Structural Damage Identification Based On Stochastic Subspace Identification

Structures server in complex environment may suffer all kinds of damage, theaccumulation of those damage will lead to catastrophic accidents.So, learning on theproblem of early damage identification of structure is very important and practical forthe safety of the structure. For the index of structure damage identification, there aretwo main ideas at home and abroad. First is using the baseline finite element model andcombining the fem updating method and pattern matching method to identify thedamage of structure; Second is directly using structure modal parameters or changes ofstructure responses to reflect the damage of structure without using baseline finiteelement model. However, it’s difficult to get the baseline finite element model orvibration model, especially when the structure is under a complex environmentexcitation. Even if you get them, the precision can be quite low. In contrary, the secondmethod without finite element model can directly use response data of structure todevelop damage indicators, it gradually cause the attention of many researchers. Thestochastic subspace identification (SSI) is a kind of identification method which basedon the vibration data in time domain. It’s concept is clear, and it’s theory is rigorous. Inrecent years, it has became the basic identification algorithm in the field of modalparameter identification and being widely used in the dynamic analysis of some reallarge construction. But how to use this method in the field of damage identification isstill a problem which need further research.Therefore, this paper studied stochastic subspace identification and the damageidentification index which based on SSI. To sum up, the main work and conclusions ofthis paper were as follows:1. Studied a important problem in SSI theory: the selection of system order. Byintroducing the singular entropy theory, the writer provides a effective method todetermine the system order without using the Stabilization diagram theory or singularvalue decomposition.2. Discussed two important damage identification theory which based on SSI.identification: Null subspace-Based Damage Detection and Novelty Analysis theory.Study and write the programs of three damage identification index which based on thetwo theory. Use them to identify the happen of the damage and the location of thedamage, respectively. 3. Analyzed those different weighted method and algorithm in SSI theory,especially when using them in the field of damage identification. Then use a example tocalculate and compared the results of choosing different weighting matrix and differentalgorithm. Analyzed the possible factors which could lead to those differences anddiscrepancies. And select the best weighting matrix and algorithm identify the happen ofdamage and the location of the damage.4. Considering about the complex work environment of the transmission tower,only use the reduction of stiffness to simulate the damage of the structure is not enough.Other factor like temperature or ice thickness could be too important to ignore it fortransmission tower which usually locate in mountains. So this article analyze how thosefactors influence the precision and accuracy of the result of damage identification.