Piezoelectric Transducer-Based Damage Monitoring for Reinforced Concrete Beams at Lap Splices of Steel Reinforcement

This study proposes a novel method for damage assessment in reinforced concrete beams using bonded piezoelectric transducers (PZTs). By analyzing the transmission and reception of high-frequency waves through PZT pairs attached near lap splices in tensile reinforcement, a wavelet packet-based damage index (DIE) was developed. Four reinforced concrete beams with varying lap splice lengths were subjected to cyclic loading, and the electrical signals from PZT sensors were analyzed. A significant reduction in signal amplitude (33–56%) was observed in lapped splices compared to continuous bars, indicating the discontinuities in the splice regions. The proposed DIE showed strong sensitivity in detecting internal damage before surface cracks became visible. In beams with insufficient lap splice lengths, the DIE values reached above 98% of the maximum damage threshold when 57% and 53% of breaking load were reached, confirming its high sensitivity to brittle splitting behavior. In contrast, beams with sufficient lap lengths showed a gradual increase in DIE values, reaching final damage levels of over 98% when 83% and 78% of the breaking load were attained, respectively, corresponding to ductile flexural failure.