This research studies finite element (FE) model updating formulations utilizing the measured frequency-domain modal properties, i.e. resonance frequencies and mode shapes. The modal properties provided by an FE model are usually different from the ones experimentally measured from an as-built structure. To update the FE model parameters, optimization problems are formulated to minimize the difference between experimental and simulated modal properties. Two modal property difference formulations are presented in this research, one using MAC values and the other using direct differences between eigenvectors. To find the optimal solution of the formulated optimization problem, two optimization algorithms are studied for comparison, i.e. the Levenberg-Marquardt and the trust-region-reflective algorithms. Randomly generated starting values of optimization variables are adopted to increase the chance of finding global minimum. The model updating formulations with different optimization algorithms are studied with a space frame example.
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