Automatic Identification And Response Characteristics Of Vortex-induced Vibrations Of Long-span Bridges Based On Monitoring Data

With the vigorous development of China's transportation industry,large span,light and low damping bridges are constantly emerging,making the bridge structure more sensitive to wind load,which is easy to vortex-induced vibration response at low wind speed.Vortex-induced vibration is a common disease of wind induced vibration of large span bridges,and this phenomenon has been observed in dozens of bridges at home and abroad.Vortex-induced vibration is a wind-driven limiting amplitude.It is easy to occur at low wind speeds,and it will cause fatigue damage to bridges,and excessive amplitude will affect human comfort and even affect driving safety.Vortex-induced vibration is related to the nonlinear effect of fluid structure interaction,and the mechanism is very complex.At present,a reliable vortex-induced vibration model has not yet been established.Vortex-induced vibration is a very important problem in bridge wind engineering.On line monitoring technology provides a powerful means to study vortex-induced vibration by measuring the flow parameters and dynamic response of structures when vortex-induced vibration occurs.However,there is a large amount of structural health monitoring data,most of which are wind buffeting,vehicle vibrations,or a combination of both,with only a v ery small number of vortex-induced vibration responses.How to automatically identify the vortex-induced vibration from the measured data is the need of engineering practice and the need of vortex-induced vibration.Under different incoming wind speeds,large span suspension bridges and continuous steel box girder bridges may have different vertical modes of vortex-induced vibration,semi-active tuned mass dampers can achieve adaptive control of vortex-induced vibration of different vertical modes,the on-line discriminant of the vortex-induced vibration is also a prerequisite for the realization of the semi-active control of the vortex-induced vibration.Based on comprehensive analysis of the status quo of research on the domestic and foreign application of this paper,by using the measured data of the structural health monitoring system,a series of studies on the automatic identification of vortex-induced vibration and the characteristics of the vortex-induced vibration are carried out.The main work and achievements of this paper are as follows:(1)Using the stochastic decrement technique of analytical model decomposition,the modal frequency and modal damping ratio characteristics of the main girder measured from the Xihoumen bridge health monitoring system are extracted.The results show that:(i)with the increase of wind speed,the modal frequencies of all vertical modes remain basically unchanged,(ii)When the wind speed is less than the vortex-induced resonant wind speed locked zone,the damping rati os of the corresponding modes are discrete,but little change.When the wind speed is in the locked zone,the damping ratio decreases,and then as the wind speed increases,the damping ratio shows an increasing trend.(2)The modal damping ratio of the identified vertical mode of the Xihoumen bridge is analyzed statistically.The 50-bit value and average value of the vibration damping ratio of each order: the first order are mode 0.323% and 0.428%;the second order mode are 0.305% and 0.347%;the third order mode are 0.196% and 0.224%;the fourth mode are 0.266% and 0.292%;the fifth order mode are 0.266% and 0.292%;the ninth order mode are 0.422% and 0.429%.In general,the vibration damping ratio of most of the vertical bending modes is less than 0.5% of the proposed standard in our country,and the damping ratio of the anti symmetric mode(fifth and ninth)is higher than that of the symmetrical vertical bending mode.(3)Using the significant difference between ambient vibration and vortex-induced vibration time-distance signals,a vortex-induced vibration automatic identification method based on stochastic decrement technique was proposed.The method was verified by numerical simulation.The results show that the proposed method can be effective distinguish between environmental vibration and vortex-induced vibration.(4)According to the significant difference between the environmental vibration and the vortex-induced vibration power spectrum,a novel vortex-induced vibration automatic identification method based on the novel detection technology is proposed.The method considers the environment vibration of the bridge as a normal state.The training is established through the BP neural network.In the state mode,when vortex-induced vibration occurs,abnormal modes occur and vortex-induced vibration is recognized.The feasibility of the method is verified by simulation.(5)Using the proposed vortex-induced vibration automatic identification method,the vortex-induced vibration of the Xihoumen bridge health monitoring system was automatically identified,and the characteristics of the vortex-induced vibration were statistically analyzed.The results show that:(a)Both of the proposed methods can accurately and accurately identify the vortex-induced vibration;(b)The vortex-induced vibration occurs in the second to the ninth order of the bridge.When the vortex-induced vibration is excited the main beam is a single-mode vibration.The wind direction is basically perpendicular to the longitudinal direction of the main girder.The vortex-induced vibration of each mode has a significant wind speed locking zone.When vortex-induced vibration occurs,the turbulence intensity is mostly below 15%.