| At present,the seismic resistance and earthquake absorption of bridges analysis at home and abroad is mainly based on the traditional conventional ground motion,which rarely involves the influence of long-period ground motion.From the seismic design code to the seismic design method,the research on the influence of long-period ground motion on the flexible structure is relatively weak.However,the long-period ground motion has abundant low frequency and relatively concentrated energy,which has very severe impact on the flexible structures such as cable-stayed bridges.Therefore,aiming at the possible damage caused by long-period ground motion,it is necessary to deeply analyze the characteristics of long-period ground motion,to study the mechanical response of cable-stayed bridges under long-period ground motion,and to put forward the corresponding seismic reduction design methods from the perspective of structural and ductile seismic resistance.In this paper,relayed on the double-tower cable-stayed bridge with the main span of 926 m as the engineering background,based on the analysis and study of the long-period ground motion characteristics,Fourier Decomposition Method is proposed for signal decomposition and characteristics analysis of long-period ground motion.Under the premise condition of considered the cable vibration characteristics,considered the cable sag effect,large displacement effect and other geometric non-linear characteristics,the first-order modal non-linear vibration equation of the cable and the non-linear vibration equation of the double cable under the axial dynamic load at the end of the beam are derived.The local vibration of the cable is considered by the number of cables elements,the dynamic response characteristics of cable-stayed structures are compared and analyzed when Single-Element Cable System(SECS)model and Multiple-Element Cable System(MECS)model are used to simulate cable-stayed structures,based on the long-period ground motion structural response,applied particle swarm optimization,and used ANSYS finite element simulation,proposed a parameter optimization method of viscous dampers for cable-stayed bridges under long-period ground motion.At the same time,from the perspective of ductile seismic design of cable-stayed bridges,carried out the quasi-static test of steel fiber reinforced concrete column with high strength reinforcement.By comparing the failure modes and mechanical properties of each component in the test process,analyzed the influence of hysteretic performance and seismic resistance ability of steel fiber reinforced concrete.According to the test results,based on the OpenSees analysis platform,determined the constitutive relationship parameters of the material model for steel fiber reinforced concrete,and established the nonlinear beam-column unit analysis model.Based on the parameter analysis of the plastic hinge length of high-strength steel fiber reinforced concrete columns,proposed the fitting formula of plastic hinge length for steel fiber concrete columns.The main research contents of this paper include:(1)From the point of view of seismic source,combined with the characteristics of long-period long-field ground motion,the Fourier decomposition algorithm is proposed to decompose the signal of long-period long-field ground motion and analyze the time-frequency energy spectrum,so as to quickly judge the energy concentration frequency of long-period ground motion.(2)Based on the vibration characteristics of cables,the vibration characteristics of single cable and the influence of cables on the vibration of adjacent cables is studied.By using multi-truss element to simulate the local vibration characteristics of cables,synthesized calculating efficiency and simulation accuracy,proposed a reasonable method to divide the cables into segments.After considering the local vibration effect of cables,analyzed the excitation effect of long-period ground motion on the vibration of cable-stayed bridges.(3)From the point of view of damper seismic absorption,analyzed the design and the reasonable parameters optimization of viscous dampers for cable-stayed bridges under long-period ground motions.According to the effect of viscous dampers on seismic resistance response,used particle swarm optimization,and based on ANSYS finite element simulation,proposed a parameter optimization method of viscous dampers for cable-stayed bridges under long-period ground motion.(4)From the point of view of bridge ductile seismic resistance design,experimentally studied the seismic resistance performance of steel fiber reinforced concrete columns with high-strength steel bars,concluded the seismic reduction effect of the component.According to the test data,modified the finite element constitutive model of steel fiber reinforced concrete column with high strength reinforcement,and verified the test results.The main innovations of this paper are as follows:(1)Based on the study of ground motion characteristics,the Fourier decomposition algorithm is proposed for the long-period ground motion signals for the first time to decompose the components and to analyze the time-frequency energy spectrum.Using this algorithm,the concentrated energy frequency of long-period ground motions can be estimated quickly,that can determine the main frequency of the influence of ground motions on structures.(2)Based on the influence of long-period ground motion on the nonlinear seismic behavior of cable-stayed bridges,used particle swarm optimization and ANSYS finite element simulation,proposed a parameter optimization method of viscous dampers for cable-stayed bridges under long-period ground motion.This method can effectively obtain the optimal parameters of the reasonable viscous damper of cable-stayed bridge under long-period ground motions.(3)Based on the experiment and simulation analysis,the seismic resistance performance of reinforced steel fiber concrete columns with high strength is studied.From the point of view of ductile seismic resistance design of cable-stayed bridges,proposed a fitting formula for calculating the length of plastic hinge considering pier height,axial compression ratio,longitudinal reinforcement ratio and short side length,which is suitable for high-strength steel fiber reinforced concrete. |
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