Earthquake damage detection in the Imperial County Services Building II: Analysis of novelties via wavelets

The former Imperial County Services (ICS) Building is a rare case of an instrumented building damaged by an earthquake. In this paper, it is used to test a structural health monitoring method, based on detecting novelties in the recorded seismic response, by examining the correlation between their occurrence, spatial distribution and magnitude with the degree of the observed damage. The novelties are detected using expansion in a basis of bi-orthogonal wavelets. For this building, most of the larger novelties can be associated with the observed damage. The novelties suggest that damage first occurred at about 6.4 s, proceeded between 8.2 and 9.2 s, and culminated at about 11.2 s with the collapse of the first story columns at the east end of the building. These times are consistent with large inter-story drifts, and significant drops in the NS and EW system frequencies, reported previously. The major damage followed large pulses of input power within about 2 s. The time delays between novelties in different recording channels indicate velocity of propagation of the disturbances within the structure, consistent with other independent estimates.