Application of Modal Flexibility and Its Derivatives in Structural Identification

Abstract Using erroneous test data can be misleading in nondestructive evaluation practice. The objective of this paper is to discuss what experimental data to use and how to mitigate experimental error when a modal test is used. In this paper, the modal flexibility and its derivative, uniform load surface (ULS) are analyzed for their truncation effect and sensitivity to experimental error. The ULS is found to have much less truncation effect and is least sensitive to experimental error. These features make it a critical experimental index in the structural identification as needed in nondestructive evaluation. This paper also discusses how to utilize pretest analysis to determine the test frequency band that will lead to the least truncation error. The ultimate usefulness of the approach presented in this paper is that it can lead to effective and accurate nondestructive evaluation. A numerical example and a real structure, the Cross-Country Highway Bridge in the Cincinnati, Ohio, area, are analyzed for the truncation effect.