Analysis Of Concrete Gravity Dams Research Articles

Modeling Variability in Seismic Analysis of Concrete Gravity Dams: A Parametric Analysis of Koyna and Pine Flat Dams

This study addresses the vital issue of the variability associated with modeling decisions in dam seismic analysis. Traditionally, structural modeling and simulations employ a progressive approach, where more complex models are gradually incorporated. For example, if previous levels indicate insufficient seismic safety margins, a more advanced analysis is then undertaken. Recognizing the constraints and evaluating the influence of various methods is essential for improving the comprehension and effectiveness of dam safety assessments. To this end, an extensive parametric study is carried out to evaluate the seismic response variability of the Koyna and Pine Flat dams using various solution approaches and model complexities. Numerical simulations are conducted in a 2D framework across three software programs, encompassing different dam system configurations. Additional complexity is introduced by simulating reservoir dynamics with Westergaard-added mass or acoustic elements. Linear and nonlinear analyses are performed, incorporating pertinent material properties, employing the concrete damage plasticity model in the latter. Modal parameters and crest displacement time histories are used to highlight variability among the selected solution procedures and model complexities. Finally, recommendations are made regarding the adequacy and robustness of each method, specifying the scenarios in which they are most effectively applied.

Failure modes-based seismic fragility analysis of concrete gravity dams considering concrete heterogeneity

The heterogeneity of mass concrete often leads to the initiation of micro-cracks in gravity dams, while the accumulation of damage of concrete on the meso-scale leads to the cracking behaviour on the macro-scale. To improve the seismic safety of the dam, a comprehensive study on the effect of heterogeneous properties is crucial in seismic fragility analysis. A novel methodology considering concrete heterogeneity for seismic fragility analysis was developed by combining damage element model for seismic failure analysis, a five-level standard for failure modes-based seismic damage state and a method to generate seismic fragility curves. Then, seismic failure analysis of the Koyna gravity dam was taken as an example to verify the correctness of the damage element model, the damage process of dam from micro-cracks to macro-cracks were simulated. Finally, the seismic fragility of a practical dam in China was studied to verify the effectiveness of the proposed methodology. The results showed that simulated failure modes-based fragility curves were suitable for the target dam and more capable of considering the uncertainty of concrete material parameters. The obtained fragility curve proved valuable in optimizing seismic design, reinforcement and maintenance measures and improve seismic capability of the dam.

Performance of 2D-spectral finite element method in dynamic analysis of concrete gravity dams

This article presents a two-dimensional spectral finite element formulation for dynamic analysis of concrete gravity dams. Finite element method (FEM) is the one of the most extensively used analysis tools for solving problems of dynamic analysis of structures. However, it needs extensive computational resources and time for large structures, leading to the development of alternate computationally efficient modeling techniques over the past few decades. Some of these techniques are broadly termed as “Spectral Finite Element Methods” (SFEMs). Frequency domain-based SFEM (FDSFEM) and time domain-based SFEM (TDSFEM) are the most commonly used SFEMs found in the literature. This article provides a brief review of these methods identifying their key advantages and disadvantages; and explores the feasibility of applying such methods in the dynamic analysis of concrete gravity dams. Here, the TDSFEM has been used to perform the dynamic time history analysis of a concrete gravity dam due to its relative advantages over FDSFEM, which is challenging for irregular geometry and finite domain. Sensitivity analysis and convergence studies have been performed using 4-noded and 9-noded elements. The foundation of the dam has been modeled using two-dimensional infinite elements in both FEM and TDSFEM analysis, which is a novel application in the case of TDSFEM. This article quantifies the computational efficiency of TDSFEM over the conventional FEM by comparing the computation time in both methods and thus emphasizes the applicability of TDSFEM in dynamic analysis, especially in case of complex geometries and large two-dimensional structures (like concrete gravity dam). The results demonstrate the computational efficiency of TDSFEM over FEM when higher order elements are considered. Modal analysis and time history analysis results point that the use of higher order elements of TDSFEM can be a viable alternative to the use of the conventional FEM leading to significant saving in computational time with reasonable accuracy for dynamic analysis of large structures like concrete gravity dams.

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.

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.

Reliability Analysis of Concrete Gravity Dams Based on Least Squares Support Vector Machines with an Improved Particle Swarm Optimization Algorithm

A reliability analysis method based on least squares support vector machines with an improved particle swarm optimization algorithm (IPSO-LSSVM) is proposed to calculate the reliability of concrete gravity dams when explicit nonlinear limit-state functions are difficult to obtain accurately. First, the main failure modes of concrete gravity dams and their influencing factors are determined. Second, Latin hypercube sampling is used to create samples. A finite element calculation batch program of concrete gravity dams is written to calculate the safety indexes of each sample. Third, based on the samples, the IPSO-LSSVM model is established to replace the finite element calculation. Finally, the failure probability of concrete gravity dams is obtained by using the Monte Carlo (MC) method. The case study for a typical concrete gravity dam in the Yunnan Province of China shows that the dam is reliable because the failure probability is 8.87 × 10−5. The proposed reliability analysis method is efficient and feasible for calculating the reliability of concrete gravity dams.

Nonlinear dynamic analysis of concrete gravity dams utilizing a simplified continuum damage model and different damping algorithms

Nonlinear dynamic analysis of concrete gravity dams utilizing a simplified continuum damage model and different damping algorithms

Push-over analysis of concrete gravity dams due to flood inflow

Push-over analysis of concrete gravity dams due to flood inflow

Similarity Research on the Action of a Centrifuge Scaled Near-Field Underwater Explosion on a Concrete Gravity Dam

Concrete gravity dams are a common form of dams. The dynamic response analysis of concrete gravity dams under the action of underwater explosions is indispensable for survivability assessments. Due to the constraints of the environment and other conditions, an underwater explosion test of a prototype concrete gravity dam is difficult to achieve. The centrifuge scaled-down test that satisfies similarity theory provides a new way to study the dynamic response of underwater explosions on concrete gravity dams. In a near-field explosion, the shock wave of an underwater explosion will cause direct damage to the gravity dam, and the detonation products after the shock wave will aggravate the damage. Under the premise of verifying the concrete dynamic response material parameters and the fluid–solid coupling model of the underwater explosion, numerical calculations of the scaled underwater explosion model of the centrifuge and the prototype underwater explosion were carried out, and the similarity between the scaled dam response model of the underwater explosion centrifuge and the prototype was discussed. The analysis shows that the scaled-down centrifuge model can better reflect the local damage of the prototype dam subjected to shock waves. The difference between the scaled centrifuge model and the prototype model of underwater explosion damage to the dam is concentrated on the overall damage. The damage effect of detonation products on the prototype dam body is mainly concentrated in the middle and lower parts of the dam body, while the damage effect of detonation products on the dam body in the scaled-down model is mainly concentrated in the middle and upper parts of the dam body.

Failure analysis for concrete gravity dam subjected to underwater explosion: A comparative study

The failure analysis of concrete gravity dams subjected to noncontact underwater explosions (UNDEXs) plays a significant role in evaluating the safety of dams. In this paper, two types of numerical models were developed to predict the failure behavior of a typical concrete gravity dam, i.e., the fully-coupled and semi-coupled model, which can provide a cross validation of the analysis results. The two models were verified by the experimental data and then adopted for the failure analysis. The results show that the shock wave can produce peak value in the blast responses and concentrated damage directly opposite to the explosive source. Even after the energy transmission at the fluid–structure interface, the UNDEX load still had influence on the failure behavior of the dam and can induce a total swelling in the velocity response.

A new numerical approach in the seismic failure analysis of concrete gravity dams using extended finite element method

In this paper, a new approach has been developed to conduct seismic failure analysis of concrete gravity dams using extended finite element method and evaluated numerical parameters of dam-foundation-reservoir system. Failure analysis of concrete gravity dams are investigated using Extended finite element method (XFEM) combined with time integration by α-method. To perform the failure analysis and dynamic fracture behavior of a cracked dam, dynamic stress intensity factors based on interaction integral with dynamic effects are utilized. The penalty method is used in this study to model the opening and closing of cracks due to seismic loading. In addition, to apply the interaction between dam, foundation and reservoir in finite element model, zero thickness six-nodal contact elements are used in which the system formulated with lagrangian approach.To achieve this goal, several examples are first reviewed to validate the proper performance of a written code, and the results are then compared with those reported in the literature. Then, numerical parameters in seismic failure analysis such as length of crack growth, angle of initial crack, assembling of mass matrix, using high-order elements and penalty parameter discussed. The results show when cracks start to propagate, in the numerically approach, tip elements will switch to elements that fully cut by cracks. This transformation produces shockwaves during failure analysis. Obtained results show by using crack tip element, the analysis is numerically unstable and does not end. Using eight-node elements with four nodes enriched only by the Heaviside jump function and elimination of enrichment functions of the crack tip are reduced the failure analysis costs while good accuracy. In addition, a different crack path created when diagonal and consistent mass matrix used in the failure analysis.

Hierarchical Bayesian framework for uncertainty reduction in the seismic fragility analysis of concrete gravity dams

Concrete gravity dams are critical infrastructures for communities to meet the basic human needs as well as rising standards of living. Most of the existing concrete gravity dams in Italy were built before the introduction of seismic regulations. Although no concrete gravity dams have as yet suffered a catastrophic collapse during or after a seismic event, their preservation remains a key aspect for communities, also in view of that older dams may have deteriorated to a critical level. For these reasons, researchers and practitioners in dam engineering are working to improve seismic fragility, and ultimately seismic risk, assessment procedures. Since no case histories are available, numerical modelling plays an important role, even though many uncertainties can affect the models and then the estimation of the seismic fragility.This paper presents a robust hierarchical Bayesian framework for the calibration of dynamic parameters of dam numerical models based on ambient vibrations, which allows an analyst to reduce uncertainties in the seismic fragility derivation. A probabilistic predictive model of the dam modal behaviour based on the general Polynomial Chaos Expansion is adopted in order to reduce the computational burden and a numerical algorithm for the solution of the inverse problem based on Markov Chain Monte Carlo is also presented.The proposed approach is applied to an existing large concrete gravity dam in Italy, and the effect of epistemic uncertainty reduction is finally evaluated in terms of fragility curves.

Hybrid asynchronous SEM/FEM co-simulation for seismic nonlinear analysis of concrete gravity dams

The aim of this work is to take full advantage of Spectral Element (SE) and Finite Element (FE) codes by setting up a SEM/FEM co-simulation strategy for soil structure interaction problems, involving a SE code to generate and propagate elastic waves in the soil, while a FE code enables the detailed representation of the studied structure. The spatial coupling is managed by the standard coupling mortar approach, whereas the time integration is dealt with an hybrid (explicit/implicit) asynchronous (different time steps) time integrator. The SEM/FEM co-simulation strategy is set up for linear or nonlinear transient dynamics. A seismic analysis of a concrete dam is considered in order to demonstrate the versatility of the co-simulation approach, assuming a linear rheology or a nonlinear damaging behaviour of the concrete.

Transient analysis of concrete gravity dams by Wavenumber-TD method for general excitation

In seismic analysis of concrete gravity dam and reservoir systems using finite-element models, finding an appropriate and simple reservoir upstream truncation condition has been a challenging issue for researchers. The Sommerfeld condition is the classical approach most engineers use for this purpose and it is widely available in commercial finite-element software. In 2012, Wavenumber method was proposed as an alternative approach. The main goal of the present study is to modify this approach so it can handle vertical as well as horizontal ground motions. Moreover, the aim of the study is to evaluate the performance of the approach more thoroughly in comparison to the Sommerfeld truncation boundary, especially for vertical ground motions. With this aim, Pine Flat dam in the USA is used as a typical example. Several models are considered with different values of normalised reservoir length. The dynamic loading considered is the local Taft earthquake record of 1952. Furthermore, two types of reservoir base condition – full reflective and absorptive – are adopted. Overall, this allowed for a thorough examination and evaluation of the effectiveness of the wavenumber-TD approach for seismic analysis of concrete gravity dams.

Three-dimensional seismic analysis of concrete gravity dams considering foundation flexibility

Abstract Concrete dams are considered as complex construction systems that play a major role in the context of both economic and strategic utilities. Taking into account reservoir and foundation presence in modeling the dam-reservoir-foundation interaction phenomenon leads to a more realistic evaluation of the total system behavior. The article discusses the dynamic behavior of dam-reservoir-foundation system under seismic loading using Ansys finite element code. Oued Fodda concrete dam, situated at Chlef, in North-West of Algeria, was chosen as a case study. Parametric study was also performed for different ratios between foundation Young's modulus and dam Young's modulus E f /E d (which varies from 0.5 to 4). Added mass approach was used to model the fluid reservoir. The obtained results indicate that when dam Young's modulus and foundation Young's modulus are equal, the foundation soil leads to less displacements in the dam body and decreases the principal stresses as well as shear stresses.

Reliability Assessment and Sensitivity Analysis of Concrete Gravity Dams by Considering Uncertainty in Reservoir Water Levels and Dam Body Materials

An elaborate safety assessment of the Pine Flat (PF) concrete gravity dam (CGD) has been conducted in this paper. Structural analysis was performed by taking into account the uncertainties in the physical and mechanical properties of the dam body materials and the reservoir water level. The coefficient of variation of 5 and 10 percent and the Gaussian distribution (GAUS) are assigned to random variables (RVs). Sensitivity analysis (SA) of the RVs is done, and important parameters introduced. SA is done to identify the most influential RVs on the structural response. Also, the modulus of elasticity of concrete is the most effective parameter in response to horizontal deformation of the dam crest. The concrete density and US hydrostatic pressure height are the most effective parameters, and the Poisson's ratio is the insignificant parameter on the dam response. To be confident in the safety of the dam body under usual loading, including the dam weight and the upstream (US) hydrostatic pressure, the reliability index (RI) has been obtained by Monte Carlo simulation. The RI for the coefficients of variation of 5 and 10 percent were obtained at 4.38 and 2.47, respectively. If the dispersion of RVs is high, then the dam will be at risk of failure.

Space–time FEM with block-iterative algorithm for nonlinear dynamic fracture analysis of concrete gravity dam

In this paper, space–time finite element method is developed for the dynamic fracture analysis of dam–reservoir (DR) system which is supported on a perfectly rigid foundation. In this method, an auxiliary variable q representing the first-order time derivative of hydrodynamic pressure is treated as the primary unknown for the reservoir domain. Similarly, velocity v is the primary unknown for the solid domain. A three point Gauss–Lobatto quadrature rule is employed for computing time integral of those terms which contain stress term. Further, a partitioned method based on a block-iterative scheme is employed to incorporate the material nonlinearity of the concrete and to enforce the coupling between the two domains in a single iteration loop. A co-axially rotating crack model with exponential strain softening rule is employed to model the fracture of the concrete. Afterwards, numerical performance of the proposed scheme is demonstrated by analyzing two situations of dynamic fracture of Koyna concrete gravity dam.

A New Probabilistic Framework for Structural System Fragility and Sensitivity Analysis of Concrete Gravity Dams

Concrete gravity dams are widely constructed owing to their advantages of low maintenance cost and relatively low risk of sudden failure. However, the structural failure rate has been reported to be higher than other dam types. Although various studies have been conducted to assess the structural fragility of concrete gravity dams, not enough emphasis was placed on system-level fragility and sensitivity analyses, which provide crucial information for mitigating dam failure. This study proposes a new probabilistic framework for system fragility and sensitivity analysis by employing a finite element model for concrete gravity dams. The proposed framework consists of four steps, namely, structural analysis modeling considering the realistic loading conditions, component fragility analysis employing finite element reliability analysis, system fragility analysis employing system reliability analysis, and system sensitivity analysis using the finite difference method, which require several numerical algorithms and computational techniques. The proposed framework is applied to a numerical example of a typical concrete gravity dam in South Korea, and the analysis is completed successfully. As a result, the example dam is found to be relatively more vulnerable to sliding and concrete overstress than ground overstress. In addition, it is revealed that the dam system is more likely to fail in the overflow part than in the non-overflow part. The most critical factor in preventing these failures is the concrete mass density, followed by the silt mass density and the concrete compressive strength. Based on these analysis results, it is confirmed that the proposed framework provides valuable information for risk-informed structural design and failure mitigation of concrete gravity dams.

Seismic Soil–Structure Interaction Analysis of Concrete Gravity Dam Using Perfectly Matched Discrete Layers with Analytical Wavelengths

ABSTRACT For heavy structures like concrete gravity dams, soil–structure interaction has a great effect on the structural behavior. One of the important features of soil–structure interaction problems is absorbing boundary conditions for the unbounded soil domain. In this study, perfectly matched discrete layers with analytical wavelengths (AW-PMDLs), which was developed recently by the authors, is applied to concrete gravity dam analyses. Free-field motions during earthquakes with the presence of absorbing boundary conditions need to be included. A Free-field element is presented to take into account the free-field motions. The hydrodynamic pressure from the reservoir to the dam is introduced by using Westergaard added mass method. A procedure with the combination of the AW-PMDL elements, Free-field elements, and Westergaard added masses is proposed to analyze concrete gravity dams considering soil-–structure interaction. For the sake of numerical analyses, AW-PMDLs, Free-field elements, and Westergaard added masses are implemented by using user-defined elements (UEL) in ABAQUS. The validation of the proposed procedure is made by comparing the results with a previous study and the results obtained from SASSI, a program used to analyze the soil–structure interaction problems in the frequency domain. Then, the linear and nonlinear analyses of the dam system are observed for various soil stiffness. It can be seen that the nonlinear analyses need to be considered for a rigorous dam structure analysis.

A nonlinear local equivalent stress method in stress analysis of concrete gravity dam

Abstract When the stress state of the structure is analyzed by the finite element method (FEM), the stress at the stress concentration points such as the dam’s heel and toe gets infinitely larger as the element size decreases. In order to overcome this defect, many equivalent stress methods of normal stress have been proposed to convert the FEM stress into equivalent stresses on the boundary between the dam and the foundation. This paper proposes a nonlinear local equivalent stress method that reflects the mechanical equivalent conditions and material continuity in the areas near the dam’s heel and toe and proves that the stress state obtained by the nonlinear local equivalent stress method is close to the actual stress state through calculation experiment.