AERODYNAMIC STABILITY OF A CABLE STAYED BRIDGE

Aerodynamic stability of a proposed Cable Stayed Prestressed Concrete Bridge of span 480 m under wind loads has been studied. Flutter and buffeting responses due to wind loads was investigated on a sectional mode to the scale of 1:200. The model was tested in a wind tunnel for two values of structural damping (0.03 and 0.06) in both torsional and vertical motions with different combinations of live loads at the ratio of frequencies of torsional and vertical oscillations is equals to 1.2. The model exhibited coupled vertical and torsional oscillations in wind. In addition, another uncoupled mode in the form of rolling oscillation about the longitudinal axis of the tunnel was also consistently observed. This type of oscillation has not been reported in the literature and is believed to be due to the overtone flexural oscillation of the main span of the bridge. After trying out several curative measures, it was found that provision of small holes in the bottom of the deck, controlled the vertical and rolling oscillations. The test results were compared with the theoretical (design) values and conclusions drawn for predicting flutter and buffeting responses due to wind loads.