Self-sufficient and self-contained sensing for local monitoring of in-site bridge structures

While conventional vibration-based monitoring provides an overall assessment of a bridge structure’s condition, it often fails in providing early warning for local damage. In this study, two separate sensor modules are developed for online tracking of post-tension (PT) tendon force loss and fatigue crack detection. An embeddable PT tendon force monitoring sensor, which periodically inspects the force level of the PT tendons inside a pre-stressed concrete (PSC) bridge, is developed based on eddy current measurement, and magnetic inductive coupling is used to transmit power and data between an external measurement system and the eddy current sensor embedded inside a PSC bridge. Next, a wireless fatigue crack detection sensor is developed to detect nonlinear ultrasonic modulation produced by a fatigue crack, and the sensor module is powered by a multi-mode energy harvester, which harnesses energy from sun light, low-frequency vibration and RF signals. Laboratory and field tests have demonstrated that the proposed techniques can detect a fatigue crack smaller than 100 m in width and about 40% loss of the initial PT tendon force.