| As a typical example of long-span bridge,cable-stayed bridge plays a key role in transportation engineering,and its seismic performance has attracted much attention.In the longitudinal direction of cable-stayed bridge,the floating system is usually used to reduce the seismic internal force of the structure,and the viscous damper is set between the tower and girder to control the seismic displacement of the girder.The cable-stayed bridge with floating system is a typical flexible system,and the characteristics of ground motion have a great influence on its dynamic response,but also on the damping effect of the damper.In order to study the effect of ground motion characteristics on the damping effect of viscous damper for cable-stayed bridge with floating system,based on the dynamic response characteristics of cable-stayed bridge with floating system,a double-mass simplified analysis model was established,and analyzed the simplified analysis model using the sine wave loads.Meanwhile,a refined full-bridge analysis model was established for a double-tower cable-stayed bridge with floating system,and nine typical actual ground motion records with different characteristics were selected to study the influence of damper parameters and ground motion characteristics on the damping effect of viscous damper,which was verified by comparison with the analytical solution of the simplified model.Finally,a parameter optimization method of viscous damper for cable-stayed bridge with floating system considering ground motion characteristics was proposed according to the response surface principle.The main research work and conclusions are as follows:(1)Based on the stiffness method,a simplified calculation formula for the longitudinal first-order natural vibration period of the cable-stayed bridge with floating system was derived,and compared with the finite element calculation results of ten built cable-stayed bridges in China.The results are well agreeable with an average error of-0.38%.It shows that the simplified calculation formula has high precision,can be used to estimate the natural vibration period of cable-stayed bridge with floating system.(2)The comparative analysis of the dynamic characteristics and seismic time history results shows that the simplified analysis method of the double-mass model has high accuracy,strong practicability and wide applicability.Compared with the full-bridge finite element model,the double-mass model is simple to model and efficient to calculate.It can adapt to various complicated seismic load input when solving numerically,and can provide a more efficient model for damper parameter optimization.(3)The comparative analysis between the double-mass simplified model and the full-bridge finite element model shows that the viscous damper is set between the tower and girder can not only effectively control the seismic displacement of the girder,but also improve the force condition at the tower base.Among them,the damping coefficient C_d has a great influence on the energy dissipation capacity of the damper,while the influence of the velocity indexαis very small,which only reflects the nonlinear characteristics of viscous damper.(4)The ground motion characteristics have a great influence on the damping effect of viscous damper for cable-stayed bridge.With the increase of ground motion intensity,the damping effect of damper with the same parameters gradually decreases,and the damping effect of damper is more sensitive to the high-frequency components of the ground motion spectrum characteristics.Therefore,when the parameters of viscous damper for cable-stayed bridge are optimized,the ground motion intensity A_pshould not be used as a single reference indicator,but the parameter of A_p/V_p can be used as a supplementary indicator.Moreover,in addition to A_p,A_p/V_p and other indicators,particular attention should also be paid to the possible unexpected effect of the acceleration time-history curve characteristics of ground motion in individual cases.(5)The functional expression for the seismic response of key components of cable-stayed bridge with respect to the damper parameters was fitted according to the response surface method.The results of residual analysis and variance analysis show that the errors of each response surface model follow the normal distribution,and the decision coefficients are all greater than 0.95,which indicates that for the bridge example in this paper,the fourth-order polynomial response surface model has good fitting accuracy.The model accurately simulates the complex implicit relationship between structural seismic response and viscous damper parameters to ensure the precision requirements of the damper parameter optimization.(6)The response surface method is used to optimize the parameters of viscous damper for cable-stayed bridge with floating system.The problem of the damper parameter optimization is transformed into a nonlinear programming problem,which can not only consider the comprehensive influence of local site differences,ground motion intensity and other factors,but also avoid the uncertainty caused by purely selecting damper parameters based on experience,and has a positive reference significance for the seismic analysis and shock absorption design of similar cable-stayed bridges. |
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