Sensitivity of modal parameters for damage detection in corroded beam elements of the Pescara benchmark

Sensitivity and identifiability problems of the modal parameters in the presence of corrosion damage are studied. The first concerns the rate of change of the modal parameters against the damage increase. The second concerns the uncertainty intervals overlapping of the modal parameters between the sound and damaged states. To this end, different testing methods, different identification methods (time, frequency and time-frequency methods), different corrosion levels and different thermal condition (summer-winter) are considered. Prestressed concrete beams of identical geometry endowed with low to high reinforcement ratios are dynamically tested. The free decaying vibrations are used to identify the modal parameters: frequency, modal shapes and damping. The prestressing force is found to be not a variable of the problem. The damage levels range from very low to moderate. It is found that reliable damage identification is possible only for moderate damage. In spite of higher scatter, damping reveals a more stable and sensitive indicator than frequency. Modal shapes shows regular changes, but within the range of the uncertainty intervals.