Experimental study on flexural behavior of precast concrete beams in-span joined with UHPC

Efficient connection design is critical for the performance and applicability of precast concrete structures. This study proposes a novel in-span connection strategy using Ultra High Performance Concrete (UHPC) to assemble two standardized short precast concrete beams into a single unit, referred to as a Precast Beam Unit (PBU). This configuration relocates the joint from the beam ends to the mid-span, reducing local weakening and premature failure in high-stress regions while enhancing constructability. Static loading tests were conducted on five PBUs, with one cast-in-place beam serving as a control. The reinforcement ratio and the length of the UHPC corresponding to the diameter of the steel bar were employed as the main design parameters. The flexural behavior and failure mode of specimens were analyzed based on load displacement curves, crack propagation, and strain responses. Results showed that PBU-1 exhibited a 6.3 % higher ultimate flexural capacity than the cast-in-place beam. PBU-5, with a reinforcement ratio of 1.65 % demonstrated a 140.2 % higher ultimate bearing capacity compared to PBU-1 (0.64 % reinforcement ratio). PBUs also showed reduced deflection, narrower crack widths, and enhanced stiffness. The study proposed calculation methods for cracking analysis, short-term stiffness, and the normal section flexural capacity of PBU. Moreover, a finite element model developed in ABAQUS was employed to verify the damage situation and ultimate bearing capacity of the specimens, with good agreement with the experimental results. These findings confirm the safety and applicability of PBU and demonstrate its favorable connection performance.