1D system identification of buildings during earthquakes by seismic interferometry with waveform inversion of impulse responses—method and application to Millikan library |
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| Institution: | 1. Mechanical Design and Production Dept., Faculty of Engineering, Zagazig University, Egypt;2. Centre of Nanotechnology, Zagazig University, Egypt;3. Mechanical Engineering Dept., Faculty of Engineering, King Abdulaziz University, Saudi Arabia;1. Department of Ocean and Mechanical Engineering, Florida Atlantic University, Boca Raton, FL 33481-0991, USA;2. Université de Bretagne Sud UBS, University of South Brittany, FRE CNRS 3744 IRDL, Centre de Recherche, Rue de Saint Maudé, BP92116, 56321 Lorient Cedex, France;1. School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;2. Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry, Department of Civil Engineering, Tsinghua University, Beijing 100084, China;3. Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, OH 43210-1275, USA;1. Department of Civil Engineering, Dalian University of Technology, Dalian, China;2. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China;3. China Machinery International Engineering Design & Research Institute Co., Ltd, Changsha 410007, China |
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| Abstract: | Two new algorithms have been introduced as a further development of a robust interferometric method for structural health monitoring (SHM) of buildings during earthquakes using data from seismic sensors. The SHM method is intended to be used in an automatic seismic alert system, to issue a warning of significant damage during or immediately after the earthquake, and facilitate decision making on evacuation, to avoid loss of life and injury from possible collapse of the weekend structure during aftershock shaking. The method identifies a wave velocity profile of the building by fitting an equivalent layered shear beam model in impulse response functions (virtual source at roof) of the recorded earthquake response. The structural health is monitored by detecting changes in the identified velocities in moving time windows, the initial window being used as reference. Because the fit involves essentially matching phase difference between motion at different floors, the identified velocity profile is not affected by rigid body rocking, and soil-structure interaction in general, as demonstrated in this paper. Consequently, detected changes in wave velocity during an earthquake are not affected by changes in the soil-foundation system, which is a major advantage over SHM by detecting changes in the observed modal frequencies. Further, the method is robust when applied to real buildings and large amplitude earthquake response, as demonstrated in previous work. The new fitting algorithms introduced are the nonlinear least squares (LSQ) fit and the time shift matching (TSM) algorithms. The former involves waveform inversion of the impulse responses, and the latter - iterative matching of the pulse time shifts, both markedly reducing the identification error as compared to the previously used direct ray algorithm, especially for more detailed models, i.e., with fewer floors per layer. Results are presented of identification of the NS, EW and torsional responses of the densely instrumented Millikan Library (9-story reinforced concrete building in Pasadena, California) during a small earthquake. |
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