Response Of Concrete Gravity Dams Research Articles

Experimental investigation on dynamic response of concrete gravity dam under shock wave and bubble pulsation

The main components of underwater explosion loads are the shock wave and bubble pulsation. However, there are few studies on the combined effects of shock wave and bubble pulsation on the dynamic response of concrete gravity dams (CGDs). In this study, a 1:100 scaled-down model of a CGD was designed, and ten tests were conducted. The load characteristics of the shock wave and bubble pulsation, and the acceleration and velocity time histories of the CGD caused by underwater explosions were recorded. The distribution laws of peak acceleration and velocity in the CGD due to shock wave and bubble pulsation were analyzed. Additionally, the influence of standoff distance, explosive weight, and detonation depth on the dynamic response of the CGD was systematically discussed. The study also explored the mitigation effects of bubble curtain on the CGD’s response to underwater explosion. Findings reveal that the peak pressure generated by bubble pulsation represents approximately 10.41–15.03 % of that by the shock wave, and the impulse from the bubble pulsation is nearly equivalent to that of shock wave. Contact or near-field explosion shock wave induces a strong local response in the dam, with maximum acceleration occurring directly opposite the detonation. In contrast, the shock wave causes the overall response of the dam during far-field explosion, with maximum acceleration at the junction between the dam head and body. Bubble pulsation predominantly affects the dam’s overall response. The average ratio of peak acceleration induced by bubble pulsation to that induced by shock wave is 4.69–17.11 %, and the average ratio of peak velocity ranges from 13.08 to 36.27 %. The response of the CGD caused by the explosion suspended in water is notably greater than that caused by a bottom explosion. Bubble curtains can reduce peak acceleration due to shock wave by 93.8–97.26 %, and almost completely shield against bubble pulsation.

An improved numerical manifold method for crack propagation of concrete gravity dams under seismic loads

In the safety analysis of concrete gravity dams it is necessary to consider the external load and internal load of the dam body within a reasonable range, in which the influence of strong earthquake can not be ignored. The modified Mohr-Coulomb strength criterion is introduced into the numerical manifold method (NMM), meanwhile, the calculation mechanism of dynamic load is introduced, and the calculation part considering the Hydro-Mechanical coupling principle is added to the NMM. The effectiveness and accuracy of the improved NMM are verified by the displacement of the central point of the circular arch under dynamic load containing an analytical solution. Based on the improved NMM, the crack propagation of concrete gravity dam is predicted and analyzed. The crack propagation of Koyna concrete gravity dam under seismic conditions is analyzed, and the results are compared with XFEM and experimental results. The influence of adding Hydro-Mechanical coupling module on crack propagation and seismic response of concrete gravity dam is discussed and it is proved that the improved NMM can accurately predict the crack propagation of concrete gravity dams under dynamic load and the advantage of NMM in dealing with continuous-discontinuous problems.

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.

Seismic Response of Concrete Gravity Dams Considering Hydrodynamic Effects

Abstract This paper presents a dynamic analytical study to assess the effect of dam height as well as fluid compressibility on the gravity response of a concrete dam, considering the effects of hydrodynamic interaction. The analysis is carried out using the ADINA Finite Element software for empty and full reservoir conditions by considering several models. In the first model, the mass of fluid is taken into account by the concept of Westergaard added mass, in the second model; an acoustic fluid element is used to simulate the effect of water on the reservoir. The height of the dam is one of the main factors affecting the seismic response of gravity dams; because the change in height provides different responses depending on the natural periods, displacements and stresses obtained from static and dynamic analyses. The numerical results showed that the effect of interaction between the dam and the reservoir plays an important role in the precise estimation of the dynamic response of gravity dams. The hydrodynamic water pressure from the reservoir increases stresses in the dam body and horizontal displacements at the crest. The seismic response obtained by the incompressible water model (Westergaard) is compared with that of the compressible water model.

Effects of bedrocks on the dynamic response of concrete gravity dams subjected to underwater explosions

Reservoirs and dams often play critical roles in economics and politics. They are frequently considered as the primary targets during wartime or in terrorism attacks. In this study, the behaviors of concrete gravity dams subjected to underwater explosions are numerically investigated. Three-dimensional finite element models are developed according to the design drawings of a concrete gravity dam built in China. The effects of an underwater explosion, including the shock wave and bubble oscillations, are modeled based on the pressure time-histories. The water is modeled using the acoustic method, for which the propagation of the pressure histogram is well reproduced as an acoustic wave. The concrete dam is modeled using solid elements. The damage and failure of the concrete are reproduced by the damage-plasticity model with strain rate dependence. To investigate the influence of bedrocks, three types of numerical models are developed, which are validated by comparing the predictions with the centrifuge tests on a scale concrete gravity dam. Systematic numerical results indicate that the developed numerical model is capable of capturing the features of concrete gravity dams subjected to underwater explosions. Furthermore, the bedrocks play an important role in the dynamic responses of the dams. Thus, the bedrocks should be considered for the accurate modeling of the underwater explosion systems of concrete gravity dams.

Numerical investigation on crack propagation process of concrete gravity dams under static and dynamic loads with in-crack reservoir pressure

Proper consideration of external and internal loads acting on concrete gravity dams is of vital importance in concrete dam engineering, since it plays a significant role in the stability assessment of cracked dams under static/dynamic conditions. Several factors which may affect the mechanical response of concrete gravity dams, however, have not been comprehensively accounted for in most previous crack propagation analyses. To adequately evaluate the crack propagation response of concrete gravity dams, a finite element-based numerical analysis is carried out to estimate the crack propagation in a concrete gravity dam under static and seismic loads. In this work, the effects of the water pressure inside the stress-free crack and the fracture process zone (FPZ), the cohesive force within the FPZ, the hydrostatic water pressure, and the dam-reservoir interaction are incorporated via a series of reasonable assumptions. On the basis of a stress intensity factor (SIF)-based mixed mode I-II crack propagation criterion, a generic numerical algorithm is proposed to estimate the crack growth process of concrete gravity dams under static and seismic loads. Application of this algorithm to two case studies of concrete gravity dams under different loading conditions demonstrates the validity of the algorithm in estimating the static and seismic crack propagation response. It is found that when a concrete gravity dam is subjected to static loading, crack initiation does not occur before the reservoir water level exceeds the dam height, and that the water pressure inside stress-free cracks has a slight negative effect on the structural resistance against cracking while the water pressure within the FPZ has no effect on the dam capacity. The seismic crack growth analysis indicates that the water pressure inside cracks causes the crack to propagate at a larger downward angle towards the downstream face with a larger crack growth length.

Uncertainty quantification of the effect of concrete heterogeneity on nonlinear seismic response of gravity dams including record-to-record variability

Although the effects of the concrete heterogeneity on the seismic response of concrete gravity dams have been explored based on random finite element method, the results of different studies vary greatly and there are few quantitative studies on the effects. In addition, the correlation between concrete modulus and strength is usually ignored, which is a departure from the reality. In this study, the effects of the concrete heterogeneity on the nonlinear seismic response of concrete gravity dams under different input ground motions are systematically studied based on random field theory. The dispersion and uncertainty of the seismic responses and the damage pattern are quantified. In addition, the effects of the correlation between concrete modulus and strength are also investigated and quantified based on the cross-correlated random fields simulation method. It is found that the effects of the concrete heterogeneity on the nonlinear dynamic response of concrete dams are strongly dependent on the input seismic motions, which provides an explanation for the conflicts in the previous studies. The results also show that the correlation between concrete modulus and strength has important effects on the dispersion of the seismic response and damage pattern of concrete gravity dams. Under certain ground motions, ignoring the correlation may underestimate the failure probability of the dams.

Seismic response of concrete gravity dams under near field and far field ground motions

Near field ground motions trigger higher damage to the structures due to the presence of distinct velocity pulses which are absent in far field ground motions. The present study deals with the time history analysis of dam-reservoir-foundation coupled system using finite element technique under near field and far field ground motions. Koyna dam, which is a concrete gravity dam, is taken as case study for the present investigation. Six ground motions, recorded near to the ruptured fault are selected as near field ground motions. Whereas, six other ground motions, recorded at other stations located far away from fault plane, of the same earthquake events, are considered as far field ground motions. Along with the comparative study of seismic response of Koyna dam, qualitative assessment of the seismic performance of the dam are also evaluated. The results obtained from the analysis demonstrate the different impact of near field and far field ground motions on the seismic response of concrete gravity dams. Further, the study also ascertain the importance of selection of far field ground motions on seismic safety of concrete gravity dams.

Design, Manufacturing and Testing of Small Shaking Table

The seismic performance and the dynamic response of concrete gravity dams can be verified by several techniques. Both geotechnical centrifuge apparatus (under N-g values) and shaking table (under 1-g) are the commonly used techniques in the world. This paper deals with designing, manufacturing, and testing of small shaking table to investigate different geotechnical and engineering problems. The main body of the designed shaking table consists of steel frame (local iron) manufactured as a hollow box with steel plate, 6mm in thickness and one-direction movable platform (as a basket carrying the container of the model). Inside this main box, all the mechanical parts that work as one system to generate the motion of the seismic wave with an acceleration that needed to the test. The facilities of this shaking table, the movable base has a dimension of 0.8m x1.2m and the platform mass approximately 2 kN, the maximum allowable model weight of 10kN, the range of frequency from 0 to 20 Hz, the maximum acceleration amplitude of 1.2g and maximum displacement of 14mm. It can simulate only the single frequency motion (i.e. sinusoidal wave). The measured accelerations at different soil model level for the tested shaker under 0.6g sinusoidal waveform gave a reasonable prediction for the dynamic response and the amplification characteristics.

Seismic analysis of reservoir-gravity dam-massed layered foundation system due to vertically propagating earthquake

Seismic analysis of complex structures such as concrete dams has been the subject of numerous studies. One of the challenges in seismic analysis of such systems is proper modelling of massed foundation. Since concrete dams’ foundations are usually layered, this makes the homogenous half-space assumption relatively unrealistic. In this paper, the effects of massed layered foundation on seismic response of concrete gravity dams in dam-reservoir-foundation systems are investigated. Seismic finite element analysis of the system carried out using domain reduction method. This approach is compared with another available method named, free-field column. First set of analysis considers the effect of modular ratio between layers on seismic response of the gravity dam. Second set of analyses investigate the effects of layers’ geometry, location and orientation on obtained responses. Results highlight the considerable effects of massed layer foundation assumption against its homogenous counterpart. Besides, results show that layer properties dictate how severely they can affect the dynamic responses of the dam.

Seismic Improvement of Gravity Dams Using Isolation Layer in Contact Area of Dam–Reservoir in Smeared Crack Approach

This study has been conducted to evaluate the effect of the isolation layer on the seismic improvement of concrete gravity dams considering dam–reservoir interaction. Koyna dam in India, due to both horizontal and vertical components of Koyna earthquake, is modeled as a case study to show the effect of the upstream isolation layer on the seismic response of concrete gravity dams, and also the interaction effect is considered in models. The water is taken as a compressible, inviscid fluid and the foundation as rigid. Gravity dams are considered as 2D structures due to long dimension in cross-stream direction and plane strain assumptions. ANSYS software was used for analysis so that the fixed smeared crack model is used to consider the nonlinear behavior of mass concrete. A flexible layer which is attached to the upstream face of the dam under different thickness and material properties is considered. The response of unisolated and isolated dams is compared under various conditions. Finally, the effect of unisolated and isolated layers in the reduction of the seismic response of the concrete is evaluated under various thicknesses comparatively. Considering obtained results revealed that the layer can have the reducing effect on responses and crack propagation process of dam model because of damping the induced hydrodynamic pressure due to the earthquake.

Effects of close proximity underwater explosion on the nonlinear dynamic response of concrete gravity dams with orifices

Abstract In order to meet the demand for power, irrigation, flood control, drinking water, etc., many orifices are usually designed on the dam body. This paper is aimed to evaluate the close proximity underwater explosion effects on the nonlinear dynamic response of concrete gravity dams with orifices. The accuracy and reliability of the coupled model is calibrated against a previous experimental test. The effects of the existing orifice on the damage processes of concrete gravity dams to close proximity underwater explosion are investigated. Damage characteristics of gravity dams with the orifice under close-in, inlet and internal underwater explosions are compared. The influence of the reinforcement and the water inside the existing orifice on the nonlinear dynamic response of concrete gravity dams is also discussed. The results show that the dam with orifice suffers more serious damage subjected to close proximity underwater explosion than the dam without orifice. Closing the gate of the orifice will significantly reduce the damage level of the dam.

Assessment of Foundation Mass and Earthquake Input Mechanism Effect on Dam–Reservoir–Foundation System Response

Concrete dams are one of the most important infrastructures in every country and the seismic safety assessment of them is a major task in dam engineering field. Dam–foundation–reservoir system analysis is a complex interaction problem because this system consists of three domains with different behaviors. For accurate analysis of this system, some important factors should be considered such as foundation mass and earthquake input mechanism. In this paper, the effect of foundation mass and earthquake input mechanism on seismic response of concrete gravity dam is investigated. For this purpose, two different methods are introduced for modeling of massed semi-infinite foundation in finite element method, namely free-field boundary condition and domain reduction method (DRM). To verify the feasibility of proposed methods for seismic analysis of dam–foundation–reservoir system, the displacement and stress outputs using proposed methods are compared with EAGD-84 results. The obtained results indicate that both methods are accurate enough for finite element modeling of massed foundation. Finally, Koyna concrete gravity dam is analyzed for rigid, massless and massed foundation cases using DRM and it is concluded that the foundation has significant effect on dam response and the common massless foundation approach overestimates the dam response.

Nonlinear dynamic response of concrete gravity dams considering the deconvolution process

In order to model any physical system, including concrete dams, one needs to apply simplifications to the real system to make the modeling feasible. To study the dynamic response of concrete dams, relevant assumptions are made regarding foundation modeling, input motion mechanism, dam-reservoir interaction, and material behavior. Some of these simplifications may lead to more conservative and uneconomical outcomes. In this paper, nonlinear time-domain dynamic analyses are conducted to evaluate the effect of the input motion mechanism on the concrete gravity dam response. An ideal model of a dam-reservoir-foundation system, considering the inertia of the foundation, appropriate boundary conditions and precise deconvolved base motions, is selected as the reference model. The process of deconvolution of seismic waves through the frequency- and time-domain approaches is discussed, and suggestions for the selection of an appropriate damping model for the rock foundation are presented. The results are compared to those of the standard model of a massless foundation system as recommended by the US Army Corps of Engineers. The numerical results indicate that, generally, the nonlinear response of the two dam models follow similar patterns, but with a larger amplitude for the massless system. It is noted that the consequence of neglecting the dynamic effect of the foundation can be significant. Additionally, the results demonstrate that the degree of overestimation varies dramatically for the various seismic excitations. The average overestimation of the massless system for the crest displacement, crest acceleration, and the contact opening and sliding are 57%, 45%, 152%, and 90%, respectively. It is further shown that the use of the deconvolved input excitation at the base of the finite foundation derived from the frequency-domain approach can yield discrepancies between the target and convolved surface ground motions, which can also have a considerable effect on the dam response.

Transient Response of Concrete Gravity Dam Considering Dam-Reservoir-Foundation Interaction

This article deals with the finite element analysis of dam with and without fluid-structure, soil-structure and soil-structure-fluid interaction. A two-dimensional direct coupling methodology is proposed to obtain the response of dam-reservoir-foundation system considering fluid-structure and soil-structure interaction simultaneously. The displacement based finite element technique is used to formulate the dam and foundation. The reservoir is modeled by pressure based finite element to reduce the degree of freedoms and there by the computational cost. The responses of dam, reservoir, and foundation with and without fluid-structure, soil-structure and soil-structure-fluid interaction are compared to study the influence of reservoir and soil foundation on the behavior of these respective sub systems. The fundamental frequency of individual sub system decreases with the consideration of coupling effect among these sub systems. On the comparison of the responses of dam, it is observed that the displacement and principal stresses are increased if the effect of reservoir and foundation are considered and the worst responses were observed when both the fluid-structure and soil-structure interaction effects are considered simultaneously. The magnitude and distribution of stresses within the foundation change with the consideration of soil-structure-fluid interaction. Similar to wstresses in the foundation, the hydrodynamic pressure within the reservoir also gets magnified due to interaction effects. The velocity distribution within the reservoir becomes distorted when the fluid-structure and soil-structure-fluid interaction are considered.

Effects of Base and Lift Joints on the Dynamic Response of Concrete Gravity Dams to Pulse-Like Excitations

Near-fault earthquakes with forward-directivity effects produce pulse-like excitations. This article studies the dynamic response of monolithic and cracked sections of gravity dam under symmetric and anti-symmetric pulse-like excitations. The pulses are generated by the modified Gabor Wavelet transform. Two main characteristics of the pulses are pulse period and amplitude. The prescribed cracks are located along the base and two distinct lift joints through the dam body. The dam is modeled along with its reservoir using finite element method. The effects of base and lift joints, pulses shape, period, and amplitude, and reservoir height on the dam dynamic response are studied.

A general definition of integrated strong motion duration and its effect on seismic demands of concrete gravity dams

Various duration definitions have been proposed to describe the effective strong motion duration based on a single component of ground motions. However, multi-component accelerograms are usually selected as the seismic excitations to evaluate the seismic performance of important infrastructures. Duration definitions able to consider the duration contributions from all components of ground motions are still lacking. In this paper, a general integrated duration definition for multi-component seismic excitations is proposed based on the existing concept of strong motion duration. According to the proposed definition, integrated bracketed duration, integrated uniform duration, and integrated significant duration are presented to measure durations for multi-component ground motions. Twenty as-recorded accelerograms with a broad range of durations are considered to investigate the correlation between integrated and single component durations. A series of nonlinear dynamic analyses are performed to quantify the influence of different integrated ground motion durations on several seismic demands (i.e. peak displacement, damage dissipation energy, and local damage index) of concrete gravity dam-reservoir-foundation systems. In addition, the results also reveal the effects of vertical seismic excitations on the seismic response of concrete gravity dams and emphasize the necessity to consider vertical motions in seismic performance assessment of such infrastructures.

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.

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.