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An Experimental Investigation of Water Level Effects on the Dynamic Behavior of a Large Arch Dam
Abstract
The need for full‐scale dynamic tests, which are recognized as the most reliable method to evaluate a structure's vibration properties, is increasing as new analysis techniques are developed that take into account the complex interaction phenomenons that occur in dam–reservoir–foundation systems. They are extremely useful to obtain reliable data for the calibration of newly developed numerical methods.
The Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke has been developing and applying dynamic testing methods for large structures in the past 10 years. This paper presents the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam in Switzerland. Repeated forced‐vibration tests were carried out on the dam during four different periods of the reservoir's filling cycle during a one‐year span. Acceleration and hydrodynamic pressure frequency responses were obtained at several locations while the dam was subjected to horizontal harmonic loading. The variation of the resonant frequencies as a function of the reservoir level is investigated. A summary of the ongoing numerical correlation phase with a three‐dimensional finite element model for the dam–reservoir–foundation system is also presented. Copyright © 2001 John Wiley & Sons, Ltd.
... For example, this may be a time-varying external load, without causing defects. In the case of hydroelectric dams, such a load, which is usually seasonally varying, is the water pressure from the reservoir [7][8][11][12][13]. In heavy and complex structures, which include hydroelectric dams, the standing wave field has a complex structure, to determine which, it is necessary to perform measurements with high detail [14]. ...
... There are various ways to study the natural frequencies of structures. For example, based on the registration of oscillation under the influence of artificial sources of vibration type or explosions [11,[15][16], or under the influence of earthquakes [9]. ...
... In general, with the growth of the upstream level, the frequencies decrease. Such a dependence is characteristic of hydroelectric dams [7][8][11][12][13] and is explained by researchers as the change in the added mass of water (the larger the mass, the lower the natural frequency). We then considered what other factors, in addition to the added mass, can affect the values of frequencies. ...
The article presents a method for monitoring the natural frequencies of HPP dams according to
continuous seismic observations. The object of the research is the largest arched dam in Russia, the Chirkey
HPP located in the Caucasus. If damaged, it could cause great loss of property and human life, but disasters
can be minimized by using effective dam structural health monitoring. The study for changes in the natural
frequencies of engineering structures is one of the most common methods of remote control over their
structural health. However, the determination of values of natural frequencies of huge concrete dams is a very
difficult procedure due to their have complex construction. Moreover, interpretation of changes in the natural
frequencies values is difficult due to the significant influence of the water level in the reservoir. Consequently,
at the initial stage, we performed a detailed study of the natural oscillations of the dam using the method of
coherent restoration of the standing wave fields with the definition of both the natural frequencies of the
structure and their modes. They were conducted twice at the minimum and maximum upstream level and for
the first time highlighted the features of seasonal changes in the full field of standing waves. The normal modes
were determined that are present in oscillations at different upstream levels and which frequencies can be
detected continuously from the records of seismic equipment. The series of frequency changes during the
year are calculated. For the first time we established that, frequency changes are by 5 to 11 days behind
reservoir level changes and assumed that relaxation processes of the dam body and / or its base cause the
delay after the upstream level changes. We calculated dependencies for predicting the frequency values from
the reservoir level, taking into account the delay time. As a result, we proposed an approach for monitoring of
the dam structural health based on a comparison of the observed natural frequencies with the predicted ones.
The developed method can be applied to monitor the structural health of concrete dams of other HPPs.
... Fanelli et al. [2,3] presented the dynamic behavior of the Talvacchia Arch Dam in Italy in forced vibration tests and earthquake records and investigated the influence of environmental conditions (water level and temperatures) and the structural characteristics of the dam dynamic response. The study reported the phenomenon in which resonant frequencies initially increase with rising water level and then decrease with a further rise, as well as subsequent studies [4][5][6][7][8][9][10]. This phenomenon is usually attributed to the comprehensive effects of the added mass from water pressure, stiffness change (opening and closing of contraction joints), and damping ratio. ...
... As reported in the literature [2][3][4][5][6][7][8][9][10]22], the resonant frequencies of arch dams initially increase with rising water level and then decrease with a further rise after a certain water level has been reached. The critical water level is approximately 70% of dam height. ...
... water level and then decrease with a further rise after a certain water level has been reached. This finding was also presented by several previous studies [2][3][4][5][6][7][8][9][10]22]. This phenomenon could be attributed to an increase in the stiffness of the dam caused by the compression of the construction joints under increasing hydrostatic pressure. ...
The true dynamic characteristics of dams, namely, natural frequencies, damping ratios, and mode shapes, are important to earthquake-resistant design. Thus, system identification based on in-site measurements is useful for numerical analysis and health monitoring. The well-instrumented strong motion array on an arch dam in Southwestern China recorded some seismic response data. The dynamic properties of the dam are identified from records of the top five strongest earthquake motions using power spectral density functions, transfer functions, and the ARX model. The identified modal parameters of the different seismic events are compared, and the stability of the stiffness of the dam system from 2002 to 2008 and the nonuniformity in the input ground motion are indicated. A linear finite element model of the dam and a nonlinear model that considers contraction joints are constructed and calibrated to reproduce the frequencies determined from the system identification. The modal analysis highlights potential information about the dynamic characteristics of the dam. The comparison of the results of the system identification and calibration shows that the use of the nonlinear model may be reasonable in simulating the dynamic response of the Ertan Dam.
... Therefore, hydraulic structure damage and environmental hazards are the two major problems induced by the vibration during the process of high dam flood discharge. In the past several years, numerous studies on vibration mechanisms, health monitoring, safety assessment, and reduction measures have been carried out [5][6][7][8][9][10][11]. ...
... Generally, the dominant frequency of flow-induced pressure fluctuation ranges from 0 to 2 Hz and the high frequency vibration is unlikely to be caused. However, the fluctuating pressure generated by the high-velocity discharge flow may consist of high-frequency components [35], and the high-frequency vibration of the hydraulic gate occurs frequently in engineering practice [6,36]. The detailed mechanism for the flow-induced vibration of hydraulic gates needs further investigation. ...
According to the results of a dynamic prototype test for the surface outlet radial gate on the Jinping high arch dam during the flood discharging process, a novel cause of vibration fundamentally different from the traditional causes of flow-induced radial gate vibration, is analyzed for the first time. Under the condition that the flood is discharged only from mid-level outlets, an accompanying vibration of the surface outlet gate is induced by the vibration of the closely spaced mid-level outlet gates. It is counterintuitive that the most intense vibration occurs when the surface outlet gate is closed and, on the contrary, the vibration is reduced when the gate is opened and subjected to flow excitation. In order to analyze and explain this accompanying vibration phenomenon, a theoretical model is developed based on the conventional theory of passive vibration absorbers. The difference between the proposed and conventional theoretical models is that more complex load and damping conditions are considered, and more attention was paid to the dynamic behavior of the accessory structure. Then, the cause and mechanism for the surface outlet gate vibration is clarified in detail, based on the proposed theoretical model. The comprehensive analysis and mutual verification of the prototype test, theoretical derivation and numerical simulation, indicate that the clarification and the proposed theoretical model is reasonable and accurate. The research reported in this paper will be beneficial for the design, operation and maintenance of the hydraulic gates installed on high arch dams.
... Various researchers presented the modal analysis outcome of the dam in their studies (Hariri-Ardebili and Saouma 2016; Maity 2016, 2018;Adhikary 2021a, b, 2022;. Proulx et al. (2001) presented the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam. They have performed forced and ambient vibration test on the dam. ...
This work follows the latest development trend in resilient structures by arresting inelastic damage in a small replaceable link at a predetermined location. Toward this, here innovative beam fuse has been proposed with circular, triangle, square, and elliptic openings. These openings are also provided with a stiffening plate of 5 mm thickness to reduce the stress concentration effects inside the opening edge. Comparative analysis has been carried out for four beam-column sub-assemblages in ABAQUS FEM software. In this modeling, the bolted end plate has been omitted as the focus is only on the connection's pure fuse behavior. SAC loading protocol has been adopted to evaluate the cyclic behavior of the connections. Strength degradation, ductility, and energy dissipation have been studied. All the fuse connections show excellent ductility under the cyclic loading. For all the fuses based on rupture, index cracking may occur between the web plate and the stiffening plate of the fuse. Here, fuse with a circular opening shows the highest amount of energy dissipation.KeywordsReplaceable fuseEnergy dissipation capacityStiffening plateResilient structuresFEMcyclic
... ，强迫振动又 需要大型激振试验装置 [6] ，因此，基于环境激励 振动试验识别拱坝的模态参数成为一种常用的分 析方法 [5,[7][8][9][10][11] 。环境激励振动是指结构在风、交通 或水流等激励荷载下的动态响应，其激励源不可 测，可假定为高斯白噪声。目前基于环境激励的 模态参数识别算法有频域分解法(FDD) [12][13][14] 、 特征系统实现算法(ERA) [15][16][17] 、随机子空间法 (SSI) [18][19][20] 和盲源分离算法(BSS) [21][22][23] 等。不 同算法各有优缺点 [24] ...
随着一系列高拱坝在西南地区兴建，坝体的健康状况及其真实的抗震性能成为近年来研究的热点。模态参数反映坝体结构的动态特性，可用于评估坝体的健康状况及更新坝体抗震分析有限元模型。本文基于永善县两次地震记录和环境激励数据，分别采用带外源输入的自回归（ARX）模型、随机子空间法（SSI）和频域分解法（FDD），识别溪洛渡拱坝的模态参数。结果显示，在相同工况下，不同算法识别结果的差异较小；当水位一致时，基于环境激励数据识别结果与基于地震记录识别结果基本一致，当库水水位从566 m 变化到598 m时，坝体第一阶自振频率从1.63 Hz 减小到1.51 Hz；地震前后识别结果基本一致，表明溪洛渡拱坝在经历两次地震作用后，坝体振动特性不变，坝体处于正常运行状态。
With a train of high arch dams built in Southwest China, the health of dam structures and
their anti-seismic properties have become a hot issue in recent years. Modal parameters reflect the dynamic characteristics of dam structures and are applicable to evaluating dam health status and updating the finite element models for arch dam anti-seismic analysis. This paper presents a study on the identification of modal parameters for Xiluodu arch dam using the ARX, SSI and FDD procedures separately, based on two earthquake recorders located in Yongshan County and ambient vibration test data.
The results show the modal parameters identified using ambient vibration tests agree with those identified using the recorded data. When the reservoir stage varies from 566 m to 598 m, the fundamental vibration frequency of this dam is lowered from 1.63 Hz to 1.51 Hz. And similar frequencies identified before and after the earthquakes indicate that the dam is in the normal operation condition.
... The classical way, known as experimental modal analysis (EMA), is to excite the target structure through artificially generated forces, measure the responses and then analyse the input-output data. 1,2 During the two last decades, operational modal analysis (OMA), which uses the vibration data under ambient noises (e.g., wind or traffic), has received great attentions [3][4][5][6][7][8] since it can provide more practical conveniences than EMA. For example, OMA enables continuous measurements of a structure's vibration for the structural health monitoring. ...
Modal analysis, aiming at estimating modal characteristics such as natural frequencies and mode shapes, is fundamental for studying structural dynamic behavior. This paper presents a modal analysis of an arch dam using three different techniques. The reference one is based on the statistical analysis of the ambient vibration data collected from the dam crest. The two other approaches are both numerical but with different methods (fluid-element and Westergaard) for the modelling of the reservoir and its interactions with the dam. By applying the three techniques to the studied dam and comparing their results, it is demonstrated that: (1) analysing the ambient vibration data through an operational modal analysis method is able to extract the dam modal characteristics; (2) the fluid-element method is effective for arch dams since the first 10 natural frequencies can be accurately predicted once the material parameters are calibrated on the first 3 modes; (3) the Westergaard method, a technique with only additional masses, produces significantly under-estimated frequencies for the first few modes if same parameters are used as the fluid-element method; the underestimation can be corrected for several modes by using a higher stiffness parameter but the required value is unrealistic for the case study. Furthermore, a modified Westergaard method is introduced in this paper by using a reduced added-mass coefficient. This method, once the coefficient is calibrated on the 1st mode, is able to well predict the partially coupled modes as illustrated with the case study of the Saint-Guérin dam.
... The effects of seismic action on embankment dams have been widely studied (Chen and Harichandran, 2001;Proulx et al., 2001;Wu, 2001;Swaisgood, 2003;Calayir and Karaton, 2005;Arabshahi and Lotfi, 2008;Chen et al., 2008;Bilici et al., 2009;Sevim et al., 2011;Zou et al., 2013). The stress concentration, soil liquefaction, ground deformation, and crushing damage in the zone of the slabs are the common failure patterns for embankment dams. ...
Numerous landslide dams have been induced in recent years as a result of frequent earthquakes and extreme climate hazards. Landslide dams present serious threats to lives and properties downstream due to potentially breaching floods from the impounded lakes. To investigate the factors influencing the stability of landslide dams, a large database has been established based on an in-depth investigation of 1,737 landslide dam cases. The effects of triggers, dam materials, and geomorphic characteristics of landslide dams on dam stability are comprehensively analyzed. Various evaluation indexes of landslide dam stability are assessed based on this database, and stability evaluation can be further improved by considering the dam materials. Stability analyses of aftershocks, surges, and artificial engineering measures on landslide dams are summarized. Overtopping and seepage failures are the most common failure modes of landslide dams. The failure processes and mechanisms of landslide dams caused by overtopping and seepage are reviewed from the perspective of model experiments and numerical analyses. Finally, the research gaps are highlighted, and pathways to achieve a more complete understanding of landslide dam stability are suggested. This comprehensive review of the recent advances in stability and failure mechanisms of landslide dams can serve as a key reference for stability prediction and emergency risk mitigation.
... For instance, when testing concrete dams, it usually should be expected to measure low vibration levels [20], given the massive nature of these structures and the isolated locations where many of them are positioned, so superior equipment is needed to perform successful experimental campaigns. Nevertheless, the dynamic testing of concrete dams based on the recording of ambient induced vibrations has been carried out before ([21], [22], [23], [24], [25]) quite often as a supplement to forced vibration campaigns. Recently, the execution of these tests on dams to correct numerical models and to corroborate structural assumptions became more common ( [26], [27], [28], [29]), prompting the implementation of structural health monitoring systems based on the recording of vibrations that rely entirely in environmental excitation and on dependable measuring and acquisition equipment [30] [31]. ...
Historically, the dynamic testing of concrete dams has been associated with experimental modal analysis (EMA) and the performance of forced vibrations tests. Nevertheless, this type of tests requires the use of a heavy equipment and the interruption of the regular operation of the structure. An alternative to EMA relies on the application of operational modal analysis (OMA), through the performance of ambient vibration tests, and thus, it is essential to investigate if the application of OMA to concrete dams can provide good results with high levels of accuracy. In this context, this work addresses the performance of ambient vibration tests on concrete dams with quite diverse geometrical attributes and on the application of state-of-art output-only modal identification methods, to gain awareness of the issues that may occur during the application of OMA methods to signals with such low amplitudes (of the order of micro g), such as those that are usually recorded when dealing with these massive structures. More specifically, the paper describes the ambient vibration tests executed on six very different concrete dams. The most relevant modal properties are estimated through the application of modern output-only modal identification techniques, stressing the good level of accuracy achieved, which is quantified through the calculation of modal properties’ uncertainties. Finally, a novel approach considering the uncertainties estimated is used to study the effect of noise on the quality of modal estimates and to qualify the adequacy of sensors to perform these tests on dams.
... where T i denotes the i-th target object in target object set. Incorporating equation (2) in equation (1), the Lagrangian function can be defined as ...
Due to the frequently occurred adverse vibration of hydraulic structures, vibration risk assessment is significant for the water energy efficiency of hydropower station and the safety of people and structures. Recently, the abnormal vibration of hydro-turbine-generator in a large hydropower station occurred and the main influencing factors of vibration are analyzed based on the prototype data and engineering experience. Different from the deterministic variable features in traditional support vector domain description (SVDD) algorithms, the feature of vibration amplitude is actually a random variable so that the different target objects will be obtained at different confidence levels. In order to assess the vibration range and excessive vibration probability, the original SVDD boundary at relatively low confidence level is firstly calculated. Then, the boundary extension operation with detailed theoretical deduction is performed and the extended boundary is further optimized inspired by path planning problem. The advantage of proposed approach is that it can improve the data fitting performance for single dimension (i.e. vibration amplitude) without leading to complex boundary which cannot be used for vibration risk assessment. By applying this approach to the practical vibration problem, the quantitative and slightly conservative assessment results are conveniently obtained, which indicate that this approach is reasonable and cost-effective.
... The natural environment is inevitably disturbed and many environmental and ecological issues can result [1][2][3][4][5][6][7] if insufficient water resources planning, unreasonable operation schemes, and obsolete construction technology are applied. The vibration problems of hydraulic structures (e.g., a dam body [8,9], a hydraulic gate [10][11][12], a gate pier [13,14], a guide wall [15,16], and a plunge pool floor [17]) induced by high dam flood discharge are originally an engineering problem that has an adverse impact on structural safety and normal operation. However, ground vibrations induced by the flood discharge of several large hydropower engineering projects have recently been observed, and adverse effects on the nearby building safety and the physical and mental health of surrounding residents have been identified [18][19][20]. ...
Ground and environmental vibrations induced by high dam flood discharge from the Xiangjiaba hydropower station (XHS) has significant adverse effects on nearby building safety and the physical and mental health of surrounding residents. As an effective approach to simulate the flow-induced vibration of hydraulic structures, the hydro-elastic experiment approach has been extensively applied and researched by Chinese scholars, but the relevant systematic research is rarely reported in international journals. Firstly, the hydraulic and structural dynamic similarity conditions that should be satisfied by the hydro-elastic model are briefly reviewed and derived. A hydro-elastic model of the XHS was further constructed using self-developed high-density rubber, and the vibration isolation system (including open trenches and flexible connects) was applied to avoid the external disturbances of pump operation, vehicle vibration and other experiments in the laboratory. Based on the data of model and prototype dynamic tests, a back propagation (BP) neural network was established to map the acceleration of the physical model to the ground in the prototype. In order to reduce the ground vibration, experiments were carried out to meticulously evaluate the ground vibration intensity under more than 600 working conditions, and the optimal operation scheme under different discharge volumes is presented here in detail. According to the prototype test data in 2013, 2014, and 2015, ground vibrations were significantly reduced by applying the presented optimal operation principle which indicates that the presented hydro-elastic approach and the vibration attenuation operation scheme were effective and feasible.
... Tarinejad and Damadipour [9] proposed the Frequency Domain Decomposition (FDD)-wavelet method to identify the modal parameters using earthquake recorders, and the effects of non-synchronous sensing of sensors for arch dams [10] are investigated. Considering that there are few arch dams with adequate seismic recorders for modal parameter identification [11] and the forced vibration test requires the use of extremely heavy and expensive devices [12], the identification of modal parameters of arch dams with ambient vibration tests is essential [2,3,11,[13][14][15]. For the ambient vibration test, the process of extracting modal parameters from the structural response is called operational modal analysis or output-only modal analysis [16]. ...
The covariance-driven stochastic subspace identification (SSI-COV) is widely used in the operational modal analysis of structures. However, the appropriate selection of user-defined parameters in the SSI-COV algorithm remains a challenging issue, especially for the modal tracking. This study aims to analyze the effect of the four user-defined parameters in SSI-COV for the modal identification of high arch dams. Two finite element (FE) models of the Dagangshan dam are investigated by the SSI-COV to identify the modal parameters. The FE model with the massless foundation is analyzed to investigate the effect of four user-defined parameters on the identification of dynamic properties, and the selection suggestions are proposed for each parameter. The FE model recognizing the semi-unbounded size of foundation rock is further analyzed to investigate the radiation damping effect based on the proposed suggestions of user-defined parameters. The results show that the radiation damping effect of the semi-unbounded foundation rock is approximately 0.6%-2.0% for the first four modes. Moreover, the modal parameters of the Xiluodu dam (285 m) are identified using ambient vibration test, which illustrates that the proposed suggestions for selecting user-defined parameters are effective and reasonable. This study is very beneficial for the modal tracking and structural health monitoring of arch dams in the future.
... However, the technological progress that occurred in the field of data acquisition systems during the past few decades promoted the emergence of operational modal analysis as a reliable alternative that gradually became more frequent. Even though operational modal analysis today is more common in bridges, wind turbines, towers and other lighter structures, there are already some successful examples of the application of such modal identification techniques to dams, both through the performance of ambient vibration tests [4] [5] and through the installation of vibration-based health monitoring systems [6] [7]. Nevertheless, when compared to forced vibration tests, much lower levels of vibration and much lower signal to noise ratios should be expected under natural excitation [8], thus very sensitive sensors and high-resolution digitizers are required to obtain good results. ...
The Laboratory of Vibrations and Structural Monitoring (ViBest) of FEUP is presently responsible by the development of the research project DAM_AGE (Advanced Online Dynamic Structural Health Monitoring of Concrete Dams). One of the first tasks of this project consists on the performance of ambient vibration tests on concrete dams with different typologies and stiffness characteristics and on the application of state of art output-only modal identification methods, getting better sensitivity to the problems raised by the very low collected signals (of the order of micro g) when dealing with such massive structures. In this context, this paper describes a set of ambient vibration tests performed on different Portuguese concrete dams and presents the most relevant modal estimates obtained with the application of modern output-only modal identification techniques, stressing the good level of accuracy in general achieved, despite the very unfavourable signal-to-noise ratio in comparison with other civil engineering applications.
... ese parameters have obvious physical meanings and represent the practical dynamic characteristics of structures. Some researchers have made efforts to address the modal identification problem of concrete dams based on earthquake response records [1][2][3][4][5][6]. However, the modal identification methods adopted in the past studies are restricted to linear systems and stationary processes, and using such methods would require the assumption that the damreservoir-foundation system is linear and time invariant for the duration of a vibration measurement. ...
To investigate the time-varying dynamic characteristics of concrete dams under the excitation of large earthquakes for online structural health monitoring and damage evaluation, an online modal identification procedure based on strong-motion records is proposed. The online modal identification of concrete dams is expressed as a subspace tracking problem, and a newly developed recursive stochastic subspace identification (RSSI) method based on the generalized yet another subspace tracker (GYAST) algorithm, which exploits both the accuracy of the subspace identification and fast computational capability, is used to extract the time-varying modal parameters of concrete dams during earthquakes. With the simulated vibration response records, a numerical example is used to verify the accuracy, robustness, and efficiency of the proposed GYAST-based, time-varying modal identification method. Then, the realistic strong-motion records of the Pacoima arch dam are analysed using the proposed modal identification procedure, and the time-varying characteristics of the concrete arch dam during three different earthquakes are analysed.
... Even though the modal identification of dams is historically associated to forced vibration tests [1] [2], there are already some successful examples of operational modal analysis applied to this type of structures, both through the performance of ambient vibration tests [3] [4] and the installation of vibration-based health monitoring systems [5] [6]. Nevertheless, when compared to forced vibration tests, much lower levels of vibration and much lower signal to noise ratios should be expected under natural excitation [7]. ...
At present time, the accurate estimation of modal properties of large civil structures (e.g. buildings, bridges, chimneys, wind turbines) can be easily achieved by applying state of art output-only modal identification methods (e.g. SSI-cov, SSI-Data, p-LSCF) to the data obtained with ambient vibration tests performed with appropriate sensors and data acquisition systems. However, when dealing with massive structures like concrete dams, the signals are very low (of the order of micro-g) and the signal to noise ratio very challenging in terms of modal identification. In this context, this paper describes an investigation developed on the Alto Lindoso dam (a double curvature arch dam in the North of Portugal, 110 m high) with the purpose of analysing the level of accuracy achieved, in terms of modal identification with the alternative use of different type of accelerometers (force-balance, piezoelectric, MEMS), developing a complete ambient vibration test along the dam crest.
... Usually, a 5% damping ratio is selected for the dam and a similar value for the foundation. Proulx [17], Darbre [18] and Alves [15] measured the damping ratio of the dam-reservoir-foundation system for the Emosson Dam, Mauvoisin Dam and Pacoima Dam, respectively. Chopra and Wang [19] compared the calculated and experimental values of damping ratio for Mauvoisin Dam and Pacoima Dam, and concluded that the current practice is likely to lead to excessive damping in the overall dam-water-foundation-rock system and should be abandoned. ...
Simulation of the infinite foundation is a key issue in the seismic response analysis of high dams. This paper studies how the major characteristics of foundation models influence the nonlinear dynamic response of arch dams when the radiation damping effect is taken into account. The nonlinear dynamic responses of the 217 m high Yebatan arch dam under construction in China is performed as a numerical example. Several key factors, including truncated size, material damping and non-uniformity of the foundation, are analyzed comprehensively. The results show that the material damping and the size of the foundation affect the dynamic response of the dam when the incident wave method is used. Neglect of the material damping of the foundation is proposed to solve this problem, and its rationality is verified. In addition, the results show that the realistic non-uniformity of the foundation should be considered in the earthquake response of arch dams.
... Usually, a 5% damping ratio is selected for the dam and a similar value for the foundation. Proulx [17], Darbre [18] and Alves [15] measured the damping ratio of the dam-reservoir-foundation system for the Emosson Dam, Mauvoisin Dam and Pacoima Dam, respectively. Chopra and Wang [19] compared the calculated and experimental values of damping ratio for Mauvoisin Dam and Pacoima Dam, and concluded that the current practice is likely to lead to excessive damping in the overall dam-water-foundation-rock system and should be abandoned. ...
Simulation of the infinite foundation is a key issue in the seismic response analysis of high dams. This paper studies how the major characteristics of foundation models influence the nonlinear dynamic response of arch dams when the radiation damping effect is taken into account. The nonlinear dynamic responses of the 217m high Yebatan arch dam under construction in China is performed as a numerical example. Several key factors, including truncated size, material damping and non-uniformity of the foundation, are analyzed comprehensively. The results show that the material damping and the size of the foundation affect the dynamic response of the dam when the incident wave method is used. Neglect of the material damping of the foundation is proposed to solve this problem, and its rationality is verified. In addition, the results show that the realistic non-uniformity of the foundation should be considered in the earthquake response of arch dams.
... For this purpose, several numerical simulations of Cabril dam (shown in Figure 1(a)) were performed, considering different water levels. This is a common procedure [23][24][25] as the natural frequencies of the system depend on the reservoir water level. Cabril dam, built in 1954, is the highest Portuguese arch dam. ...
We consider a dam-water system modeled as a fluid-structure interaction, specifically, a coupled hyperbolic second-order problem, formulated in terms of the displacement of the structure and the fluid pressure. Firstly, we investigate the well posedness of the corresponding variational formulation using Galerkin approximations, energy estimates, and mollification. Then, we apply the finite element method along with the state-space representation of the discrete problem in order to perform a 3D numerical simulation of Cabril arch dam (Zêzere river, Portugal). The numerical model is validated by comparison with available experimental data from a monitoring vibration system installed in Cabril dam.
... These modal parameters may be useful for structural damage detection, finite element model updating, structural safety evaluation, structural health monitoring, estimating dynamic behavior, and estimating the effectiveness of repairing or strengthening techniques [4][5][6][7][8][9][10][11][12]. In this context, modal testing has been implemented successfully by researchers on different types of civil engineering structures and scaled structure models such as dams [13][14][15][16][17][18][19][20], bridges [1,[21][22][23][24][25][26], and buildings and towers [27][28][29][30][31][32][33][34]. ...
This paper presents numerical modelling, modal testing, finite element model updating, linear and nonlinear earthquake behavior of a reinforced concrete building model. A 1/2 geometrically scale, two-storey, reinforced concrete frame model with raft base were constructed, tested and analyzed. Modal testing on the model using ambient vibrations is performed to illustrate the dynamic characteristics experimentally. Finite element model of the structure is developed by ANSYS software and dynamic characteristics such as natural frequencies, mode shapes and damping ratios are calculated numerically. The enhanced frequency domain decomposition method and the stochastic subspace identification method are used for identifying dynamic characteristics experimentally and such values are used to update the finite element models. Different parameters of the model are calibrated using manual tuning process to minimize the differences between the numerically calculated and experimentally measured dynamic characteristics. The maximum difference between the measured and numerically calculated frequencies is reduced from 28.47% to 4.75% with the model updating. To determine the effects of the finite element model updating on the earthquake behavior, linear and nonlinear earthquake analyses are performed using 1992 Erzincan earthquake record, before and after model updating. After model updating, the maximum differences in the displacements and stresses were obtained as 29% and 25% for the linear earthquake analysis and 28% and 47% for the nonlinear earthquake analysis compared with that obtained from initial earthquake results before model updating. These differences state that finite element model updating provides a significant influence on linear and especially nonlinear earthquake behavior of buildings.
... In the case of dams, forced vibration tests [6] [7] are historically the most common tests performed with the aim of identifying the structure dynamic properties, and the dynamic monitoring systems are generally just concerned with the characterization of the structure response during earthquakes [8] [9]. Dynamic tests using ambient vibration have already been conducted in the past [10] [11] [12] [13] [14], often as an addition to forced vibration campaigns, and in recent years the performance of these tests on dams with the aim of calibrating numerical models became more common [15] [16] [17] [18]. On the other hand, the installation of vibration-based health monitoring systems on dams is still very uncommon. ...
The Baixo Sabor dam is a concrete double-curvature arch dam, 123 m high, located in the north-east of Portugal, which is being monitored by a dynamic monitoring system that comprises 20 uniaxial accelerometers. The paper starts with the description of the structure and of the installed monitoring equipment, as well as the monitoring software used to process the data that is continuously retrieved from site through an internet connection. Then, the results obtained during the system's first six months of operation are presented, which include the characterization of acceleration levels for major events, such as the opening of spillway gates after intense rain, and the evolution of the dam modal properties (natural frequencies, modal damping ratios and mode shapes) during the reservoir first filling. In particular, the continuous characterization of the dam modal properties during important variations of the water level is a very unique experimental result (up to the authors knowledge, this is the first journal paper describing the continuous tracking of the modal parameters of a dam during its first filling), which is particularly interesting for the calibration of numerical models that take into account water-structure interaction. Additionally, it should be noted that the accurate tracking of the modal properties, in quite demanding conditions motivated by the very low vibration levels, associated to the massive nature of the structure, and by the presence of harmonics induced by the turbines of the hydroelectric power plant, was only possible thanks to the use of a carefully designed installation and advanced processing methodologies. At the end of the paper, it is presented a comparison between the results estimated with ambient excitation and the ones obtained with a forced vibration test and also predicted by a numerical model that includes the water effect with the added mass technique.
... To support the seismic safety evaluation, Hydro-Québec decided to conduct an experimental program to evaluate the dynamic properties of the dam-reservoir-foundation (DRF) system, in collaboration with the Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke, Quebec, Canada, because of its experience in characterizing and modeling the dynamic behavior of large concrete dams (Proulx and Paultre 1997;Proulx et al. 2001;Paultre et al. 2002). The aim of this study was to get a three-dimensional (3D) finite-element model of the DRF system suitable for further seismic analyses, but the seismic analyses themselves are outside the scope of this study. ...
Forced-vibration tests were conducted on the Daniel-Johnson multiple-arch dam located in northeastern Quebec, Canada. This outstanding structure for its size and complexity is the largest multiple-arch dam in America. The tests aimed to determine the dynamic properties of the dam-reservoir-foundation (DRF) system to be used as a basis for the update of a finite-element model of the system required for further seismic performance assessment. The test procedure is described and the modal properties derived from the recordings are presented together with the extraction procedure, which was particularly complicated because of the coupling of the numerous global and local modes of such a complex structure. Several linear three-dimensional finite-element models were developed to be correlated with the measured dynamic properties. A parametric study on the dam-foundation elasticity was first performed, and the influence of the reservoir water modeling was then extensively studied. The selected model properties resulting from the numerical correlation study enabled reproduction with good accuracy of eight of the measured vibration modes, making the model suitable for seismic analyses.
... Moreover, the reader should notice that the assumed damping ratio for the dam and foundation (Table 1) may increase the total damping ratio of the coupled system beyond 10% (this will be shown later). However, several forced vibration tests and earthquake measurements revealed a cap of ∼7% for overall damping in the system (Alves and Hall 2006, Chopra 2012, Proulx et al. 2001, Rea et al. 1974. ...
The seismic risk of concrete dams may be assessed using various numerical techniques, ranging from simplified methods to linear and nonlinear ones. Such methods should be combined with probabilistic concepts to account for the randomness in both demand and capacity. This paper proposes a random version of a simplified response spectrum method (involving equivalent static lateral forces) for gravity dams by means of propagating uncertainties through the input parameters. Input parameter sensitivity is quantified and the extended procedure explained step-by-step. Results are then generalized for the different dam classes. The impacts of sampling size and technique (i.e. pseudo- and quasi-random) are also discussed. A time-based performance is evaluated and fragility curves are derived. This method may be used during the initial stages of a design process or safety analysis for existing dams.
... Therefore AVTs are quite attractive compared to FVTs. Many studies in the literature report the implementation of experimental modal analyses on different types of structures such as dams (Deinum et al. 1982;Loh and Wu 1996;Proulx et al. 2001;Sevim et al. 2011), bridges (Brownjohn et al. 1992;Altunışık et al. 2011;Ribeiro et al. 2012), buildings and towers (Ventura et al. 2002;Wu and Li 2004;Skolnik et al. 2007), and masonry structures (Gentile and Saisi 2007;Altunışık et al. 2016). ...
Finite-element (FE) model updating is a very effective procedure for determining the uncertainty parameters in a structural model and minimize differences between experimentally and analytically identified dynamic characteristics. This procedure can be practiced with manual and global/local automatic model updating procedures. Automatic model updating is very popular because of its applicability to all kinds of engineering structures to minimize differences, and its damage localization and structural health monitoring. This paper considers a historical masonry bastion to obtain its dynamic characteristics numerically with the finite-element method and experimentally with ambient vibration tests (AVTs). Sensitivity analyses for the uncertainty parameters and manual and automated model updating to minimize differences are also performed. A castle bastion located in Trabzon, Turkey is selected as an application. The FE model of structure is developed in commercial software. The first three natural frequencies are obtained between 5 and 10 Hz, and AVTs are performed under natural excitation using enhanced frequency domain decomposition (EFDD) and subspace structural identification (SSI) techniques. The first three natural frequencies are obtained between 4 and 7 Hz. The comparison of analytically and experimentally identified dynamic characteristics shows a close agreement between mode shapes, but 26% difference in natural frequencies. To minimize the difference, the FE model of the bastion is updated using manual and global/local automated updating, changing its material properties of Young's modulus and material density. The maximum differences are reduced from 27 to 3% with manual updating, and to 0.02% with automated model updating.
... Darbe et al. (2000) achieved the resonance frequencies of the 250-m-high arch dam of Mauvoisin by using ambient vibration test. Proulx et al. (2001) investigated the water level effects on the dynamic behavior of arch dams. Darbre and Proulx (2002) preferred the continuous ambient vibration monitoring studies and their results related to Mauvoisin arch dam. ...
This paper presents the structural identification of an arch dam model for the damaged, repaired and strengthened conditions under different water levels. For this aim, an arch dam-reservoir-foundation model has been constructed. Ambient vibration tests have been performed on the damaged, repaired and strengthened dam models for the empty reservoir (0 cm), 10 cm, 20 cm, 30 cm, 40 cm, 50 cm and full reservoir (60 cm) water levels to illustrate the effects of water levels on the dynamics characteristics. Enhanced Frequency Domain Decomposition Method in the frequency domain has been used to extract the dynamic characteristics. The dynamic characteristics obtained from the damaged, repaired and strengthened dam models show that the natural frequencies and damping ratios are considerably affected from the varying water level. The maximum differences between the frequencies for the empty and full reservoir are obtained as 16%, 33%, and 25% for damaged, repaired and strengthened model respectively. Mode shapes obtained from the all models are not affected by the increasing water level. Also, after the repairing and strengthening implementations, the natural frequencies of the arch dam model increase significantly. After strengthening, between 46-92% and 43-62% recovery in the frequencies are calculated for empty and full reservoir respectively. Apparently, after strengthening implementation, the mode shapes obtained are more acceptable and distinctive compared to those for the damaged model.
... To support the seismic safety evaluation, Hydro-Québec decided to conduct an experimental program to evaluate the dynamic properties of the dam-reservoir-foundation (DRF) system, in collaboration with the Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke because of its experience in characterizing and modelling the dynamic behavior of large concrete dams [1,2,3]. The aim of this study was to get a 3D finite element model of the DRF system suitable for further seismic analyses. ...
The Daniel-Johnson dam is a 1314-m long multiple-arch-buttress dam composed of 14 buttresses and 13 arches with a central arch of 214 m high. The upper part of the dam is composed of gravity dam supported by the arches. Its height, length and the 2 million cubic meters concrete used for its construction make it the largest dam of its type in the world. Hydro-Québec and the University of Sherbrooke carried out forced-vibration tests on the Daniel-Johnson dam that are presented in this paper. The tests aimed to determine the dynamic properties of the dam-reservoir-foundation (DRF) system to be used as a basis for the update of a 3D finite element model of the system. The outstanding size and the complex geometry of the dam are of great interest in this study, because they involved challenges in the experimental work not usually found for smaller dam of simpler geometry. The forced-vibration tests involved the use of an eccentric mass shaker generating forces up to 89 kN. The accurate modal identification of the dam required four different locations of the shaker, 52 measurement stations distributed along the crest of the dam and in the inspection galleries, and overall 13 tests configurations. These tests showed that it is possible to measure useful signals along the whole crest of a very large and massive concrete dam and as far as in the very lower inspection galleries, even with a relatively small excitation force. The analysis procedure of the experimental data were however quite complicated due to the numerous close local and global modes of the multiple-arch dam and their coupling. Twenty-two vibration modes were clearly identified. A 3D finite element model of the DRF system is briefly presented, and was correlated with the measured vibration modes.
... These modal parameters may be useful for structural damage detection, finite element model updating, structural safety evaluation, structural health monitoring, estimating dynamic behavior, and estimating the effectiveness of repairing or strengthening techniques [4][5][6][7][8][9][10][11][12]. In this context, modal testing has been implemented successfully by researchers on different types of civil engineering structures and scaled structure models such as dams [13][14][15][16][17][18][19][20], bridges [1,[21][22][23][24][25][26], and buildings and towers [27][28][29][30][31][32][33][34]. ...
An improved finite element model was used to obtain more accurate modeling of engineering structures. The main goal of this paper was to determine how this improved modeling procedure affects the dynamic response of buildings based on experimental modal parameters such as natural frequencies, mode shapes and damping ratios. For experimental assessment, three small, one-story, two-bay, reinforced concrete buildings with raft foundation were constructed under laboratory conditions. The initial three -dimensional finite element models, built with the ANSYS software, were used to analytically identify modal parameters, including natural frequencies and mode shapes. Following the analytical study, the ambient vibration tests were performed to obtain modal parameters, experimentally. The enhanced frequency domain decomposition method and the stochastic subspace identification method were used to identify the modal parameter. The analytical and experimental modal parameters were compared and then initial finite element models were updated to minimize the differences by changing of some uncertain parameters such as materials properties. With model updating, the maximum difference between the measured and initially obtained frequency was reduced from 28.47 to 4.88 %. To show the model updating effect on dynamic response of building models, dynamic analysis with the experimental computed damping ratios and 5 % damping ratio were carried out using 1992 Erzincan earthquake ground motion record. For the experimental damping ratios, the maximum differences in the displacements and stresses between the initial and updated models were obtained as 23 and 32 %, respectively. These differences were calculated as 43 and 15 % for the 5 % damping ratio. Comparisons of dynamic analyses results for the initial and updated model show that the finite element model updating affects the dynamic response of the buildings considerably.
... Recently, the research on dynamic FE model calibration of a structure has attracted much attention [5,6]. For example, Zhang et al. [7] studied the structure system identification and the dynamic FE model updating method of a suspension bridge based on an ambient vibration test; Ntotsios et al. [8] used the optimization method to identify the modal parameters of two bridges in Greece, and then the FE model of the bridges was corrected; Proulx et al. [9], Alves et al. [10] and Sevim et al. [11] studied the modal identification and the dynamic FE model updating problem of Emosson dam, Pacoima dam and Berke dam, respectively; Feng et al. [12] developed a dynamic elastic modulus back analysis method of concrete gravity dams, based on the simulated annealingsimplex shape algorithm. Because dams and other hydraulic structures are giant and complex structures, computational efficiency must be considered when dynamic FE model calibration is implemented. ...
In this work, a new finite element (FE) model calibration method of concrete dams based on strong-motion records and multivariate relevant vector machines (MRVM) is proposed. The modal features of a dam are extracted using second order blind identification (SOBI) based method at first. For some selected combinations of uncertain parameters of the FE model using the Latin hypercube design, the corresponding structural modal features are calculated using the finite element method (FEM). With these data, a procedure to calibrate the uncertain parameters of a dam’s dynamic FE model is developed. By taking the uncertain parameters as inputs and the calculated structural modal features using FEM as outputs, the MRVM model is trained to record the complex relationship between them. Then, the genetic algorithm (GA) is adopted to solve the optimization problem corresponding to the dynamic FE model calibration problem, and the trained MRVM model, instead of FEM, is used to obtain the modal parameters of a dam for different feasible solutions during the optimization search process to improve the computational efficiency. Using the simulated seismic response records of a numerical example the accuracy, robustness and computation efficiency of the proposed dynamic FE model calibration method is verified. The analysis result using the strong-motion records of a realistic concrete dam indicates that the proposed dynamic FE model calibration method has good performance.
... Ziyad (1998) conducted a finite element analysis and experimental measurements on the Morrow Point Arch Dam in Colorado to determine the dam-water interaction effect and water's compressibility. Proulx et al. (2001) showed the effects of water level on the dynamic behavior of arch dams. Darbre and Proulx (2002) preferred continuous ambient vibration monitoring studies and presented with reference to the Mauvoisin Arch Dam in Switzerland. ...
Continuous health monitoring and regular condition assessment is of vital importance for engineering structures in general and especially for arch dams. These structures can be exposed to many different loads such as earthquake, blast, wind, ice, and water pressure, which may cause deterioration and loss of structural integrity. Such development may have severe economic consequence and, more importantly, may present a serious risk to public safety. Therefore, the structural behavior of arch dams must be monitored at regular intervals during their service life, although the overall failure rate of these dams is around 1%. Experimental measurements by ambient vibration test methods are among the most commonly preferred inspection techniques for the evaluation of structural performance and safety. The aim of this research is to examine the retrofitting effect on the dynamic properties of a damaged arch dam model, with and without reservoir water, after retrofitting with high-strength structural repair mortar and carbon fiber reinforced polymer composite material. To this end, an arch dam-reservoir-foundation model was built. In the study, ambient vibration tests were carried out for three test-cases to determine changes in dynamic properties, such as natural frequency, mode shape, and damping ratio before and after retrofitting. The three cases were (1) a severely damaged dam with full reservoir (Case-A), (2) a repaired dam with full reservoir (Case-B), and (3) a strengthened dam with full reservoir (Case-C). In addition, all the measurement tests were repeated with an empty reservoir to extract the effect of water. Data for the ambient vibration tests were gathered from the dam body during vibrations by natural excitations. These excitations were provided through small impacts, and the response signals were measured by sensitivity accelerometers placed at the crest points. To obtain the experimental dynamic properties, the enhanced frequency domain decomposition method in the frequency domain was used. Comparisons of experimentally identified dynamic properties for the damaged and the retrofitted dam showed that the retrofitting application affected the structural behavior of the arch dam considerably. It was very effective in restoring the structure's original dynamic properties.
... The ambient vibration testing has been frequently used by many researchers to investigate the structural performance and/or structural safety of large dams (Deinum et al. 1982;Loh and Wu 1996;Duron 1988;Daniell and Taylor 1999;Darbre et al. 2000;Proulx et al. 2001;Oliveira and Mendes 2006;Weng and Loh 2010;Bayraktar et al. 2011). Although the physical conditions are quite difficult for excitation of large dams, and tests become too expensive and require much time, results achieved by ambient vibration test are very useful. ...
This technical note presents an investigation about the changing of dynamic characteristics of an arch dam model before and after strengthening considering reservoir water. To this end, an arch dam-reservoir-foundation model has been constructed in the laboratory. Ambient vibration tests have been performed on the damaged and strengthened arch dam models for empty and full reservoir to determine the effect of water on the dynamics characteristics. Enhanced frequency domain decomposition method has been used to extract the dynamic characteristics. Finally, the dynamic characteristics obtained from the damaged and strengthened dam models have been compared to with each other. Also, the natural frequencies for damaged and strengthened models are compared to detect the effect of strengthening application on the frequencies. Results indicate that the natural frequencies and damping ratios are changed with the full reservoir. However, mode shapes are not changed. Results also show that the natural frequencies of damaged dam considerably increase after strengthening applications.
... To extract the dynamic characteristics from experimental records, frequency response functions are used. Proulx et al. (2001) presented the water level effects on the dynamic behavior of arch dams. The dam is located on the border of France and Switzerland, between Chamonix and Martigny, near the Mont Blanc mountain range. ...
This paper investigates the time dependent changing of dynamic characteristics of laboratory arch dam models using ambient vibration test. For this aim, a prototype arch dam-reservoir-foundation model is constructed in laboratory conditions. The first experimental measurement tests are performed after the poured concrete aged for 10 months for some damage scenarios such as undamaged, minor-damaged and severely damaged of dam body in November 2009. To extract the experimental dynamic characteristics such as natural frequencies, mode shapes and damping ratios, a small impact effect is used as a source of ambient vibrations. Experimental measurements tests are repeated using same excitations considering severely damaged conditions with and without reservoir water in February 2014, and the dynamic characteristics are obtained, experimentally. Enhanced Frequency Domain Decomposition Method in the frequency domain is used to extract the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics are compared with each other and time effects are investigated in detail. Maximum differences between the natural frequencies obtained as 15.36% and 14.38% in the third mode for empty and full reservoir conditions, respectively. It is thought that the increase of the natural frequencies is resulted from gaining of rigidity of the concrete, ageing, temperature and different environmental effects.
... Valliappan et al. [44] presented the nonlinear seismic response of arch dams. Proulx et al. [35] showed the effects of water level on the dynamic behavior of arch dams. Darbre and Proulx [14] preferred continuous ambient vibration monitoring studies related to the Mauvoisin arch dam. ...
The purpose of this study is to investigate the effect of retrofitting dynamic characteristics of a damaged laboratory arch dam model, subsequently repaired with high-strength structural mortar and strengthened with composite carbon fiber reinforced polymer. This study constructed in laboratory conditions is a prototype arch dam–reservoir–foundation model. Five test cases of ambient vibration on the arch dam model illustrate the changes in dynamic characteristics: natural frequency, mode shape, and damping ratio, before and after retrofitting. The ambient vibration tests collected data from the dam body during vibrations by natural excitations which provided small impacts and response signals from sensitivity accelerometers placed at crest points. Enhanced Frequency Domain Decomposition Method in the frequency domain extracts the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics obtained from all test cases have been compared with each other. Apparently, after the retrofitting, the natural frequencies of the dam body increased considerably, demonstrating that the retrofitting, including repairing and strengthening is very effective on the flashback of initial dynamic characteristics.
... However in analytical studies, finite element models of the structures are constituted assuming the some acceptances in design. One of the important inspections is to apply ambient vibration tests to existing dams to estimate their dynamic characteristics (Proulx et al. 2001). ...
The Berke Arch Dam is the highest arch dam constructed in Turkey. The dam height is 201 m, and the crest length is 270 m. This paper describes the Berke Arch Dam, its finite-element modeling, ambient vibration testing, finite-element model calibration, and earthquake behavior before and after model calibration. First, three-dimensional (3D) models of dam-reservoir-foundation interaction were developed to obtain analytical dynamic characteristics, such as natural frequencies and mode shapes using the Ansys finite-element program. In the analyses, reservoir water was represented by a Lagrangian approach. Then, ambient vibration tests were conducted on the dam on 4 days in May 2009 to obtain experimental dynamic characteristics. In ambient vibration tests, the sensitive accelerometers were placed on several points on the arch dam, and signals were collected from accelerometers. The enhanced frequency domain decomposition technique was used in the extraction of experimental natural frequencies, mode shapes, and damping ratios. After that, 3D finite-element models of the Berke Arch Dam were calibrated using ambient vibration test results. Finally, earthquake behaviors of initial and calibrated models of the Berke Arch Dam were obtained using the Adana-Ceyhan Earthquake in 1998. It was observed that model calibration affects the results considerably. DOI: 10.1061/(ASCE)CF.19435509.0000264. (C) 2012 American Society of Civil Engineers.
This paper focuses on vibration-based analysis for model calibration and structural condition assessment of large concrete dams. The case study is the 170 m-high Cahora Bassa arch dam, Mozambique. In operation for almost 50 years, the dam presents deterioration signs due to concrete swelling, and in 2010 it was instrumented with a continuous dynamic monitoring system. In this work, the vibrations measured under ambient/operational conditions for more than a decade are analyzed in order to estimate the modal parameters of the dam, which are then used to calibrate and validate a new finite element model of the Cahora Bassa dam-reservoir-foundation system. After that, finite element analyses are performed to simulate the dynamic behavior of the dam for future years, considering a scenario of progressive damage due to concrete swelling. The presented results show that the dynamic performance of Cahora Bassa dam in normal operating conditions is not being affected by the existing concrete swelling phenomenon, and that vibration-based analysis can provide valuable data for detecting structural changes in concrete dams due to progressive deterioration.KeywordsVibration-based analysisModel calibrationStructural condition assessmentProgressive deteriorationConcrete swelling
Vibration characteristics, i.e., natural frequency and mode shape of structure or structural component are essential parameters in its earthquake resistant design. Modal analysis helps to calculate natural frequencies and mode shapes of the structure in free vibration. The present paper investigates the modal analysis of the gravity dams for varying reservoir and tailwater heights and interaction effects. For modal analysis, two gravity dams (e.g., Koyna and Outardes-3 gravity dams) are chosen. The Lanczos algorithm is used in Abaqus to find out dams undamped natural frequencies and mode shapes. Various reservoir and tailwater heights are considered for the gravity dams. In addition, the effect of dam–foundation–reservoir and dam–reservoir interaction are considered for the modal analysis of the gravity dam. In finite element meshing, a 4 node plane strain elements are utilized for modeling purpose of both the dam and foundation domains; whereas a 4 node acoustic elements are used to model the reservoir domain. The effect of reservoir surface waves is not considered in the numerical study. In modal analysis, lower reservoir water level causes more horizontal crest deformation; however, the consideration of higher reservoir and tailwater levels of the dam makes it more flexible; and thus reduces the system’s natural frequencies. As compared to dam–reservoir interaction, dam–foundation–reservoir interaction causes lower natural frequency for the system.KeywordsGravity damReservoir and tailwater heightsDam–foundation–reservoir interactionDam–reservoir interactionModal analysis
In general, the methods in structural analysis and design can be classified into two main groups: (1) deterministic simulations and (2) probabilistic simulations. In the case that the finite element method (FEM), used for discretization of the medium, is combined with statistics and reliability methods, the so-called probabilistic finite element method (PFEM) is developed and can be applied to both linear and non-linear systems. Uncertainty can be propagated in both the finite element and applied load. Different sampling techniques based on crude MCS or more efficient techniques can be used. This chapter discusses three elements: (1) Mathematical review on sampling techniques, (2) Propagation of uncertainty in the response spectrum method (loading) and proposing the “random response spectrum method” (RRSM), and (3) Propagation of uncertainty directly in finite element and discussion on random finite element method (RFEM).
A method is proposed for monitoring the natural frequencies of hydro power plant dams using continuous seismic observation data. The object of the research is the largest in Russia arched Chirkey dam located in the Caucasus. At the initial stage, a detailed study of the natural oscillations of the dam was performed using the method of coherent restoration of the standing wave fields with the definition of both the natural frequencies of the structure and their modes. The features of seasonal changes in the total field of standing waves are studied and factors affecting changes in natural frequencies are established. At the next stage, the values of natural frequencies were determined from the spectra of microseismic oscillations recorded by seismic equipment installed on the object. Observation points located in the antinodes of standing waves were used. The values of the natural frequencies of the Chirkey dam, as a whole, decrease with increasing upstream level. It was determined that there are additional factors leading to the hysteresis effect in the relationship between the values of the upstream level and natural frequencies, presumably associated with relaxation processes in the dam body and/or in the dam-base system after the change of level. A method for monitoring the state of the dam is proposed, based on a comparison of the observed values of natural frequencies with the predicted ones. The latter are determined by linear dependencies on the upstream level, taking into account the time shifts associated with relaxation processes
Modal parameters, including fundamental frequencies, damping ratios, and mode shapes, could be used to evaluate the health condition of structures. Automatic modal parameter identification, which plays an essential role in real-time structural health monitoring, has become a popular topic in recent years. In this study, an automatic modal parameter identification procedure for high arch dams is proposed. The proposed procedure is implemented by combining the density-based spatial clustering of applications with noise (DBSCAN) algorithm and the stochastic subspace identification (SSI). The 210-m-high Dagangshan Dam is investigated as an example to verify the feasibility of the procedure. The results show that the DBSCAN algorithm is robust enough to interpret the stabilization diagram from SSI and may avoid outline modes. This leads to the proposed procedure obtaining a better performance than the partitioned clustering and hierarchical clustering algorithms. In addition, the errors of the identified frequencies of the arch dam are within 4%, and the identified mode shapes are in agreement with those obtained from the finite element model, which implies that the proposed procedure is accurate enough to use in modal parameter identification. The procedure is feasible for online modal parameter identification and modal tracking of arch dams.
Structural Health Monitoring (SHM) is becoming the fourth driving force of engineering science and technology progress, in addition to the basic theory, numerical simulation and model test. In this paper, a definition of dam SHM is presented, its basic connotation is analyzed, and the general problems in existing researches are summarized. Then the sensitivity analysis of the static performance of concrete gravity dam is reviewed. For a hypothetical concrete gravity dam, a preliminary nonlinear finite element model is established. By means of the variance-based global sensitivity analysis method, phenomenological analysis of the static performance of the dam is carried out from three different horizons. And then the results are discussed in detail according to the common components of SHM. Overall, this paper provides a framework for sensitivity analysis of dams, or a way to explore the complexity of the dam system. In the long run, this paper should still be positioned as a generic and qualitative study in view of the complexity of dam system. There are still many issues as pointed out in the text need to be further understood and studied, and sensitivity analysis is a good tool.
The characterization of the dynamic behavior of an arch dam, and its evolution throughout the structure's lifetime, provides important data for the safety control process. Forced vibration tests remain a reliable technique for this purpose. The Baixo Sabor dam is a 123 m high arch dam recently built in Portugal. Forced vibration tests were performed before and after the reservoir filling. Two techniques for forced vibration test are compared, discrete frequency scanning, the standard methodology, and continuous frequency scanning (sine sweep), a new proposed methodology, which allowed faster results without loss of precision. For the interpretation of test results two numerical models of the dam‐reservoir‐foundation system were built, and calibrated with the experimental data. A good match of numerical and experimental results was obtained for the six lowest frequencies and corresponding mode shapes.
For the characteristics of arch dam pouring process and the disadvantages of previous simulation tools, this paper proposes the idea of generating dam body in real time by 3D cutting method. With this method, only one 3D model of the dam body need to be established, then other 3D models can be generated based on the input data of the users, which can accurately and efficiently simulate the pouring process.
The aim of this study is to clarify the parameter-determination issue with regard to the viscous damping and contraction joint friction in the underwater explosion (UNDEX) resistant design of arch dams. A 141-m-high double-curvature arch dam is chosen as the study subject, and the finite-element program ABAQUS/Explicit is employed. Both the dam-reservoir interaction and the contraction-joint nonlinearity are considered. The calculation results suggest that in a routine range of values for the viscous damping ratio (less than 0.05), the damping effect on the UNDEX-induced displacement and damage responses of the arch dam seem limited. To be conservative in the design, the viscous damping ratio could be assigned a zero value (neglecting the damping effect). The calculation results have highlighted the importance of the monolith-to-monolith friction to the tensile damage to the dam base. We believe that a value of 0.65 assigned to the friction coefficient should be appropriate for the UNDEX resistant design of an arch dam in case the shear keys' shear-transferring roles are not considered.
The performance evaluation of concrete arch dam under dynamic excitation is a challenging task which requires the comprehensive knowledge of modeling aspects. This paper summarizes important and critical parameters to be considered during dynamic analysis of concrete arch dams. A comprehensive review work is carried out in order to identify the factors which influence significantly the three-dimensional analysis of arch dams.
Two different back-analysis frameworks based on multivariate machine learning models used to determine the material dynamic parameters of concrete gravity dams are proposed. For the framework I, the back-analysis is performed by solving an optimization problem and a multivariate machine learning model is trained to replace the FEM calculation during the optimization process. While the framework II uses a multivariate machine learning model directly and the material dynamic parameters are predicted using the machine learning mode. By using a numerical example and an experimental investigation, the robustness, accuracy, computation efficiency of these proposed back-analysis methods is verified.
According to theoretical analysis, a general characteristic of the ground vibration induced by high dam fl ood
discharge is that the dominant frequency ranges over several narrow frequency bands, which is verifi ed by observations from
the Xiangjiaba Hydropower Station. Nonlinear base isolation is used to reduce the structure vibration under ground excitation
and the advantage of the isolation application is that the low-frequency resonance problem does not need to be considered due
to its excitation characteristics, which signifi cantly facilitate the isolation design. In order to obtain the response probabilistic
distribution of a nonlinear system, the state space split technique is modifi ed. As only a few degrees of freedom are subjected
to the random noise, the probabilistic distribution of the response without involving stochastic excitation is represented by
the δ function. Then, the sampling property of the δ function is employed to reduce the dimension of the Fokker-Planck-
Kolmogorov (FPK) equation and the low-dimensional FPK equation is solvable with existing methods. Numerical results
indicate that the proposed approach is effective and accurate. Moreover, the response probabilistic distributions are more
reasonable and scientifi c than the peak responses calculated by conventional time and frequency domain methods.
A direct finite element method is presented for nonlinear earthquake analysis of interacting dam–water–foundation rock systems. The analysis procedure applies viscous damper absorbing boundaries to truncate the semi-unbounded fluid and foundation-rock domains and specifies at these boundaries effective earthquake forces determined from the design ground motion defined at a control point on the free surface. The analysis procedure is validated numerically by computing the frequency response functions and transient response of an idealized dam–water–foundation rock system and comparing with results from the substructure method. Because the analysis procedure is applicable to nonlinear systems, it allows for modeling of concrete cracking, as well as sliding and separation at construction joints, lift joints, and at concrete–rock interfaces. Implementation of the procedure is facilitated by commercial finite element software with nonlinear material models that permit modeling of viscous damper boundaries and specification of effective earthquake forces at these boundaries. Copyright
The mean square deviation (MSD) of an arch dam dynamic displacement response during a flood discharge period is an important indicator used to evaluate the vibration intensity. The whole distribution of the MSD of the dynamic displacement response reflects the whole dynamic displacement field. Inversion of the whole dynamic displacement field of the arch dam based on limited measuring points is of significance. In this study, the Ertan arch dam was used to propose an inversion algorithm for the whole prototype dynamic displacement field of the arch dam. First, inversion theory of flow-induced vibration response for the arch dam is introduced. Second, the arch dam prototype vibration test under flood discharge excitation is conducted to determine the dynamic displacement response of limited measuring points. Third, the full-scale finite element model of the Ertan arch dam is set up to conduct modal analysis, and the first nine modes are cutoff to extract the modal parameters for the inversion of equivalent excitation source load spectra. Finally, the whole dynamic displacement field of the arch dam is calculated by flow-induced vibration response positive analysis based on the equivalent excitation load spectra. Inversion results show that the whole arch dam dynamic displacement field is obtained through only seven dynamic displacement response measuring points arranged on the crest of the dam. Simultaneously, the inversion and measured values are in good agreement. This method provides a novel technique to reasonably evaluate the high arch dam during the flood discharge period.
From researches on the positive and negative vibration frequency of adjacent submerged cylinder piles, hydrodynamic pressure distribution of water body around the piles and how it changes with the distance between the piles, it is found that the vibration mode of negative vibration of adjacent piles will enhance the hydrodynamic effect on pile shafts. With four-pile pile-group foundation models as the test objects, modal tests were conducted on a normal pile-group foundation and three composite foundations at different water depth in a pool to study the dynamic performance of pile group-truss composite foundation. As an example, the seismic responses of a four-span bridge before and after adopting deep-water pile-group foundation were analyzed with seismic response spectrum and were compared to study the seismic performance and application of this new type of foundation.
A response spectrum analysis (RSA) procedure, which estimates the peak response directly from the earthquake design spectrum, is available for the preliminary phase of design and safety evaluation of concrete gravity dams. This analysis procedure includes the effects of dam-water foundation interaction, known to be important in the earthquake response of dams. This paper presents a comprehensive evaluation of the accuracy of this RSA procedure by comparing its results with those obtained from response history analysis (RHA) of the dam modeled as a finite-element system, including dam-water-foundation interaction. The earthquake response of an actual dam to an ensemble of 58 ground motions, selected and scaled to be consistent with a target spectrum determined from a probabilistic seismic hazard analysis for the dam site, was determined by the RHA procedure. The median of the peak responses of the dam to 58 ground motions provided the benchmark result. The peak response was also estimated by the RSA procedure directly from the median response spectrum. Comparison of the two sets of results demonstrated that the RSA procedure estimates stresses to a degree of accuracy that is satisfactory for the preliminary phase in the design of new dams and in the safety evaluation of existing dams. The level of accuracy achieved in the RSA procedure is noteworthy, especially considering the complicated effects of dam-water-foundation interaction and reservoir bottom absorption on the dynamics of the system, and the number of approximations necessary to develop the procedure. (C) 2014 American Society of Civil Engineers.
While the static behavior of concrete has been the subject of numerous works, the same cannot be said for the dynamic behavior. This book sets out to remedy this situation: it begins by presenting the most frequently used experimental techniques in the study of the dynamic behavior of concrete, then continues by examining seismicity and seismic behavior, soil behavior, models of concrete structures subject to seismic activity, seismic calculation methods of structures, and paraseismic engineering.
Forced-vibration tests were completed on Outardes 3 gravity dam, located in northeastern Quebec, Canada. The experimental results were subsequently used as a basis for a numerical correlation study to evaluate the performance of state-of-the-art finite element programs for earthquake analysis of concrete dams. The experimental procedure is presented and involved the recording of acceleration responses on the 84-m-high dam under harmonic loading. Hydrodynamic pressures were also recorded at several locations in the reservoir, up to a distance of 90 m from the dam face. Extensive studies were carried out with two- and three-dimensional models. The effects of several calibration parameters are discussed, including the dam and foundation stiffnesses and damping as well as water compressibility. Numerical results are compared with complete frequency responses for accelerations and pressures obtained on site. It is demonstrated that the two-dimensional approach could only predict the fundamental resonance of the system, and that a three-dimensional model for the damñreservoirñfoundation system including water compressibility could reproduce the experimental behaviour with accuracy. This project complements similar work carried out on a large arch dam, and constitutes direct evidence of water compressibility effects for a large gravity dam.
Realistic modelling of the behaviour of large-scale structures for dynamic analysis is considered. The importance of well-documented and reliable testing procedures is emphasised. Several structures were tested under ambient and forced vibrations: a suspension bridge, a gravity dam and the inclined tower of the Montreal Olympic Stadium. Evaluations of frequency responses and dynamic properties are presented for each structure. The use of these results in finite element correlation studies is discussed and the prediction of analytical models are compared with experimental findings.
Dynamic bridge testing techniques used at the University of Sherbrooke on a series of highway bridges in the province of Quebec, Canada, are presented. These procedures were developed to obtain a reliable evaluation of the dynamic amplification factor for existing bridges, as part of an ongoing rehabilitation program of the province's road network. Vertical acceleration responses are obtained under normal or controlled traffic using different test vehicles and loading patterns. The vibration frequencies and mode shapes are calculated from a frequency analysis of the measured data, and used to calibrate finite-element models for each structure. The experimental methods and data-processing techniques are described. The need to establish standard testing procedures is discussed and some recommendations are presented. Examples of test results and comparisons with finite-element eigenvalue analyses are given for three different bridges.
A new system of four synchronized eccentric mass vibrators has been used in forced vibration tests on dams. Corresponding calculations have been made using two-dimensional and three-dimensional finite elements, and for the gravity dam a proposed empirical formula for the fundamental period of vibration has been assessed. For the finite element calculations, the variation of material properties with depth was assessed from P wave velocities measured at the surface in conjunction with empirical formulae.
The resonance frequencies of the 250-m-high arch dam of Mauvoisin are obtained by way of ambient vibration tests. It is observed that the resonance frequencies initially increase with rising water level and then decrease with a further rise. This is linked to the two competing features of increasing entrained mass of water (reduction of the resonance frequencies) and of dam stiffening due to closing of the vertical construction joints (augmentation of the resonance frequencies). The ambient vibration test results are complemented by those obtained during earthquakes at an array of 12 accelerographs. Copyright © 2000 John Wiley & Sons, Ltd.
Measured accelerations and water pressures obtained during a recent forced vibration test on a large thin arch dam at high water are compared to predictions from a finite element model for which water compressibility is both included and neglected. The numerical model is calibrated using the antisymmetric response data because they are only slightly affected by water compressibility; good agreement is obtained. In the effort to reproduce the symmetric response data, for which water compressibility plays a strong role, the calibrated model shows better correlation when water compressibility is included, but the agreement is still inadequate. A successful isolation of the fundamental water resonance from the experimental data shows significantly different features from those of the numerical water model, indicating possible inaccuracy in the assumed geometry and/or boundary conditions for the reservoir. Some other results at low water level are also included.
Measurements have been made of vibrations induced in the 180 m high Emosson arch dam in Switzerland3 by a system of mechanical eccentric-mass vibrators and by the natural wind. Details are given of the dam itself, the tests and the experimental results obtained. Finite element calculations made before the tests, which include reservoir and foundation effects, are compared with the measurements.
Knowledge of the dynamic and earthquake behaviour of concrete dams comes from four sources: observations made from actual earthquakes including recorded histories of the dam response, experiments conducted on prototype dams for the purpose of determining their dynamic properties, experiments conducted on model dams including shaking table tests, and analytical investigations. The first three sources are extensively reviewed in this paper, while analytical investigations are included only if they were conducted to establish correlation to earthquake observations or experimental results. The subject of nonlinear constitutive modelling of concrete and foundation materials, together with its large body of experimental data, is omitted. While the review of the indicated subjects is by no means complete, it represents a much greater effort than has previously been attempted. Significant gaps occur with the non-English literature, including Japanese, Chinese and Russian, and with the work performed at ISMES in Italy and LNEC in Portugal which has not appeared to much extent in the earthquake engineering literature. A summary with recommendations for future work follows the review.
The available substructure method and computer program for the earthquake response analysis of arch dams, including the effects of dam-water interaction, reservoir boundary absorption, and foundation rock flexibility, is extended to include the effects of dam-foundation rock interaction with inertia and damping of the foundation rock considered. Efficient techniques are developed for evaluating the foundation impedance terms, computationally the most demanding part of the procedure.
Strong-motion instrumentation schemes are developed for dams. Emphasis is put on the observation of the free-field motions at the dam sites, of the effective motions at the abutments and of the global dam responses from which the dynamic properties of the dams are also obtained. Array configurations that are compatible with these observation goals are developed for arch, gravity and embankment dams. The associated accelerograph and array specifications are also presented.
Thesis (Ph. D. in Engineering)--University of California, Berkeley, May 1985. Includes bibliographical references (leaves 176-178).
EACD-3D, A computer program for three-dimensional earthquake analysis of concrete dams
- K L Fok
- J F Hall
- A K Chopra
Fok KL, Hall JF, Chopra AK. EACD-3D, A computer program for three-dimensional earthquake analysis of
concrete dams. Report #UCB=EERC-86=09, University of California, Berkeley, California, July 1986; 151.
Observation of the dynamic behaviour of two arch dams
- Jmw Brownjohn
- R T Severn
- C A Taylor
Brownjohn JMW, Severn RT, Taylor CA. Observation of the dynamic behaviour of two arch dams. In
International Workshop on Arch Dams, Seraÿm JL, Clough RW (eds) Coimbra, Portugal, april 1987;429-439.
EACD-3D A computer program for three-dimensional earthquake analysis of concrete dams
- Chopraak Fokkl Halljf
Earthquake analysis and response of concrete arch dams
- Fokkl Chopraak
Observation of the dynamic behaviour of two arch dams
- Taylorca Brownjohnjmw Severnrt