Field Observations on Modal Properties of a Tall Building

Abstract

This paper presents field observations on the modal properties of a tall building under ambient conditions. Acceleration data was collected by a force-balance triaxial accelerometer at one corner of the building. It was divided into non-overlapping time windows to investigate the amplitude dependence of natural frequencies and damping ratios. Four modes were identified by Bayesian Operational Modal Analysis (BAYOMA) where the first two modes are closely-spaced while the others are well-separated. The results show that there is an inverse trend between the natural frequencies and modal root-mean-square value (RMS) while the damping ratios show a positive correlation with the modal RMS.