Recorded Shear-Wave Travel Times in Buildings for System Identification and Damage Detection

Abstract eng:
Response of multi-story buildings can be formulated as a one-dimensional wave propagation problem in terms of wave velocities and frictional damping values at each story, and the wave reflection and transmission coefficients at each floor. When compared to commonly used modal analysis and its parameters (i.e., modal frequencies, damping values, and mode shapes), the wave propagation approach provides a better insight into the response and its parameters are more sensitive to damage. A critical parameter of the wave propagation approach is the wave velocities (or, wave travel times) in the building. The commonly used approaches to calculate wave travel times from vibration records have been to use the phase shift of a characteristic peak in the records, or the delay time for the peak of the cross-correlation function of the records. These two approaches do not give accurate wave velocities, because the damping in the building also alters the phase of the records. The phase differences in the records from two successive floors are caused by the combined effects of wave travel times, plus the phase distortions due to damping. In multi-story buildings, wave travel times can be calculated more accurately if the records are deconvolved by the roof record. The deconvolution eliminates the upgoing wave components in the signals, resulting in a simple downgoing wave. The deconvolved waves represent the impulseresponse functions for a roof-level impulse, and provide a much cleaner signal for the calculation of wave travel times. The phase shifts introduced by damping on the impulse-response functions can be eliminated if the wave travel times are calculated from the envelope functions of the impulse-response functions, rather than the original functions. The envelope function is determined by taking the Hilbert transform of the signals, and then calculating the corresponding analytic function. It can be shown that for narrow-band signals that are propagating in a frequency-dispersive medium, the envelope functions are not affected by the dispersive properties of the medium By using the methodology above, shear-wave velocities are calculated in three multi-story buildings by using their vibration records from earthquakes. The buildings are a 17-story steel-frame building, a 10-story RC frame-shear wall building, and a 62-story RC frame-shear wall building. The calculated velocities are around 150 to 250 m/sec. for translational motions, and higher for torsional motions.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket