Damage Identification Of Shearing Structure Based On Dynamic Parameters

With the rapidly development of the structure in our country, the research and the application using the system identification technique to detect the security of the structures has become one of the leading subjects of the constructional engineering. If the structure is damaged, mechanical property of it, such as the stiffness and the strength, will drop. The variation of the structure dynamic property will be affected by this reduction of the mechanical property. Therefore, the damage of the structure can be researched by analyzing the physical parameter and the dynamic property variation of the structure. In this paper, traditional structure rating of merit is changed into precision analysis and estimation of the input and output signal of the structure, frequency-domain analysis is introduced to system identification. Research work consists of the identification of the structure parameter based on frequency-domain analysis and the identification of the structure damage based on dynamic parameter. Research work and conclusions in details are given in the flow: In the first part, modal parameter and its identification are introduced, including frequency, mode, and damping ratio of the structure. Theoretical value of the structure modal parameter is got by proper equation. The frequency-domain analysis technique is introduced to system identification. Frequency-domain identification method is introduced, and identification value of the structure modal parameter is got by it. Comparing the identification value with the theoretical value will arrive at a conclusion that the precision of the modal parameter of the first order got by the method of frequency-domain identification is good and the high order ones are bad. In the second part, the difference of modal strain is introduced. The difference of modal strain is got by the first-order mode identified from the first part above, which then be used to identify single damage. Layer remaining stiffness is deduced by integrative modal parameter which is the mode and frequency of the first order identified, and then layer remaining stiffness is used to identify multiple damage. Structural natural modality is reflected by the difference of modal strain, which has one-to-one correspondence with the modal strain. So, for any modal strain of any order, there is a distribution of the difference of modal strain corresponding. This difference of modal strain corresponding to modal strain can be used to identify single damage accurately of shearing structure. Comparing the layer remaining stiffness to the ones of undamaged structure, multiple damage can be identified, not only can the location of the damage be identified, but also can the degree of the damage be quantified, and the result of the identification is very visual. In the third part, an example is given. In this paper, a shearing model of four layers is analyzed. Assuming there is damage of different degree in one or more than one layer by stiffness reduction factor, then single or multiple damage of the structure can be identified, including judging if there is any damage, identifying location of damage, and quantifying damage degree. In the last, deficiency of the research at the present time is analyzed, and there is some succeeding research work needed to be done in the future.