Mechanical Characterization of Ultrahigh-Performance Concrete under Combined Tensile and Shear Loads Using Rectangular Double-Notch Specimens

Ultrahigh-performance concrete (UHPC) increasingly is recognized in structural engineering for its exceptional mechanical characteristics. Despite valuable insights gained from previous research on uniaxial tension and pure shear, characterizing the behavior of UHPC under combined tensile-shear loading remains a challenge. To address this gap, this study proposes a novel method to systematically examine the mechanical properties of rectangular double-notch UHPC specimens with various steel fiber volume fractions (1.0%–3.0%) by applying loads at different angles (0°–90°). The findings demonstrated that the deflection angle of the primary crack closely correlated with the loading angle (≤60°). Additionally, the quantity of microcracks increased in conjunction with the fiber content, which was attributed to the enhanced crack-bridging effect. Furthermore, increasing the steel fiber volume fraction from 1.0% to 2.0% led to maximum improvements of 1.27× in the initial cracking load and 1.55× in the peak load. In contrast, a further increase in the steel fiber volume fraction from 2.0% to 3.0% yielded only 1.12× and 1.19× enhancements of initial cracking and peak loads, respectively. The experimental findings provide insight into the relationship between tensile and shear strength, which led to the establishment of an interaction curve model to predict the tension–shear strength of UHPC with various steel fiber volume fractions.