Inclined stay cables on cable-stayed bridges are prone to wind-induced vibrations due to their long flexible nature and low structural damping. Severe stay cable vibrations under either the combined effect of rain and wind or wind only have been observed in field and wind tunnel tests which caused great concerns to bridge designers. To suppress these vibrations, fluid dampers are often attached to the stay cables near the anchorages. In order to facilitate effective and economical design of dampers for stay cable vibration mitigation, thorough understanding of both the vibration characteristics and the dynamics of the cable-damper system is necessary. Nevertheless, existing studies are limited to deterministic-based analysis of which the uncertainties of structural parameters (such as cable tension and damper capacity) and wind parameters (such as speed, direction, etc.) over the service life of a bridge are totally neglected. Thus, to provide complete information regarding the aerodynamic response of a damped cable, the problem should be more rationally studied from a probabilistic-based sense. This would offer bridge engineers a more reliable analytical tool for performance assessment of cable-damper systems. The current study aims at improving the current practice of external damper design by proposing a time-variant reliability-based framework model of a damped stay cable subjected to wind load conditions. Two types of cable vibrations that are more probable, i.e. rain-wind-induced cable vibrations, and/or critical, i.e. dry-inclined cable galloping, than the others are investigated. The research outcomes are drawn to ensure reliability of design and enhance maintainability of external dampers for bridge stay cables. The flexible applications of the proposed time-variant reliability-based framework tool are demonstrated through some case study examples.
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