Modeling Of Unsteady Ground Motion And Its Application To Random Response Analysis Of Extradosed Cable-stayed Bridge

The low tower cable-stayed bridge is a composite structural system bridge between cable-stayed bridge and continuous beam bridge.Because of its convenient construction,beautiful appearance and good economic benefits,many low tower cable-stayed bridges have been built in China since the 21 st century.Non-stationary ground motion modeling is an important prerequisite for studying the seismic dynamic response of long-span bridges.At present,time history analysis method and response spectrum method are widely used in seismic response analysis of bridges.However,the above methods use deterministic seismic excitation,and the results can not reflect the random characteristics of structural response.Therefore,this paper establishes a non-stationary model of ground motion based on wavelet analysis,and uses the statistical random vibration method to analyze the ground motion response of the low tower cable-stayed bridge.The research work of this paper mainly includes the following contents:(1)In this paper,the evolutionary power spectrum theory,the development and research status of low pylon cable-stayed bridge are summarized,and different seismic response analysis methods of bridge are summarized.(2)The actual energy spectrum of ground motion is extracted based on generalized harmonic wavelet,the nonstationary ground motion model is established by using the energy distribution function in frequency domain and energy accumulation envelope function proposed by Ding Wang et al,and the model is compared with the real situation of seismic energy changes.The effectiveness of the model is verified by comparison,and the limitations of the method are given.The influence of different parameters on the model fitting effect is analyzed.Finally,the influence of different wavelet scales on the power spectrum image is studied.(3)The theoretical method of solving bridge seismic response power spectrum based on convolution summation is expounded.(4)A model of low tower cable-stayed bridge with five towers and six span is established by using the finite element software Midas/Civil,and its first 20 order natural vibration characteristics are analyzed.Based on the numerical solution of triangular pulse convolution,the response power spectrum and variance of the key parts of the low tower cable-stayed bridge are solved.Combined with the dynamic characteristics of the structure,the time-frequency characteristics of the response power spectrum and structural response characteristics of low tower cable-stayed bridge are analyzed.Three seismic waves are selected according to site parameters,and the influence of consistent site conditions on the relative displacement of the main approach bridge is analyzed.The effects of uniform and non-uniform site conditions on seismic response of bridge structures are studied.