Dynamic Characteristics of a Twenty-Story Instrumented Building in Anchorage, Alaska Identified By Seismic Interferometry

Abstract eng:
Seismic interferometry by deconvolution is used for system identification of a twenty-story steel, moment-resisting frame building (Robert B. Atwood Building) in downtown Anchorage, Alaska. This regular-plan mid-rise structure is instrumented with a 32-channel accelerometer array at ten levels. The impulse response functions (IRFs) are computed based on waveforms recorded from five local and regional earthquakes. The earthquakes occurred from 2005 to 2014 with moment magnitudes between 4.7 and 6.2 over a range of azimuths at epicentral distances of 13.3 to 183 km. The traveling waves, identified in IRFs with a virtual source at the roof are used to estimate the intrinsic attenuation associated with the fundamental modes of the structure, and shear-wave velocity in the building due to linear response. The median shear-wave velocity from the IRFs of five earthquakes is 191 m/s for the east-west (EW), 205 m/s for the north-south (NS), and 176 m/s for the torsional responses. The building’s average intrinsic-damping ratio is estimated as 3.7% and 3.4% along the EW and NS directions, respectively. These results are intended to serve as a reference for undamaged condition of the building, which may be used for tracking changes in structural integrity during and after future earthquakes.

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