Experimental and Numerical Study on the Flexural Performance of Prefabricated RC Beams with UHPC–Cogging–Grouted Sleeve Composite Joints

This study investigates the flexural performance of prefabricated reinforced concrete (RC) beams with a novel UHPC–cogging–grouted sleeve composite joint. Five beam specimens—one cast-in-place reference and four prefabricated examples—were tested under four-point bending. The key parameters included the presence of interface shear keys and the configuration of middle connecting reinforcement. The results demonstrate that the proposed joint is generally consistent with the “strong joint, weak member” design philosophy. The specimen with shear keys and dedicated connecting bars (W2) achieved the highest peak load of 224 kN, 7.7% higher than the CIP beam, with the joint crack width limited to 0.2 mm at failure. Replacing dedicated bars with two bent-up bottom bars (W4) maintained acceptable performance (219 kN, 5.3% above CIP), while bending up four bars (W5) reduced the capacity to 200 kN, below the CIP level, inducing a near-under-reinforced flexural failure. The UHPC joint and shear keys effectively delayed cracking and suppressed joint damage but shifted the failure mode from flexural to shear-compression. The stress development in the rebars was fully consistent with the failure modes: the midspan rebar dominated in flexure-dominated specimens (580–596 MPa), whereas the loading-point rebar dominated in shear-compression-dominated ones (585–590 MPa). Plane section assumption was validated before cracking. Finite element models developed in ABAQUS reproduced the experimental behavior with deviations within 10%, and the stiffness degradation distributions accurately captured the damage patterns. Preliminary design recommendations are provided, suggesting that the proportion of bent-up bars should be conservatively controlled, subject to further experimental verification.