Acoustic Emission-Based Shear Fracture Characterization of Ultra-High-Performance Concrete With Varying Steel Fiber Contents

This study investigates the shear fracture behaviors in ultra-high-performance concrete (UHPC) under direct shear conditions using Z-shaped specimens and acoustic emission (AE) monitoring. The effect of steel fiber (SSF) contents (1%, 2%, 2.5%, and 3%) on the failure process and the relative slip of cracks at different loading stages were measured and evaluated. The results indicate that increasing the SSF content significantly enhances the ultimate shear stress and ductility, effectively limits crack propagation and formation, and reduces the extent of damage for UHPC. During the failure process, an increase in the SSF content results in higher cumulative AE energy and a tendency for the peak frequency to shift towards the low-frequency range. Additionally, increasing the SSF content expands the range of wavelet entropy values and delays the occurrence of wavelet entropy. Due to the reinforcement effects of SSF, the primary crack type evolved from shear to tensile during the failure process.