Experimental Study on Damage Identification of Dynamically Excited Structures

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AbstractThere is an increasing interest in the vibration data-based detection, localization, andquantification of damage in civil engineering structures exposed to earthquake, wind, and otherloads. Early motivation for this was provided by the discovery of hidden damages in steelstructures caused by the 1994 Northridge and 1995 Great Hanshin (Kobe) Earthquakes, and alsoby the fact that structural element are usually inaccessible after construction. Several analyticalmethods have been proposed in the literature and still more are being developed for this.Currently simulated data are being used to check the effectiveness of these methods; however,their validation and comparison on actual experimentally obtained data is yet to be done.In this exploratory project, it is proposed to experimentally study and validate theeffectives of the autoregressive with exogenous input model, wavelet transform, eigensystemrealization algorithms (ERA), and subspace identification (SSI) approaches for comprehensivemodal and damage identification of civil engineering structures. For damage localization andquantification the flexibility and rotational flexibility matrices with and without and damage locatingvectors will be used. Further analytical improvements in these methods will also be made formore reliable damage quantification. The tests will be conducted on a scaled three-story, ninedegrees-of-freedom structure model prepared such that its stiffness properties can be changedby planned changes in one or more braces, by sudden removal of one or two braces in real-timeusing magneto-rheological dampers, and by loosening the connecting hardware at few selectedjoints. The major cost of preparing this changeable scaled model will be borne by the PIsinstitution. The scaled model will be excited at its base by the 5' by 5' shaking table at VirginiaTech. The model would also have the capability of being excited by shakers installed at any ofthe three levels. The dynamic measurements of the acceleration response will be made usingten accelerometers, three placed at each floor level in two orthogonal directions plus one on thetable.The SGER funding is being sought to identify validated damage localization andquantification methods which will be needed in a more comprehensive follow-up study. Thisfollow-up study to be proposed later will develop an integrated system consisting of the validateddamage identification techniques with online consequence prognosis followed by onlineactuation, if necessary, of a control system to maintain the performance of the structure at anacceptable level. The successful outcome of this exploratory work will also be a very useful toolfor direct practical implementation in structural diagnostics and health monitoring.The Intellectual merit of this study is in the development of experimentally verifieddamage identification (detection, localization, and quantification) schemes for a comprehensivestructural health monitoring.Broader impacts of this research will occur at two levels: theeducation and training of graduate and undergraduate students and the availability of a muchneeded tool and data to researchers and practitioners involved in structural health monitoring. Agraduate student and an undergraduate student will work on this project. The undergraduatestudent will be supported through the REU program. She/he will be selected through the Centerfor the Enhancement of Engineering Diversity (CEED) at Virginia Tech from the pool of availableAfrican American, Hispanic, American Indian, and women students. The dissemination ofinformation and data generated in this research to other students, researchers and practitionerswill be done through class room teaching, website creation, presentations in conferences, andpublications in archival journals and conference proceedings.