Structural damage assessment and finite element model refinement using measured modal data

This study investigates the problems of model refinement and structural damage assessment. The essence of the model refinement problem is to adjust finite element models (FEM's) of structures with the intent of producing a correlation between experimental and analytical modal properties. Recently, the framework of model refinement has been adopted to determine the location and extent of structural damage. Damage will result in changes to the modal properties of the healthy structure. A further refinement of an accurate FEM of the structure using damaged modal parameters is expected to generate adjustments to the FEM at locations associated with damage. Analysis of these adjustments can then be used to assess damage. In this investigation, four algorithms relevant to the subjects of model refinement and damage detection are presented. The development of a model refinement algorithm with its basis in inverse theory is first presented. The algorithm, termed the inverse/hybrid approach, is illustrated in a comparative computer simulated study. Next, an existing eigenstructure assignment model refinement algorithm is improved to better approach the damage assessment problem. The enhanced algorithm is evaluated and compared to other techniques using simulated and experimental data. The algorithm is shown to perform well in assessing damage and refining FEM's. A damage location algorithm that bypasses the general framework of model refinement is discussed. The damage location algorithm, termed the subspace rotation, is similar to the modal force error criteria proposed by several researchers. Greater insight to the modal force error criteria along with s new viewpoint that reduces the effects of measurement noise are discussed. Furthermore, an efficient damage extent algorithm based on a minimum rank perturbation theory (MRPT) is developed. The formulation of the MRPT is consistent with the effect of most structural damage on FEM's. The characteristics of the subspace rotation algorithm and the minimum rank perturbation theory are illustrated using simulated and experimental testbeds. The decomposition of the damage assessment problem into location and extent subproblems is shown to be advantageous from both a computational efficiency and engineering insight viewpoint.