Research On Modal Recognition And Safety Assessment Of Bridge Structure Based On GNSS Signals

Global Navigation Satellite System(GNSS),as one of the means of structural overall response monitoring,has attracted increasing attention with technological advancement.In recent years,the successfully construction of the Beidou Satellite Navigation System(BDS)and its available for civilian use make it possible for developing bridge structural dynamic monitoring and safety assessment system with GNSS.Taking the Shenzhen North Railway Station Bridge,a concrete-filled steel tube arch bridge with a main span of 150 m,as the engineering background,the main objective of this research is to establish a GNSS-based method for modal parameter identification and safety assessment of bridge structures.The main work of this research is summarized as follows:(1)An environmental vibration test and a cable force measurement were carried out on the Shenzhen North Railway Station Bridge.An initial finite element(FE)model of this bridge was established according to the design drawings of the bridge.(2)A structural health monitoring system was designed and installed on the Shenzhen North Railway Station Bridge,which includes a displacement monitoring system based on BDS and a conventional dynamic response monitoring system for acceleration,cable force,temperature,etc.(3)A stochastic subspace identification method based on wavelet transform is developed.The wavelet transform is used to depart the GNSS signals into several frequency bands and reduce the noise in each band.The stochastic subspace identification method is used to generate a stable map to identify the modal parameters from GNSS signals and the identification results were compared with that from acceleration signals.(4)The interval response surface model of Shenzhen North Railway Station Bridge was established.The affine algorithm is introduced to modify the interval median value and interval length.The established interval response surface model is updated based on the GNSS monitoring data identification interval,and the uncertainty of the finite element model parameters is quantified.(5)Relying on the data from the health monitoring system of Shenzhen North Railway Station Bridge,select modal frequency,dynamic displacement,and cable force as safety assessment indicators,and determine the index weights according to the uncertain analytic hierarchy process,data integrity and game theory methods,to establish an online safety assessment method for concrete-filled steel tube arch bridge.Based on the preceding works,the following conclusions can be drawn.(1)The basic characteristics of the through-type concrete-filled steel tube arch bridge with a main span of 150m—Shenzhen North Railway Station Bridge were identified from the result of the environmental vibration test and the cable force measurement,with the transverse fundamental frequency of 0.350 Hz,the vertical fundamental frequency of 0.705 Hz,the torsion fundamental frequency of 1.430 Hz,the longitudinal fundamental frequency of3.807Hz;the overall distribution of the cable forces is relatively uniform.(2)A stochastic subspace identification method based on wavelet transform was proposed,and the algorithm was implemented based on Matlab program.The developed method was used to identify the modal parameters from numerical examples and real-bridge data.Analysis results showed that the method can depart signal into several frequency bands,effectively filter white noise and colored noise from the real structure signal,identify multi structural modal parameters.This indicates that the proposed method can be used for bridge modal parameter identification from GNSS measured bridge response signals with strong noise.(3)An interval response surface model updating method based on affine algorithm is proposed and was used to update the initial FE model of Shenzhen North Railway Station Bridge.The frequency interval of Shenzhen North Railway Station Bridge computed with the updated FE model was compared with that identified from BDS signals,which showed a deviation of less than 5%.This method can quantify the uncertainty of the parameters of the concrete-filled steel tube arch bridge in complex service environments.(4)Based on the established online safety assessment method for concrete-filled steel tube arch bridges and the recorded data from the health monitoring system,the condition of the Shenzhen North Railway Station Bridge was assessed with the comprehensive scores all above 80.It can be concluded that the Shenzhen North Railway Station Bridge still maintains a relatively good overall working state after being severiced for 20 years.