Seismic Vibration Mode Analysis Of Cable-stayed Bridge Based On Actual Monitoring Data

Cable stayed bridge has the characteristics of large span capacity,reasonable structure and good mechanical performance.It has been widely used in bridge construction in our country.Cable-stayed bridges in seismic risk areas need to have good seismic performance.It is of engineering significance to explore the vibration mode of cable-stayed bridges under actual ground motion.Based on this,this study takes Sutong Bridge as the engineering object,and uses the dynamic response data recorded by the structural health monitoring system in the Wenchuan earthquake to analyze the vibration mode and nonstationary characteristics of the bridge in the earthquake.Firstly,the monitoring system of Sutong Bridge is described,and the position of acceleration and displacement sensors in the monitoring system on the bridge is given.The finite element model of Sutong Bridge is carried out by using ABAQUS software,and the vibration modal analysis is carried out.The vibration modes and natural frequencies of the bridge are extracted,and the vibration characteristics of the bridge are analyzed.Then,the acceleration response of the main beam and main tower,and the displacement response of beam end displacement measured in Wenchuan earthquake are analyzed.Through the fast Fourier transform method,the spectral characteristics of the transverse and vertical bridge acceleration response of the main beam and the transverse and longitudinal bridge acceleration response of the main tower are calculated,and the Fourier amplitude spectrum is obtained.Combined with the bridge vibration modes obtained from the finite element model,the dominant vibration mode of Sutong Bridge under real ground motion is obtained.At the same time,the law of the longitudinal displacement of the beam end varying with temperature and the residual displacement of the beam end are analyzed.Finally,the nonstationary response of the bridge is analyzed.Through the timefrequency analysis of the acceleration response data of the main beam and the main tower through the short-time Fourier transform,the time-varying amplitude spectrum of the response is obtained,and the change of the intensity of each frequency component of the bridge with time is obtained.At the same time,the time-varying characteristics of ground motion spectrum are analyzed,and the vibration time of each frequency component is calculated.The research in this paper shows that the vibration of bridge in earthquake has obvious nonstationarity.The frequency range of vibration of main beam and main tower caused by Wenchuan earthquake is between 0.1-0.5Hz.The response of the main beam is greater than that of the main tower,the vertical bridge vibration of the main beam appears before the transverse bridge direction,and the transverse bridge vibration of the main tower appears before the longitudinal bridge direction.The vibration of the mid span position of the main beam is the most obvious in the earthquake.In the future design,we need to focus on the seismic safety here.The results of this paper can provide a reference for the seismic design of cable-stayed bridges.