Wind-induced oscillations of groups of bridge stay-cables

An experimental study of wind-induced oscillations of groups of bridge stay-cables was conducted in two wind tunnels, one in Japan and one in Canada, to develop a method for suppressing the instability. At first, the parallel cable models were connected rigidly to each other with spacers, forming a coupled cable group whose surface-to-surface separation, or gap, could be varied from 0 to 2 cable diameters. This modification stabilized the wake galloping but it was found that a different form of instability then occurred at higher wind speeds. In this case the group of cables, rather than just the downwind cable, was unstable. With zero gap, the group was most stable, being unstable only near wind angles of 5° and aerodynamically stable otherwise. When the cable group with zero gap was twisted into a shallow helix, it was found to be aerodynamically stable for all wind angles.