Research on Load-Bearing Performance and Damage Evolution of Prefabricated Dual-Mortise Bolt Joints

The load-bearing response of grouted double mortise–tenon joints depends on interactions between interlocking concrete components and auxiliary connections. This study examines deformation and damage in a standard joint and an enhanced joint incorporating bosses on one side and two threaded rods. Comparative tests based on a prefabricated metro station project in Qingdao combined crack observations with measurements of concrete and steel strains and displacements to analyze responses during the final loading stage at a nominal axial force of 1000 kN. Cracks propagated from the tenon roots toward the interlocking region and the vicinity of the bosses, while increasing rod strains accompanied nonuniform joint opening. The enhanced specimen’s nominal failure bending moment was 805 kN·m, 39.39% higher than the standard specimen’s 577.5 kN·m. At matched bending moments of 500 and 550 kN·m, its mean deflection increments were 6.69% and 13.89% smaller, respectively, than the standard specimen’s. Concrete surface strain changes further reflected the evolution of local responses. A three-dimensional concrete damage model showed damage concentration near the tenon roots and bosses. Together, measured responses and numerical observations explain how the interlocking region and connecting rods participate in resisting bending during damage development.