Seismic Response Analysis And Vibration Mitigation Research For Long Span Cable-Stayed Bridges

With the development of the national economy, the long-span bridges have got very rapid development in our country. It is well known that the long-span bridges are the hinge of transportation, which are heavily invested in, and have important influence on national economy. Once destroyed, it will lead to huge economic loss and heavily influence the work of salvage and rehabilitation of disaster area. So it is very important to adopt the efective seismic fortification measures to insure the safety of the structure in earthquake. The installation of viscous dampers in the long-span bridges can't increase the stiffness of the structure and the grider can deform freely because of temperature fluctuation. At the same time, it can reduce the vibration responses of the long-span bridge, because viscous dampers can consume a lot of energy created by earthquake and wind. So it is an ideal vibration mitigation technique for the long-span bridge.The Lanqi Songhua River Bridge in Jilin City is a concrete cable-stayed bridge with double towers and single cable plane, the main span is 240 meter long. The earthquake intensity of the site of this bridge is VII. This presents the basic theory of seismic response analysis and based on it, the author makes an analysis to the bridge with two methods: spectrum response analysis and elastic time-history analysis of earthquake. This paper studies damped energy-dissipated earthquake-reduction design. The main content of this paper includes:(1) The advanced analysis program ANSYS is used to calculate the dynamic behavior of the bridge. The analysis model, a modified lumped-mass model, that can be adopted for seismic analysis of bridge pier-pile-soil interaction.(2) The standard seismic response spectrum is input in longitudinal, transverse and vertical direction respectively. Two kinds of seismic combinational modes, which are longitudinal plus vertical vibrations and transverse plus vertical vibrations are considered. In order to ensure the precision, the CQC (Complete Quadratic Combination) approach is applied.(3) The spectral analysis is linear so the nonlinear factors cannot be taken into account. The dynamic analysis of the Bridge are calculated also with dynamic time-history analysis considering the nonlinear factors. The earthquake response is gained according to the calculation results of the two methods.(4) According to the aspect of the aseismatic design, several structural systems of cable-stayed bridges were analyzed and compared, such as half floating system, damped energy-dissipated system and Lock-Up system. The results show that the boundary condition has great effect on the seismic response of the cable-stayed bridge. It is also show that the damped energy-dissipated system is more advantageous.(5) This paper proposes that viscous dampers are set between the piers and the girder. Effectiveness of viscous dampers on the cable-stayed bridge is studied using the computer program ANSYS. It's concluded that the use of viscous dampers can drastically reduce displacements and forces of the structure.(6) In this paper, the main design parameters are described. The effect of damping coefficient and velocity exponents on the seismic response of the structure are studied. At last, based on the results obtained, some suggestions about the design of viscous dampers in the long-span cable-stayed bridges are presented.