Multimode cable vibration control using a viscous‐shear damper: Case studies on the Sutong Bridge

This study investigates multimode damping effects of a long cable attached with a viscous-shear damper (VSD). A typical VSD comprises a casing box containing viscous medium and shearing plates with parts submerged in the medium. It dissipates vibration energy through shear deformation of the viscous medium. The VSD is low-cost and invulnerable to leakage or increasing joint play and hence requires low maintenance effort. For studying its damping effects on long cables, three VSDs were designed respectively for three long cables of the Sutong Bridge, a cable-stayed bridge with a main span of 1,088 m, and then tested in laboratory under forced sinusoidal displacements with various frequencies and amplitudes. Their dynamic behaviors were found to be accurately modeled using a viscous damper with intrinsic stiffness, while the viscous and stiffness coefficients depend on frequency and amplitude. The VSDs were subsequently attached to the cables respectively, and modal damping ratios of in-plane modes of each cable without dampers and with the VSD were measured by free-decay testing. The measurements obtained for most in-plane modes with frequency less than 3 Hz show that the VSD provides satisfactory multimode damping effects with efficiency factors between 30% and 50% as compared to an ideal viscous damper and the damping decreases slightly for higher modes. The measurements are also found consistent with the results of complex modal analysis of a shallow cable with a Kelvin–Voigt damper considering frequency- and amplitude-dependent damper properties. Particularly, analytical prediction using the damper properties tested under small deformation amplitude provides the lower bound of the damping effect.