LAUSR

Abstract We show how complex, three-dimensional modes of vibration of an irregular building can be identified by ambient vibration measurements. We present two-dimensional cross sections of the three-dimensional mode shapes and describe a measuring strategy for identifying the building properties when the excitation consists of nonstationary microtremors and short and weak wind bursts. We employ cross-correlations of measured accelerations to identify predominance of excitation by microtremors (causing wave propagation from the ground up into the building), or by weak bursts of wind (wave propagation within the building and down towards the foundation). We describe the two lowest frequencies of vibration at 10.5 Hz and at 11.9 Hz and their mode shapes.