Response Of Dams Research Articles

Support vector machine based reliability analysis of concrete dams

This paper presents possible combination of structural responses of concrete dams with machine learning techniques. Support vector machine (SVM) method is adopted and two broad applications are presented: one for a simplified flood reliability assessment of gravity dams and the other for detailed nonlinear seismic finite element method (FEM) based analysis. Up to seventeen random variables are considered in the former example and the results of SVM contrasted with classical reliability analyses techniques (i.e., first- and second-order reliability methods, Monte Carlo simulation, Latin Hypercube and importance sampling techniques). For the latter example, a FEM-SVM based hybrid methodology is proposed for reduction of number of nonlinear analyses. A discussion is provided on the relation between the optimal earthquake intensity measures, the damage states and the accuracy of prediction. It is found that the family of SVM (i.e. standard, least squares, multi-class and regression) is an useful and effective tool for classification, response prediction and reliability analysis of the concrete dams with reasonable accuracy.

Assessing seismic response of a 2D roller-compacted concrete dam under variable reservoir lengths

Finite element method (FEM) is effectively used for evaluating roller-compacted concrete (RCC) dams, especially in high seismicity zones. The aim of this study is to investigate the effect of various reservoir lengths on the seismic response of a selected RCC dam under strong ground motion effects. Six different reservoir lengths, the lengths varies from h/2 to 10h (h, the height of dam), are used within finite element models. The hydrodynamic pressure of the reservoir water is modelled with the 2D fluid finite elements based on the Lagrangian approach. The horizontal and vertical components of the 1989 Mw 6.9 Loma Prieta earthquake are utilized in numerical analyses. The non-linear time-history analyses of those six models are investigated by using Drucker-Prager material model. According to the numerical analysis, it is obvious that the seismic behavior of the RCC dams is considerably dependent on the reservoir length. By increasing the length, we have obtained higher displacement values, which exist until the reservoir length reaches the 3h; at increased lengths, the values remain stable. This result proposes that 3h reservoir length is adequate to assess the seismic response of RCC dams. The principal tensile stresses are relatively lower in non-linear analysis compared to linear analyses. However, the principal compression stresses are close to each other in linear and non-linear analyses. The results imply that the non-linear response is influential on the total seismic response of a dam, which cannot be neglected in numerical analysis.

Simulating Structural Responses of a Generic AAR-Affected Arch Dam Considering Seismic Loading

Alkali-Aggregate Reaction (AAR) is a deteriorative phenomenon for concrete that impresses the performance of structures. This study focuses on the seismic and post-earthquake behavior of an AAR-affected dam. A computer program is developed for simulating the structural behavior of AAR-affected dams including the seismic and post-earthquake durations. A thin high double-curvature arch dam is selected as case study and is modeled in a series of analyses within the assumed 30-year operating period. Each analysis includes an earthquake excitation in a different specified time. In each analysis, the seismic record is applied to the dam at different status of AAR progression considering the proposed ARI index. The results show that AAR affects seismic performance of the dam, i.e. with the AAR progression; the dynamic responses are significantly changed. On the other side, the effect of earthquake occurrence time on the dam post-earthquake behavior is not noticeable. This may be explained by the linear elastic behavior assigned to the body material in the provided FE model.

Deterministic 3D seismic damage analysis of Guandi concrete gravity dam: A case study

This paper presents an original investigation of the seismic cracking behavior of Guandi concrete gravity dam, which is located in the highly seismic zone of China. For this purpose, three dimensional nonlinear finite element analyses are carried out for the Guandi dam-reservoir-foundation system, with the effects of contraction joints and cross-stream seismic excitation considered. The Concrete Damaged Plasticity (CDP) model is utilized to model concrete cracking under seismic loading. The opening/closing and sliding behaviors of contraction joints during earthquake events are modeled using two different surface-to-surface contact models (soft and hard pressure-clearance relationships), which aims to quantify the effect of grouting materials between the joint surfaces. The dynamic interaction between the impounded water and the dam-foundation system is explicitly taken into account by modeling the reservoir water with three dimensional fluid finite elements in the Lagrangian formulation. Several case studies are examined and the results reveal the significant influence of contraction joints and cross-stream ground motions on the dynamic response and damage-cracking risk of the Guandi concrete gravity dam.

Elastic foundation effects on arch dams

Earthquake response of an arch dam should be calculated under ground motion effects. This study presents three-dimensional linear earthquake response of an arch dam. Thereby, we considered different ground motion effects and also foundation conditions in the finite element analyses. For this purpose, the Type 3 double curvature arch dam was selected for application. All numerical analyses are carried out by SAP2000 program for empty reservoir cases. In the scope of this study, linear modal time-history analyses are performed using three dimensional finite element model of the arch dam and arch dam-foundation interaction systems. According to numerical analyses, maximum horizontal displacements and maximum normal stresses are presented by dam height in the largest section. These results are evaluated for rigid and various elastic foundation conditions. Furthermore, near-fault and far-field ground motion effects on the selected arch dam are taken into account by different accelerograms obtained from the Loma Prieta earthquake at various distances.

Seismic performance of arch dams on non-homogeneous and discontinuous foundations (a case study: Karun 4 Dam)

The present study set out to investigate the nonlinear seismic response of the dam–reservoir–rock foundation system, taking into consideration the effects of change in the material properties of discontinuous foundation. To this end, it is important to provide the proper modeling of truncated boundary conditions at the far-end of rock foundation and reservoir fluid domain and to correctly apply the in situ stresses for rock foundation. The nonlinear seismic response of an arch dam mainly depends on the opening and sliding of the dam body’s contraction joints and foundation discontinuities, failure of the jointed rock and concrete materials, etc. In this paper, a time domain dynamic analysis of the 3D dam–reservoir–foundation interaction problem was performed by developing a nonlinear Finite Element program. The results of the analysis of Karun-4 Dam revealed the essential role of modeling discontinuities and boundary conditions of rock foundation under seismic excitation.

Initial service life data towards structural health monitoring of a concrete arch dam

This paper presents a statistical framework to monitor the performance of an operational concrete arch dam using sensory data acquired during its initial service life. One of the major challenges in dealing with a newly constructed dam is to predict its long-term behaviour by forecasting appropriate thresholds using limited data exhibiting nonstationarity. In this paper, a hybrid model is implemented to predict dam responses using environmental—hydrostatic, seasonal, and temperature—as well as age-related variables. The data from multiple sensors are first analyzed using principal component analysis to incorporate overall dam behaviour into a prediction model. The proposed prediction framework is then employed to estimate the residuals and control limits required to calculate thresholds under nonstationary operating conditions during its initial service life. The dam performance is then monitored using statistical control charts and anomalies are detected by comparing the test statistics, square prediction error, and Hotelling T-squared, calculated from the residuals with the preset control limits. The issue of limited data is addressed by updating the model parameters and thresholds periodically, which is aimed at minimizing the false alarm rate. The proposed method is demonstrated using a 130-m-high double-arch concrete dam located in Bulgaria.

상시미동의 수평/수직 스펙트럼비를 이용한 예당댐체의 지진응답특성 분석

상시미동의 수평/수직 스펙트럼비를 이용한 예당댐체의 지진응답특성 분석

Seismic plastic–damage analysis of mass concrete blocks in arch dams including contraction and peripheral joints

Seismic nonlinear analysis of concrete arch dams is a topic having been extensively studied in the last two decades. Due to the existence of different joints within the body of arch dams, the discrete crack (DC) approach utilizing interface elements for the joints is the most realistic method. In fact, it could be the first step to assess the seismic safety of an arch dam. Furthermore, since the mass concrete blocks may crack due to severe ground excitations, a plastic–damage (PD) model well capturing stiffness degradation and permanent deformation due to tensile cracking and compressive crushing might be needed. In this study, a special finite element program called SNACS is developed based on the combined discrete crack and plastic–damage (DC–PD) technique. The dam–reservoir interaction as an important factor affecting the seismic response of arch dams is also treated by the Lagrangian–Eulerian formulation. The joints modeling strategy adopted herein is addressed first and then, a brief review of the plastic–damage model proposed by Lee and Fenves and extended herein to 3-D space is presented. Afterwards, the nonlinear seismic analysis of a typical thin arch dam is performed based on the combined approach and the response is compared with the results of each method. It is emphasized that employing the combined DC and PD models gives more reliable and consistent response in comparison with using DC or PD approaches applied alone. Therefore, the DC–PD technique could be considered as a major step toward a more accurate seismic safety evaluation of concrete arch dams.

Response Spectrum–Based Stochastic Method for Earthquake Analysis of Gravity Dams

AbstractTime-history response analysis is necessary to account accurately for the dam–foundation rock and the dam–reservoir water interaction effects in the earthquake response of gravity dams. Thi...

Effect of a Stiff Thin Foundation Soil Layer's Depth on Dynamic Response of an Embankment Dam

In 2002, Zeyzoun Dam failure, that is an embankment dam located at the northwest of Syria, made a big Awareness of the effects of the lack of Geotechnical investigations and seismic conditions of the site of the dam. The dam located, in the vicinity of the Dead Sea fault, which emphasizes the importance of analyzing the effects of lithological stratum in dam foundations on dam seismic stability. This paper is concerned with the influence of a high permeable soil layer that has different static and dynamic properties, and exists at different depths in dam foundation. Numerical models arepreparedto analyze that effectbyapplying finite element method and considering seepage, dynamic analysis and slope stability. The results shows thatphreatic line rises in the dam body because of decreasing in permeable layer depth, which is resulting in two effects, The first is increasing in pore-water pressure, and destabilizing forces in dam body, The second is decreasing in stabilizing forces and factors of safety. The effective stresses decrease above phreatic line due to decreasing in suction pressure, and will decrease under phreatic line due to increasing in pore water pressure. The foundation stratum has a damping effect of decreasing the factor of safety under seismic conditions by 5%, except the case where Layer 3-1 is located near ground level (where the dam failed), where it has amplification effect.

Numerical prediction of stress and displacement of ageing concrete dam due to alkali-aggregate and thermal chemical reaction

The damage of concrete due to the expansion of alkali-aggregate reaction (AAR) and thermal-chemical reactions affecting the strength of concrete is studied. The empirical equations for the variations of expansion of AAR, compressive strength and degradation of the modulus of elasticity with time, and compressive strength with degradation of the modulus of elasticity are proposed by analysing numerous experimental data. It is revealed that the expansion of AAR and compressive strength increase with time. The proposed combination of the time variations of chemical and mechanical parameters provides a satisfactory prediction of the concrete strength. Seismic analysis of the aged Koyna dam is conceded for two different long-term experimental data of concrete incorporating the proposed AAR based properties. The responses of aged Koyna dam reveal that the crest displacement of the Koyna dam significantly increases with time while the contour plots show that major principal stress at neck level reduces with time. As the modulus of elasticity decreases with ages the stress generated in the concrete structure get reduces. On the other hand with lesser value of modulus of elasticity the structure becomes more flexible and the crest displacement becomes very high that cause the seismic safety of the dam reduce

Study of modified Westergaard formula based on dynamic model test on shaking table

The dynamic model test of dam-reservoir coupling system for a 203m high gravity dam is performed to investigate effects of reservoir water on dynamic responses of dam during earthquake. The hydrodynamic pressure under condition of full reservoir, natural frequencies and acceleration amplification factors along the dam height under conditions of full and empty reservoir are obtained from the test. The results indicate that the reservoir water have a stronger influence on the dynamic responses of dam. The measured natural frequency of the dam model under full reservoir is 21.7% lower than that of empty reservoir, and the acceleration amplification factor at dam crest under full reservoir is 18% larger than that under empty reservoir. Seismic dynamic analysis of the gravity dams with five different heights is performed with the Fluid-Structure Coupling Model (FSCM). The hydrodynamic pressures from Westergaard formula are overestimated in the lower part of the dam body and underestimated in its upper part to compare with those from the FSCM. The underestimation and overestimation are more significance with the increase of the dam height. The position of the maximum hydrodynamic pressure from the FSCM is raised with the increase of dam height. In view of the above, the Westergaard formula is modified with consideration in the influence of the height of dam, the elasticity of dam on the hydrodynamic pressure. The solutions of modified Westergaard formula are quite coincident with the hydrodynamic pressures in the model test and the previous report.

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.

Probability density evolution method for seismic liquefaction performance analysis of earth dam

SummaryTo investigate the seismic liquefaction performance of earth dams under earthquake loading, we present a new methodology for evaluating the seismic response of earth dams based on a performance‐based approach and a stochastic vibration method. This study assesses an earthfill dam located in a high‐intensity seismic region of eastern China. The seismic design levels and corresponding performance indexes are selected according to performance‐based criteria and dam seismic codes. Then, nonlinear constitutive models are used to derive an array of deterministic seismic responses of the earth dam by dynamic time series analysis based on a finite element model. Based on these responses, the stochastic seismic responses and dynamic reliability of the earth dam are obtained using the probability density evolution method. Finally, the seismic performance of the earth dam is assessed by the performance‐based and reliability criteria. Our results demonstrate the accuracy of the seismic response analysis of earth dams using the random vibration method. This new method of dynamic performance analysis of earth dams demonstrates that performance‐based criteria and reliability evaluation can provide more objective indices for decision‐making rather than using deterministic seismic acceleration time series as is the current normal practice. Copyright © 2016 John Wiley & Sons, Ltd.

Nonlinear seismic response of a gravity dam under near-fault ground motions and equivalent pulses

In this paper, the nonlinear seismic response of gravity dams to forward-directivity and ordinary (non forward-directivity) near-fault earthquake ground motions is investigated. Considering Pine Flat dam as case study, it is numerically modeled along with its full reservoir using the finite element method. Two sources of nonlinearity are considered in the analysis: (1) the material nonlinearity of dam concrete, and (2) the geometric nonlinearity by inserting a joint at the base of the dam. Seventy-five forward-directivity and sixty ordinary near-fault ground motions are used to obtain statistically significant results. The equivalent representative pulses of the selected forward-directivity ground motions are extracted using a well-known methodology. The dam-reservoir model is analyzed under the equivalent pulses as well to identify the cases for which the equivalent pulses can capture the structural response to the actual forward-directivity ground motions. Finally, the effects of pulse period, amplitude and energy on the seismic response of the dam-reservoir system are studied.

Static Analysis of Gravity Dams Considering Foundation-Structure Interaction

A dam is an artificial barrier constructed across a stream channel to impound water. Analysis of stresses and displacements are inevitable for the structural design and failure analysis of dams. This paper deals with the numerical simulation of structural response of gravity dams, duly considering the foundation-structure interaction. The optimum depth and width of foundation extend to be considered in the numerical model is also studied. A parametric study based on the stiffness of the foundation is also exercised. As an application of the developed model, a case study of Peechi gravity dam is presented. This study proved the importance of consideration of foundation-structure interaction in the structural analysis of dams. The developed numerical model can be further improved for performing seismic analysis of gravity dams, considering the foundation-structure as well as fluid-structure interactions.

Relevance of the incidence angle of the seismic waves on the dynamic response of arch dams

This paper aims at studying the influence of the nature and direction of incidence of impinging seismic waves on the dynamic response of arch dams. A model for the seismic excitation is proposed in which the three free-field accelerograms defining the seismic input signal at ground surface are generated by different sets of simultaneous obliquely-incident P and S planar body waves. The dynamic response of the Morrow Point dam under such seismic excitations is studied considering the situation of a full reservoir and the existence of bottom sediments. Such response is computed by means of a multidomain boundary element code that allows the direct dynamic analysis of problems. It is found that, for the cases studied herein, oblique incidence produces seismic responses significantly larger than those observed for vertical incidence, which suggests that analyses considering only vertical incidence could be underestimating the seismic response of this type of structures.

Ambient modal testing of a double-arch dam: the experimental campaign and model updating

A finite element model updating of a double-curvature-arch dam (La Tajera, Spain) is carried out hereof using the modal parameters obtained from an operational modal analysis. That is, the system modal dampings, natural frequencies and mode shapes have been identified using output-only identification techniques under environmental loads (wind, vehicles). A finite element model of the dam-reservoir-foundation system was initially created. Then, a testing campaing was then carried out from the most significant test points using high-sensitivity accelerometers wirelessly synchronized. Afterwards, the model updating of the initial model was done using a Monte Carlo based approach in order to match it to the recorded dynamic behaviour. The updated model may be used within a structural health monitoring system for damage detection or, for instance, for the analysis of the seismic response of the arch dam- reservoir-foundation coupled system.

Arrival direction effects of travelling waves on nonlinear seismic response of arch dams

The aim of this study is to investigate arrival direction effects of travelling waves on non-linear seismic response of arch dams. It is evident that the seismic waves may reach on the dam site from any direction. Therefore, this study considers the seismic waves arrive to the dam site with different angles,