Title

Structural damage detection and identification using system dynamic parameters

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Eric M. Lui

Keywords

System dynamic parameters, Structural damage, Damage detection, Nondestructive evaluation

Subject Categories

Civil and Environmental Engineering | Engineering

Abstract

In this thesis, several structural damage detection studies using system dynamic properties are presented for the identification and quantification of damage that leads to a change in the structure's mass and/or stiffness properties. The damage detection methods require the use of finite elements to model the structure in its undamaged state as well as information on the dynamic properties, such as frequencies and mode shapes, of the structure in its damaged state. The technique is applicable to any structure that can be accurately modeled using the finite element method and whose frequencies and mode shapes can be reliably measured.

All damage detection methods can be separated into two independent models: the damage location model and the damage severity identification model. The damage location model employs a structure pseudo force vector derived from the residual force method in conjunction with a matrix condensation approach to isolate the damage regions of the structure to which the damage severity identification model will be applied. The damage severity identification model, using only eigenvalues of the damaged structure as well as eigenvalues and eigenvectors of the undamaged structure, is developed to detect and quantify mass and stiffness proportional damage in the structure, by calculating the change in the mass and stiffness matrices of the damaged elements in the structure, respectively. The method is extended to detect non-proportional cross-section damage in frame structures in which a damage severity model making use of both the eigenvalues and eigenvectors of the damaged structure is developed. A best-measured eigenvectors selection approach is introduced to guarantee the accuracy of the results. Moreover, a structural damage severity index based on the disturbed state concept is introduced to evaluate the damage severity of the overall structure. Finally, using layered finite element structural modeling, the damage severity model is employed to detect interlayer damage in laminated structures.

The validity of these methods is demonstrated by applying them to different structures. It is shown that the proposed methods can be used to detect structural damage accurately even when the measured system dynamic properties are slightly erroneous.

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