Effect of Fiber Content Variation in Plastic Hinge Region of Reinforced UHPC Flexural Members

Ultra-high performance concrete (UHPC) is used for the construction of resilient structures that can sustain dynamic loadings such as blast, impact, and earthquake loadings, among others. In structural components subjected to such loading, it is essential to ensure the formation of a ductile plastic hinge mechanism for suitable load transfer mechanisms and global stability of the structure. Experimental research is needed to understand the formation of plastic hinges in UHPC materials and the impact of plastic hinges on the rotation capacity of reinforced UHPC structural components. The study presented herein aims to understand the spread of plasticity and formation of plastic hinge regions in reinforced UHPC flexural members. Two reinforced UHPC beams with variation in fiber volume fraction (i.e., \( V_{f} \) = 1% and 2%) were subjected to monotonic loading. The test results demonstrated that the reinforcement plasticity length increased by 26% with a decrease in fiber volume fraction from 2% to 1%. The plastic hinge region of specimens with 2% fiber content had crack localization within the maximum moment region, whereas the specimen with 1% fiber content had a more uniformly distributed localized crack pattern. Further, analytical models and a recently proposed equivalent plastic hinge length equation were used to predict and compare the flexural strength and rotation values at various damage states.