Damping estimation of high-rise buildings considering structural modal directions

One widespread problem in damping estimation of high-rise buildings is the neglect of structural modal directions, which may induce beating in measured dynamic responses along building geometric axes and thereby induce errors in damping estimations to some extent. Based on a proposed two degrees of freedom (2-DOF) simulation model, the effects of neglecting the modal directions on damping estimate are systematically investigated. The results show that the angular differences between the modal directions and the building geometric axes, as well as the frequency difference between the involved modes, both have significant effects on the damping estimate of high-rise buildings. This paper proposes a spectral method to determine the modal directions of high-rise buildings and further validate this method by an analysis of full-scale measurements from four skyscrapers. The damping ratios estimated based on the responses along the identified modal directions are more accurate than those based on those measured along the building geometric axes. Furthermore, an empirical prediction model for damping ratio of high-rise buildings with heights over 200 m is proposed based on the field measured damping results of several buildings with consideration of the modal directions. The objective of this study is to improve the accuracy of damping estimation of high-rise buildings and therefore provide useful information for the structural design of future skyscrapers.