Vibration-Based Structural Damage Detection with Applications to Structures with Bolted Joints

A structural damage detection method that uses changes in natural frequencies to detect damage has advantages over conventional nondestructive tests in detecting various types of damage using minimum measurement data. Two major challenges associated with the applications of the vibration-based damage detection method to practical engineering structures are addressed: accurate modeling of test structures and the development of a robust inverse algorithm to identify damage, which are defined as the forward and inverse problems associated with the damage detection method, respectively. To resolve the forward problem, new physics-based finite element (FE) modeling techniques for fillets in thin-walled beams and bolted joints are developed, so that complex structures with thin-walled beams and/or bolted joints can be accurately modeled with a reasonable model size. To resolve the inverse problem, a robust iterative algorithm using a trust-region method, called the Levenberg-Marquardt (LM) method is developed to accurately detect the locations and extent of damage using a minimum number of measured natural frequencies. The LM method can ensure global convergence of the iterations in solving severely underdetermined systems and deal with damage detection problems with relatively large modeling error and measurement noise. The vibration-based damage detection method developed is applied to various structures including lightning masts, a space frame structure and one of its components, and a pipeline. The locations and extent of damage can be successfully detected in experimental damage detection. In the numerical simulation where there is no modeling error and measurement noise, the exact locations and extent of damage can be detected.