Gu Chongshi

Review on hidden trouble detection and health diagnosis of hydraulic concrete structures

A large number of hydraulic concrete structures have hidden defects such as cracks, erosion, freeze and thaw, thermal fatigue, carbonization. These hidden defects seriously affect the strength, stability and durability of structures. These problems are studied mainly by single monitoring or diagnosis methods at present. The integration of multiple monitoring and diagnosis methods is not applied widely. Besides, the analysis theory on these problems is not developed very well. The systemic study on the aging mechanism of hydraulic concrete structures, time-variation model and health diagnosis is still not enough. The support for engineering practice is limited. Aimed at these major scientific and technological problems and combined with specific projects, study on detection of hidden defects and health diagnosis of hydraulic concrete structure has been carried out. This study includes the following content: field non-destructive examination of hidden defects of hydraulic concrete structures, seepage detection, the construction of in-situ sensing system, the combination of field detection and in-situ monitoring, the mechanism of crack, freeze and thaw, erosion and carbonization of hydraulic concrete structure, mechanism of combination aging; time-variation model of hydraulic concrete structure, theories and methods for health diagnosis of hydraulic concrete structures.

Study on coupling model of seepage-field and stress-field for rolled control concrete dam

Based on the construction interfaces in rolled control concrete dam(RCCD), the methods were proposed to calculate the influence thickness of construction interfaces and the corresponding physical mechanics parameters. The principle on establishing the coupling model of seepage-field and stress-field for RCCD was presented. A 3-D Finite Element Method(FEM) program was developed. Study shows that such parameters as the thickness of construction interfaces, the elastic ratio and the Poissons ratio obtained by tests and theoretical analysis are more reasonable, the coupling model of seepage-field and stress-field for RCCD may indicate the coupling effect between the two fields scientifically, and the developed 3-D FEM program can reflect the effect of the construction interfaces more adequately. According to the study, many scientific opinions are given both to analyze the influence of the construction interfaces to the dams characteristics and to reveal the interaction between the stress-field and the seepage-field.Based on the construction interfaces in rolled control concrete dam(RCCD),the methods were proposed to calculate the influence thickness of construction interfaces and the corresponding physical mechanics parameters.The principle on establishing the coupling model of seepage-field and stress-field for RCCd was presented.A 3-D Finite Element Method(FEM)program was developed.Study shows that such parameters as the thickness of construction interfaces ,the elastic ration and the Poissons ratio obtained by tests and theoretical analysis are more resasonable ,the coupling model of seepage-field and stress-field for RCCD may indicate the coupling effect between the two fields scientifically,and the develpped 3-D FEM program can feflect the effect of the construction interfaces more adequately.According to the stydy,many scientific opinions are given both to analyze the influence of the construction interfaces to the dams characteristic,and to reveal the interaction between the stress-field and the seepage-field.

Comprehensive evaluation methods for dam service status

More than 87000 dams have been built in China, and about one third of them are risky projects. A number of high and ultra-high dams are being constructed in China’s western region. The current dam construction practice tends to focus on socio-economic benefits and neglect the environment and ecology. Furthermore, periodic examinations are intended to ensure the structural safety of dams. This paper proposes a general evaluation principle for dam service. This principle stipulates that dam projects should have maximum socio-economic benefits and minimum negative effects on the environment and ecology. To satisfy the general principle of mutual harmony, socio-economic benefits, dam safety, environment, and ecology are analyzed, and the evaluation methods for dam service status are discussed. Then, a fusion algorithm of interlayer assessment is proposed on the basis of evidence theory and the fuzzy comprehensive analysis method. Finally, a comprehensive evaluation model is established. Example analysis shows that the proposed theories and methods can fulfill scientific assessment of the service status of dams.

A new method of estimating the equivalent elastic modulus of RCCD

Based on the composite material mechanic theory, the analysis method for the equivalent elastic moduli which are parallel and vertical to the construction interface of RCCD is studied in this paper. The differences between the equivalent elastic moduli which are vertical to the construction interface of RCCD gotten from different methods are discussed in detail. The variation range of the equivalent elastic modulus which is vertical to the construction interface of RCCD is studied based on the principle of minimum complementary energy and the principle of minimum potential energy. The effect of the related influential factors on the equivalent elastic modulus is analyzed. The estimation formula of the equivalent modulus which is vertical to the construction interface of RCCD is proposed. The feasibility of the approach proposed in this paper is analyzed through an example.

Analysis model on gradual change principle of effect zones of layer face for rolled control concrete dam

The effect zones of layer face for RCC (rolled control concrete) dam have gradual change characteristics. Based on the analysis thought of complex material, a model was built to analyze above principle of RCC dam by use of series-wound and shunt-wound connection. Some methods were proposed to determine the instantaneous Young’s modulus, delayed Young’s modulus and viscosity coefficient of effect zones of layer face. Above models and methods were used to mine the principle of gradual change of key calculation parameters which can response the characteristics of effect zones. The principle of gradual change was described. A model was established to analyze the three-dimensional viscoelastic problem of RCC dam. Above programs were developed. The examples show that the proposed models and methods to determine the key calculation parameters of effect zones can reflect the status of RCC dam accurately.

Risk analysis of gravity dam instability using credibility theory Monte Carlo simulation model.

Risk analysis of gravity dam stability involves complicated uncertainty in many design parameters and measured data. Stability failure risk ratio described jointly by probability and possibility has deficiency in characterization of influence of fuzzy factors and representation of the likelihood of risk occurrence in practical engineering. In this article, credibility theory is applied into stability failure risk analysis of gravity dam. Stability of gravity dam is viewed as a hybrid event considering both fuzziness and randomness of failure criterion, design parameters and measured data. Credibility distribution function is conducted as a novel way to represent uncertainty of influence factors of gravity dam stability. And combining with Monte Carlo simulation, corresponding calculation method and procedure are proposed. Based on a dam section, a detailed application of the modeling approach on risk calculation of both dam foundation and double sliding surfaces is provided. The results show that, the present method is feasible to be applied on analysis of stability failure risk for gravity dams. The risk assessment obtained can reflect influence of both sorts of uncertainty, and is suitable as an index value.

Ill-conditioned problems of dam safety monitoring models and their processing methods

The focus of this paper is the ill-conditioned problems in the dam safety monitoring model. The reasons to give rise to the ill-conditioned problems in statistical models, deterministic models and hybrid models are analyzed in detail, and the criterions for ill-conditioned models are investigated. It is shown that safety monitoring models are not easy to be ill-conditioned if the number of influence factors is less than seven. Moreover, the models have a high accuracy and can meet the engineering requirements. Another frequently encountered problem in establishing a safety monitoring model is the existence of inflection points, which are often present in the mathematical model for the hydraulic components in deterministic models and hybrid models. The conditions for inflection points are studied and their treatments are suggested. Numerical example indicates that the treatments proposed in this paper are effective in removing the ill-conditioned problems.

Application analysis of empirical mode decomposition and phase space reconstruction in dam time-varying characteristic

In view of some courses of the time-varying characteristics processing in the analysis of dam deformation, the paper proposes a new method to analyze the dam time-varying characteristic based on the empirical mode decomposition and phase space reconstruction theory. First of all, to reduce the influences on the traditional statistical model from human factors and assure the analysis accuracy, response variables of the time-varying characteristic are obtained by the way of the empirical mode decomposition; and then, a phase plane of those variables is reconstructed to investigate their processing rules. These methods have already been applied to an actual project and the results showed that data interpretation with the assists of empirical mode decomposition and phase space reconstruction is effective in analyzing the perturbations of response variables, explicit in reflecting the entire development process, and valid for obtaining the evolution rules of the time-varying characteristic. This methodology is a powerful technical support for people to further master the rules of dam operation.

Analytic model of deformation of construction interfaces of rolled control concrete dam

The construction interfaces of RCCD have a distinct influence on the deformation of dams. The characters and rules on deformation of construction interfaces are studied. The methods simulating the deformation of the interfaces at different stages are proposed. A thickness analytic model and a no-thickness analytic model of construction interfaces are built. These models can reflect the elastic deformation, the attenuation creep deformation, the irreversible creep deformation and the accelerating creep deformation of interfaces. The example shows that these proposed models can simulate the deformation of the dam structure objectively. Especially, the results of the thickness analytic model which simulates the gradual changing regularities of interfaces can tally with those of monitoring in situ preferably. The methods proposed and the analytic models can be generalized and applied to general concrete dams, especially to the analysis on deformation rules of fault and interlayer in dam base.

Study on time-varying effects of monitoring data for dam based on the wavelet and EMD

The combined method of wavelet and EMD is used to analyze the time-varying effect of the dam monitoring data. According to some projects, it can be concluded that the curve shapes of the time-varying effect components of the dam safety monitoring data separated by the different wavelet bases are inconsistent; The smoothness of the form of the monitoring data denoising by the wavelet are different, while the forms of the time effect trend components of are more consistent and are more similar to the practical ones, when the dam safety monitoring data denoising have separated by the EMD; The wavelet denoising has reduced the decomposition layers of the dam safety monitoring data and the accumulative end errors on later decomposition. This method improves a lot in the precision of the separation of the time-varying effect components of the dam safety monitoring data, providing more direct analysis and effective support for the states assessment of the working dam.