Bouc-Wen modelling of asymmetric Stockbridge damper for suspension bridge hangers

Stockbridge dampers are increasingly adopted for mitigating wind-induced vibrations of suspension bridge hangers, where their size and vertical installation differ substantially from traditional overhead-line applications. Recent works reported cases of premature failure of these devices for this kind of application [1], [2]. Existing modelling approaches are often calibrated for smaller, symmetric devices and rely on linear or black-box representations. This paper presents a nonlinear dynamic model for asymmetric Stockbridge dampers intended for bridge applications, aimed at preserving physical interpretability while remaining suitable for system-level simulations. The formulation employs a four degree-of-freedom representation in which the hysteretic bending behaviour of the messenger cables is captured through Bouc–Wen–type constitutive laws expressed in suitably defined generalised coordinates. Model parameters are identified from laboratory tests on a full-scale damper installed in a vertical configuration representative of field conditions. The calibrated model reproduces the amplitude-dependent shift of resonance frequencies and the variation of force transmission observed experimentally, without resorting to amplitude-specific impedance functions. Validation against both harmonic and broadband excitations demonstrates the capability of the model to predict the transmitted force and internal damper dynamics over a wide frequency range. Compared to conventional impedance-based approaches, the proposed framework enables consistent treatment of nonlinear effects under arbitrary excitation histories and provides a practical tool for integration into hanger–damper vibration analyses.