A Theoretical Study to Predict the Flexural Strength of Singly and Doubly Reinforced Ultra-High Performance Concrete Beams

Ultra-high performance concrete (UHPC) characterizes by a significant tensile strength that cannot be neglected in structural analysis, besides more than 150 MPa compressive strength, high ductility, durability, and toughness. The available analytical methods for traditional concrete beams disregard the tensile strength and strain-softening behavior in tension and compression; therefore, they are not suitable for analyzing UHPC beams. This paper presents a theoretical study to predict the flexural capacity of UHPC beams based on an analysis method that considers the effect of material properties. Predicting the bending moment in singly and doubly reinforced UHPC beams depends on adopting a simplified tensile and compressive constitutive response of UHPC.The procedure adopts several factors that affect the behavior of UHPC upon loading. Previous factors like volume fraction, shape, length, diameter, and orientation of fibers are considered for estimating the tensile stress and a bending moment of UHPC. In addition, a new factor related to silica fume content is adopted to estimate the bonding force between fibers and the matrix and the tensile stress. Also, the initial tensile strength of UHPC is deemed in the tensile stress equation due to the dual action of fibers on confining the matrix and the bridging effect by transferring the stress upon cracking. The equations are proposed for counting the tensile stress, neutral axis position of the beam section, and bending moment. These equations agree with the experimental results for tensile stress and a bending moment of beams implemented by other researchers. © 2022. School of Science, IHU. All rights reserved.