The Seismic Research On Long-span Arch Bridge Based On Stochastic Theory

It's doubtless that long-span arch bridge is playing a major role in the communication and transportation network, as well as its special position in the national economy. However , in view of the defects of the present seismic analysis methods and the lacking specialty seismic code to meet the requirement of practical project, besides the three elements of earthquake ground motion(duration,intensity, frequency spectrum)which show uncertainty, obviously, it is extremely necessary to apply the theory of stochastic vibration to the seismic analysis of long-span arch bridge. This paper based on stochastic vibration theory and combined with a long-span arch bridge, the stochastic seismic response of long-span arch bridge is developed, the main contents including the fo1lowing aspects:1. The situation and development of present research of the long-span arch bridges are discussed, and the advantages and disadvantages of seismic analysis theories are summed up. Finally, the feasibility and necessity of random seismic analysis are analyzed, some expressions about earthquake ground motion model are introduced in this paper, and discusses the advantages and disadvantages of each model to determine power spectrum model related parameters, the above research provides references for future stoehastic seismic analysis.2. The traditional and pseudo excitation method of random vibration analysis under the uniform seismic excitation of structural are specified, the basic principle of random vibration analysis of power spectrum method applied to long-span arch bridge has been expressed, and the solution of long-span bridge excited by random seismic that consider the traveling wave effect and coherent effects are discussed. The computation formula of stoehastic responses of structures under seismic excitations is presented based on stoehastie vibration theory.3. Based on the power spectrum model of ground motion which are used widely now, combining with actual bridge types and site conditions, the input earthquake ground motion power spectral model is chosen. Study the long-span arch bridge dynamic responses under multidimensional uniform excitations and seismic ground motions with spatial variations by establishing the finite element model of long span arch bridge and using random vibration analysis method, including dynamic characteristics, response spectrum method and random vibration comparative analysis, multidimensional excitation, local site effect, incoherence effect and wave passage effect. For different seismic effects, there are different in characteristic of impact level and rules for seismic ground motion with spatial variations. therefore, in view of different cases, the analyses would have different results.4. The effect of parameters change, such as span ratio, modal number, site conditions and seismic ground motion PSD model, on response of long-span arch bridge was analyzed in detail based on random vibration theory. The results show that, the seismic response bending moment peak is increase with increasing span ratio for different span ratio bridges under the longitudinal seismic action, while the seismic response axial force peak is reverse, the seismic response internal force decreases gradually along with the increasing of site soil stiffness. and the dynamic response of structure has great different value when choosing different power spectral function, therefore, it is especially significance to select acceleration power spectrum function model reasonably.