Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Han-Ping Hong

Abstract

Abstract

Dams play an essential role in society. Many concrete gravity dams in Korea and the world have been in service for some time and may already exceed their design working life. These dams are subjected to natural loads such as seismic loads. These old dams may need to be requalified by carrying out safety and reliability assessments. The reliability assessment is complicated by the fact that the strength and stiffness of the concrete are uncertain and time-varying. The uncertainty in both the material properties as well as in the loads needs to be considered in evaluating the reliability of existing dams using simple or sophisticated techniques reliability analysis techniques.

An overall framework to assess the fragility and safety of concrete gravity dam subjected to the seismic load is presented in the present thesis. The framework emphasizes the practical issues on the time-dependent seismic fragility curves assessment of gravity dam. The components of this framework consist of the nonlinear inelastic finite element modeling and dynamic analysis, the modeling of time-dependent concrete strength due to aging and degradation, the probabilistic analysis procedure leading to the fragility curves by considering failure criteria (i.e., limits state functions), and simple reliability analysis by considering seismic hazard.

The valuable and very limited number of samples from an actual dam is used to develop and validate the adopted time-dependent model of concrete strength. Nonlinear inelastic finite element models of an existing concrete gravity dam - Chungju Dam in Korea are developed and used to show the applicability of the proposed framework to assess the time-dependent seismic fragility curves and reliability. Two finite element software (one proprietary and the other commercially available software) are used to validate the developed finite element models. A sensitivity analysis of the dynamic characteristics of the dam to the material variability is presented by using the developed finite element models.

For the development of seismic fragility curves, several limit state functions based on cracking and displacements are considered, nonlinear inelastic time history analysis is performed, and the Latin hypercube sampling technique is employed for the probabilistic analysis. The results show the importance of considering the time-dependent concrete strength degradation in evaluating the time-dependent seismic fragility curves and reliability.

Summary for Lay Audience

Dams are essential facilities. Many concrete gravity dams have been in service for some time and may already exceed their design working life. Existing old dams may need accurate assessments of performance and safety. However, the assessment of the dam is performed according to very simplified procedures and ignored the nonlinear inelastic behavior under earthquakes and the uncertainty in material properties over time.

This study focuses on the development of the overall framework to evaluate the seismic fragility curve and reliability of concrete gravity dams. The framework highlights the need to consider the material properties over time to assess the seismic fragility curve and reliability of the dam. The main tasks of this framework consist of the nonlinear inelastic finite element modeling and dynamic analysis, the modeling of time-dependent concrete strength due to aging and degradation, the probabilistic analysis procedure and simple reliability analysis by considering seismic hazard.

A valuable and very limited number of samples collected from actual dams are used to develop and validate the time dependent concrete strength model adopted. Nonlinear Inelastic Finite Element Model of Existing Concrete Gravity Dam - Domestic Chungju Dam is developed and used to show the applicability of the proposed framework to evaluate seismic vulnerability curves and reliability over time.

For the development of seismic fragility curves, several limit state functions based on cracking and displacements are considered, nonlinear inelastic time history analysis is performed, and Latin hypercube sampling technique is employed for the probabilistic analysis. The results show the importance of considering the time-dependent concrete strength degradation in evaluating the time-dependent seismic fragility curves and reliability.

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