“…However, vibration and displacement monitoring of bridges has shown challenges in detecting this type of damage, since global vibration characteristics (e.g., resonant frequency, damping ratio) change slightly with local damage [5,6]. In addition, most conventional testing methods (e.g., ultrasonic testing [7,8], impact echo measurement [9], thermographic images [10], and electro-magnetic radar [11,12]) detect damage near-surface of concrete structures, but face difficulty in exposing internal cracks, voids, and delamination located far beneath surfaces.…”