of ground motions is selected and applied to the base-case model and the model sensitivity to reservoir bottom absorption is investigated. Finally, to show the effectiveness of the sensitivity and probabilistic analysis procedure presented in this paper the response of Koyna and Pine Flat dams with respect to the horizontal component of El Centro earthquake is investigated as real models. The obtained results show that the sensitivity curves of output parameters are linear or bilinear relative to the models and ground motion records.

Earthquake Damage Analysis of Concrete Gravity Dams: Modeling and Behavior under Near-Fault Seismic Excitations

In the near-fault region of an earthquake, ground motions are strongly affected by complex mechanisms and can be significantly different from typical far-fault ground motions. Although the significance of near-fault ground motions has been widely recognized, its influence on the earthquake performance of concrete gravity dams has not yet been fully quantified. This article investigates the effects of near-fault ground motions on the nonlinear seismic response behavior of concrete gravity dams. In particular, the characteristics of different aspects of near-fault ground motions are evaluated and the significance of various near-fault ground motion parameters is examined.

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.

The effect of foundation’s modulus of elasticity on concrete gravity dam’s behavior

Investigation on the behavior of dams against the seismic loads is a key factor for safety requirement. One of the most important problems in evaluation of seismic behavior of concrete gravity dams is dam-reservoir-foundation interaction. In this paper, we study the effect of dam-reservoir-foundation interaction on nonlinear behavior of concrete gravity dams, a two-dimensional approach was used including the finite element method and smeared crack approach. Effective parameters in the models are physical properties of concrete such as modulus of elasticity, tensile strength and specific fracture energy. Their importance in the nonlinear analysis was investigated in a parametric study. Different boundary conditions were used in foundation in order to determine the seismic response of concrete gravity dams. Results show that when the nonlinear analysis includes the dam- foundation interaction and the foundation's mass, flexibility and radiation damping, the seismic response of concrete gravity dam will be reduced to a realistic level. Decreasing in ratio of foundation's modulus of elasticity to dam's modulus of elasticity (EF/ES) causes increasing in dam crest displacement. The crack profile is expected to reduce due to mass of foundation and it's damping effects in massed foundation system.

Nonlinear behavior of concrete gravity dams and effect of input spatially variation

In the present article, effect of non-uniform excitation due to spatially variation of seismic input on nonlinear response of concrete gravity dams is considered. The reservoir is assumed compressible. Isotropic damage mechanics approach is used to model static and dynamic nonlinear behavior of mass concrete in 2D space. The validity of utilized nonlinear model is considered using available theoretical results under static and dynamic conditions. The tallest monolith of Pine Flat dam is selected as a case study. Two cases are analyzed for considering the effect of limited wave propagation velocity on seismic behavior of the dam-reservoir system in which travelling velocities are chosen as 2000 m/s and infinity. It is found that tensile damage in neck and toe regions and also, in the vicinity of the base increase when the system is excited non-uniformly.

Seismic Cracking and Strengthening of Concrete Gravity Dams

Concrete gravity dams designed in compliance with the present specification are likely to experience cracking under intense shaking like maximum credible earthquakes. Dangerous cracking in dam body should be prevented in advance to ensure the serviceability of dams. In this paper, the safety of concrete gravity dams under strong ground motions is investigated. First, the dam response during earthquakes is simulated by the FE-BE method, including the damfoundation-reservoir interaction. The nonlinear tensile behavior of concrete is represented by the smeared crack model to predict the possible earthquake-induced cracking in the dam body. Then some measures to prevent the cracking of dam body are presented. The measures are, for example, adjustment of dam section, local reinforcement and post-tension technique. The adjustment of dam section will reduce the tensile stress in dam body and avoid the occurrence of cracking. Local reinforcement at possible cracking positions is expected to resist the propagation of cracks and reduce the damage of dam body, although it might not prevent the initial cracking. Post-tension technique exerts pre-compressive stress in dams to offset the tensile stress during earthquakes. Effects of these measures are evaluated by numerical simulation. It is shown that these measures could improve the cracking-resistant behavior of concrete gravity dams effectively.

Several issues to be considered for long-term better behavior of concrete gravity dams

Along with economic, social quick development and urbanization, dams and reservoirs are of strategic importance for flood control, water supply, electricity production, irrigation, etc., both for developed countries and for developing countries. Climate change is a new challenging issue to be considered which will speed up the development of hydropower in developing countries. More and more attention will be paid on the long-term better behavior of dams to guarantee the safety of the people involved and the better development of the world. There are about 50000 old dams in the world and a lot of them have been completed and operated for more than 50 years. However, how do we evaluate the dams’ safety? How do we make the decision to do rehabilitation work or to rebuild a new dam based on evaluation results? The life span and the real safety status of old dams becomes a challenging task for the dam society, especially for China because it has more than 6000 dams to be evaluated and rehabilitated within the next few years. Based on the investigation of the Fengman gravity dam, which is 91.7 m high, operated since 1943 and suffered uplift pressure, freeze and thaw problems, etc., discussions on the life span evaluation of old concrete gravity dams have been made. The reasonable coefficient of dam safety has been discussed. The social decision for the final choice after comprehensive studies has been introduced.

Effect of Seismic Uplift Pressure on the Behavior of Concrete Gravity Dams with a Penetrated Crack

Proper consideration of the uplift pressure at the base of a concrete gravity dam is of great importance in practical engineering, since it is crucial to the safety of the dam, specifically for a cracked dam under seismic conditions. However, constant uplift pressure, which is suitable for the static case only, was adopted in almost all the seismic analyses of cracked concrete gravity dams. To adequately estimate the seismic behavior of cracked concrete gravity dams, a seismic uplift pressure model is proposed for a penetrated crack. In this model, the amount and the distribution of the uplift pressure along the assumed rigid crack walls are determined by the earthquake acceleration, the water heads, the aperture of the crack, and the opening/closing velocity. Application of the model to a typical concrete gravity dam with a penetrated crack at the base reveals that the seismic behavior of the dam is markedly affected by the seismic uplift pressure. In general, the residual downstream sliding is considerably enlarged compared to that of constant uplift pressure. Computations show that the seismic uplift pressure can be several times higher than the constant one, increasing the dynamic instability of the cracked dam. It is also revealed that the dynamic water flow plays the role of a wedge while the upper mouth of the crack is closing. When the dam rocks back to upstream, the uplift pressure increases until it is so high that the pivot at the toe is raised up and the whole dam loses its contact. Then the resultant uplift pressure remains constant until the dam is inclined to the upstream. During this period of time, the cracked dam is normally drifting towards the downstream due to the hydro pressure.

Comportamiento de presas de gravedad de hormigón con problemas de ataque interno por sulfatos

En este trabajo se presenta la metodología seguida con vistas a evaluar la expansión del hormigón debido al ataque sulfático interno y su repercusión en el comportamiento anómalo de presas de hormigón de gravedad. Para ello se presenta el análisis, en distintas fases del estudio, de tres presas españolas afectadas por las reacciones sulfáticas. En el nivel microscópico se ha procedido a la caracterización del árido y del hormigón de la presa de Torán, identificando el principal sulfuro de hierro y los productos generados en el proceso de alteración del árido y su posterior ataque al hormigón. Por otro lado, el estudio en el nivel macroestructural de los movimientos remanentes observados se hace mediante un modelo matemático aplicado a las presas de Graus y Tavascán.