Structural Health Monitoring and Damage Assessment Using Measured FRFs from Multiple Sensors, Part I: The Indicator of Correlation Criteria

This paper presents two criteria for correlating measured fre quency responses from multiple sensors and proposes to use them as indicators for structural dam ge detection. The first criterion is a global shape correlation (GSC) function that is se n itive to mode shape differences but not to relative scales. The second criterion, a global amplitude corr lation (GAC) function, is based on actual response amplitudes. Both correlation criteria are a funct ion of frequency and uniquely map a set of complex responses to a real scalar between zero and unity. The averag ed integrations of GSC and GAC functions along the frequency points over the measurement r ange, also called damage indicators, are used to describe the correlation between two sets f vibration data. When a structure state remains unchanged, both correlation criteria are a s close to unity simultaneously. Otherwise, the correlation with the reference data will be decr eased with changes of structure states. Using GSC and GAC functions has the advantage of being able to deal w ith incomplete measurements. Also, all available response data are used and hence t here is no critical selection of frequency points for damage detection. The above correlation criteria w e applied to a bookshelf structure and various cases such as undamaged states, damage locati ons (single and multiple), damage levels, as well as environmental variability are discuss ed. As expected, it was found that indicators of correlation criteria were able to identify all various cases c orrectly.