Behavior of ultra-high-performance concrete under combined tensile and bending action

This paper attempts to investigate the mechanical behavior of ultra-high-performance concrete (UHPC) under combined tensile and bending action. For this purpose, a total of 72 specimens were tested under axial tension, pure bending, and eccentric tension loads, respectively. The test parameters included the steel fiber content (0%, 1%, 2%, and 3%) and eccentricity ratio (0, 0.1, 0.2, 0.4, 0.8, and ∞). It was found that all the specimens failed due to crack localization. The stresses and strains at cracking, peak, and ultimate load increased as the eccentricity ratio and steel fiber content rose. For specimens with a higher steel fiber content, the eccentricity ratio's effects on cracking and peak strength were more pronounced. For specimens with a commonly used fiber content of 2%, specifically, cracking and peak strength increased by 29% and 63%, respectively, as the eccentricity ratio rose from 0.1 to 0.8. With the aid of full-field measurement on the specimen surface using digital image correlation, the fiber bridging mechanism of UHPC under combined tensile and bending loads was discussed. Then, a calculating method for determining the cracking load was proposed by introducing the plastic influence coefficient, which depended on the eccentricity ratio and steel fiber content. Finally, a unified approach for predicting the coupled strength of UHPC under combined tension and bending action was derived, and its robust applicability was verified through a database collected from the available literature.