Study On Aerodynamic Performance Of A Square Section Pylon With Chamfers By Wind Tunnel Test And The Vibration Reduction Design Method

Bridge towers are main supportting structures of bridges and the height will be significantly improved with the increase of the bridge span. For the bridge tower of large span bridges with chamfers, flexible structure, light mass, and small damping ratio, the tower will be easily susceptible to the galloping and vortex-induced vibration. The paper studies the galloping and vortex-induced vibration performance and vibration reduction design method by using TMD for bridge tower whose cross section is square with chamfers. The working contents of the paper are as following:(1) The worst wind angle for galloping of the tower whose cross section is square with chamfers was studied and two set of methods aiming at improving the aerodynamic performance (tower stability performance) was advanced. The methods include adding the circular deflectors on the chamfers and adding the vertical rectangularflange. On top of this, the influence regulation of circular arc radius of thedeflectorsand ventilation rate of the vertical rectangularflangeeffect on improving the tower galloping performance.(2) Based on the theory that the galloping is the single degree of vertical flutter, the flutter derivatives (H1*andH4*) are introduced to the issue of galloping. Therefore, the quasi-steady effect has been taken into consideration on the analysis of galloping issue and the change law of H1*and non-dimensional wind speed V, of the bridge tower with this cross section.(3) The tower galloping critical wind speed is calculated based on Den Hartogquasi-steady theory and the critical wind speed is compared with the speed obtained by the wind tunnel tests of tower aeroelastic model. The comparison suggests that the galloping critical wind speed obtained by quasi-steadytheory tends to be conservative. The galloping critical wind speed by considering the quasi-steady effect (the inclusion of flutter derivatives H1*and H4*) is calculated and the value is almost the same with the value obtained by e wind tunnel tests of tower aeroelastic model.(4) The vortex-induced vibration performance of the tower is studied by adopting a likely half width of the power law to determine the aerodynamic parameters of linear vortex-induced forces model and the accuracy of the determined aerodynamic parameters is checked. The study suggests that the accuracy could meet the engineering needs. Also the influence effect of structural damping ratio and the adding of aerodynamic measures on the vortex-induced vibration performance is studied.(5) The vibration reduction design method by using TMD is discussed in the paper. By using a single degree of freedom system with a TMD, the basic TMD parameters, including damping ratio ξT, frequency ratio f, and mass ratio μ, influence on the reduction of vibration. And the TMD parameter optimization design method is intensively analyzed for two working conditions:harmonic loadsincentive and random load incentive. Also the comparison and analysis regarding TMD parameter optimization are made for the two working condition acting on the main structure or the foundation.(6) For the conventional TMD based vortex-induced vibration reduction design, the issue of aerodynamic stiffness and aerodynamic damping of vortex-induced aerodynamic forces could not be considered. The theory TMD parameter optimization design model by considering the vortex-induced forces aerodynamic stiffness and aerodynamic damping is established by the aerodynamic parameters of linear vortex-induced forces model obtained by the quasi half broadband method.