Uncertainty analysis of modal parameters obtained from system identification methods

In civil engineering structures, damage prognosis depends on a great extent on accurate identification of dynamic characteristics (natural frequencies, damping ratios and mode shapes). So, it?s extremely significant to investigate the factors affecting the accuracy of identifying modal parameters. In order to do this, two different outputs-only system identification methods, namely, Natural Excitation Technique coupled with Eigensystem Realization Algorithm (NExT-ERA) and Enhanced Frequency Domain Decomposition (EFDD) are programmed in Matlab®. The experimental modal analysis applied to the model steel bridge on the Dokuz Eylul University mechanical laboratory and the acceleration response acquired by sensors which placed at several different points on this model structure?s body. The uncertainty/variability of identifying modal parameters due to uncertainty/variability of some input factors such as spatial sensor density, response data length and measurement noise level are investigated using an updated analytical model of a steel bridge. Similarity of the calibrated finite element model to their real model counterpart is realized by comparing the identified dynamic characteristic of both the actual and analytical models. As a result of this process by changing in mass and stiffness matrices of finite element model, modal assurance criteria (MAC) values are checked to approve that the analytical model is properly updated. Finally, the investigation of the input factors released by simulating data from the calibrated finite element model. Consequently, In order to accurately identify damage in structural health monitoring with non-destructive testing technology, three input factors investigated are very important and must be given utmost attention in system identification process.