Loads Transferring And Research Of Structure Seismic Analysis Mehthod

Long span structures are wildly used these years. Most of them are important and expensive. Their damage will bring much loss. When the seismic response of long span structure is analyzed, the space effect must be considered, which includes the wave passage effect, partial coherency effect and local effect.There are three kinds of seismic analysis methods: response spectrum method, stochastic vibration method and time history method. Response spectrum is easy to understand and use, but it is based on single seismic excitation and is difficult to be applied in the analysis of long span structures. Time history method depends heavily on the selected earthquake waves. Generally, a few earthquake waves must be selected but that needs quite long time on calculating the responses. Earthquake-induced motions are aptly characterized as stochastic process. So it is rational to apply stochastic vibration method in earthquake engineering. During past forty years, the theory of stochastic method is developed quickly, while until now it can't be wildly applied in earthquake engineering. An important reason is due to the complexity of available computational method. Since 1980's, a highly efficient and accurate algorithm series for stochastic analysis of long span structures, i.e. the pseudo-excitation method(PEM) has been established by Prof. Lin Jia$hao. It has shortened the distance between the stochastic vibration theory and engineering. And the stochastic vibration analysis method is going to be used in the Bridge Codes,which is under stipulation. However, there is not enough material of power spectral density available, which describes the ground motion. In this paper, the methods of transferring the response spectrum curve to power spectral density curves are investigated. A transferring method is recommended, and then the response spectrum method, time history method and stochastic vibration method are compared by means of computing two real bridges.The main work of the paper is:1,Transfer the response spectrum curves of the Structure Seismic Design Codes(GBJll-89), of Structure Seismic Design Codes(edition of 1999), of Caltrans Seismic Design Criteria and of Structural Eurocodes 8 (ENV) to power spectrum density curves by means of iteration method. 2,Fit the parameters of Models by Hu Yuxian and Zhou Xiyuan, by Ou JinPing　and Niu Ditao and by Ruiz and Pension. 3, Computing the stochastic seismic response of structures, by means of powerspectral density transferred from acceleration response spectrum, and compare the result with the result of response spectrum method.4,Compare the wave effects with and without wave passage effect, by means of response spectrum method, time history method and stochastic vibration method(PEM). Two large bridges were analyzed.