Flexural behaviours of pretensioned prestressed concrete-UHDC composite beams reinforced with CFRP bars

Prestressing fiber reinforced polymer (FRP) bars is widely acknowledged as an effective method for exploiting their high strength. However, compared to FRP reinforced concrete structures, prestressed FRP reinforced concrete structures exhibit weaker deformation capacity. To address this issue, ultra-high ductile concrete (UHDC) was employed to enhance the flexural behaviours of pretensioned prestressed concrete (PPC) beams reinforced with carbon fiber reinforced polymer (CFRP) bars, while additional aluminium alloy ribs (ARs) were utilized to ensure proper anchorage. A total of eight beams were designed and tested, consisting of four PPC beams and four PPC-UHDC composite beams, which featured different types of CFRP bars, reinforcement ratios and UHDC placement. The test results revealed that the CFRP-reinforced PPC-UHDC composite beams exhibited significantly improved flexural performance in terms of cracking load, ultimate load and ultimate displacement. For specimens with lower reinforcement ratio, the UHDC effectively controlled the cracks and promoted uniform strain in the CFRP bars, leading to increased ultimate load capacity and ultimate displacement. For specimens with higher reinforcement ratios, the flexural performance was comprehensively improved when the UHDC was placed in the compression zone. Numerical analysis was conducted to further investigate the flexural behaviours of PPC-UHDC composite beams under various conditions.