Mechanics of longitudinal joints in segmental tunnel linings: Role of connecting bolts

• A nonlinear semi-analytical model is developed to predict the multi-stage behavior, contact pressure distributions, and stress-deformation fields of bolted and boltless longitudinal joints subjected to compression-bending loading. • The effects of connecting bolts, including their influence on joint stiffness, bearing capacity, and separation progression, are analyzed, alongside the roles of bolt prestressing, bolt position, and bolt dimensions. • The impact of water-proofing gaskets on joint bending mechanics is evaluated under varying internal forces. • A simplified joint design model is proposed to accurately predict M-θ relationships for bolted and boltless joints, supported by a practical design application tool (design App). In order to accurately evaluate the moment-rotation relationship for longitudinal joints and to thoroughly elucidate the role of connecting bolts on the mechanism of longitudinal joints subjected to compression-bending scenarios, a nonlinear semi-analytical joint model is developed. This model incorporates the nonlinear behavior of the concrete within the joint influence zone, as well as the contribution of connecting bolts, gaskets, and the contact deformation. The proposed semi-analytical model can simultaneously predict the distribution of the contact pressure, and the stress and deformation field in the vicinity of the joint as well as moment-rotation relationships for both bolted and boltless joints. According to the reference joint test and the proposed semi-analytical model, it is concluded that, under positive bending moment conditions, the load-bearing process of bolted joints can generally be divided into six stages separated by five characteristic points. A comparison of the response of bolted joints versus boltless joints reveals that connecting bolts can effectively delay the expansion of the detached surface, leading to a smoother distribution of the contact pressure, and lower peak contact pressure. The introduction of connecting bolts substantially contributes to maintaining the joint bending stiffness and enhancing the joint bearing capacity, providing bolted joints with greater resilience under environmental disturbances. The influence of the water-proofing gasket on joint behavior is also discussed. Furthermore, parametric analyses are conducted to explore the influence of bolt prestressing, bolt position, and bolt dimension on the mechanical behavior of bolted joints. Based on these findings, a joint design model, based on analytical expressions, is proposed to predict the M-θ relationships for both boltless and bolted joints considering multiple parameters, including axial force levels, bolt contribution, joint configuration, and contact deformation. The joint design model exhibits a high prediction accuracy compared with the semi-analytical joint model, while requiring only simple calculations by analytical equations. To facilitate real-world applications, a design tool based on the proposed joint design model has been developed, which enables efficient and reliable prediction of mechanical behavior of longitudinal joints in segmental tunnel linings.