SUMMARY
Wind induced vibrations are considering as one of the major concerns of the owner, the engineers and contractors of stay cable bridges. This paper presents in premier lieu the assessment of the vibration monitoring data from the pre-installed accelerometers on the longest cables of the Bach Dang bridge, Quang Ninh province. The identified cables natural frequencies based on the ambient vibration monitoring data were then compared to the taut string vibrating model calculation based on lift-off tension forces showing a good concordant. The enhanced damping of the cables stayed were then estimated and compared to the damping test results of another stay cables bridge recently performed in Vietnam with similar range of cables length. The damping prediction are quite in line with the damping test results and comparable also to those given in most of International Standard for stay cable. Finally, the identified natural frequencies and predicted intrinsic damping were used for an assessment of the wind induced vibration instability including the wind/rain induced vibration, wake galloping and vortex excitation.