Combined passive and active ultrasonic stress wave monitoring of a full-scale laboratory reinforced concrete bridge column subject to reverse-cyclic lateral loading

Abstract Effective monitoring of reinforced concrete structures requires techniques that detect early-stage material change and active, localized cracking. This study investigates a combined structural health monitoring approach using passive acoustic emission and active ultrasonic methods on a full-scale reinforced concrete bridge column subjected to reverse-cyclic lateral loading. Active monitoring, based on coda wave interferometry, was used to track changes in wave velocity and waveforms, while passive acoustic emission monitoring was used to detect crack activity. The instrumentation consisted of three embedded ultrasonic transducers and three surface-mounted acoustic emission sensors. The results show that active ultrasonic monitoring is most effective prior to visual damage, successfully detecting the onset of internal cracking via wave velocity decreases exceeding 0.4%, and distinguishing load-induced effects from permanent damage. However, its utility diminished in later stages of damage progression, as strong signal decorrelation hindered further data interpretation. Additionally, active US measurements allowed a comparison of damage severity in different parts of the column. Conversely, passive acoustic emission monitoring effectively tracked the formation of concrete cracks throughout the experiment, with distinct event clusters and high-amplitude signals (> 60 dB) confirming ongoing fracture processes in all damage states. This study confirms that combining these methods results in a more robust structural health monitoring strategy by leveraging their complementary strengths. Active techniques excel at tracking continuous material changes in early damage states, while passive methods are superior for detecting discrete cracking events as damage progresses. Importantly, both methods can utilize the same measurement equipment, enabling a cost-effective approach to continuous damage tracking.