Signal Filter Design for Acceleration to Measure Displacements of Masonry Walls

Abstract

Since masonry structures are vulnerable to earthquakes, it is important to estimate damage by measuring displacement response. Due to the restrictions of the displacement sensor (LVDT) installation, the displacement is calculated indirectly by filtering and integrating the accelerometer measurements. This study proposes a method to obtain displacements at arbitrary points on masonry single wall by post-processing the data measured at the locations where the accelerometer and LVDT are installed. A 3-axis accelerometer and a LVDT are installed on the masonry wall and the wall is excited simultaneously by both x- and y- directional seismic loads. The feature of signals such as rigid body motion, linear trend, and white noise is removed from the acceleration in the LVDT direction. Acceleration is denoised using Butterworth bandpass filter and displacements are derived by integrating the denoised signal. The cutoff frequency and order of the filter are adjusted to derive the displacements similar to those measured by LVDTs. To verify the designed filter, an accelerometer and two LVDTs for two directions at an arbitrary point are installed, and the displacements in two directions are obtained from both LVDT and filtered accelerations. In comparison between computed displacement and data, they show similar values in the aspect of peak values and phases. To conclude, displacements at any point on the masonry wall can be derived with the Butterworth filter designed at a specific point.