Analysis Of Concrete Arch Dams Research Articles

Multi-zone parametric inverse analysis of super high arch dams using deep learning networks based on measured displacements

Parametric inverse analysis/identification provides significant information for structural damage detection and construction in dam engineering. The main challenge in inverse analysis is to enhance the computational accuracy and efficiency for complex structures, especially for super high arch dams with many zone parameters. This study developed a high-precision deep learning-based surrogate model for rapid inverse analysis of concrete arch dams. The relationship between mechanical parameters and multi-point displacement response is interpreted by convolutional neural networks (CNN)-based surrogate model. The proposed model is integrated with the Latin hypercube sampling and a meta-heuristic optimization algorithm for rapid inverse analysis strategy. The objective function is defined as the distance between the displacement predicted by the surrogate model and the measured displacement. The proposed approach is tested on an actual super high concrete arch dam. Results show that the proposed approach can achieve high accuracy and improve the computational efficiency by 95.83 % compared with the direct finite element method.

XFEM analysis of concrete arch dam to assess deformations and propagation of artificial crack due to the combination of earthquake and uplift pressure

In this study, the extended finite element method (XFEM) is further generalized to study the crack propagation in the concrete arch dam. Static and dynamic analysis performed on scaled-down prototype plane concrete arch dam to assess the deformation occurs due to water pressure and moderate earthquake magnitude of 5.8M. The most obvious finding to emerge from this study is that XFEM allows the entire crack to represented independently of the mesh, and so re-meshing is not necessary to model crack growth. The study has also shown that emergence of new cracks in different locations on the dam’s body.

Seismic fracture analysis of concrete arch dams incorporating the loading rate dependent size effect of concrete

The purpose of this study is to investigate the size effect, loading rate, and smeared crack models in the nonlinear seismic behavior of concrete arch dams. One of the important parameters in the design of arch concrete dams is the tensile strength of unreinforced mass concrete. Various fracture parameters obtained from experimental results reported for concrete in order to study the size-effect is used in this paper. In the present analysis, the smeared crack method is used in finite element analysis of the Morrow Point arch dam subjected to three components of the TAFT earthquake as a case study. The dependence of fracture, and especially of the size effect, on the loading rate is described. Models incorporating nonlinear analysis in three cases with and without the size effect of dam concrete and fluid-structure interaction are employed to evaluate and compare them. The water is taken as an inviscid, compressible fluid, and the foundation is rigid. From the study, it is concluded that the participation of the size effect leads to higher values of maximum displacements and stresses in benchmark points compared to the model that ignores the size effect. The crack initiation criterion based on the maximum tensile stress according to the size effect of concrete, and also the dynamic loading range should be defined. Results show considering fixed smeared crack models used in the concrete specimen as well as the size effect of concrete materials, will lead to the crack profile is more realistic and will represent near to real behavior of concrete fracture. The results are of significant interest for the concrete fracture of dams; hence the loading rate should be adopted for fracture properties obtained in dams.

Seismic analysis of arch dams using anisotropic damage-plastic model for concrete with coupled adhesive-frictional joints response

A finite element model for seismic analysis of concrete arch dams is proposed. Material inelasticity as well as joints nonlinearity is considered. A damage-plastic formulation governs nonlinear behavior of concrete. Degeneration occurring during nonlinear behavior of concrete induces anisotropy into its microstructure. This anisotropy becomes more complex in seismic simulations, in which the state of stress expeditiously changes with time. Thus, anisotropic formulation is preferred over classical isotropic models. Utilizing rate-dependent anisotropic damage-plastic model, irreversible deformations, stiffness degeneration, induced anisotropy, closing/reopening of cracks, and viscous response of concrete are attained. Non-penetration condition, frictional behavior, and adhesion resulted by grouting of contraction and peripheral joints are also modeled in a coupled and rate-dependent manner. Different combinations of material and joints nonlinearities are used to model a system of dam-foundation-reservoir. The system is excited using three components of an earthquake, and effect of different sources of nonlinearities is investigated through comparison between results. In addition, capability of the anisotropic damage-plastic model is compared against an available isotropic formulation. A sensitivity analysis is also performed to investigate the effect of properties of joints on responses. Owing to high convergence rate of material and joints constitutive models, implicit time integration is employed, which leads to stable and accurate solutions.

Seismic analysis of concrete arch dams considering hydrodynamic effect using Westergaard approach

Earthquake response of arch dams should be calculated under strong ground motion effects. In this study, three-dimensional linear response of an arch dam is investigated. Different ground motion effects and also foundation conditions are considered in the finite element analyses. For this purpose, the Type 3 double curvature arch dam was selected for numerical examples. All numerical analyses are carried out by SAP2000 program for empty reservoir cases. 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 five different elastic foundation conditions. The selected foundation conditions of the all models have different sandstone material parameters. 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.

Risk-based probabilistic thermal-stress analysis of concrete arch dams

The probabilistic risk of arch dam failure under thermal loading is studied. The incorporated uncertainties, which are defined as random variables, are associated with the most affecting structural (material) properties of concrete and thermal loading conditions. Karaj arch dam is selected as case study. The dam is numerically modeled along with its foundation in three-dimensional space; the temperature and thermal stress distribution is investigated during the operating phase. The deterministic thermal finite element analysis of the dam is combined with the structural reliability methods in order to obtain thermal response predictions, and estimate the probability of failure in the risk analysis context. The tensile overstressing failure mode is considered for the reliability analysis. The thermal loading includes ambient air and reservoir temperature variations. The effect of solar radiation is considered by an increase in the ambient temperatures. Three reliability methods are employed: the first-order second-moment method, the first-order reliability method, and the Monte-Carlo simulation with Latin Hypercube sampling. The estimated failure probabilities are discussed and the sensitivity of random variables is investigated. Although most of the studies in this line of research are used only for academic purposes, the results of this investigation can be used for both academic and engineering purposes.

FEA model for the simulation of the hydration process and temperature evolution during the concreting of an arch dam

Temperature plays a significant part in the cracking phenomenon of mass concrete structures, and therefore thermal analysis is of major importance, especially during construction, due to the heat of hydration of the cement. A transient coupled 3D finite element analysis of the thermal behaviour of Alqueva dam during construction is presented in this paper. The method used for the thermal analysis is described in detail, along with the simulation of the different actions. The thermal state of the dam is affected not only by climatic actions but also by concrete’s constituent materials and by the construction methods. The chemo-thermal problem is solved using a heat transfer model. An exponential function was calibrated taking into account the heat of hydration of the cement at 3, 7 and 28 days and the function obtained was then used to establish the chemical affinity relationship. The temperatures predicted using the numerical model are compared with the actual temperatures recorded in situ. Despite the uncertainties characteristic of this type of problem, results lead to the conclusion that the methodology applied in this paper can be effectively used for the chemo-thermal analysis of concrete arch dams, which is particularly relevant during the construction phase.

Statistical modeling for deformation analysis of concrete arch dams with influential horizontal cracks

Several concrete dams all over the world exhibit severe cracks. It is very important to investigate the influence of cracks on the long-term behavior of dam structures to ensure safe operation. The interpretation of measured dam displacements is usually based on statistical hydrostatic-seasonal-time and hydrostatic-thermal-time models. The main purpose of this article is to present a statistical hydrostatic-thermal-crack-time model to interpret displacements of concrete arch dams with influential horizontal cracks. The hydrostatic-thermal-crack-time model is applied to analyze the Chencun dam, an arch–gravity dam with a large-scale horizontal crack on the downstream face. The crack stretches horizontally across most of the dam blocks. Its crack mouth opening displacement had been continually increasing even after reinforcement treatment, accompanied by abnormal deformation characteristics of the arch–cantilever system. A three-dimensional finite element model, containing the pre-existing crack using special gap elements, is built to reproduce the structural response, assess the contribution of the crack on the registered movements, and obtain the relationship between the crack mouth opening displacement and the dam crest displacement. Based on this, the hydrostatic-thermal-CMOD-time model considering crack mouth opening displacement is developed. Compared with the traditional models, the hydrostatic-thermal-crack-time model is expected to provide a better fit accuracy. The results also show that the crack and the corresponding reinforcement measure have a significant effect on the deformation behavior of the dam. This can provide some useful indications for concrete structures with similar problems.

Free vibration analysis of concrete arch dams by quadratic ideal-coupled method

This paper is devoted to two new techniques for free vibration analysis of concrete arch dam-reservoir systems. The proposed schemes are quadratic ideal-coupled eigen-problems, which can solve the originally non-symmetric eigen-problem of the system. To find the natural frequencies and mode shapes, a new special-purpose eigen-value solution routine is developed. Moreover, the accuracy of the proposed approach is thoroughly assessed, and it is confirmed that the new scheme is very accurate under all practical conditions. It is also concluded that both decoupled and ideal-coupled strategy proposed in the previous works can be considered as special cases of the current more general procedure.

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.

Cracking Behavior of a Concrete Arch Dam with Weak Upper Abutment

The cracking behavior and failure mode of a 78 m high concrete double-curvature arch dam with weak upper abutment are investigated through performing cracking analysis. The mechanical behavior of concrete is simulated using a smeared crack model, in which a combination of the compression yield surface and the crack detection surface with a damaged elasticity concept is employed to describe the failure of concrete. The arch dam with practical mechanical properties of the upper and lower abutments is firstly studied with emphasis on its cracking behavior during overloading. Then, a comprehensive sensitivity analysis is carried out to investigate the influence of the ratio of the mechanical properties of upper abutment to those of lower abutment on dam failure with prime attention placed on the failure mode. Simulation results indicate the adopted smeared crack model is well-suited to the crack analysis of concrete arch dam. It is shown that cracking is localized around the interface between upper and lower abutments, which leads to a fast crack growth in the through-thickness direction of dam and finally causes the dam failure. Furthermore, the sensitivity analysis presents three types of failure modes corresponding to different ratio value, wherein Modes II and III should be avoided since the weak upper abutment plays a predominant role in the cracking and failure of concrete arch dam.

Failure analysis method of concrete arch dam based on elastic strain energy criterion

The arch dam is a type of massive water-retaining structure made of concrete. The overall failure mechanism and corresponding analysis criterion are key issues of concern in the dam engineering field. In this paper, the energy evolution of arch dams in the failure process is studied first, which can be decomposed as energy dissipation accompanied by concrete damage and elastic strain energy absorption and release during elastic deformation. An evaluation criterion for failure analysis of concrete arch dams is then established based on elastic strain energy. An orthotropic damage constitutive model for dam concrete is then proposed along with its numerical simulation method, which is established for structural failure analysis. Numerical simulations show that the elastic strain energy in elements increases with increasing overload safety coefficient and finally converges to the concrete material surface energy, at which time the locally plastic damage area develops rapidly and finally leads to cracking failure of structures. The proposed failure analysis criterion for concrete dams under integrated loads is suitable for analyzing dam instability failure, which has great operability and value in engineering applications in the future.

Orthotropic Material and Anisotropic Damage Mechanics Approach for Numerically Seismic Assessment of Arch Dam–Reservoir–Foundation System

In contrast with modeling of the contraction joints, the performance and influence of lift joints are usually neglected in numerical analysis of concrete arch dams. In this paper, the seismic nonlinear response of a concrete arch dam–reservoir–foundation system is investigated with considering the effects of lift joints using orthotropic-based material. An anisotropic damage mechanics approach is introduced and modified to take into account the effects of weak horizontal planes between concrete lifts during the construction phase. This model is capable to consider the pre-softening behavior, the softening initiation criterion and anisotropic cracking behavior in mass concrete. The coupled equation of motion in dam–reservoir system is solved by staggered displacement method while the foundation rock is assumed as a mass-less and rigid mediums. The coupled system is excited using three-component ground motion in the maximum credible level. It is found that using orthotropic-based material increases crest displacements and also leads to more damage in the dam body in comparison with the case using the common isotropic-based material.

Numerical prediction of swelling in concrete arch dams affected by alkali-aggregate reaction

A chemo-damage model is presented for anisotropic swelling analysis of concrete arch dams affected by alkali-aggregate reaction (AAR). The model combines the AAR kinetics and the plastic-damage model, and the chemical and mechanical phases are coupled. A redistributing weight function, determined by the applied stresses in the concrete, is introduced to control the AAR-induced anisotropic expansion of the concrete. Creep strain is also included in the approach using the Kelvin–Voigt model. Accelerated tests, in which the specimens are confined with steel rings and subjected to axial loads, are first analyzed using the proposed model. The computed strains of the specimens are in good agreement with the experimental measured strains. The application to the AAR-affected Kariba dam is then carried out. The radial and vertical displacements of the dam due to AAR are reproduced with sufficient accuracy. The stresses within the dam are significantly redistributed during the AAR process. Severe cracking and damage appear to occur in the dam heel and the downstream face on both sides of the dam-foundation interface. It demonstrates Kariba dam is facing an increased risk of collapse associated with the increasing compressive stresses within the dam and developing cracks on both sides of the downstream face during the development of AAR.

Nonlinear Dynamic Analysis of Concrete Arch Dam Using Concrete Elasto-Plastic Models

In this research, materially nonlinear dynamic analysis of concrete arch dam using Concrete Elasto-Plastic models is attempted. At first, common models for nonlinear analysis of massive plain concrete structures are investigated and finally concrete material model of Wiliam–Warnke (five parameters version) for tensional and compression failure is selected. This model is used versus other usual models such as Mohr-Coulomb and Drucker-Prager models for analysis of Morrow Point concrete arch dam under an intensive ground motion of order of 1.0g for the peak ground acceleration. A suitable algorithm for stress integration and conversion of engineering stresses to objective ones is proposed. This stress calculation is particularly desired in large deformations analysis. Fluid-structure interaction is also considered including water compressibility and reservoir bottom absorption. Staggered approach is used for coupled-fluid structure solutions. Although the foundation is considered as rigid. It is demonstrated that usual nonlinear plastic models such as Mohr-Columb and Drucker –Prager models unlike special concrete models are not capable to capture real behavior of such concrete structure. It is suggested that special concrete models such as William–Warnke must be used for the plastic nonlinear analysis of concrete arch dam.

Linear analysis of concrete arch dams including dam–water–foundation rock interaction considering spatially varying ground motions

AbstractThe available substructure method and computer program for earthquake response analysis of arch dams, including the effects of dam–water–foundation rock interaction and recognizing the semi‐unbounded size of the foundation rock and fluid domains, are extended to consider spatial variations in ground motions around the canyon. The response of Mauvoisin Dam in Switzerland to spatially varying ground motion recorded during a small earthquake is analyzed to illustrate the results from this analysis procedure. Copyright © 2009 John Wiley & Sons, Ltd.

Direct frequency domain analysis of concrete arch dams based on FE-BE procedure

A FE-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by finite elements, while foundation rock is handled by three dimensional boundary element formulation. This would allow a rigorous inclusion of dam-foundation rock interaction, with no limitations imposed on geometry of canyon shape. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various ratios of foundation rock to dam concrete elastic moduli under an empty reservoir condition. Furthermore, the effects of canyon shape on response of dam, is also discussed.

Linear dynamic analysis of arch dams utilizing modified efficient fluid hyper-element

The accurate dynamic analysis of concrete arch dams relies heavily on employing a three-dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of this fluid hyper-element is dependent on the solution of a complex eigenvalue problem for each frequency. In the present study, a modified efficient procedure is proposed, which simplifies this procedure significantly, and results in great computational time savings. Moreover, the accuracy of this technique is examined thoroughly and it is concluded that modified efficient procedure is also extremely accurate under all practical conditions. It is also shown that the original efficient method proposed in a previous study can be considered as a special case of the present more general procedure.

An efficient three-dimensional fluid hyper-element for dynamic analysis of concrete arch dams

The accurate dynamic analysis of concrete arch dams relies heavily on employing a three-dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of this fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient procedure is proposed which simplifies this procedure amazingly, and results in great computational time saving. Moreover, the accuracy of this technique is examined thoroughly and it is concluded that efficient procedure is incredibly accurate under all practical conditions.

Frequency domain analysis of concrete arch dams by decoupled modal approach

A modal approach is proposed for dynamic analysis of concrete arch dam-reservoir systems in frequency domain. The technique relies on mode shapes extracted by considering the symmetric parts of total mass and stiffness matrices. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various conditions. The method is proved to be very effective and it is an extremely convenient modal technique for dynamic analysis of concrete arch dams.