Tensile behavior of confined lap-spliced bundled-bar connections for prefabricated box retaining walls

In prefabricated box retaining walls, the corner connection region is characterized by congested reinforcement and limited construction space, making it difficult for conventional connection details to simultaneously ensure rapid assembly and reliable force transfer. To investigate the axial tensile behavior of such connections, eleven valid confined lap-spliced bundled-bar specimens with triangular cross-sections were tested. Four specimen types were considered to examine the effects of lap length and bundled-bar arrangement under approximately equal total reinforcement area. A finite element model was also developed for validation. The results show that none of the valid specimens failed by bar fracture or complete pullout of the bundled bars. The observed failure was characterized by transverse cracking, crack coalescence, and local spalling of the precast concrete in the lap region. The load–displacement responses exhibited three stages: an approximately linear stage, a nonlinear development stage, and a post-peak descending stage. Increasing the design lap length from 540 mm to 720 mm increased the mean ultimate loads of the 6C16 and 4C20 configurations by approximately 12.6% and 13.9%, respectively. At approximately equal total bundled-bar areas, the 6C16 and 4C20 configurations exhibited similar mean ultimate loads at equal design lap lengths. The finite element results agreed well with the experimental observations, and the relative errors in the simulated yield and ultimate loads did not exceed 3.2%. The findings provide a basis for the detailing design and engineering application of bundled-bar connections in prefabricated box retaining walls.