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The risk management of cascade reservoir systems (CRSs) is a major public challenge, and the establishment of risk criteria is critical to solving this issue. In this paper, an approach is presented to establish risk criteria of for CRSs in China based on statistical data (reservoir dam break accidents; fatalities due to reservoir dam breaks; the construction date of defective reservoirs; and the current situation of CRSs), F–N curves, F–E curves, F–I curves, and the as low as reasonably practicable (ALARP) principle. This paper has some innovations in the following aspects. First, the characteristics of CRSs are revealed for the first time. Second, risk criteria for CRSs are suggested. Third, the engineering safety level, risk exposure level, and risk level of CRSs in China are determined. The research results of this paper provide abundant information for the operation management, maintenance and reinforcement of CRSs in China.

This study examines the effects of hydraulic pressure and tectonic stress on fracture initiation in rock flaws by using the finite element method. A square domain with double flaws is analyzed under vertical load, different horizontal loads (modeling tectonic stresses), and various hydraulic pressures.

This paper investigates the free vibration of a homogeneous Euler–Bernoulli beam with multiple transverse cracks under non-symmetric boundary conditions. The differential equation is formulated by introducing Dirac’s delta function into the uniform flexural stiffness, and the close-form solution of mode shapes is then derived by applying the Laplace transform technique. The proposed method is validated against existing experimental method for damaged cantilever beams. With the validated method, a parametric study is performed to study the effect of crack numbers, damage parameters and crack locations on the natural frequencies and mode shapes for three non-symmetric boundary conditions (pinned–clamped, clamped–free shear and pinned–free shear).

The principal means of conserving water and utilizing hydropower in China is to exploit the use of a series of reservoirs in a cascade. This method and its inherent engineering safety problems are receiving increasing attention nowadays. In the field of engineering safety analysis, much work has focused on single reservoir projects in the past few years, but there is little research available on the safety risk analysis of cascade reservoirs, either within China or internationally. Therefore, a framework for risk analysis on the cascade reservoir system based on the theory of system engineering is constructed in this article. A cascading failure model is established and the connection degree factor discussed. In addition, the importance degree of the subsystem, which can be calculated by combining the analytical hierarchy process and the entropy weight method, is explained. According to brittleness theory of a complex system, brittle risk entropy is proposed as a performance index for measuring the collapse uncertainty of the cascade reservoir system. In addition, the brittle risk of the cascade reservoir system is predicted, which provides a reference for safety analysis in water conservation and hydropower construction projects in China.

Damage in the structures alters the structural dynamic behavior. Damage generally occurs locally in the components of structures, and its effect often exhibits in the changes of both local and global characteristics of structures. Better understanding of this relationship helps to monitor and assess the condition of structures and develop dynamics-based structural health monitoring techniques. In this study, the relationship between the local damage and structural dynamic behavior is investigated. To validate the concept, an experiment of a three-dimensional (3-D) steel frame structure with different magnitudes of local damage is illustrated. The experimental results indicate that the change of global resonant response between the intact and damage structure is not obvious. The change of local resonant responses measured near the location of saw-cut crack damage is quite significant. The experimental study conducted indicates that the local resonant responses at the low order resonance can be used as an effective damage identification method to detect and quantify the local damage in the 3D frame structures.

It is a common method to strengthen the damaged RC structures with bonded steel plates. At present the ultimate bearing capacity of RC structures strengthened with bonded steel plates is calculated mostly using the theory based on the test. Four beams, including one reference beam, two strengthened concrete beams in primary force and secondary force respectively, and one strengthened concrete beam which was not anchored enough, were tested under four-point bending (4PB) in order to get the data of strain of longitudinal bars, bonded bottom steel plate in tension and deflection of beams in the middle span. The experimental program was supported by a three-dimensioned finite analysis using ABAQUS. At the end of experiments and finite analysis, it is concluded that the investing strengthening technique can significantly improve the load-carrying capacity and the phenomenon of stress concentration at the end of interface, as well as the damage at interface, can be well simulated with cohesive element provided by ABAQUS.

The global stability of high arch dam is one of the key problems in the safety study of arch dams, but no feasible method with theoretical basis is available. In this paper, based on the stability theory of mechanical system, it is demonstrated that the global failure of high arch dams belongs to a physical instability starting from local strength failure, which is the extreme point instability according to the characteristics of load-displacement curve obtained from the failure process of dam-foundation system. So the global failure of dam-foundation system should be studied with the stability theory of mechanical system. It is also pointed out that the current stability analysis methods used in engineering are consistent with the stability theory, but not established according to the mechanical system stability theory directly. A perfect method can be obtained through the study of physical disturbance equations.

A general initial water penetration (seepage) fracture criterion for concrete is proposed to predict whether or not harmful water penetration (hydraulic fracturing), other than microcracking, will occur in concrete structures in a severe high water pressure environment. The final regression, of the different macroscopic failure types in concrete to microscopic Mode I cracking, allows the use of only one universal criterion to indicate the damage. Thus, a general initial water penetration fracture criterion is approximately defined as a strain magnitude of 1000×10−6, based on the concept of tensile strain derived from experimental results in the relevant literature. Then, the locations of harmful water penetration fracture (hydraulic fracture) in the high arch dam mass of the Jinping first class hydropower project are analyzed using the nonlinear finite element method (FEM) according to the proposed criterion. The proposed criterion also holds promise for other concrete structures in high water pressure environments.

This paper studies the influence of a stress relaxation zone caused by foundation excavation on the performance of Jinping-I arch dam, using the orthogonal experiment method. Firstly, by adopting the characteristic stress of the dam as an index and coupling it with range analysis, the most significant factors and the degree of relaxation influence on the arch dam performance are found. This is then combined with monitoring data from the dam, and the extent of influence on the arch dam performance caused by the relaxation is evaluated through numerical analysis. The results show that the relaxation of foundation excavation has a negative impact on the performance of the arch dam in general, the extent of elastic modulus degradation in the relaxation zone being the main factor affecting stresses in the dam. The relaxation of the rock mass leads to an increase in dam stress in local areas near the relaxation zone, but has little effect on more distant areas.

In this paper, the problem of modeling crack in 2D viscoelastic media is studied using the extended finite element method. The paper focuses on the definition of enrichment functions suitable for cracks assessment in viscoelastic media and the generalized domain integrals used in the determination of crack tip parameters. The opening mode and mixed mode solutions of crack tip fracture problems in viscoelastic media are also undertaken. The results obtained by the proposed method show good agreement with the analytical methods and provide reasonable background information to enhance the modeling of crack growth in viscoelastic media.

To get the actual ultimate bearing capacity of concrete dam, the effect of geometric nonlinearity and strain softening on it, which appears in the failure process of concrete dam, is studied. Overload method is adopted to obtain the bearing capacity of a concrete dam by taking into consideration strain softening in the material constitutive law, geometric nonlinearity in geometric equation and equilibrium differential equation. Arc-length method is used to find the extreme point and descending branch of the load-displacement curve of the dam. The results present that the effect cannot be ignored. And geometric nonlinearity of structure and strain softening of materials should be considered for numerical analysis of ultimate bearing capacity of a concrete dam.

Gravity dam is a typical structure that has been frequently used in the fields of water conservancy engineering, and the safety of the structure has received widespread attention recently. Due to earthquakes or other reasons, gravity dams normally have damage such as cracks in practical service. Damage in the structures can alter the structural dynamic behavior and seriously affect structural performance. Maintaining safety and integrity of the gravity dam structures requires a better understanding of dynamic response of structure with damage and associated damage detection method. In order to study thoroughly the dynamic behavior of gravity dam with damage, the sweep vibration responses of the gravity dam with and without damage are investigated. The experimental results show that the peak-peak acceleration responses all increase for the structure is with crack. At the same time, a structural damage detection method, i.e., the local damage factor (LDF) method, is considered in the study of gravity dam damage detection when the dam is subjected to the base excitation. It is shown that the LDF method can be used as a damage index and is capable of evaluating both the presence and relative severity of structural damage, and it can be used as a viable condition assessment and damage identification technique to detect and quantify the damage in the gravity dam.

The paper is devoted to proposing a constitutive model based on micromechanics. The joints in rock masses are treated as penny-shaped inclusion in solid but not through structural planes by considering joint density, closure effect, joint geometry. The mechanical behavior of the joints is represented by an elasto-plastic constitutive law. Mori-Tanaka method is used to derive the relationship between the joint deformations and macroscopic strains. The incremental stress-strain relationship of rock masses is formulated by taking the volume average of the representative volume element. Meanwhile, the behavior of joints is obtained. By using implicit integration algorithms, the consistent tangent moduli are proposed and the method of updating stresses and joint displacements is presented. Some examples are calculated by ABAQUS user defined material subroutine based on this model.

An improved neuro-wavelet modeling (NWM) methodology is presented, and it aims at improving prediction precision of time-varying behavior of engineering structures. The proposed methodology distinguishes from the existing NWM methodology by featuring the distinctive capabilities of constructing optimally uncoupled dynamic subsystems in light of the redundant Haar wavelet transform (RHWT) and optimizing neural network. In particular, two techniques of imitating wavelet packet transform of RHWT and reconstructing the major crests of power spectrum of analyzed data are developed with the aim of constructing the optimally uncoupled dynamic subsystems from time-varying data. The resulting uncoupled dynamic subsystems make the underlying dynamic law of time-varying behavior more tractable than the raw scale subwaves arose from the RHWT, and they provide a platform for multiscale modeling via individual modeling at the uncoupled dynamic subsystem level. Furthermore, on each uncoupled dynamic subsystem, the technique of optimal brain surgeon in conjunction with a new dynamic mechanism refreshing is employed to optimize the neural network, and the recombination of the modeling outcomes on every subsystem constitutes the overall modeling of time-varying behavior. The improved NMW methodology offers a feasible framework of multiscale modeling due to its flexibility, adaptability and rationality, and it is particularly useful for prediction applications of time-varying behavior of engineering structures. As an illustrative example, the improved NWM methodology is applied to model and forecast dam deformation, and the results show that the methodology possesses positive advantages over the existing multiscale and single scale modeling techniques. The improved NMW methodology is promising and valuable for the safety monitoring and extreme event warning of engineering structures.

The extended finite element method (XFEM) is a new numerical method for modeling discontinuity. Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally, the method is verified by two examples and the advantages of the XFEM for hydraulic fracturing analysis are displayed.

In rock-fill dams of 200 to 300 m high, maximum compressive stress can exceed 6 MPa. At such a high stress level, rock-fill materials may experience particle crushing during shear. The material behavior is highly sophisticated exhibiting pressure and density dependency as well as particle crushing effects. Through scrutinizing the relevant experimental data on rock-fill materials and sands published in the literatures, this paper is focused on understanding basic mechanical characteristics of this sort of materials in the light of constitutive modelling.