Mechanical performance and damage characteristics of segmental joints in semi-rigid element immersed tunnel under bending deformation: A combined experimental and numerical study

• The bending resistance of semi-rigid element segment joints is primarily provided by the prestressed cables on the open side. • As the rotation angle increases, the shear force of the shear keys first decreases and then increases. Shear keys mainly function in shear rather than bending. • Tensile and compressive damage concentration zones oriented at 45° form near the shear keys in both the middle-wall and side-walls of the segments. Tensile damage at the side-wall shear keys occurs earlier. • High ductility concrete (HDC) vertical shear keys effectively delay the occurrence of plastic damage and improve the bending performance of segmental joints. The mechanical performance of segmental joints in semi-rigid element immersed tunnels is influenced significantly by differential settlement. The mechanical behaviors and failure mechanisms of segmental joints under longitudinal differential settlement were investigated in this study. The validity of the numerical simulation methods was verified through 1:10 scale physical model tests. Subsequently, a full-scale segmental joint model of the Hong Kong-Zhuhai-Macao Bridge (HZMB) immersed tunnel was established. Systematic analyses of the mechanical responses, damage evolution, and sensitive damage zones were conducted. Based on the observations, an optimized design scheme was proposed. It provides theoretical and technical support for structural health monitoring and optimization. The results indicate that the bending resistance of semi-rigid element segment joints is provided primarily by the prestressed cables on the open side. As the rotation angle increases, the rotation center moves upward, and the contact stress concentrates on the top plate. The shear force of the shear keys first decreases and then increases. This is related to their mechanical performance. Shear keys function mainly in shear rather than bending. Tensile and compressive damage concentration zones oriented at 45° form near the shear keys in both middle-wall and side-walls of the segments. The tensile damage at the side-wall shear keys occurs earlier. At 0.004 rad, tensile damage is observed at the middle-wall shear keys (also oriented at 45°). Based on the damage characteristics of the segmental joint, an optimized design scheme using high ductility concrete (HDC) for vertical shear keys was proposed. After optimization, the toughness of the shear keys was enhanced significantly, and the plastic damage was delayed effectively.