Nonlinear dynamic characteristics of short stay cables with unilateral constraints considering eccentricity and contact clearance

Guide devices and dampers mounted on stay cables of cable‑stayed bridges form unilateral constraint boundaries with inherent eccentricity and clearance. To date, few studies have systematically investigated the coupled effects of such geometric imperfections and contact nonlinearities on stay‑cable dynamic behaviours. This paper establishes a refined finite‑element dynamic model incorporating eccentricity, clearance‑induced unilateral constraint, contact stiffness, cable inclination and gravity, to analyse static and dynamic responses of stay cables under unilateral constraints. In this model, clearance is assumed considerably larger than vibration‑induced deformations, such that the guide device is treated as a unilateral constraint without requiring an explicit clearance value. Numerical results reveal that constraint eccentricity transforms the cable’s static sag profile from a single concave curve into an M‑shaped configuration. Both static and dynamic simulations confirm that tension fluctuations over the entire stay cable remain below 0.001% of the reference tension, which validates the uniform‑tension assumption widely adopted in cable‑tension identification. Frequency‑sweep tests show that strong excitation triggers repeated contact‑separation alternations and notable stiffness‑softening behaviour. Excitation amplitude, cable inclination andeccentricity collectively form a critical‑threshold mechanism controlling state transitions between nonlinear low‑frequency impact vibration and linear full‑contact vibration. Gravity can maintain continuous cable‑constraint contact, improve boundary energy dissipation and greatly accelerate vibration attenuation. This work provides fundamental insights into the nonlinear‑vibration mechanics of unilaterally‑constrained stay cables, and offers technical support for vibration‑signal‑based cable‑tension monitoring and constraint‑interface health assessment.