Prediction model for flexural capacity of ultra-high-performance fiber-reinforced concrete beams

Purpose This research is significant as it addresses the increasing use of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams in modern construction, where their superior strength, durability and crack resistance make them well suited for demanding applications, such as bridge structures and high-rise buildings. By compiling and analyzing a comprehensive dataset of 60 UHPFRC beams reported in previous studies, this work systematically evaluates key factors influencing flexural capacity, including fiber characteristics, longitudinal reinforcement ratios and governing failure modes. The study identifies inconsistencies in previously reported findings and applies the American Concrete Institution (ACI) Committee 544 approach to compare predicted and experimental moment capacities. In doing so, it provides deeper insight into the contribution of mixture constituents to structural performance and establishes a foundation for developing a more reliable and practical design methodology for UHPFRC beams, thereby promoting improved structural efficiency and sustainability. Design/methodology/approach The model modifies the ACI Committee 544 (1988) approach by modifying the equivalent rectangular compressive stress block coefficient in accordance with ACI ITG-4.3R-07 and by replacing the conventional tensile stress block with a trapezoidal stress distribution. The trapezoidal tensile stress block incorporates a strength coefficient dependent on the fiber aspect ratio, thereby providing a more realistic representation of the tensile stress distribution. These modifications are validated using a compiled database of 60 UHPFRC beam tests reported in the literature, encompassing a broad range of material properties, fiber types (short and long), failure modes and reinforcement ratios. Findings The results confirm the suitability of the equivalent rectangular compressive stress block for UHPFRC beam design. The proposed model demonstrates strong predictive capability, achieving an average predicted-to-experimental moment capacity ratio of 1.006, a standard deviation of 0.075 and an average error of 5.7%. Accordingly, for the structural design of UHPFRC beams, the proposed prediction model incorporating an aspect-ratio-dependent trapezoidal tensile stress block is recommended. Originality/value This article provides deeper insights into the contribution of components to structural performance and lays the groundwork for developing a more reliable and practical design method for UHPFRC beams, promoting both structural efficiency and sustainability.