Influence of fiber dosage, fiber type, and level of prestressing on the shear behaviour of UHPFRC I-girders

Abstract

Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) has excellent mechanical and durability properties compared to conventional concrete. It offers lightweight structures compared to reinforced concrete. In this study, the shear behaviour of post-tensioned UHPFRC girders is experimentally studied. The parameters considered in this study are (i) the level of prestressing, i.e., 0%, 35%, and 70% of ultimate tensile strength of strand (fpu), (ii) the volume fraction of fibers (Vf), i.e., 1.0%, and 2.0%, and (iii) different types of steel fibers; straight fibers, hybrid fibers (straight and hooked ended). The principal tension and compression strain of beams along and across the cracks were measured throughout the loading and compared with localization strains from the direct tension test. Due to increase in prestress from 0% to 70% of fpu, the ultimate load-carrying capacity increased from 18% to 39% in girders with a 1% fiber volume fraction. Similarly, it increased from 24% to 50% for 2% fiber reinforced girders. This is due to increased active stress transfer across the concrete cross-section, which reduces the crack angle from 44° to 34°. Similarly, the shear cracking load increased, and the post-cracking reserve capacity reduced with an increase in fiber dosage. Digital image correlation analysis reveals that strain distribution across the crack is uniformly distributed at all loading stages.