Concrete Arch Dam Research Articles

Quantifying the Qualitative Limit-States Using IDA Approach in Concrete Arch Dams

Limit states in concrete arch dams are qualitative. In this paper, the qualitative descriptions of the specified limit-states are quantified for the very first time using the IDA approach. A thin high arch dam was selected as case study. Nine natural earthquake records in three specified levels (design base level, maximum design level and maximum credible level) were used for exciting the provided finite element model of the dam–reservoir–foundation coupled problem. The mean annual frequency of exceedance was calculated using performance based earthquake engineering frameworks and for each limit-state, a return period was identified. This paper demonstrates that IDA curves can provide quantitative information for qualitative descriptions of limit-states in high arch dams.

Integrative seismic safety evaluation of a high concrete arch dam

An integrative seismic safety evaluation of an arch dam should include all sources of nonlinearities, dynamic interactions between different components and the external loads. The present paper investigates the calibration procedure and nonlinear seismic response of an existing high arch dam. The first part explains the conducted analyses for the static and thermal calibrations of the dam based on site measurements. The second part investigates the nonlinear seismic analysis of the calibrated model considering the effect of joints, cracking of mass concrete, reservoir–dam–rock interaction, hydrodynamic pressure inside the opened joints and the geometric nonlinearity. Penetration of the water inside the opened joints accelerates the damage process. The integrative seismic assessment of a case study shows that the dam will fail under the maximum credible earthquake scenario. The dam is judged to be severely damaged with extensive cracking and the joints undergo opening/sliding. A systematic procedure is proposed for seismic and post-seismic safety of dams.

Elastic Strength Diagnosis of the Dez Concrete Arch Dam Using Thermal Inverse Analysis

AbstractStrength degradation of mass concrete of the Dez concrete arch dam was evaluated using inverse analysis methods. A three-dimensional nonlinear finite element model (FEM) was developed here for such an evaluation by considering the effect of interaction between vertical adjacent blocks of the dam. The special attention was paid to the thermal loads. The Young’s modulus and Poisson’s ratio and thermal expansion coefficient of mass concrete of the dam were selected as variable indices for monitoring the strength degradation of dam concrete in the proposed model. An iterative solution scheme was performed to determine the mentioned indices in such a way that a predefined error function would be minimized. An error function has been considered as the sum of the squares of the errors in the nodes of the mesh. An error in a node was defined as the difference between computed displacement vector based on the developed model and the recorded displacement vector with the instruments located in the dam body....

Impact of load combination on the stability analysis of an arch dam subjected to stochastic non-uniform excitations

In the present paper, impact of the non-uniform excitation due to spatially varying earthquake ground motion (SVEGM) is investigated on the linear response of a typical concrete arch dam. An iterative scheme is utilised to generate the stochastic acceleration time histories at several locations along the foundation boundaries which are compatible with the target response spectra and are correlated according to a given complex coherence function. A typical arch dam is selected as the case study in which the reservoir is modelled as a compressible medium and the foundation is assumed to be massless. Various load combinations are considered based on the corresponding reservoir water levels and the thermal loads. It is observed that, in general, considering SVEGM leads to higher tensile stresses and increases the percentage of the overstressed area within the dam body especially in vicinity of the foundation in comparison with uniform excitation. Thus, for more realistic assessment of the dam behaviour, SVEGM effect should be incorporated in seismic analyses especially in high seismicity regions.

Construction of decision rules for early detection of a developing concrete arch dam failure scenario. A discriminant approach

To improve the effectiveness of concrete dam safety control in real time, a method is presented for the construction of decision rules for the early detection of developing failure scenarios. The decision rules are based on the use of linear discriminant models developed with data obtained through mathematical models of the dam’s behaviour. The aim is to combine the physical quantities measured by the automated monitoring system of the dam, appropriately weighted, into a new single index allowing the classification of the observations into one of two classes (normal behaviour and development of a failure scenario).

Temperature Rebound Influenced by Environment Temperature Analysis of the Irrigated Area of a High Arch Concrete Dam under Constrcution

For a temperature rebound in the irrigated high arch dam during the construction period, using finite element method to research the influence of environment temperature to temperature rebound of the irrigated high concrete arch dam. Assuming that the initial temperature of the dam concrete is the joint grouting temperature. This paper presents a simulation of the temperature rebound of the high arch dam which is caused by the monthly average environment temperature, and performs sensitivity analysis to research the influence of thermal conductivity and surface heat preservation on the temperature rebound. According to the analysis,when the high arch dam sealing temperature is lower than the dam site annual average temperature, the dam site temperature inevitably would flow backward,slowly,to the irrigation area.The larger the thermal conductivity is,the quicker the temperature rebound speed will be. And benzene board insulation can reduce concrete temperature rebound rate, if the heat preservation benzene board is thicker,the temperature rebound rate is smaller.

Investigation and evaluation of increasing uplift pressure in an arch dam: A case study of the Huaguangtan Dam

The investigation of abnormal increases in uplift pressure can lead to the discovery of seepage paths that may cause damage to concrete arch dams. A new methodology has been developed in this study in order to analyze the causes of abnormally high uplift pressure increases and their influence on the structural safety assessments of dams. A series of borehole video tests were performed on an area of the Huaguangtan Dam and its foundations in order to investigate seepage phenomena under different working conditions. The reasons for the existence of the seepage paths causing abnormally high uplift pressures were identified by examining stresses on the dam, using a detailed three-dimensional numerical model. The results from the monitoring and on-site inspection showed that the high uplift pressure did not constitute a direct threat to the dam’s safety. However, grouting treatment of the existing cracks was recommended so as to prevent them from developing further within the dam’s foundations and to ensure the long-term stability of the foundation seepage. It was concluded that the methodology in this study could be used to solve practical engineering problems effectively as well as acting as a frame of reference for similar projects.

THERMAL AND STRUCTURAL ANALYSIS OF RCC DOUBLE-CURVATURE ARCH DAM

This paper focuses on the development, verification and application of a three-dimensional finite element code for coupled thermal and structural analysis of roller compacted concrete arch dams. The Karun III Arch dam located on Karun River, Iran, which was originally designed as a conventional concrete arch dam, has been taken for the purpose of verification of the finite element code. In this study, RCC technology has been ascertained as an alternative method to reduce the cost of the project and make it competitive. A numerical procedure to simulate the construction process of RCC arch dams is presented. It takes into account the more relevant features of the behavior of concrete such as hydration, ageing and creep. A viscoelastic model, including ageing effects and thermal dependent properties is adopted for the concrete. The different isothermal temperature influence on creep and elastic modulus is taken into account by the maturity concept. Crack index is used to assess the occurrence of crack and evaluate the level of safety of the dam. This study demonstrates that, high tensile stress concentration has been observed at the lower part and the abutment boundaries of the dam.

Hazard and seismic reinforcement analysis for typical large dams following the Wenchuan earthquake

The primary aim of this research is to analyze the hazards and seismic performance of reservoirs and typical large dams based on a field investigation following the Wenchuan 8.0 earthquake. The current seismic performance standards being achieved are discussed and further suggestions are given for super high dams. Based on field investigations, statistics are also given on damaged small reservoirs and damage severities, due to the many various types of earthquake threat. It is of interest to note that the major structures of the medium-sized hydropower stations on the Minjiang river did withstand the Wenchuan earthquake, despite earthquake intensity exceeding engineering design expectations. All the dams remained overall stable. The Shapai roller-compacted concrete (RCC) arch dam and the Zipingpu concrete-faced rockfill (CFR) dam suffered damage. The main earthquake-induced hazards to the dam structures and to both abutments are detailed. Case study analyses of the hazards and reinforcement provision revealed that: 1) The Wenchuan earthquake proved very dangerous for small reservoirs, with destroyed reservoirs widely distributed. The risk of failure of small dams can be classified into three levels based on field investigation. 2) The damage to and behavior of the large dams in the area affected by the earthquake prove that the Chinese codes relating to the seismic design of large dams are appropriate. 3) Appropriate reinforcement can increase the overall stiffness of abutments, riverbed foundation and the adjacent slopes, further improving the seismic performance of dams. 4) The design and management of emergency responses, to cope with extreme conditions, should be improved, and a unified response platform, covering all hydropower engineering projects in each valley should be established. The effects to be expected and the seismic design measures to be taken still pose great challenges for engineers in respect of large dams.

Seismic analysis of a coupled dam-reservoir-foundation system considering pressure effects at opened joints

In this paper, seismic response of a coupled dam-reservoir-foundation system is investigated under different types of artificially generated ground motions. Nonlinear behaviour of the arch dam is originated by modelling the vertical contraction and the curved peripheral joints based on discrete crack approach. Fluid–structure dynamic interaction is modelled based on Euleian–Lagrangian approach and the hydrodynamic pressure effect is considered inside the opened joints during the seismic action using heuristic approach. Foundation rock is modelled as massed medium and the viscous boundary model is applied on the exterior surface of the foundation finite element model. Artificial ground motions are applied to the coupled system using different durations and intensities. Various ground motion intensity measures (IMs) and engineering demand parameters (EDPs) are used for interpretation of the parametric study. It is shown that almost in all cases considering the pressure effect inside the joints, the demand parameter increases. Nonlinear behaviour of arch dams is sensitive not only to ground motion intensity but also its duration. This study shows that the specific energy density is the most appropriate IM almost for all the EDPs of concrete arch dams.

The Numerical Analysis of Gradient Material Replacement on Arch Dam of Stress Concentration Area

During operation, due to change of outside temperature, edge of abutment and central part of concrete arch dam is prone to stress concentration, Concrete of tensile stress concentration area appears too large tensile stress easily, which results cracks to affect dam safety. This paper, by changing the material properties, that obtained high strength low elastic modulus of concrete, replaced arch rings with gradient material replacement method, to improve the stress state of dam and enhance strength for dam safety. By comparing the temperature rise with drop of the arch stress distribution area, the relationship of changing elastic modulus and stress has got. Using the VT technology acquire critical values of mutation elastic modulus.

Research Progress of Protected Plunge Pool of High Arch Dam

The security researches of energy dissipation were always the focus in the High arch dams. Statistically, the trajectory type energy dissipation is the most widely used in the built high arch dams, and the protected plunge poor were always set downstream the dam body. However, the widely used protected plunge poor need large investment with the disadvantage of complicated operation and maintenance. Along with the construction of concrete high arch dam in the Southwest China, the “Reventment-Protected and Non-Bottom-Protected Plunge Pool” has been studied and proposed, which has the advantage of more simplified project design and more economy investment.

Evaluation of Various Temperature Control Schemes for Crack Prevention in RCC Arch Dams During Construction

Temperature stress is one of the main reasons causing the cracking of high roller compacted concrete (RCC) arch dams during rapid construction. For the construction organization design and implementation of RCC dams, it is an important point to establish the scheme for temperature control and crack prevention, and evaluate its effect. The technology of concrete mixed with MgO is a new developing way for crack prevention of RCC dams. The expansion of MgO can compensate effectively for the tensile stress generated in the cooling period of RCC. To improve the effect of crack prevention for high RCC arch dams, the aforementioned technology needs to be combined with the conventional methods. FEM is used to implement the temperature stress calculation for high RCC arch dams mixed with MgO. The basic principle and process of simulation algorithm are introduced first. According to the actual characteristics of a high RCC arch dam, the following three schemes for temperature control and crack prevention are given. They are “no MgO and no joint”, “mixed with MgO and no joint”, “mixed with MgO and two induced joints”, respectively. The corresponding FEM models are established to calculate the equivalent temperature field and temperature stress of the RCC arch dam mixed with MgO or not. The calculated results under above three schemes are used to appraise the effect controlling the temperature stress by mixing MgO. The positive impact of the combined scheme is analyzed. Some valuable conclusions for the design and construction of actual dams are obtained.

Full-scale experimental modal analysis of an arch dam: The first experience in Iran

Forced vibration field tests and finite-element studies were conducted on the Shahid Rajaee concrete arch dam in Northern Iran to determine the dynamic properties of the dam–reservoir–foundation system. The first forced vibration tests on the dam were performed with two different types of exciter units, with a limited maximum force, bolted on the dam crest for alternative in-phase and out-of-phase sequencing. Because of an insufficient number of recording sensors, two arrangements of sensors were used to cover sufficient points on the dam crest and one gallery during tests. Two kinds of vibration tests, on–off and frequency sweeping, were carried out on the dam. The primary natural frequencies of the coupled system for both symmetric and anti-symmetric vibration modes were approximated during on–off tests in two types of sequencing of exciters, in phase and out-of-phase, with a maximum frequency of 14Hz. The principal forced vibration tests were performed at precise resonant frequencies based on the results of the on–off tests in which sweeping around the approximated frequencies at 0.1Hz increments was performed. Baseline correction and suitable bandpass filtering were applied to the test records and then signal processing was carried out to compute the auto power, cross power and coherence spectra. Nine middle modes of vibration of the coupled system and corresponding damping ratios were estimated. The empirical results are compared against the results from calibrated finite-element modeling of the system using former ambient vibration tests, considering the dam–reservoir–foundation interaction effects. Good agreement is obtained between experimental and numerical results for eight middle modes of the dam–reservoir–foundation system.

A study on the contraction joint element and damage constitutive model for concrete arch dams

A new contraction joint element model for the interface in different meshes between the arch dam sections is constructed. The study on the elastic-plastic damage constitutive model for concrete, which is applied to multi-axial stresses, is also taken. The models of the dam-foundation-reservoir system for Xingbiling and Jinping concrete arch dams, China are calculated using the proposed contraction joint elements and the elastic-plastic damage constitutive model to verify the proposed models. Results showed that the proposed contraction joint element model has a high precision in simulating the behavior of contraction joints and the elastic-plastic damage constitutive model has a high precision in simulating the behavior of the damage to the concrete.

Vibration based damage identification of concrete arch dams by finite element model updating

Vibration based damage detection is very popular in the civil engineering area. Especially, special structures like dams, long-span bridges and high-rise buildings, need continues monitoring in terms of mechanical properties of material, static and dynamic behavior. It has been stated in the International Commission on Large Dams that more than half of the large concrete dams were constructed more than 50 years ago and the old dams have subjected to repeating loads such as earthquake, overflow, blast, etc.,. So, some unexpected failures may occur and catastrophic damages may be taken place because of theloss of strength, stiffness and other physical properties of concrete. Therefore, these dams need repairs provided with global damage evaluation in order to preserve structural integrity. The paper aims to show the effectiveness of the model updating method for global damage detection on a laboratory arch dam model. Ambient vibration test is used in order to determine the experimental dynamic characteristics. The initial finite element model is updated according to the experimentally determined natural frequencies and mode shapes. The web thickness is selected as updating parameter in the damage evaluation. It is observed from the study that the damage case is revealed with high accuracy and a good match is attained between the estimated and the real damage cases by model updating method.

Investigation into in situ stress fields in the asymmetric V-shaped river valley at the Wudongde dam site, southwest China

The Wudongde Reservoir, now being constructed on the lower reaches of the Jinsha River, will be the forth largest hydropower plant in terms of capacity in China. This project includes a concrete arch dam and two large-span underground caverns in both abutments. For their design and construction, in situ stress measurements and geological survey were conducted. In this study, following an introduction of the geological conditions and topography, an interpretation on the test results of in situ stresses is presented for clarifying the distribution features of natural stresses in the engineering area. It is interesting to find that the vertical stress is predominant in the project area and that the horizontal stress reduces largely in the relaxation zone near the bank slopes, while concentrates at the valley bottom and becomes normal in the depth of both abutments. Also analyzed are the effects of valley topography, geological conditions in the project area as well as the macro-regional tectonics on the distribution of in situ stresses at the dam site. A noteworthy finding is that topography and thickness of overburden are the main factors for the intermediate–low stress levels, that regional tectonics governs the stress orientation at the regional scale, and that river erosion, caprock structure and karstic processes have also contributed to the evolution of the valley and in situ stress state.

Finite Element Simulation Analysis of Concrete Hyperbolic Arch Dam

Arch dam is a water retaining structure which has beautiful bodily form and reasonable structure form, in recent years, arch dam has been widely used. This paper adopts finite element method to carry out three-dimensional finite element simulation analysis for Haierwa reservoir concrete hyperbolic arch dam, researching variation law of the dams stress and displacement in operating process. Research results show that, Haierwa reservoir concrete hyperbolic arch dam is reasonable structure, good mechanical performance, every index meets the requirements for design.

Numerical Analysis on Temperature Rise of a Concrete Arch Dam after Sealing Based on Measured Data

The thermal boundary conditions in the construction and operation phases of a concrete arch dam are always complex. After sealing, differences between the arch dam temperature and its sealing temperature can cause compressive or tensile stresses. Based on measured temperature of an arch dam located in China, a temperature rise phenomenon (TRP) is found in the after-sealed regions of the arch dam. By mining and analyzing the temperature data of various monitoring apparatus embedded in the arch dam, higher environment temperature is considered to be the main cause for the occurrence of the TRP. Mathematical methods for complex thermal boundary conditions, including external boundary conditions and internal heat source conditions, are proposed in this paper. A finite element model is implemented with the concern of the construction phase and operation phase of the arch dam. Results confirm good agreement with the measured temperature and verify the conjecture that the TRP occurs mainly because the external temperature of the arch dam is higher than its sealing temperature.

Are There Any Differences in Seismic Performance Evaluation Criteria for Concrete Arch Dams

Differences between stress-based and strain-based criteria are investigated in seismic performance evaluation of the arch dams in time domain. A numerical model of the coupled dam-reservoir-foundation system is prepared with the finite element technique. Reservoir is modeled using the Eulerian approach as a compressible domain, and the foundation rock is assumed to be massless. Dynamic equilibrium equations for the coupled system are solved using Newmark’s time integration algorithm. Seismic performance of the arch dam is evaluated according to parameters such as demand-capacity ratio, cumulative inelastic duration and overstressed (or overstrained) areas obtained from linear elastic analyses. The results show, although there are some similarities between stress-based and strain-based criteria, evaluation of the performance based on the strain gives different results which can be led to different decision making in dam safety related projects.