Research Of The Modal Parameters Identification Method For The Bridge Structure Base On The Wind Loading Excitation

During the bridge service time, the damages will easy appear by many reasons, anyway, the bridge safe and durability are correlated with people's life. By identify the modal parameters of the bridge structure, may detect the possible damage. By testing the bridge structural dynamic characteristic, testing the structural parameters changing by damage, could forecast the bridge damage on the early period, save the fixing and maintain cost of the bridge, and could prevent the collapse of the bridge and other serious accident. Protect the people's life and property. So, bridge structure modal parameters identification, real on time monitoring on the bridge, construct the structure health monitoring system, intelligent assessment are very important.The traditional modal test analysis methods require the excitation on the bridge structure, the heavy excitation is expensive, will rise the cost of system identification, and may damage the structure with close the structure or cut the communication, it is uncomfortable for the busy structure. Therefore, the modal test by ambient excitation method could be solving this problem, the input data is not necessary in the ambient vibration response data to identify the modal parameters method, the excitation is unknown, such as, for the bridges, ocean structures, sky scraps and other robust structures, excitation is not necessary, only obtain the output signal could identify the structure modal parameters, just like the wind loading, communication, ground fluctuating and the other ambient exciting. Apply the ambient exciting vibration signal to identify the modal parameters, the vibration response signal need pretreatment, make them according to the suitable signal form for time-history identification method, just like by the Stochastic Minus method to extract the vibration signal from the vibration response signal, using NExT method to instead the fluctuating response parameters as the modal parameters time history identification input data by the cross-correlation function of the different testing point vibration response signal. The modal test based on ambient vibration, expensive exciting device and communication cutting are not necessary, same as the bridge structure real service condition, becomes the most active research focus. The paper focus on the condition of unknown exciting structure, bridge structure as the research object, Natural Exciting Technology (NExT) and Earmark Reality Actual (ERA) method application in the ambient vibration modal analysis area is very important research. The paper also researches the stochastic minus and ITD method, which is the supplement of the NExT/ERA method.First, expound the application background and important signification of the ambient vibration modal analysis in the engineering area, review the state of the art of the research around the global, and circumstantiate the developed process of the methods in this area, explain the research condition of the correlation methods.Second, introduce the theory basement of the Stochastic Minus/ITD method, and compose the algorithm program for the modal parameters identification by MATLAB.Third, research the time-history combine algorithm of ambient vibration analysis: NExT/ERA method. For the disperse state space method model of structural vibration, introduce the NExT/ERA method identification theory, compose the structure modal parameter identification program by MATLAB. By the continuous beam mathematical model, the response by the white excitation on the structure is simulated. Apply the NExT/ERA method identification theory identify the modal parameters of the model, point out the NExT/ERA method effect, and validate the accuracy and the anti-noise ability of the NExT/ERA method.Four, apply the Ansys FEM software to simulate a concrete continuous beam bridge space FEM model, consider the element type, boundary condition and material characteristic. Then calculate the FEM time-history signal on the space FEM by simulate the wind loading, obtain the response signal, and consider the outside noisy affect. Use the Stochastic Minus/ITD and NExT/ERA method to analyze and manage the simulating testing signal, obtain the bridge space vibration models. Compare the identification result and the simulating result of the two methods; prove the research effect of the two methods of the ambient exciting modal testing analysis, and confirm the NExT/ERA method is better than the Stochastic Minus/ITD method on the bridge structural modal parameters ability.