Nonlinear Time Domain Buffeting Response Analysis Of Long-Span Suspention Bridge

With the modern bridges becoming more long-span, slender and flexible, the research on buffeting has gotten more and more important, and the prediction of wind-induced buffeting response has turned to be of major concern in the design of long-span bridges. In this thesis, based on the present time domain analytical methods, a nonlinear time domain approach for predicting the buffeting response of long-span bridges is presented. This approach has taken into account both structural geometric nonlinearity and aerodynamic nonlinear factors. The geometric nonlinear factors include initial deformation caused by dead loads and static wind loads, stiffening effect, initial strain effect and large displacement. The aerodynamic nonlinear factors are wind incidence angle effect and nonlinearity of aerodynamic forces (such as static wind loads and buffeting force) caused by wind incidence angle effect. Applying this nonlinear approach, the buffeting problem of a long-span suspension bridge in operation stage is analyzed in this thesis.The research works are mainly concerned with the following aspects:Firstly, an approach and corresponding procedure for analyzing nonlinear aerostatic problem of suspension bridges based on ANSYS are introduced. Based on fore-mentioned approach, a program is developed using ANSYS/APDL programming language. Using this program, the nonlinear aerostatic stability of Xihoumen Bridge is analyzed.Secondly, the essential relations among beam element, truss element and stable element are discussed, and also tested by some typical examples to provide theoretical support and sound explanation to finite element model of suspension bridges.Thirdly, an approach for simulation of three-dimensional fluctuating wind field on long span bridges based on field measured data of wind time histories is presented. Based on the fore-mentioned approach, a program for simulating wind velocity field is developed using MATLAB programming language. Applying this program, three-dimensional fluctuating wind field on Xihoumen Bridge has been simulated to demonstrate the capabilities and efficiency of the proposed approach, with the simulated results checked.Finally, as the core work of the thesis, a nonlinear time domain approach for predicting the buffeting response of long-span bridges is presented. Based on the fore-mentioned approach, a program is developed using ANSYS/APDL programming language. Applying this program, through nonlinear time domain buffeting analysis of Xihoumen Bridge, compared with the results of wind tunnel tests, the capabilities and efficiency of the proposed approach is demonstrated. Moreover, the nonlinearity of static wind forces and buffeting forces and their effects on the computational results are investigated. Computational results of traditional experiential power spectral density (PSD) functions and field measured PSD functions are compared to investigate influence of the PSD functions to buffeting responses.