When a steel pylon of cable-stayed bridge is standing alone before setting stay-cable, the pylon is susceptible to vibration under wind action. Especially the vibration of bridge axis tends to occur even in a lower wind velocity. The pylon of the Sakae-gawa Bridge was designed as the modified A-shaped one with rectangular cross sections, that is well known as one of sections unfavorable from aerodynamic aspects, and that, depending on side ratio, usually induces the vortex-excited vibration in lower wind velocity and galloping in higher wind velocity. Unfortunately, at the time requiring the aerodynamic investigation, there was no enough time to change the shape of cross section of the pylon. The authors tried to improve the aerodynamic characteristics by means of simple device attaching the vertical plates on the surface of the pylon, based on the separation interference method developed by Kubo. The effectiveness of the method is reported in the present paper.
