Frequency-Domain Analysis Of Long-span Bridge Buffeting Under Skew Winds With Effect Of Static Wind Displacement

Wind-resistance is one of the key issues in the design of long-span bridges. With the increasing of the bridge span, structures become more and more flexible, and the static wind-induced displacements increase conspicuously. This will exert a certain influence on the bridge buffeting responses. The static wind-induced displacements affect the bridge buffeting responses mainly through the two ways as follows: one is that larger static wind-induced displacements may change the structural stiffness, and then affect the inherent dynamic behaviors of the bridge and further the buffeting responses; the other is that the torsion of the bridge components due to the static wind loads will arouse the additional attack angels of wind, changing the buffeting forces and the self-excited force on the bridge components, further affecting the buffeting responses.Based on the current research achievements, this dissertation aims to improve the current approach of buffeting response analysis for a long-span bridge under skew winds for considering the effects of static wind-induced displacements, and to verify the reliability of the proposed approach via a wind tunnel test of aeroelastic full model of the third Nanjing Bridge over Yangtze River. The whole work of this dissertation consists of the following four parts:1. To measure the six-component aerodynamic coefficients of bridge deck under skew winds with different directions using a wind tunnel test of sectional model supported by two six-component force balances at first, and to study the variation pattern of the six-component aerodynamic coefficients with the change of wind direction afterwards.2. To investigation the influence of static wind-induced displacements on the bridge inherent dynamic behaviors using finite element approach. At first, the static responses of the bridge under skew winds are computed. Then, the inherent dynamic behaviors are analyzed based on both the initial place of the undeformed structure and the new balance place of the deformed structure under static wind-load, and are compared finally. 3. To put forward the basic procedures and major formulae of the buffeting analysis of long-span bridges under skew winds with the effect of static wind-induced displacements.4. To verify, at first, the reliability and reasonableness of the proposed approach for the buffeting analysis of long-span bridges under skew winds with the effect of static-wind displacements via a wind tunnel test of aeroelastic full model, taking the Third Nanjjing Bridge over Yangtze River as a engineering background. Then, to carry out a serious parametric analysis on the bridge buffeting to research the effects of various aerodynamic admittances, self-excited forces, static wind-induced displacements and wind directions on the buffeting responses.The results presented in this dissertation show that, for the cable-stayed bridges with main spans of about 650m, static-wind-induced displacements are not significant, leading to relatively small influence on the structural inherent dynamic behaviors and buffeting responses. The aerodynamic admittance and self-excited aeroelastic forces affect the bridge buffeting responses remarkably. The increase the vertical, lateral and torsional buffeting responses of bridge deck due to the ignorance of the self-excited aeroelastic forces may reach 76%, 58% and 39%, respectively.