Post-Earthquake Damage Identification Of Bridge Structures Based On Improved HHT

Bridge structure health monitoring system(BSHMS)is an important guarantee of the safe operation of existing bridge structures.As a crucial link in BSHMS,the accuracy of damage identification is directly related to the efficiency of BSHMS,thus the research about high-precision damage criterion is of great theoretical and practical value.This thesis start with a review of the research status and trend of structure damage identification,after analyzing the deficiency of existing damage criterion,a post-earthquake bridge structure damage identification criterion based on improved HHT was raised and it was verified based on a cable-stayed bridge shaking table test model,the main contents and conclusions are as follows:(1)In allusion to the deficiency of traditional linear filter when dealing with nonlinear and nonstationary structure response signal,a recently invented morphology filter was adopted as a noise reduction method in this thesis.Then the circle structure element was chosen as the best structure element through a simulation signal.The noise reduction result illustrated that the morphology filter can maximum reserve the structure response signal while reducing the noise.(2)Three mode mixing improvement method:EEMD,CEEMD,AEEMD,were introduced in this thesis,both their advantage and disadvantage were analyzed,combined with morphology filter and permutation entropy,PAEEMD was raised and its effect on mode mixing was verified based on the cable-stayed bridge shaking table test model,which illustrated that the mode mixing phenomenon is most serious in EMD,while its decomposition efficiency is fastest;the development of EEMD and CEEMD in mode mixing is limited,but their decomposition efficiency is rank only second to EMD;AEEMD performs well on the mode mixing problem,but its low decomposition efficiency restricted its application in real time bridge structure health monitoring;with the help of morphology filter,PAEEMD performs slightly better than AEEMD,and the decomposition efficiency was improved sharply,this method can be used to construct the damage criterion in BSHMS.(3)Finally the improved HHT was applied to post-earthquake bridge structure damage identification,an IMF characteristic energy ratio method was raised as the damage criterion and applied to evaluate the bridge structure damage status under 5 working conditions,then the identification result was compared with the result of traditional frequency damage criterion.The result illustrated that the damage criterion raised in this thesis can effectively identify the mild damage and precisely locate the damage,it's an effective structure damage criterion.