Abstract
The Tohoku earthquake of magnitude 9.0 occurred on March 11, 2011. As a result, the need for Structural Health Monitoring (SHM) was highlighted. To assess the health of buildings, modal parameters such as natural frequencies and damping ratios are the basic and important damage indicators. In addition, maximum inter-story drift angle is also recognized as the important indicator. If we would like to estimate these indicators precisely, ideally we need to install accelerometers on all floors. However, this situation is not realistic due to the cost. Thus, in realistic SHM systems, the number of sensors is limited. In such cases, the excitation (input) is assumed to be measured and available. However, in some cases, some sensors including the input sensor may not be available. Thus, in this paper, we propose a method for estimating inter-story drift angle using only one accelerometer without input.
In our method, we set two assumptions. One is that the response is represented by the superposition of the response of only lower modes. The other is that mode vectors and participation factors are available from the design model or by other means. Then, first, we estimate modal frequencies and damping ratios using the subspace method from obtained acceleration data. Second, we decompose observed acceleration data to each mode by band pass filtering. Third, we calculate mode response by solving on the vibration equation of each mode. The vibration equation allows us to obtain mode response using the observed output response as input to this equation. It was verified that this method could successfully estimate the modal response as well as the inter-story drift angles. The overall accuracy of the method was much better than the existing method.
