Study On The Application Of Modal Analysis Methods In Detection For Bridge Based On Ambient Vibration

According to the present research, the research works is explored and developed deeply for modal analysis methods in detection for bridge based on ambient vibration in this paper, and it works on four aspects have been done around the purpose.First of all, it is introduced the basic concept of the modal analysis, investigated roundly the basic theory of the ambient vibration method, and analyzed systematically the main methods of ambient vibration identification. Then we established the finite element model of structural dynamics and test model and analyzed their mutual relation and gave the subspace method and correlation function method based on continuous model, which is multi-harmonic retrieve technique. Due to the unknown input force of the modal analysis method based on ambient vibration, the mode scaling factor can not be estimated; only the un-scaled mode shape can be obtained from Frequency Response Functions. This paper introduces one simple method of adding masses on the structure. The natural frequency shift caused by the structure mass change is used to get the scaling factor and scaled mode shapes.Secondly, through carried on the simulation testing in a four degrees-of-freedom lumped system it can confirm feasibility and the reliability of the modal analysis method based on ambient vibration by increased the mass to obtain the modal parameter.Then it is carried on the survey to an actual bridge obtained the modal data with the modal analysis method based on ambient vibration. It is confirmed this law feasibility in reality.Last, the influence of measurement error on damage detection and the causation of waveform distortion in practical structural measurement are also discussed.