Bolt Preload Effects in Insulated Rail Joints: Numerical Modelling, Static–Dynamic Testing, and Modal-Based Condition Assessment

Rail transport is widely recognized as one of the most sustainable and safest mobility solutions, yet specific components of the superstructure remain highly vulnerable to degradation. Among them, insulated rail joints (IRJs) constitute essential elements for train detection but introduce geometric and mechanical discontinuities that drastically reduce rail service life and have been implicated in catastrophic failures. Their structural integrity is governed by a complex interaction of track support conditions, material properties, and operational loading. A largely unexplored yet critical factor is the progressive loss of bolt preload, which alters stiffness distribution, increases stress concentrations, and accelerates damage evolution—while remaining difficult to detect visually. This PhD research aims to characterize and monitor the mechanical response of IRJs under varying bolt preload conditions, supporting the development of predictive maintenance strategies and advanced structural health monitoring. A comprehensive methodology is adopted, combining finite element modeling with extensive static and dynamic laboratory testing using traditional sensors and non-contact technologies. Results provide insight into stiffness evolution, local stress mechanisms, and modal behavior associated with preload degradation. The findings contribute to a deeper understanding of IRJ performance and offer practical foundations for improved inspection procedures and future data-driven monitoring systems capable of mitigating failure risks within railway networks.