ESTIMATION CURVE FOR MODAL DAMPING IN STAY CABLES WITH VISCOUS DAMPER

To simplify the procedure of designing viscous dampers for stay cables in bridges, a universal estimation curve is proposed that relates the modal damping ratio of the cable with attached damper, the mode number, the damper size, the damper location, and three parameters of the cable: span, mass per unit length, and fundamental frequency. The curve is obtained from numerical complex-eigen-value analysis of a taut cable with a single damper near the anchorage, with judicious grouping of these parameters into nondimensional factors. Several numerical examples illustrate the convenient use of this design aid, as well as show realistic values of the required damper size and location and the expected additional damping in the first few modes. The damping to be attained is usually high enough to suppress most vibrations induced by wind. However it is noted that a small sag of the cable and slight nonviscous properties of the damper may reduce the damper effectiveness. A modified design curve may have to incorporate these parameters to provide better accuracy.