Experimental Investigations on effectiveness of viscous and viscous inertial dampers on reducing the multimodal vibrations of stay cables

The additional damping ratios provided by viscous dampers (VDs) and viscous inertial damper (VID), were tested in the laboratory to estimate the effectiveness of these dampers on mitigating the multimodal vibrations of stay cable. First, two plate eddy current dampers (PECDs), in which the damping coefficients can be conveniently adjusted, were specially designed and manufactured. The mechanical property of these PECDs was obtained by tests and numerical simulations. Second, the natural frequencies of a test stay cable were carefully determined by tests and numerical analysis, and the effect of cable sag was carefully analyzed. Third, a series of tests including 12 test cases were carried out to validate the effectiveness of a single VD, a single VID, and two VDs, in which PECD is a typical VD, an additional mass is attached on the test stay cable near the PECD and the output is similar to that of a VID. The amplitude and frequency of the vibration have little effect on the mechanical properties of PECD. The inherent damping ratios of the first 25 modes are in the range from 0.068% to 0.22%. It appears that low efficiency to simultaneously enhance the damping ratios of the first 25 modes can be found by adding a single VD and a single VID with the installation position of 4.75%l. However, two VDs installing on 2.75%l and 4.75%l has a significant improvement on the damping ratios of the 15th similar to 25th modes, and should be considered to a reasonable countermeasure to simultaneously reduce the low-order rain-wind induced vibrations and high-order vortex-induced vibration by raising the modal damping ratios.