Nonlinear characteristics of semirigid and semiflexible segment joints of submerged floating tunnels under the combined axial force and bending moment

As an important part and a weak link in submerged floating tunnels (SFTs), segment joints are related to the safety of the overall structure. However, there is still a lack of research on joint structural designing and joint characteristics under complex external loads. In this paper, the semirigid and semiflexible SFT segment joint structure is proposed, and the stiffness mathematical model and numerical model of the joint structure are established based on the geometric deformation coordination, mechanical equilibrium conditions and the infinitesimal method. The above model was used to investigate the coupling effects of the axial force and bending moment on the axial displacement, rotation angle and stiffness of the joint, as well as the nonlinear characteristics of the SFT joint under the combined load of the axial force and bending moment. The results show that the nonlinear characteristics of the SFT joints are linked to the nonlinear properties of the materials at the joints as well as the multiple working states of the joints, as reflected in the characteristics of three loading modes and two transition points. Under the axial force-bending moment combined load, the axial force controls the working state and nonlinear characteristics of the joint, while the bending moment affects the working state and nonlinear characteristics of the joint on the basis of the axial force. The research results provide a theoretical basis and technical support for the study of the overall dynamic response of SFTs and the construction of the project.