Ultrasonic Acoustoelastic Coefficients for Stress Evaluation in Concrete Member Subjected to Flexural Loading

Abstract

This study investigates the acoustoelastic response of concrete elements subjected to flexural loading, with the objective of determining acoustoelastic coefficients for non-destructive stress estimation. While most existing research on the acoustoelastic effect in concrete focuses on uniaxial compression, this work extends the methodology to flexural conditions, where tensile and compressive stresses coexist within the same element. Ultrasonic pulse velocity (UPV) measurements were performed simultaneously in both tension and compression zones using dual ultrasonic pulse analyzers under controlled incremental flexural loading. Results revealed a clear stress-dependent variation in UPV under flexural conditions. In the compression region, velocity increased linearly with stress, indicating elastic stiffening consistent with acoustoelastic theory. In contrast, the tension zone exhibited a linear decrease in velocity due to microcrack initiation and tensile softening. Despite minor deviations caused by localized cracking, the overall velocity–stress relationship remained predominantly linear across different concrete mixes. On average, the compression zone showed a 2.5% rise in velocity, while the tension zone demonstrated a 4% reduction in wave velocity. The diverging velocity–stress trend produced a characteristic left angle bracket pattern, where the separation between the compression and tension response lines which tends to serves as a reliable indicator of the stress state in flexural members. Further, Acoustoelastic coefficients were derived from linear curve fitting of the relative velocity variation versus applied stress, establishing quantitative parameters for stress evaluation in flexural members These coefficients offer a quantitative basis for stress assessment in concrete elements under flexure, enhancing the applicability of ultrasonic techniques for structural health monitoring (SHM).