Time-wave velocity analysis for early earthquake damage detection in buildings: application to a damaged full-scale RC building

An algorithm for time velocity analysis of building response is presented, which identifies the wave velocity of vertically propagating waves through the building and detects their changes. The algorithm is intended for use in SHM systems for rapid assessment of the structural health and integrity following an earthquake. The velocities are identified by an interferometric algorithm, which involves least squares fit of pulses in impulse response functions. An important feature of this method is that it is not sensitive to the effects of soil-structure interaction. The algorithm is applied to a 12-story RC building in Los Angeles, lightly damaged by the San Fernando 1971 earthquake. The results of the time velocity analysis are critically compared with results of analysis of input power, interstory drift, and instantaneous frequency. The identified average vertical wave velocity was initially 140m/s for the NS and 110m/s for the EW response and reduced by 26% and 32%, respectively. The detected reduction of the fundamental frequency of vibration was larger (44% for the NS and 48% for the EW response). The difference is interpreted to be due to softening of the soil-foundation system, to which the identified frequency of vibration is sensitive. The change was larger in the lower half of the building (31% for the NS and 37% for the EW response) as compared with the upper half (24% for the NS and 27% for the EW response), consistent with the observed damage. Copyright (c) 2015 John Wiley & Sons, Ltd.