A comparison of high frequency force balance mode shape correction approaches for predicting wind effects on a high-rise building

Abstract

Abstract The wind loads on high-rise buildings can be predicted from the high frequency force balance (HFFB) technique. This experimental technique is widely accepted among wind and structural engineers due to its simplicity and adaptability to obtain wind-induced loads and dynamic response of tall buildings. But, for the general case of non-linear and combined sway and twist mode shapes, analysis of HFFB measurements gives rise to serious challenges and various techniques have been developed using significant assumptions. In this study, a 1:300 scale model of Building A, a benchmark tall building geometry has been chosen to perform HFFB tests in a closed-circuit boundary layer wind tunnel. It has complex 3D mode shapes combining sway and twist motions. First, the base shears, overturning moments and torques for different wind directions were measured. Subsequently, different HFFB mode shape correction approaches were examined for estimating the dynamic wind effects using modal analysis in the time domain. Furthermore, the high frequency pressure integration (HFPI) wind tunnel technique was utilised to measure surface pressure information in separate tests to obtain the more precise wind effects results for validation of the HFFB predictions. The power spectral densities (PSDs) of aerodynamic base overturning moments and torques determined from both techniques are compared. The PSDs and variance coefficients of generalised wind forces for the first three modes are calculated and compared to each other to investigate the accuracy of the different HFFB-based analysis approaches. Also, the statistical properties including standard deviations and peaks of tip acceleration and tip displacement time histories are computed for comparison. The results show that the HFFB approaches overestimate the dynamic wind-induced responses and have some weakness for twist prediction. It is found that the HFFB methods with same wind loading correlation state generally seem to perform in a similar manner.