Buffeting Response Analysis Of Long-span Bridges With Emphasis On The Three-dimensional Effects Of Turbulence And The Study On The Equivalent Static Wind Loads

In this study,a long-span bridge buffeting analysis method that can take into account the 3D effects of gusty wind is established based on the three-dimensional(3D)buffeting theory proposed in aerospace engineering.A direct approach to identifying the two-dimensional aerodynamic admittance function(2D AAF)of bridge decks,which can be conducted in a turbulent flow field,is proposed.The 2D AAFs of typical bridge decks have been identified by this approach.Based on the 3D buffeting theory and the unsteady characteristic of buffeting drag force of different types of bridge decks,the separate-mode calculation method of equivalent static wind loading has been put forward.This method has very useful engineering applications.In this dissertation,the main research contents include the following points:1.The existing research and the buffeting calculation theory of long-span bridges are reviewed.The research state of aerodynamic admittance and the spanwise correlation of buffeting forces is discussed.The equivalent static wind loading calculation method is introduced along with its application to long-span bridges.The potential problems in the existing buffeting theories and the equivalent static wind loading calculation methods are discussed.2.Based on Ribner’s 3D aerodynamic theory,a generalized two-wavenumber gust loading model is proposed and a long-span bridge buffeting analysis method which can account for the 3D effects of gusty winds is established.The influence of the 3D effects of gusty winds on the buffeting response of long-span bridges with different cross-sections in the service state and the construction state is studied in cases with different aspect ratios,mean wind speeds,integral length-scales and structural damping ratios.Through comparison of the results with the buffeting responses calculated by the traditional buffeting theory,the application scope and condition of the traditional gusty loading model are determined.3.A direct approach to identifying the 2D AAFs of bridge decks in 3D turbulent flow is proposed.Based on the two-wavenumber spectrum analysis,the accuracy of the strip theory in calculating the one-wavenumber lift spectrum of the buffeting force exerted on a bridge section model with different aspect ratios is studied.The key parameters that determine the calculation accuracy of the strip theory are found.The mechanism and kernel of the proposed bridge deck 2D AAF identification approach are given in detail.4.Based on the proposed bridge deck 2D AAF identification approach,the 2D AAFs of bridge decks with streamlined sections,edge sections and truss sections are identified through the section model force measurement technique in grid-and spire-generated turbulent flow.The empirical models of the identified 2D AAFs are proposed.Meanwhile,the effects of mean wind speed,angle of attack,aspect ratio and integral length-scale of turbulence on the bridge deck 2D AAF are studied.The 2D AAFs of typical bridge decks are analyzed and compared with the Sears and Davenport functions that are commonly used in the buffeting analysis of long-span bridges.5.The separate-mode calculation method of equivalent static wind loading is proposed.The overall equivalent static wind loading of a bridge deck is determined by a combination of the equivalent static wind loading in each mode.The equivalent static wind loading in each mode is described by the gust response factor and the spatial correlation reduction coefficient.To facilitate engineering applications,the empirical formulas of the gust response factor and the spatial correlation reduction coefficient are given for cases with different bridge spans,natural vibration frequencies,ground surface types,mean wind speeds,damping ratios and bridge deck sections.The effectiveness of the proposed method is validated by numerical examples.