Effects of Rectangular Column Flanges in Steel Structures on Motion-Induced Vortex Vibration

A spring-supported test for a rectangular cross section with the side ratio of B/D = 1.18 (B: along-wind length, D: cross-wind length) was conducted to simulate the phenomenon in a closed circuit wind tunnel at Kyushu Institute of Technology. A new finding was that vibrations were confirmed in the neighborhoods of reduced wind speeds Vr = V/fD = 2 and Vr = 8 (V: wind speed (m/s), f: natural frequency (Hz)). Because the reduced wind speed in motion-induced vortex vibration is calculated as Vr = 1.67 × B/D = 1.67 × 1.18 = 2.0, vibrations around Vr = 2 were considered to be motion-induced vortex vibration. On the other hand, vibrations around Vr = 8 were considered to be Kármán vortex-induced vibrations, because Vr = 1/St = 8.1. St has a Strouhal number of 0.124 measured by wind tunnel test using a rectangular cross section of B/D = 1.18. In this paper, the authors focused on the wind tunnel model configuration. Rectangular column flanges in steel structures have not usually been taken into account when manufacturing wind tunnel test models. Wind tunnel tests were carried out in order to clarify the effects of rectangular column flanges in steel structures on motion-induced vortex vibration. Spring-supported tests, smoke flow visualizations and measurements of Strouhal number and unsteady aerodynamic lift were performed with or without flanges changing angle of attack. Models were forced-oscillating in smoke flow visualizations and unsteady aerodynamic lift measurements. All wind tunnel tests were conducted in a smooth flow. As a result, it was found that it could be very important to model rectangular column flanges in steel structures for wind tunnel tests, especially bracing members of long-spanned truss bridges from a wind engineering point of view.