Impulse Response Analysis of Layered Building Models and Lessons Learned for Structural Health Monitoring

Reduction of structural stiffness due to damage leads to increase in travel time of seismic waves propagating through the damaged part. Wave travel times through the structure can be effectively measured by tracing a pulse radiated from a virtual source, generated by deconvolution of the recorded vibrational response to earthquake shaking at different points in the structure (e.g. on different floors of a building [1]). These pulse responses are in fact the impulse response functions of the structure and can be obtained by inverse Fourier transform of the transfer functions of the response with respect to the base or roof responses. Such analyses of earthquake records in selected damaged buildings have shown that the measured increases in wave travel times are consistent with the level and spatial distribution of the observed damage [2,3]. Further, it was shown that the measured wave travel times are not affected by the soil-structure interaction, and can be used to estimate the building fixed-base frequency, which is a major advantage over the Fourier methods [4,5].