Suspender Tension Evaluation Integrating Detailed Model and Vibration Testing: Insights from the Menai Suspension Bridge

Suspender cables are crucial components in suspension bridges, directly impacting their structural safety and longevity, particularly under long-term service conditions. This study investigates the dynamic behaviour of the Menai Strait Bridge suspenders, which have been in service since 1938, through a comprehensive field programme that included forced vibration testing on 40 cables to characterise their properties and estimate in-service tensions. Custom-built accelerometers and advanced finite element modelling were employed to develop accurate suspender models, which were validated against in-situ jack tension measurements and compared with theoretical formulas incorporating different effective suspender lengths. Results demonstrate the significant influence of boundary conditions on short suspenders, particularly in support displacements and bending effects. Sensitivity analysis revealed that a 1 mm displacement of the supports could induce tension variations of up to 24.59 kN in short suspenders. Furthermore, tension redistribution between adjacent suspenders ranged between 30% and 40% when detensioning one suspender. This work highlights the critical importance of accurately representing boundary conditions and employing vibration-based techniques for tension evaluation, as well as controlling support displacements during maintenance activities. The numerical models developed in this study provide a solid foundation for structural health monitoring and future maintenance strategies for the Menai Strait Bridge suspenders.