# Evaluation of the Ultimate Strength of the Ultra-High-Performance Fiber-Reinforced Concrete Beams
###### Abstract  
Evaluation of the ultimate strength for the UH-PFRC (ultra-high-performance fiber-reinforced concrete) flexural members was conducted. In this study, an experimental program about UHPFRC beams was conducted with the effect of fiber volume fraction, shear span to depth ratio, and compressive strength of matrix as the main variables. Among them, it was found that fiber volume fraction was the variable that had the greatest influence on the ultimate strength. The inclusion of 2% volume fraction steel fiber increases the shear and flexural strength of UHPFRC beams significantly. In particular, steel fiber inclusion changed the mode of failure of beams from diagonal shear failure into flexural failure. For the classification of failure patterns, the ultimate flexural strength and shear strength of UHPFRC members were evaluated using the current design code and UHPC guidelines. Flexural ultimate strength was affected by the size and shape of the stress block and consideration of the matrix's tensile strength. For the accurate shear strength prediction of UHPFRC beams, the tensile strength of the high strength matrix and the effect of steel fiber should be considered. ultra-high-performance fiber-reinforced concrete: flexure strength: shear strength: shear strength: shear reinforcement: design recommendations: strength evaluation +
Footnote †: journal: Applied  
were significantly influenced by the placing method and significantly affected the flexural behavior of the UHPFRC beams. UHPFRC beams showed a ductility ratio of 1.7 or higher, even with a flexural reinforcement ratio of less than 1%. [PERSON] et al. [8] conducted a study on the effect of types of steel fibers on the flexural behavior of the UHPFRC beams. UHPFRC generally uses a water-cement ratio of 0.2 or less. This is because it has been shown that high strength (especially above 100 MPa) could be made at a water-binder ratio of 0.2 or less in general. Usually, to guarantee the workability of UHPFRC, short and straight steel fibers were used. However, for the development of advanced structural behavior of UHPFRC members, [PERSON] et al. [8] used long and various-shaped steel fiber and reported the increase of flexural strength and ductility. Most of the research about the flexural behavior of UHPFRC beams was conducted based on the stress-strain behavior of UHPFRC under compression and tension because design guidelines for UHPFRC recommend the use of sectional analysis with a suggested stress-strain model for the prediction of flexural strength of UHPFRC beams. Therefore, it was considered that the study on the material characteristics was more frequently conducted than the study on the flexural behavior of members. On the other hand, the study on shear strength was carried out by focusing on the evaluation of the member strength rather than the contribution of the material to the overall carrying capacity, and most of test specimens were I-shaped girder. [PERSON] [9] used UHPFRC up to 120-200 MPa of compressive strength, and short straight steel fibers with a length of 12.7 mm were used. As a result of 4-point loading tests of I-shaped girders, it was confirmed that the maximum strength was determined by the pulling out of steel fibers across the shear and flexural cracks when shear and flexural failure occurred, respectively. [PERSON] et al. [and steel fiber and stirrups as shear reinforcement. The failure mode of reinforced concrete beams was generally well known to be strongly influenced by the shear span to depth ratio. Therefore, to investigate the various flexural behavior of UHPFRC beams, the shear span to depth ratios were adjusted to 6.6, 3.4, and 2.0. The compressive strength of UHPFRC beams was determined to be 100 and 200 MPa to investigate the effect of the matrix's compressive strength on the flexural behavior of UHPFRC beams.