Applicability of contact wire splices for shinkansen overhead contact lines with respect to fatigue fracture

Contact wire splice fittings are widely used in railway systems to enable partial replacement of locally worn or damaged contact wires. However, their application has long been prohibited in the Japanese Shinkansen system due to concerns regarding loss of contact, accelerated wear, and particularly fatigue fracture. Recent reports from France of fatigue fractures near splice fittings in high-speed operation zones have highlighted the need for quantitative evaluation of splice-induced mechanical effects. This study investigates the applicability of contact wire splice fittings to Shinkansen overhead contact line systems from the viewpoint of fatigue fracture. Dynamic experiments were conducted using a full-scale test rig, and contact wire strain near splice fittings was evaluated over a range of pantograph velocities. The results show that the strain increase remains moderate at low normalized pantograph velocities but increases rapidly as the running velocity approaches the wave propagation velocity of the contact wire. To clarify the underlying mechanisms, a strain estimation method was developed that accounts for the effects of splice bending stiffness and added mass. The method successfully reproduces the experimentally observed trends, revealing that bending stiffness dominates strain increase at lower velocities, whereas splice mass becomes the governing factor at higher normalized velocities. By incorporating empirically identified dynamic effects and aerodynamic uplift of the pantograph, the applicable speed range of splice fittings was discussed in relation to a fatigue fracture reference strain. The results indicate that, from the viewpoint of contact wire fatigue fracture, splice fittings can potentially be applied safely up to a normalized pantograph velocity of approximately 0.6, which represents a conservative guideline within the proposed assessment framework. This study provides a quantitative framework for reassessing the applicability of contact wire splice fittings in high-speed railway overhead contact line systems.