Response Of Dams Research Articles

THE EFFECTS ON SHAPE-MODELING OF CONCRETE GRAVITY DAMS IN EARTHQUAKE RESPONSE ANALYSES

To clarify the effects of seismic response of concrete gravity dams under large earthquake, finite element method (FEM) analyses were carried out. In analyses, the height of dam and material properties of concrete and basement rock are same. The 2-dimensional (2D) and the 3-dimensional (3D) FEM model were made and used in earthquake response analyses. The contraction joints between dam block are concerned in 3D non-linear FEM analysis. In the case of same height of dam, the numerical results of damage states and placements in dam are different between 2D FEM model and 3D FEM model, due to the effect of difference in vibration mode of dam. In the 2D FEM model, the damage of top in cross-section becomes remarkable. In the 3D FEM model, the damage of attachment between dam body and basement rock at high-elevation becomes remarkable. The damage of 3D FEM model is smaller than that of 2D FEM model for the same acceleration level of earthquake. The influence of seismic response on contraction joints of 3D non-linear FEM dam model is smaller, which is as same as that of 3D linear FEM dam model. From the above results, the 2D FEM model gives a conservative assessment compared to the 3D FEM model.

Dynamic response of concrete gravity dams using different water modelling approaches: westergaard, lagrange and euler

The dams are huge structures storing a large amount of water and failures of them cause especially irreparable loss of lives during the earthquakes. They are named as a group of structures subjected to fluid-structure interaction. So, the response of the fluid and its hydrodynamic pressures on the dam should be reflected more accurately in the structural analyses to determine the real behavior as soon as possible. Different mathematical and analytical modelling approaches can be used to calculate the water hydrodynamic pressure effect on the dam body. In this paper, it is aimed to determine the dynamic response of concrete gravity dams using different water modelling approaches such as Westergaard, Lagrange and Euler. For this purpose, Sariyar concrete gravity dam located on the Sakarya River, which is 120km to the northeast of Ankara, is selected as a case study. Firstly, the main principals and basic formulation of all approaches are given. After, the finite element models of the dam are constituted considering dam-reservoir-foundation interaction using ANSYS software. To determine the structural response of the dam, the linear transient analyses are performed using 1992 Erzincan earthquake ground motion record. In the analyses, element matrices are computed using the Gauss numerical integration technique. The Newmark method is used in the solution of the equation of motions. Rayleigh damping is considered. At the end of the analyses, dynamic characteristics, maximum displacements, maximum-minimum principal stresses and maximum-minimum principal strains are attained and compared with each other for Westergaard, Lagrange and Euler approaches.

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.

Response of concrete gravity dam by damage model under seismic excitation

The aim of this study is to investigate the earthquake damage response of the concrete gravity dam. It is well known that simulation of concrete structures up to rupture requires nonlinear behavior of the models. The material behavior whose principle is based on the damage mechanics has been implemented in a finite element program. This model takes into account the dissymmetry of the behavior of concrete and considers cracking in tension and rupture in compression. The dynamic equilibrium equations of motion are solved by using the explicit central difference method which is based on approximation of velocities and accelerations with quotients of finite difference of known values of displacements with regular time step. For numerical application, two dimensional seismic analysis of Koyna gravity dam is performed by using the 1967 Koyna earthquake records. The results obtained are shown in the time history graphs of the horizontal and vertical displacements of the nodal point located at the crest of the dam. These are the stresses, the strains and the cumulated damage at the integration points respectively.

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.

Data-Based Models for the Prediction of Dam Behaviour: A Review and Some Methodological Considerations

Predictive models are an important element in dam safety analysis. They provide an estimate of the dam response faced with a given load combination, which can be compared with the actual measurements to draw conclusions about dam safety. In addition to numerical finite element models, statistical models based on monitoring data have been used for decades for this purpose. In particular, the hydrostatic-season-time method is fully implemented in engineering practice, although some limitations have been pointed out. In other fields of science, powerful tools such as neural networks and support vector machines have been developed, which make use of observed data for interpreting complex systems . This paper contains a review of statistical and machine-learning data-based predictive models, which have been applied to dam safety analysis . Some aspects to take into account when developing analysis of this kind, such as the selection of the input variables, its division into training and validation sets, and the error analysis, are discussed. Most of the papers reviewed deal with one specific output variable of a given dam typology and the majority also lack enough validation data. As a consequence, although results are promising, there is a need for further validation and assessment of generalisation capability. Future research should also focus on the development of criteria for data pre-processing and model application.

The Progressive Response of Sahelian Dams to Sediment Intrusion: Case of Kano State between 1976 and 2009

Reservoirs are built to store water during abundance for possible reuse during scarcity; sediment incursion is the leading phenomenon that limit reservoirs to sustain this function. Therefore, modelling the rate at which reservoir accumulates sediments is critical in understanding the nature of the problem, the time frame within which it is expected to occur, and the best mitigation strategy that will maintain the reservoir service. This study investigated the sediment influx in three typical Sahelian reservoirs in Kano state using the bathymetric method. The reservoir capacities were found to be declining at different rates but with grave consequences on the future, and economy of the state. In prolific terms, the state is losing 490 million litres of water storage each year. Presently, Magaga lost 39% of its capacity; Thomas has lost 13%; while Kafin-chiri has lost 5%. For sustainability, this trend needs to be addressed. The short and long-term best management strategies to curtail this trend have been outlined in this study.

Seismic assessment of a monolithic RCC gravity dam including three dimensional dam–foundation–reservoir interaction

In this study, the seismic response of a tall roller compacted concrete gravity dam located in a highly seismic zone is investigated. The response of this monolithic RCC gravity dam is examined by conducting analyses including three dimensional dam–reservoir–foundation interaction. The effect of the foundation/structure moduli ratio, material damping, and bottom absorption and reservoir compressibility on the performance of the dam were investigated. Selection of an optimal downstream slope was discussed based on a simplified stress based assessment method. RCC systems present a different paradigm compared to conventional gravity dams with their monolithic construction and/or wide joint spacing: The importance and necessity of a full 3D analyses for such systems were underlined by comparing the results with two dimensional analyses. For such gravity dams built in relatively narrow canyons, three dimensional analyses should be conducted for seismic safety assessment.

Legendre spectral element method for seismic analysis of dam-reservoir interaction

It is well-known that dam-reservoir interaction has significant effects on the response of dams to the earthquakes. This phenomenon should be considered more exactly in the seismic design of dams with a rational and reliable dynamic analysis method. In this research, seismic analysis of the dam-reservoir is studied as a wave propagation problem by using Legendre Spectral element method (SEM). The special FEM and SEM codes are developed to carry out the seismic analysis of the damreservoir interaction system. The results of both SEM and FEM models are compared considering the accuracy and the time consumption of the analysis. Attractive spectral convergence of SEM is obtained either by increasing the degree of the polynomials in the reservoir or by the number of elements of dam. It is shown that all boundary conditions of the reservoir domain in the SEM are evaluated by the exact diagonal matrices. The SEM leads to the diagonal mass matrix for both dam and reservoir domains. The stiffness matrices obtained from the SEM are more sparse than the corresponding stiffness matrices in the FEM consequently the SEM needs a significant less time consumption of the analysis.

Displacement response of a concrete arch dam to seasonal temperature fluctuations and reservoir level rise during the first filling period: evidence from geodetic data

The present study evaluates the dynamic behaviour of the Ermenek Dam, the second highest dam in Turkey, based on conventional geodetic measurements and Finite Element Model (FEM) analyses during its first filling period. In total, eight periods of measured deformation are considered from the end of construction until the reservoir reached its full capacity. The displacement response of the dam to the reservoir level and to seasonal temperature variations is examined in detail. Time series of apparent total displacements at the middle of the crest of the dam exhibits periodicity and linear trends. Correlation analysis revealed that periodic and linear displacement responses of the dam are related to variations of seasonal temperature and linearly increased reservoir level, respectively, indicating a relation between temperature, water load and dam deformation. It is also concluded that measured deformations based on geodetic data show good agreement with the predicted deformation obtained by the FEM analysis.

Uniform Gradient Element Formulation with Hourglass Control Scheme for Solving Fully Coupled Finite-Element Equations for Saturated Soils

AbstractA uniform gradient (UG) element formulation for a four-node quadrilateral element is derived and implemented for solving the fully coupled governing equations for the dynamics of a saturated porous medium. An hourglass control scheme is also derived for eliminating the hourglass modes that arise when using the UG element formulation. The effectiveness of the new formulations is investigated by simulating the quasi-static and dynamics response of a footing and the dynamic response of an earth dam. The results show that the level of excitation of hourglass modes is problem-dependent and mesh-dependent. The proposed method for controlling the hourglass modes is shown to be effective with minimal effect on the computed response.

Thermal and Structural Response of RCC Dams During Their Service Life

Roller compacted concrete (RCC) dams are vulnerable to cracking as a result of high tensile stresses due to material properties, thermal and mechanical loads. Making reliable prediction of stress fields, and thereby temperature cracking risk form an important part of the material modelling. The present study figures out the changes in thermal stresses and crack fields of the Kinta RCC dam at the end of the construction and its service life. Water temperature at various levels of the reservoir and its fluctuations were considered in the present study. The developed finite element program has been used in the analysis. Based on the obtained results, it is revealed that there is an increase in the thermal stresses after some years of dam completion. However, their location and distribution are mostly similar.

XFEM based seismic potential failure mode analysis of concrete gravity dam–water–foundation systems through incremental dynamic analysis

As revealed by the structural damage of concrete dams (e.g. Hsinfengkiang, Koyna, Sefid-Rud) arising in recent earthquakes, cracking damage would probably occur inside concrete dams when subjected to strong ground motions. This phenomenon is caused by the low tensile resistance of concrete. Research on the cracking damage process and failure modes of concrete gravity dams subjected to strong earthquakes is crucial to a reasonable assessment of the seismic safety of dams. In this paper, the extended finite element method (XFEM) is presented to describe the crack propagation within concrete gravity dams subjected to earthquake loads. Moreover, the interaction between the impounded water and the dam–foundation system is explicitly taken into account by modeling the reservoir water with two-dimensional fluid finite elements in the Lagrangian formulation. In order to validate the proposed algorithm, seismic crack analysis is performed to investigate the failure modes of the Koyna dam–reservoir–foundation system under the 1967 Koyna earthquake. It shows that the cracking damage profile obtained from the proposed XFEM framework agrees well with that reported in the literature. With the validated algorithm, we further apply it to study the potential failure modes of the Guandi concrete gravity dam. Seismic cracking response of concrete gravity dams considering the effects of the dam–reservoir–foundation interaction is obtained through the incremental dynamic analysis (IDA) based XFEM. 40 as-recorded accelerograms with each scaled to 8 increasing intensity levels are selected in this study. Based on the 320 numerical simulation results, typical failure processes and five potential failure modes of concrete gravity dams under the selected database of strong earthquake ground motions are presented.

Seismic response of concrete gravity dam reinforced with FRP sheets on dam surface

This paper aims at exploring the effects of anti-seismic reinforcement with the fiber-reinforced polymer (FRP) material bonded to the dam surface in dam engineering. Time-history analysis was performed to simulate the seismic failure process of a gravity dam that was assumed to be reinforced at the locations of slope discontinuity at the downstream surface, part of the upstream face, and the dam heel. A damage model considering the influence of concrete heterogeneity was used to model the nonlinearity of concrete. A bond-slip model was applied to the interface between FRP and concrete, and the reinforcement mechanism was analyzed through the bond stress and the stress in FRP. The results of the crack pattern, displacement, and acceleration of the reinforced dam were compared with those of the original one. It is shown that FRP, as a reinforcement material, postpones the occurrence of cracks and slows the crack propagation, and that cracks emanating from the upstream surface and downstream surface are not connected, meaning that the reinforced dam can retain water-impounding function when subjected to the earthquake. Anti-seismic reinforcement with FRP is therefore beneficial to improving the seismic resistant capability of concrete dams.

Application of thermodynamics-based rate-dependent constitutive models of concrete in the seismic analysis of concrete dams

This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dependent constitutive models were developed with consideration of the influence of the strain rate. They can describe the dynamic behavior of concrete and be applied to nonlinear seismic analysis of concrete dams taking into account the rate sensitivity of concrete. With the two models, a nonlinear analysis of the seismic response of the Koyna Gravity Dam and the Dagangshan Arch Dam was conducted. The results were compared with those of a linear elastic model and two rate-independent thermodynamics-based constitutive models, and the influences of constitutive models and strain rate on the seismic response of concrete dams were discussed. It can be concluded from the analysis that, during seismic response, the tensile stress is the control stress in the design and seismic safety evaluation of concrete dams. In different models, the plastic strain and plastic strain rate of concrete dams show a similar distribution. When the influence of the strain rate is considered, the maximum plastic strain and plastic strain rate decrease.

English

Dam structures that span navigable waterways are inherently at a risk for seismic vibrations and as such they must be designed to resist these vibrations. However, these earthquake vibrations are fundamentally dynamic in nature and a static analysis procedure may not be adequate in designing hydraulic structures like Dam. Therefore, dynamic analysis methods forestimating the response of a concrete gravity dam plays an extraordinary role.This paper presents the dynamic non-linear time history analysis of a concrete gravity dam by using CSI SAP 2000. A concrete gravity dam model is prepared in SAP 2000 to perform the time history analysis. Concrete gravity dam is a massive structure which retains a very large amount of water on its upstream side and it is very crucial for a dam to survive against vibrations of earthquake. So it is a matter of study to check the behaviour of a dam during and after the application of the loading. Time history is basically a method of seismic analysis for the simulation of an earthquake motion. It is an ultimate tool to study the dynamic response of a structure. This paper gives a step by step procedure to perform the non-linear time history analysis by using time-acceleration data as input function and then performance of the gravity dam is evaluated with various mode shapes and time-acceleration results

Influence of construction interfaces on dynamic characteristics of roller compacted concrete dams

To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams (RCCDs), mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary (VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam. However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes, combination quality of the RCC layers should be significantly ensured.

Numerical simulation of earthquake excited dam-reservoirs with irregular geometries using an immersed boundary method

In this work, a ghost-cell immersed boundary method is proposed for the hydrodynamic response of earthquake excited dam-reservoirs. The numerical method employs a second order accurate two-step projection algorithm including compressibility effects in pressure field due to earthquake. The effects of reservoir bottom absorption are treated by introducing damping terms into the momentum equations. Hydrodynamic response of earthquake excited dam with a sloping face is simulated to demonstrate the accuracy of the present numerical method. Numerical results compared with previous numerical and analytical solutions show that the present immersed boundary method can accurately compute the hydrodynamic forces on inclined and curved dam faces including the effects of water compressibility and reservoir bottom absorption for the possibility of resonance. The proposed numerical method was shown to have significant advantages in computational time and memory usage for the hydrodynamic simulation of large dam-reservoirs with arbitrary geometries. Hydrodynamic forces on a double curvature arch dam subjected to real earthquake induced ground motion are also simulated to demonstrate the capability of the method.

Shear strain related non-linear stochastic dynamic analysis of rock-fill dams

The effect of the non-linear material behavior of a rock-fill dam subjected to random loads is investigated by the equivalent linear method that considers the non-linear variation of soil shear moduli and damping ratios as a function of shear strain. The Keban dam constructed in Elazig, Turkey is chosen as a numerical example. The interaction of the rock-fill dam with the reservoir is neglected, but not the foundation rock. The properties of the dam materials were taken from the dam project and assumed to be isotropic in the analysis. A stationary and ergodicity assumption are made for stochastic dynamic analysis. The E-W component of the Erzincan earthquake recorded on March 13, 1992, Erzincan, Turkey is chosen as a ground motion since it occurred nearby the dam site. The component considered is applied to the dam in the horizontal direction. The non-linear stochastic responses of the Keban dam are compared to its linear stochastic and deterministic response.

The dynamic characteristics of the damage probability of a gravity dam

A first-order approximate probabilistic analytical method to investigate the damage of concrete gravity dams, based on the pseudo-excitation method (PEM), is proposed. This method constructs stochastic stiffness under stochastic stimulus using second-order perturbation. It involves the following steps. First, the PEM and the Mazar damage models are utilised to analyse the way to calculate the expected value and variance of the damage of a dam excited by a random earthquake load and a static load in the initial condition. Next, the evolutive process of the probability distribution of the tensile damage of a dam is analysed in the damage condition based on perturbation theory. Finally, a numerical example is given to verify and analyse the convergence and stability of this model. The calculated results show that the expected values of the probability distribution of the stochastic structure under a stochastic stimulus are steady under a second-order perturbation. The results indicate that, compared to PEM, the salient features of the method proposed provide a probabilistic analysis for the nonlinear response of a concrete gravity dam.