A novel longitudinal bending model of shield tunnel based on discretization of fiber section under the coupling of multiple factors

The longitudinal equivalent bending stiffness (LEBS) typically exhibits nonlinearity under the coupling of multiple environmental and construction loads. In this research, we propose the Circumferential Joint Fiber Section Model (CJFM) to analyze the longitudinal bending behavior affected by critical factors such as geometric, material, and contact nonlinearities, and the influence range of the circumferential joint. The performance of CJFM is then verified via classical analytical solutions and laboratory model experiments. Furthermore, the applicability of the proposed model is further confirmed based on the Zhanjiang Bay undersea tunnel in China. The results show that the CJFM accurately simulates the full evolution process of seven modes and employs different constitutive models. The longitudinal stress of typical section in Zhanjiang Bay undersea tunnel reveals a distinct pattern of alternating tension and compression from top to bottom, with a noticeable temporal variation of five stages. Utilizing the CJFM, a safety partition of bending mode is constructed, ranging from healthy to unsafe. Upon the estimated bending moment and axial force, the safety status of the test ring is consistently evaluated to be in normal service, and it is inferred that the subsequent state in future will maintained in normal service under similar circumstances.