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Arch dams are typically built in the mountain and gorge regions with complex terrain. In the current engineering practice, foundation models are commonly simplified as the half-space with the canyon of regular geometry. The complex topography conditions above the dam crest are neglected. This study investigates the effect of realistic valley topography on the dynamic response of arch dams. The direct finite element method is generalized and applied to the dam-reservoir-foundation system with realistic valley topography. The input ground motions are transformed into the effective earthquake loads at the truncated boundaries by performing several dynamic reaction calculations using one-dimensional (1D) and two-dimensional (2D) auxiliary finite element models. The effect of valley topography on the seismic response of the Baihetan arch dam is evaluated as a case study. Results indicate that the valley topographic irregularities significantly influence the dynamic responses of the arch dam, including relative displacement and stress distribution. Notably, the valley topography effect on the seismic response of arch dams depends on the incident ground motions and is hardly predicted in advance, demonstrating the necessity to account for the realistic topography conditions. • The direct finite element method is generalized to realistic topography sites. • Procedure to obtain the seismic forces for realistic topography sites is presented. • The effect of valley topography on the seismic response of arch dams is analyzed. [ABSTRACT FROM AUTHOR]

• An effective procedure to swiftly acquire seismic response of arch dams soon after an earthquakes • An integrated automation process spans from acceleration data acquiring to results presenting. • The application to an engineering project validates the satisfactory accuracy of the procedure. • Different usage conditions verify the wide applicability of the procedure. • The procedure has potential to offer valuable insights for similar analyses in engineering practice. The seismic safety of arch dams has long been a focal point of research. Due to the complexity of modeling and computation, analyzing the seismic response of arch dams using traditional finite element methods requires a considerable amount of time. In the event of a sudden earthquake, it is challenging to quickly obtain stress analysis results or conduct a safety assessment. To address these issues, a rapid and automated analysis procedure is proposed in this paper, providing seismic response of arch dams within hours after an earthquake. The procedure includes a pre-processing program, a computing program EACD-3D-2008, and a post-processing program, achieving a fully automated process from generating non-uniform earthquakes to analyzing dam dynamic responses and visualizing computation results. As a case study, the 294.5 m high Xiaowan arch dam in southwest China is analyzed, which is equipped with strong motion instruments that have recorded several small earthquakes. The case study revealed that accounting for the non-uniformity of the earthquake significantly improves simulation results, with maximum principal stresses typically occurring near the dam-foundation rock interface. Additionally, the procedure effectively compensates for missing data, allowing for the successful supplementation of the missing acceleration records. For stronger earthquakes, high-stress regions are clearly displayed in the result visualization, providing an effective reference for safety assessment. The case study validated the accuracy and wide applicability of the procedure, demonstrating its potential to offer valuable insights for similar analyses in various engineering projects. [ABSTRACT FROM AUTHOR]

For the first time, low-heat cement was used in the entire dam section of Baihetan Dam, but the thermal properties of low-heat cement under construction conditions have yet to be fully studied. The thermal parameter values of low-heat cement may differ significantly from the indoor test values or specification values due to factors such as ambient temperature, cooling through water, and surface insulation under actual site conditions. Therefore, in order to obtain more accurate values of the thermal parameters, the hybrid swarm intelligence algorithm and field temperature monitoring data are used to identify the concrete thermal parameters of Baihetan arch dam. To overcome the shortcomings of Particle Swarm Optimization (PSO) that is easy to fall into local optimum and Artificial Bee Colony (ABC) that has insufficient development ability, an Integrated Algorithm Based on ABC and PSO (IABAP) is established. Through eight different test functions and comparing with other different algorithms, it is verified that the IABAP algorithm has certain advantages in terms of convergence speed and accuracy. Considering the influence of ambient air temperature and multi-shift water cooling during construction, IABAP is applied to the inversion of concrete thermal parameters with the same strength, different strength and different gradation of Baihetan arch dam. The computational results show the good performance of the IABAP algorithm in engineering applications on the one hand, and the applicability and reliability of the parameter inversion on the other hand, which can meet the accuracy requirements of practical engineering. At the same time, the conjecture that the thermal parameters are consistent in adjacent dam sections was verified by bringing the thermal parameters into the adjacent dam sections for simulation calculations. Finally, the experimental values of thermal parameters of low-heat cement concrete of Baihetan Dam were compared with the inverse values to analyze the change law of thermal parameters, and it was found that the final adiabatic temperature rise of low-heat concrete was smaller than the indoor experimental values during the actual construction. [ABSTRACT FROM AUTHOR]

To establish the correlation between monitoring indexes and damage indexes for the purpose of rapid assessment of dam damage, this paper takes the Baihetan arch dam as an example and establishes a three-dimensional finite element model for dynamic analysis. Focusing on the crown cantilever, the study analyzes the correlation between different monitoring indexes and damage indexes using DCCA correlation coefficient, and constructs a Random Forest prediction model based on time history information of indexes. Using this model, the paper predicts the volume ratio of damage for the crown cantilever over time and its maximum value, comparing the results with those obtained from a model based on maximum value information, through error analysis. The results of the correlation analysis indicate a close relationship between the increase in the maximum upstream displacement, maximum upstream acceleration, and the widening of the transverse joint opening width, and the development of damage in the monolith. The error analysis results demonstrate that the prediction network established based on time history information performs well in both point prediction and interval prediction. The research presented in this paper provides a feasible approach for the comprehensive assessment of real-time seismic damage in arch dams. • Quantitative correlation studies of indexes were conducted by DCCA coefficient. • The acceleration, displacement and opening width of transverse joints closely associated with the increase of monolith damage. • Establishing a prediction model for real-time and rapid evaluation of the monolith damage. • Damage prediction model based on time history data has good prediction accuracy and precision. [ABSTRACT FROM AUTHOR]

• The multi-dimensional parallelogram convex model is developed to indicate the multi-source uncertainty in the reliability analysis. • Hybrid reliability of arch dams is evaluated considering fuzzy failure criterion. • The possible failure path of arch dam is explored and the dynamic reliability are further calculated. The loads and material parameters of arch dams during long-term service have multi-source uncertainty, but they are usually disregarded by traditional convex models, which is unfavorable for reliability evaluation. This work is a contribution to study the multi-source uncertainty in the reliability analysis of arch dams combining the multi-dimensional parallelogram convex model and the fuzzy theory. A novel multi-dimensional parallelogram convex model is firstly constructed, and its correlation angle is utilized to indicate the multi-source uncertainty of the arch dam parameters. Subsequently, the safety degree of the arch dam is evaluated to determine the correlation angle between the correlation parameters combining with the comprehensive method. Afterwards, considering with the fuzzy failure criterion of the arch dam, hybrid reliability indexes are proposed, probably failure paths are explored, and the dynamic reliability are further calculated. The effectiveness of the proposed methods is validated employing numerical simulation of the Jinping Ι arch dam. The results indicate that the methodology can evaluate the reliability and explore the possible failure modes of the arch dam during long-term service. [ABSTRACT FROM AUTHOR]

Attached outlets are integral components of arch dams to discharge flood. However, they are usually neglected in the current seismic analysis of arch dams for simplicity. This paper aims to analyze the effect of attached outlets on the nonlinear seismic response of arch dams. For this purpose, a 235 m high arch dam is analyzed as a case study. The results indicate that the effect of attached outlets on the seismic response of arch dams depends on the ground motion intensity. For the ground motions with a low peak ground acceleration (PGA), the effect of attached outlets on the concrete damage is slight and local, which is consistent with the existing perception. However, as the ground motion intensity increases, their effect extends to the entire dam body. In contrast, the influence of attached outlets on the joint opening is typically observed at the middle contraction joints. Furthermore, the model analysis demonstrates that the inertia effect of attached structures is the primary contribution to these phenomena. Finally, a simplified simulation approach is used for incorporating the influence of attached outlets by coalescing the mass to the dam surface. • The effect of attached outlets on the nonlinear response of arch dams is investigated. • Mechanism of the attached outlets' effect is analyzed. • A simplified simulation approach of the attached structures is investigated. [ABSTRACT FROM AUTHOR]

For flood control, outlet structure is generally installed in the body of the dam. After pouring, the import and export of the orifice will be covered with thermal insulation materials for insulation. When the dam body is used for water storage and diversion, it is necessary to remove the heat preservation quilt. At this time, the lower temperature water will cause a effect called 'cold shock' on the surface concrete of the bottom orifices, in addition, under the influence of a combination of external factors such as air and water temperatures, a large temperature gradient will appear on the surface of the concrete, which will easily lead to temperature cracks. In this paper, external environment temperature, water temperature, real-time concrete surface heat exchange coefficient and the effect of solar radiation fever in the high temperature season are considered in the temperature field simulation calculation of single bottom orifice during outflowing. The calculation result indicates the simulation model is highly accurate, and the inaccuracy between the calculated and the measured temperature is within 1 °C, which provides theoretical reference for deep orifices and surface orifices in water discharge, temperature control and crack prevention. [ABSTRACT FROM AUTHOR]

Highlights • Parametric analysis of semi-unbounded foundation models is performed comprehensively. • Nonlinear seismic response of arch dams is affected by the material damping and the simulation size of foundation. • We propose to neglect the material damping of foundation when the wave incident mechanism is used. • The realistic non-uniformity of foundation should be considered in the earthquake response analysis of arch dams. Abstract 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. [ABSTRACT FROM AUTHOR]

Abstract Geomechanical model test is an important way to analyze the safety of high arch dams. The traditional monitored displacements and stresses are difficult to interpret the internal failure process of dams and foundations. Acoustic emission(AE) technique was used in the geomechanical model test of arch dam to analyze its internal failure. AE 2D planar locating technology for arch dams and signal parameter analysis method were studied and applied to an arch dam geomechanical model test. The failure process of the dam body and foundation was revealed. The left dam heel of the arch dam model cracked first, continuing to expand to higher elevation along the left abutment with the increase of overload times, and the horizontal crack penetration leaded to the ultimate failure of the dam body. Safety factors for initial crack, nonlinear deformation and ultimate bearing capacity of the arch dam model had been clearly obtained based on AE technique. The results of AE analysis coincided well with the actual failure condition. So it is confirmed that AE technique is effective for geomechanical model test, and it has a bright prospect to be used in situ test of arch dam. Highlights • Acoustic emission technique is used in the geomechanical model test of arch dam. • A planar location algorithm for arch dam is established with multiple regression. • The failure process of arch dam model is obtained based on AE technique. • The three overload safety factors of the arch dam model were obtained. [ABSTRACT FROM AUTHOR]

Highlights • A neural network is used to analyse monitored uplift pressures on an arch dam. • A sensitivity analysis is used as main criteria during the tuning of the network. • This sensitivity analysis permits a thorough physical interpretation of the model. • The non additive effects of the external loads on the piezometric levels are shown. • The temporal evolution of the rock-concrete interface is highlighted. Abstract The aperture of the rock-concrete interface of arch dams can be characterised by analysing local piezometric levels. This highly non linear phenomenon involves thresholds effects. Consequently, it is poorly described by additive models such as HST (Hydrostatic, Season, Time), which is the classical multi linear regression model used in dam monitoring to assess the safety of structures. The presented study applies a more flexible statistical method, the Artificial Neural Network (ANN), so as to interpret uplift pressures in a French arch dam, via piezometric measurements. A thorough sensitivity analysis (SA) is performed in order to diagnose the evolution of the aperture of the interface. The originality of this work lies in the proposed methodology used to perform this SA avoiding extrapolation as much as possible, and on the tuning of the network which is implemented with a parametric study that integrates physically interpretable elements, as a supplement to the classical quantitative metrics. ANN turns out to be highly efficient and interpretable when used to study non linear phenomena. Finally, the gain that ANN brings to operational monitoring is discussed. [ABSTRACT FROM AUTHOR]

Abstract The internal damage of the model during the geomechanical model test is difficult to be detected. The failure and instability process of the arch dam are always accompanied by a large number of acoustic emission (AE) signals, which is related to the number of cracks in the model. AE technique was applied in the geomechanical model test of Mengdigou arch dam to analyze its failure process and overall stability. Noise filtering was conducted based on spectrum analysis of AE signal waveform. Parameter analysis was performed after noise filtering. The overall stability of the dam was evaluated by three characteristic overload safety factors: the crack initiation factor K 1 , nonlinear deformation factor K 2 and ultimate load factor K 3 , which were studied by AE parameter analysis. The failure process of Mengdigou arch dam was analyzed by the statistical analysis of AE hits and the wave velocity variation before and after test. AE analysis results were compared with the displacement and video monitoring results at the same time to verify the correctness of the evaluation method based on AE technique. The results showed that the failure process of the dam and foundation was well described by the AE technique, and the three safety factors of Mengdigou arch dam were defined more clearly. And as for Mengdigou arch dam, the fracture occurred at the dam heel area in the early stage of loading and the abutment of right bank was better than the left. The foundation damage was not serious after test and the overall instability was determined by instability of dam. Based on AE technique, the three overload safety factors was determined more clearly: K 1 = 1.5–2.0, K 2 = 4.5–5.0, and K 3 = 11–11.5, which provided an important reference for the Mengdigou arch dam construction. [ABSTRACT FROM AUTHOR]

• A comprehensive analysis model considering the radiation damping of the infinite foundation and seismic input under oblique incidence of the SV wave is established. • Dynamic mechanical parameters of concrete are investigated by introducing the dynamic increase factor (DIF). • Seismic performance of the Jinping Ⅰ arch dam under oblique incidence of SV waves is evaluated by using the incremental dynamic analysis (IDA). • Damage processes of the Jinping Ⅰ arch dam under different peak accelerations are investigated. This study investigates the seismic damage characteristics of high arch dams considering the oblique incidence of seismic waves. Based on the dynamic implicit finite element method, a viscous-spring artificial boundary is applied to consider radiation damping of the infinite foundation, the seismic wave input is converted into an equivalent nodal force of the artificial boundary, and the equivalent nodal loads of the wave input under oblique incidence of the SV wave is deduced. Taking JP Ⅰ arch dam as an example, combined with the concrete damaged plasticity (CDP) model, the nonlinear dynamic response of the dam under 25° oblique incidence of the SV wave is conducted considering the geometrical nonlinearity of contraction joints and the dynamic mechanical properties of concrete materials. Based on the incremental dynamic analysis (IDA) method, the relative displacement and transverse joint opening are selected as the damage measures for fragility analysis of the arch dam. According to the damage distribution from the analysis of a large number of seismic time-history responses, the damage levels of the arch dam are classified. Three limit states of slight damage, moderate damage and severe damage are proposed for the arch dam. The average responses of the 10 earthquakes are considered as the limit values to quantitatively describe the damage of the arch dam. By fitting the results of incremental dynamic analysis, the seismic probabilistic demand model and seismic fragility curves for the two damage measures to predict the probability of the arch dam reaching damage levels under different seismic actions have been established. The fragility curve shows that the probability of severe damage is almost zero under the maximum design earthquake (PGA = 0.1971 g) and less than 5% under the maximum credible earthquake (PGA = 0.2299 g). It is concluded that JP Ⅰ arch dam has a high degree of safety redundancy and fully satisfies the "two levels" design requirements. [ABSTRACT FROM AUTHOR]

This paper is a preliminary attempt to examine nonlinear structural responses of an arch dam to an underwater explosion (UNDEX) shock loading based on numerical simulation. The numerical simulation is based upon the explicit dynamics finite element program ABAQUS/Explicit. Both the dam-reservoir interaction and the contraction-joint non-linearity are considered. Our research has underlined the importance of the shear keys to the integrity of the arch dam. Failures of the shear keys make each monolith more independent and thus the dam structure as a whole more flexible. Two major failure modes of the arch dam have been identified: (a) a break-off failure of the monolith closest to the explosive source, and (b) tensile cracking of the dam base concrete. The presented simulation procedure based upon ABAQUS/Explicit is time-efficient and relatively undemanding owing to its cut-off computational strategy. We believe that it is more suitable for a large-scale three-dimensional UNDEX simulation involving an arch dam than the full-process simulation procedure. [ABSTRACT FROM AUTHOR]

Seismic fragility provides a measure for evaluating the safety margin of structures above specific hazard levels. This study investigates the seismic fragility of arch dams using the dynamic damage analysis model of dam–reservoir–foundation systems, in which the radiation damping of semi-unbounded foundation rock, opening of contraction joints, and damage cracking of dam concrete are taken into account. The 210 m-high Dagangshan Dam in Southwest China is analyzed as a case study. Five hundred nonlinear damage analyses are performed using the Monte Carlo simulation technique considering both epistemic and aleatory uncertainties, which are characterized by random material parameters and ground motions, respectively. Three limit states, i.e., slight damage, moderate damage, and severe damage, are proposed according to the calculated damage distribution and joint opening, and seismic fragility curves are subsequently generated using the incremental dynamic analysis approach. Analysis results show that the Dagangshan Dam may be severely damaged by strong earthquakes when uncertainties in material parameters and ground motions are considered. [ABSTRACT FROM AUTHOR]

The Baixo Sabor hydroelectric power plant, located in the northeast of Portugal, includes a reservoir with a storage capacity of 630 million m 3 of water created by a concrete double-curvature arch dam, 123 m high, which was equipped with a 20-channel vibration based structural health monitoring system. This paper, apart from describing the dam, presents the main characteristics of the monitoring system and the results obtained during the first 6 months of operation and the first filling of the reservoir. These results include in particular the characterization of the accelerations amplitude and the evolution of the dam modal parameters (natural frequencies, modal damping ratios and mode shapes). It is particular interesting to observe the influence of the water level on the modal parameters and the development of statistical models to mitigate this effect. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In actual engineering scenarios of arch dams, the incompleteness and nonstationarity of dynamic monitoring signals limit the accurate cognition of the health state. The effectiveness and robustness of damage characteristics in complex environments restrict the practical application of damage diagnosis theory. In this study, guided by the direct extraction of damage sensitivity features from the acceleration response signals of the arch dam, a seismic damage identification approach of high arch dams based on unsupervised learning is developed. Aiming at the problems of low measurement accuracy and poor identification robustness in the existing artificially designed damage-sensitive features, a denoising contractual sparse deep auto-encoder (DCS-DAE) model is proposed by exploring the mapping relationship between monitoring data and the structural state. This model integrates the advantages of denoising auto-encoder, compressive auto-encoder, and sparse auto-encoder. On this basis, based on the principle of reconstruction error and small probability, combined with box-plot and WKNN algorithm, a damage identification framework based on DCS-DAE is constructed. The effectiveness and noise resistance of the proposed method are verified by an extremely high arch dam. The results demonstrate that the damage identification framework based on multi-objective DCS-DAE constructed in this paper only requires the vibration information of the structure in the intact scenario, which provides a solution with higher stability and robustness for the seismic damage identification of high arch dams under strong noise pollution. • A novel denoising contractual sparse deep auto-encoder (DCS-DAE) model is proposed by exploring the mapping relationship between monitoring data and structural state. • A damage identification framework based on DCS-DAE is constructed. • No need for the vibration response signals of the structure under damage scenarios in this framework. • Numerical studies on a large-span double curvature arch dam are conducted to investigate the accuracy and robustness of the proposed framework. [ABSTRACT FROM AUTHOR]

In current engineering practice, artificial earthquake accelerograms are widely used in the seismic design of new dams. This study aims to investigate the seismic response and damage sensitivity of arch dams to artificial ground motions. A total of 32 accelerograms are artificially synthesized based on the design acceleration response spectrum. The nonlinear dynamic response of the Dagangshan Dam, an arch dam in Southwest China, to these artificial accelerograms is investigated. Dynamic response, including displacement and joint opening, and damage distribution are statistically analyzed. Results show that the seismic response and damage to a dam may significantly scatter for various accelerograms, even if the artificial accelerograms have the same response spectra, peak ground accelerations, velocities, and displacements. [ABSTRACT FROM AUTHOR]

The service reliability of arch dams is related to the material characteristics and load. According to statistical data regarding different material characteristics and load types, probability-based models and methods are generally used to calculate and assess the service reliability of arch dams. However, it is difficult to obtain these statistical data. In this study, we introduce the non-probabilistic reliability (N-PR) method into service reliability evaluations for arch dams. This method only requires the intervals for uncertain parameters and not the probability distributions. The dynamic N-PR calculation model for an arch dam element is built according to the time-varying characteristics of the material parameters and load. By considering the random failure of an initial element, we propose an approach that searches for the main failure modes of arch dams and a method for calculating the dynamic N-PR of the arch dam system. We evaluated the dynamic N-PR for an actual arch dam and forecasted its normal service life. [ABSTRACT FROM AUTHOR]

Thermal loads can cause significant stresses in some structures such as bridges or arch dams. Studies in arch dams show that thermal loads have the most significant effect for causing cracking than other service loads. Moreover, since researches on climate change announce that mean temperature on Earth is expected to increase, the assessment of the impact of the future temperature increase on the structural behaviour of sensitive infrastructures should be considered. This paper proposes a methodology for the assessment of the impacts of global warming on the structural behaviour of infrastructures. The paper links future climate scenarios to the thermal, stress and displacement fields of the structure. The methodology is illustrated with a case study: La Baells arch-dam. The expected stress and displacement fields of the dam under several future climatic scenarios were computed by finite element models. Concrete temperature are expected to increase up to 5.6 K, which will make annual average radial displacements increase in some cases even more than 100%. Tensile stresses are also projected to change and should be adequately monitored in the future. Finally, several adaptation strategies are outlined. [ABSTRACT FROM AUTHOR]

In this work, a ghost-cell immersed boundary method is proposed for the hydrodynamic response of earthquake excited dam-reservoirs. The numerical method employs a second order accurate two-step projection algorithm including compressibility effects in pressure field due to earthquake. The effects of reservoir bottom absorption are treated by introducing damping terms into the momentum equations. Hydrodynamic response of earthquake excited dam with a sloping face is simulated to demonstrate the accuracy of the present numerical method. Numerical results compared with previous numerical and analytical solutions show that the present immersed boundary method can accurately compute the hydrodynamic forces on inclined and curved dam faces including the effects of water compressibility and reservoir bottom absorption for the possibility of resonance. The proposed numerical method was shown to have significant advantages in computational time and memory usage for the hydrodynamic simulation of large dam-reservoirs with arbitrary geometries. Hydrodynamic forces on a double curvature arch dam subjected to real earthquake induced ground motion are also simulated to demonstrate the capability of the method. [ABSTRACT FROM AUTHOR]

In this paper, modal responses of the Brezina concrete arch dam, Algeria, are determined using the finite elements commercial packages ANSYS. The dam–water–foundation soil system is investigated based on the added mass and Lagrangian approaches. The former approach is simpler and less costly but cannot provide the sloshing frequencies. Furthermore, as reported by other researchers, the added mass approach gives higher coupled frequencies as compared to the actual ones, which are better approximated by those obtained from the Lagrangian approach. The natural frequencies of the dam–water–massless foundation model are well below those of the dam–massless foundation model (without water). But, unexpectedly, the frequencies of the dam–water–foundation model are higher than those of the dam–foundation model. This contrasts with the results of other arch dams, including the Morrow Point dam. The results found herein are likely due to the geometric characteristics of the Brezina dam, which are not typically those of an arch dam. Lastly, considering the coupled mode that yields the largest effective mass, its frequency moderately decreases with the increase of the water level, except for the 10 m water height at which the natural frequency is the highest. [ABSTRACT FROM AUTHOR]

• A DTS system is utilized for monitoring concrete temperature at different depths. • The effect of the insulation layer is within 40 cm from the surface of pouring block. • Insulation effect is affected by materials, thickness, time, and space position. The change in environmental temperature, especially a sharp decline of air temperature, is the critical factor for cracking damage to concrete arch dam structures. In this study, the field test and numerical calculation of the insulation effect of concrete pouring block surface were performed to prevent thermal cracks in concrete arch dams. In the field test, the temperature data of concrete at different depths measured by a distributed temperature sensing (DTS) system were analysed. The results showed that the temperature of concrete at different depths from the surface was significantly positively correlated with air temperature, and the influence depth was within 50 cm from the top surface of pouring block. During numerical simulation, the differences in surface insulation measures in insulation materials, insulation thickness, insulation time, and insulation space position were simulated and compared, considering the influence of the concrete insulation layer and cooling water. The numerical solutions showed that: (1) When the insulation material changed from 2 cm polyethylene insulation layer to 5 cm polystyrene insulation layer, the surface stress of concrete decreases from 0.86Mpa to 0.59Mpa; the insulation time was advanced to before the temperature drop, the surface stress from 0.86Mpa to 0.25Mpa; and the change of insulation position, the tensile stress of the top surface of pouring block was almost unchanged. (2) In this temperature drop, the surface insulation measure was recommended: the insulation material and thickness was the 5 cm polystyrene insulation layer, the insulation time is before the temperature drop, and the insulation position is the top surface, transverse joint surface and upstream and downstream surface of the pouring block. [ABSTRACT FROM AUTHOR]

Abstract: Rock mass deformation and strength property simulation plays a key role in the rupture tests of arch dam geomechanical model. Subject to the limit of geometry scale, usually the simulation of tectonic discontinuities, such as faults, disturbed belts, crush belts and weak interlayer were ignored as safety buffer, which may yield overstated safety factors. In this paper, small block masonry technique and low strength binder invented make the simultaneous simulation of the rock mass and tectonic discontinuities available, which is more coincident with real engineering conditions. Based on the material test of blocks and binder, the small blocks masonry technique has been successfully applied in the rupture test of Xiluodu arch dam. With the assistance of high-accuracy monitoring and measuring system, the stress (strain) and displacement distribution of the dam, abutments and rock foundations are obtained. By analyzing these monitoring results, the failure process, mode and mechanism of the dam body and abutments are derived for further identification of weakness. At last, the comparative analysis with other arch dam geomechanical rupture test results yields the evaluation of the dam's global stability and necessary reinforcement measures. [Copyright &y& Elsevier]

Abstract: An investigation has been undertaken on the buckling strength of concrete arch dams in the form of thin shells of single and double curvature. When subjected to the hydrostatic pressure exerted by the retained water, the shell experiences predominantly compressive internal actions, which can result in buckling failure of the thin shell. There are many factors influencing the buckling strength of the arch dam. These include the shape of the valley, the geometry of the arch surface, the degree of bulging of the arch, shell-thickness variation and support conditions. The present study makes use of FEM modelling to determine the influence of key parameters on the critical buckling pressure of cylindrical and elliptic-paraboloidal arch dams. For cylindrical arch dams, design curves giving information on factors of safety against buckling are presented. By comparing the results for the elliptic paraboloid with those for the parabolic cylindrical arch, the benefits of double curvature are evaluated. [Copyright &y& Elsevier]

Abstract: The paper focuses on recent developments in the fields of advanced 3D constitutive modeling and multi-phase modeling of concrete. In particular, the application of a 3D damage-plasticity model to the large-scale numerical simulation of an ultimate load test, conducted on a model of a concrete arch dam, and the numerical simulation of the impact of drying shrinkage on the behavior of concrete structures strengthened by concrete overlays are presented. In both cases comparisons of the computed response with available experimental data demonstrate the capabilities of the numerical models. [Copyright &y& Elsevier]

Abstract: The radial displacement of one or several points of the dam is an important time-varying behaviour indicator and it is a nonlinear function of hydrostatic pressure, temperature and other unexpected unknown causes. Nonlinear system identification is becoming an important tool which can be used to time-varying behaviour modelling of engineering structures. Identification and prediction of complex nonlinear structural behaviour are complex tasks for which non-parametric models are often used. The objective of this study is to develop a neuro-fuzzy identification model to predict the radial displacement of the arch dam. The ANFIS (adaptive network-based fuzzy inference system) models were developed and tested using experimental data collected during 11years. Comparing the values predicted by the ANFIS with the experimental data indicates that soft computing models provide accurate results. These models can be applied for prediction of displacement in further studies. [Copyright &y& Elsevier]

Abstract: This paper presents an efficient methodology to find the optimum shape of arch dams. In order to create the geometry of arch dams a new algorithm based on Hermit Splines is proposed. A finite element based shape sensitivity analysis for design-dependent loadings involving body force, hydrostatic pressure and earthquake loadings is implemented. The sensitivity analysis is performed using the concept of mesh design velocity. In order to consider the practical requirements in the optimization model such as construction stages, many geometrical and behavioral constrains are included in the model in comparison with previous researches. The optimization problem is solved via the sequential quadratic programming (SQP) method. The proposed methods are applied successfully to an Iranian arch dam, and good results are achieved. By using such methodology, efficient software for shape optimization of concrete arch dams for practical and reliable design now is available. [Copyright &y& Elsevier]

Abstract: This paper investigates the effects of finite element model updating on nonlinear seismic response of arch dam–reservoir–foundation systems. The highest arch dam in Turkey named Berke is selected for the numerical and experimental applications. Firstly, 3D finite element model of Berke Dam was constituted using an ANSYS software. In the analytical modeling, arch dam–reservoir–foundation interaction is represented by Lagrangian approach. Then ambient vibration tests were conducted to dam for four days, and experimental dynamic characteristics were estimated using an Enhanced Frequency Domain Decomposition technique. Experimental characteristics are compared with those of analytical obtained by the linear finite element analysis of the coupled system. Good agreement between mode shapes is observed during this comparison, though natural frequencies disagree by 15–20%. The linear finite element model of Berke Dam was updated by adjusting the material properties of the dam and foundation. By introducing the Drucker–Prager damage criterion, the updated linear finite element model was extended into a nonlinear model. Nonlinear seismic behavior of Berke Dam was determined considering the acceleration record of Adana-Ceyhan, Turkey, earthquake in 1998 that occurred near the arch dam region. It is highlighted that the finite element model updating provides a significant influence on the nonlinear seismic response of arch dams. [ABSTRACT FROM AUTHOR]

Abstract: An efficient optimization procedure is introduced to find the optimal shapes of arch dams considering fluid–structure interaction subject to earthquake loading. The optimization is performed by a combination of simultaneous perturbation stochastic approximation (SPSA) and particle swarm optimization (PSO) algorithms. This serial integration of the two single methods is termed as SPSA–PSO. The operation of SPSA–PSO includes three phases. In the first phase, a preliminary optimization is accomplished using the SPSA. In the second phase, an optimal initial swarm is produced using the first phase results. In the last phase, the PSO is employed to find the optimum design using the optimal initial swarm. The numerical results demonstrate the high performance of the proposed strategy for optimal design of arch dams. The solutions obtained by the SPSA–PSO are compared with those of SPSA and PSO. It is revealed that the SPSA–PSO converges to a superior solution compared to the SPSA and PSO having a lower computation cost. [Copyright &y& Elsevier]

Abstract: An efficient methodology is proposed to find the optimal shape of arch dams including fluid–structure interaction subject to earthquake ground motion. In order to reduce the computational cost of optimization process, an adaptive neuro-fuzzy inference system (ANFIS) is built to predict the dam effective response instead of directly evaluating it by a time-consuming finite element analysis (FEA). The presented ANFIS is compared with a widespread neural network termed back propagation neural network (BPNN) and it appears a better performance generality for estimating the dam response. The optimization task is implemented using an improved version of particle swarm optimization (PSO) named here as IPSO. In order to assess the effectiveness of the proposed methodology, the optimization of a real world arch dam is performed via both IPSO–ANFIS and PSO–BPNN approaches. The numerical results demonstrate the computational advantages of the proposed IPSO–ANFIS for optimal design of arch dams when compared with the PSO–BPNN approach. [Copyright &y& Elsevier]

Abstract: Optimal design of arch dams including dam-water–foundation rock interaction is achieved using the soft computing techniques. For this, linear dynamic behavior of arch dam-water–foundation rock system subjected to earthquake ground motion is simulated using the finite element method at first and then, to reduce the computational cost of optimization process, a wavelet back propagation neural network (WBPNN) is designed to predict the arch dam response instead of directly evaluating it by a time-consuming finite-element analysis (FEA). In order to enhance the performance generality of the neural network, a dam grading technique (DGT) is also introduced. To assess the computational efficiency of the proposed methodology for arch dam optimization, an actual arch dam is considered. The optimization is implemented via the simultaneous perturbation stochastic approximation (SPSA) algorithm for the various conditions of the interaction problem. Numerical results show the merits of the suggested techniques for arch dam optimization. It is also found that considering the dam-water–foundation rock interaction has an important role for safely designing an arch dam. [Copyright &y& Elsevier]

Abstract: With the development of arch dam technology, the shapes of arch dam become variable. In order to obtain the reasonable shape, optimization design is the key technology and the important part in the design of arch dam. Based on the engineering example, the geometry model of arch dam is established, the difficulties in the design of arch dam such as more design variables, nonlinearity of the mathematical function and constraint condition, have been solved by using the modified complex method, finally the perfect shape is gained. [Copyright &y& Elsevier]

Abstract: In this study, two different earthquake input models are introduced, i.e. massless foundation model and viscous-spring boundary input model considering radiation damping. Linear elastic and nonlinear contraction joint opening analyses of the 210m high Dagangshan arch dam under construction in China are performed using the two different earthquake input models. First, the responses of the three-dimensional (3-D) canyon without the dam are analyzed, respectively, with massless-truncated foundation and with viscous-spring boundary; second, linear and nonlinear analyses of the dam–foundation system are performed and compared by using the two input models. Hydrodynamic effects are considered using finite element discretization for incompressible reservoir fluid. It is concluded that stresses and displacements and contraction joint opening in the dam are significantly reduced both in linear and nonlinear analyses when using viscous-spring boundary model. Interestingly, in the case of linear analysis of the Dagangshan, the massless foundation input model with a relatively higher damping ratio of 10% leads to a comparable response of the dam to that using viscous-spring boundary model. In addition, the maximum tensile stresses from nonlinear analysis are 10–25% larger than that of the corresponding linear cases due to a partial release of the arch action. [Copyright &y& Elsevier]

[Display omitted] • A CNN-based temperature reconstructed method is proposed for arch dams. • The critical data missing due to low-frequency monitoring is overcome. • Solar radiation and climatological conditions are involved. • Nonuniform distribution of temperature is recommended for design of arch dams. • Realistic stress and possible thermal cracks on the dam face are predicted. Temperature distribution on the dam surface plays an important role in reliable thermomechanical stress analysis of arch dams. In this paper, a novel reconstruction method based on a convolutional neural network is proposed for the temperature field on the downstream surface of arch dams. The environmental variables, including solar radiation, mountain shadows, ambient temperature, and weather conditions, are considered in the reconstruction method. The temperature field of the Xiaowan dam is predicted using the proposed method and it agrees well with the monitoring data in the spatial and temporal scale. The results show that the environmental variables significantly affect the temperature on the downstream surface, and result in temporal-spatial variability of nonuniform temperature distribution. In addition, the proposed method solves the data sparseness and low-frequency acquisition problems that may miss the peak temperature values in the current monitoring system. The thermomechanical stress analysis based on the reconstructed method and finite element method is conducted, and its results illustrate that the proposed reconstructed method can give more realistic performance of the dam and predict possible thermal cracking on the dam surface. [ABSTRACT FROM AUTHOR]

Shear keys are commonly designed on contraction joints to limit joint slipping and improve the overall seismic behavior of arch dams. However, shear keys are usually over-simplified in the current nonlinear seismic analysis. This paper proposes a geometric simplification method for simulating shear key arrangement. Actual shear keys on a contraction joint are simplified into the combination of large oblique-type shear keys along the cantilever direction and horizontal direction. Key geometric features and progressive failure of shear keys can be naturally considered using the contact boundary model and the plastic-damage model. Nonlinear seismic analysis of the Xulong arch dam is implemented with different shear key models for verification and comparison. The proposed method is firstly verified by analyzing seismic responses of the dam with geometrically-simplified shear keys and fine shear keys, respectively. Furthermore, seismic responses of the dam with geometrically-simplified shear keys, free-slipping plane joints (ignoring shear keys but considering surface friction), and non-slipping plane joints (modeling perfect shear keys) are compared to investigate the effects of shear key modeling methods. Ignoring shear keys and modeling perfect shear keys underestimate and overestimate the seismic capacity of the dam, respectively. The nonlinear dynamic behavior of shear keys can be more reasonably represented with the proposed method without much increasing modeling efforts. • A geometric simplification method of shear keys for nonlinear seismic analysis of arch dams is proposed. • Key geometric features and progressive failure of shear keys can be naturally considered. • The geometric simplification method is verified using a fine shear key model. • The effects of shear key modeling methods on the seismic response of arch dams are investigated. [ABSTRACT FROM AUTHOR]

Abstract: Elasto-plastic earthquake response of arch dams including fluid–structure interaction by the Lagrangian approach is mainly investigated in this study. To this aim, three-dimensional eight-noded version of Lagrangian fluid finite element including the effects of compressible wave propagation and surface sloshing motion, and three-dimensional version of Drucker–Prager model based on associated flow rule assumption were programmed in FORTRAN language by authors and incorporated into the program NONSAP. Two new components added into the NONSAP were tested on a simple fluid tank and a simple fluid–structure system and obtained very reasonable results. Elasto-plastic earthquake analysis of an arch dam including fluid–structure interaction by the Lagrangian approach was performed using Wilson-θ method. The El Centro N–S component of Imperial Valley earthquake in 1940 was chosen as a ground motion. The component considered was applied in upstream–downstream direction. Displacements at various nodes on dam body, hydrodynamic pressures at three fluid elements near the dam–reservoir interface and yield functions at two elements predicted cracks in dam body were obtained. The elasto-plastic response of the arch dam was also compared to its linear response. It is seen that Drucker–Prager model in the representing elasto-plastic behaviour of arch dams and in estimating location of cracks in dam body is a fast tool. [Copyright &y& Elsevier]

Abstract: For FEM solution of complex hydraulic structures, a parallel method is usually needed to deal with a large amount of numerical computation. The article introduces an algorithm based on the element-by-element (EBE) scheme of the FEM and Jacobi pre-conditioning conjugate gradient method, including the EBE computation algorithm for boundary conditions and all kinds of loads. Furthermore, based on the concepts of “boundary node” and “local internal node”, a new data exchange technology is developed that realizes the collection and transmission of data and makes it suitable for EBE method to be implemented on distributed memory parallel computers. This algorithm does not generate global stiffness matrix and only stores element stiffness matrices. With this algorithm, a 3D finite element parallel computation program, PFEM, is developed and implemented on a network cluster system to perform 3D finite element computations of an arch dam–foundation system and a large-scale underground tunnel. The results showed that the memory demand of this algorithm is less than that of conventional FEM and the calculation time could be decreased. It works very well for large-scale numerical computation of 3D complex structures like arch dam and underground tunnel. [Copyright &y& Elsevier]

• The geometry centroid is defined for arch dam performance evaluation. • The space-time monitoring model for the centroid deformation is established. • The nonlinear PCA-LSSVM prediction model is developed. • Accurate prediction is achieved on the world's highest arch dam. The purpose of this study is evaluating the arch dam performance through modelling on the defined centroid deformation with the measured data. The space-time distribution characteristics of the arch dam deformation are firstly identified through the comparative analysis of typical arch dams with height of 200–300 m in China. Subsequently, the geometry centroid of the deflection curve of an arch or a cantilever, composed of multiple monitoring points, is defined to indicate the global structural behavior of the arch dams. In order to evaluate the future performance of the arch dams, the space–time monitoring model for the centroid is established by introducing its initial coordinates based on the traditional statistical models. Afterwards, a novel centroid prediction model is developed based on the least squares support vector machine to balance the empirical risk and generalization ability of the statistical regression models. The input factors of the prediction model are determined in advance by principal component analysis to eliminate the multi-collinearity and reduce the computational complexity. The model construction and validation of the centroid deformation method are implemented on the world's highest arch dam through evaluating its structural behavior and predicting the development trend. The results can provide strong technical support to better grasp its performance during long-term operation. [ABSTRACT FROM AUTHOR]

• Failure process is obtained through geomechanical model test with overload method. • A method for determining the nonlinear safety factor of arch dam is proposed. • The method is based on the Pearson product-moment correlation coefficient. • The failure mode of arch dam is more dominated by foundation. • The nonlinear deformation safety factor is similar with compressive stress safety. The nonlinear safety is very important for the system of arch dam and its foundation since it is statically indeterminate structure and the geomechanical model test is effective method to evaluate the stability of arch dam. The analysis of failure process for a double-curvature arch dam with 167.5-meter-high, located in the northwest of China, has been carried out based on overload method. A quantitative method for determining the safety factor of initial nonlinear deformation of model test is proposed based on the Pearson product-moment correlation coefficient. Through the defromation evolution of all monitoring points, the nolinear safety has been determined. Then it is verified by acoustic emission data. By comparing the model test results of arch dam with other arch dams, the overall stability and safety of narrow valley arch dam is higher, and its failure mode is more dominated by foundation, while that of wide valley arch dam is more dominated by dam. The safety factor of initial nonlinear deformation, which has the same meaning as the control index of compressive stress safety of arch dam in the design specification, correspond to the compressive stress failure of the downstream dam toe. [ABSTRACT FROM AUTHOR]

Following a comprehensive literature survey, this paper will first address the theoretical underpinnings of stochastic modeling. An algorithm to model arch dam inhomogeneity in terms of characteristic length is presented next and is applied to assess the impact of concrete's elastic modulus and volumetric AAR expansion. Results are contrasted with both a single deterministic analysis, and a series of classical Monte Carlo simulations in which non-Gaussian stochastically varying properties are used. The impact of randomness in material properties on displacements, joint openings, and stresses are investigated. It is found that whereas mean values of these responses are for the most part little impacted, standard deviations exhibit a greater variation vis a vis simple Monte Carlo simulations. Furthermore, the safety is assessed through fragility surfaces, and meta-modeling. This study determined that whereas randomness may affect local results e.g. stresses, their impact may be neglected for globally averaged responses e.g. displacements. [ABSTRACT FROM AUTHOR]

Due to the complexity of the model and the long duration of earthquake records, the nonlinear dynamic analysis of arch dams consumes a lot of calculation time. In this paper, an earthquake record truncation method based on the acceleration response spectrum (ARS) is proposed to save the calculation time of nonlinear dynamic analysis of arch dams. The nonlinear dynamic responses of the 210m-high Dagangshan dam of China are performed as a numerical example. Firstly, the statistical relationship between the Arias intensity (AI) and ARS is investigated using a large number of actual ground motion records. Secondly, the spectrum-based earthquake record truncation method is proposed. Finally, the accuracy of the proposed method is verified using the actual earthquake records, and the efficiency of the proposed method is compared with the AI-based method. Analysis results show that the proposed method, considering the structural characteristics of the arch dam, can save more calculation time than the AI-based method, while ensuring a sufficiently accurate calculation result. • The statistical relationship between ARS and AI is investigated using a large number of actual earthquake records. • It is found that the AI-based earthquake record truncating method may be conservative for arch dams. • A spectrum-based method is proposed, which considers the structural characteristics of the arch dam. • The proposed method is proved to be accurate and it has advantages in reducing calculation time over the AI-based method. [ABSTRACT FROM AUTHOR]

• Geomechanical model test based on masonry method for failure analysis of arch dam. • Comparing and verifying the results of model test and numerical calculation. • Deformation and failure evolution of dam-foundation during overloading process. • Analogy analysis of model test results of several different arch dams. • Failure of dam toe is the change point of nonlinear deformation. Mengdigou double-curvature arch dam, located in the southwest of China, is a 200-meter-high dam with complex geological conditions. Failure analysis of the arch dam coupled with the foundation is important for evaluation of the stability. In this regard, a geomechanical model test was carried out. The data pertaining to displacements, stresses, and acoustic emissions, and the entire process of the failure occurring during overloading were obtained. During the overloading process, crack initiates in the upstream dam heel. Then, a crack appears downstream at the dam toe as the load increases. After the damage of the dam toe, cracks occur in the faults around the abutment. Meanwhile, cracks develop rapidly in the arch dam. Eventually, the dam-foundation system loses its ultimate bearing capacity and fails. The results of the model test were compared with those of numerical calculation. Then, the nonlinear deformation and failure mechanism was analyzed. Finally, the safety factor of cracking of the arch dam, the safety factor of the initial nonlinear deformation, and the safety factor of the ultimate bearing capacity were obtained, which reveal that the design of the arch dam is reasonable. [ABSTRACT FROM AUTHOR]

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. • Parametric analysis of the user-defined parameters in SSI–COV algorithm is carried out for modal identification of arch dams for the first time. • Radiation damping effect of the unbounded foundation, which is approximately 0.6%–2.0% for the first four modes, is identified. • Natural frequencies of Xiluodu dam are identified based on the proposed selection suggestions using in-situ ambient vibration test. [ABSTRACT FROM AUTHOR]

Parallelization based on the overlapping domain decomposition method (ODDM) is adopted to increase the computation speed of large-scale nonlinear dynamic analysis. A comprehensive system of arch dam-reservoir-foundation is established considering the foundation radiation damping and the nonlinearity of joint opening and concrete damage. A planned 240 m-high arch dam including approximately 3.5 million degrees of freedom and 34 contraction joints is selected as a case study. In particular, to the best of the authors' knowledge, such large-scale seismic damage analysis of an arch dam-reservoir-foundation is unique and can help in understanding damage to an arch dam under an earthquake. The influence of water level on the seismic safety of the arch dam is evaluated based on the damage. New findings are revealed through sophisticated simulation. Under strong earthquake, although free blocks form under low water level conditions, there seems to be no risk of a catastrophic release of the reservoir. • Parallelization method is provided as an efficient procedure for seismic damage analysis of arch dams. • Such large-scale seismic damage analysis of an arch dam-reservoir-foundation is unique. • New findings are revealed through sophisticated simulation. [ABSTRACT FROM AUTHOR]