Identification of invisible damage in prestressed concrete bridges—A demonstrator case using coda wave interferometry

Abstract During their life cycle, prestressed concrete bridges are prone to wire breaks of their tendons due to fatigue or stress corrosion cracking. However, not all structures show visible cracking on the surface, which would provide timely warning of otherwise invisible damage. Brittle failure may occur. Continuous monitoring with suitable techniques offers a remedy. This paper proposes embedded ultrasonic sensors and coda wave interferometry, which detect strain changes in the concrete caused by losses of prestress via acoustoelastic changes in the ultrasonic wave velocity. Preliminary tests on beams have demonstrated the general suitability of the method for localization. Building on this, the contribution now takes decisive steps further: in full‐scale tests on a post‐tensioned T‐beam, six prestressing strands were successively cut through—initially without, and then with accompanying crack formation. A spatial sensor network yields 2D localization maps that correlate with strain fields from distributed fiber optic sensors (DFOS) and crack patterns from digital image correlation (DIC). Prestressing wire breaks in non‐cracked concrete are reliably localized across the height and length, and consistently quantified. In cracked members, however, decorrelation of the signals due to cracking dominates the strain changes. Then detection becomes essentially limited to the cracked region. Finally, the impact of the sensor distance on localization accuracy is discussed.