Flexural behavior of coral concrete beams reinforced with steel-FRP composite bars

To investigate the flexural performance of coral concrete beams reinforced with steel-FRP composite bars (SFCB), a four-point bending test was carried out on three SFCB-reinforced coral concrete beams and one coral concrete beam reinforced with continuous basalt fiber-reinforced polymer (BFRP). The reinforcement ratio was varied as a parameter. The study analyzed the failure mode, bending moment-deflection curve, strain evolution of SFCB reinforcement, and average strain distribution in the section. The finite element software ABAQUS was used to establish a refined model. Based on the model, an in-depth parametric analysis of the beam's flexural behavior was conducted. The results indicated that the failure modes of the test specimens all belong to normal section bending failure. The failure processes manifest as concrete cracking in the tensile zone, yielding of the inner core reinforcement of the SFCB reinforcement, and fracture of the outer fiber of the SFCB reinforcement. During the loading process of the specimen, the bonding property between the outer fiber and the inner core steel bar was good, allowed them to work together effectively. When compared to BFRP reinforced coral concrete beams, the moment-midspan deflection curve exhibited distinct characteristics of ‘ three stages and two inflection points ’. Additionally, the specimen demonstrated a more pronounced secondary stiffness, leaded to a significant improvement in ductility. The simulation results are consistent with the test results. With the increase of reinforcement ratio, the flexural bearing capacity of SFCB-reinforced coral concrete beams increases continuously. With the increase of the strength grade of coral concrete, the flexural bearing capacity increases by about 28%, while the ductility decreases by about 23%, and the brittle failure characteristics are more significant. With the increase of the area ratio of SFCB reinforcement, the secondary stiffness of the specimen is significantly improved, while the ultimate bearing capacity and ductility are decreased by about 20% and 370%, respectively. Finally, based on fundamental assumptions and the material constitutive model, a formula for calculating bearing capacity is developed using relevant specifications as a foundation. The computational results align well with the experimental values. © 2024, Central South University Press. All rights reserved.