Preliminary bridge health evaluation using the pier vibration frequency

Frequency is often considered to be an ideal safety indicator in bridge health monitoring. Many scholars have related bridge scour depth to frequency. However, few of previous studies have focused on finding a threshold frequency that corresponds to the limit state of bridge failure. Thus, this study focuses on finding a critical frequency ratio (Rc) that can be used to distinguish between undamaged and damaged bridges. The bridge limit state was calculated by subtracting the demand from the capacity of a bridge. Both the capacity and demand envelopes of a bridge were determined using pushover analyses. Nonlinear behaviors of core/cover concrete and steel reinforcement were considered. In the end of this study, a range of frequency ratio is proposed to be an on-site indicator to evaluate bridge safety. Although the proposed safety frequency ratio is consistent with a field observation, the parameters used in this study are from Taiwan only. In addition, the proposed safety ratio only considered bridges with a single pier against flood hazard. The limits should also be considered for further applications.