Anchorage performance of lap-splicing rebars in UHPC-filled connections of prefabricated tunnels: Pull-out test and bending test

This study introduces a novel rebar-lap-splicing UHPC-filled connection (RUC) for prefabricated tunnels, featuring convex tenons on the NC prefabricated components and anchor plates installed at the ends of lap-splicing rebars. 12 pull-out specimens and 6 bending specimens were designed and fabricated to investigate the effects of rebar overlap length and UHPC thickness on cracking patterns, failure modes, load-slip/displacement/strain relationships. Monolithic beam and slab specimens exhibited initial cracking at the NC midspan, whereas cracking in the RUC specimens initiated at the vertical UHPC-NC interfaces. For all specimens, the failure modes were rebar yielding or fracture, and no cracks were observed in the UHPC layer. It is recommended to choose UHPC thickness and rebar overlap length not less than 100 mm and 150 mm (9.4 d ), respectively. The research results have broken through the lower limit of Chinese codes, with the joint thickness reduced to 0.36 times the component height and the rebar overlap length reduced to 0.375 times the joint width. Also, the rebar overlap length specified by the FHWA guidance was revised to 0.55 times the embedded length. The RUC displayed superior bonding and anchorage characteristics. The rebars were exposed using a manual chisel after pull-out tests, revealing robust bond with the UHPC, a finding corroborated by the modified load-displacement curves and the computed splitting stress. The calculated bond stress at rebar yield in bending specimens was found to be lower than the bond strength documented in the literature. In addition, the applicability and accuracy of the calculation formulas for the bending capacity in Chinese standard and ACI standard has been confirmed. The results demonstrate that the prefabricated connection performs equivalently to monolithic concrete, offering a solid foundation for promoting this innovative connection technology in prefabricated tunnels.