Moment Redistribution in UHPC Continuous Beams Reinforced with High-Strength Steel Bars: Numerical Investigation and Prediction Model

Considering moment redistribution in the design of ultra-high-performance concrete (UHPC) statically indeterminate structures can fully exploit the load-bearing potential of members, simplify reinforcement details, and save construction costs. Due to the excellent properties of ultra-high-performance concrete (UHPC) that distinguish it from conventional concrete, new characteristics of the moment redistribution manifest in UHPC structures. In this study, a finite element (FE) analytical model was developed to simulate and analyze the bending behavior and moment redistribution of UHPC continuous beams reinforced with high-strength steel bars. The simulation and test results exhibited excellent agreement with the experimental research. Based on the FE model, a fine analysis for nine simulated two-span UHPC continuous beams was conducted with a detailed discussion of the failure modes, load-displacement curves, variations of support reaction forces, tensile strains of steel bars, and the whole process of moment redistribution. Subsequently, the variation rules of moment redistribution in UHPC continuous beams were explored by an extensive parametric study of 108 simulated beams. The studied parameters included a neutral axis depth factor, concrete strength, yielding strength of reinforcement, beam depth, span-depth ratio, reinforcement ratio between the mid-span and intermediate support section, as well as load forms. According to the numerical results, new formulas for estimating the two-stage moment redistribution in UHPC continuous beams with high-strength reinforcement were established. Finally, a comparison of moment redistribution between normal concrete continuous beams and UHPC continuous beams was performed. It can be observed that the elastic moment distribution in UHPC continuous beams was comparatively smaller, while the plastic moment distribution was relatively larger than those of normal concrete continuous beams. Overall, the degree of the total moment distribution in UHPC structures was greater than that of normal concrete structures due to the high ductility of UHPC. The research in this study may provide a technical reference for the practical engineering of UHPC.