Abstract:
Invisible damages in bridges, such as corrosion of rebar, may not be detected by periodic visual
inspection that is the principal method in bridge maintenance. A possible non-destructive technique which has been
investigated to assist visual inspection is vibration-based structural health monitoring. The modal properties of
bridges, such as the natural frequencies, mode shapes and modal damping ratios, are expected to change due to
damages and/or deteriorations. In the present study, damping properties of existing PC girder bridges were
identified so as to investigate the possibility of the modal damping ratios as an indicator of damage detection.
Vibration measurements were made at ten single-span PC bridges with similar dimensions under normal service
conditions by using wireless and wired sensor systems. Eigensystem realization algorithm (ERA) with an improved
screening process was applied to extracted free vibration records. Modal properties up to the fourth vibration modes
were identified for many bridges. For the third vibration mode that was identified stably in most bridges, there was
a trend that the modal damping ratio of old bridges was greater than other newer bridges. Although this result does
not necessarily indicate the relationship between the damage and damping property, it may support the possibility of
damping in the evaluation of structural state.
