Mode shape linearization for HFBB analysis of wind-excited complex tall buildings

The high-frequency base balance (HFBB) testing technique has been developed and continuously improved for two decades. A number of researches have been devoted to the development of mode shape correction factors to account for the significant uncertainties in the prediction of generalized wind forces due to the non-ideal mode shapes. However, these correction factors are mostly derived based on presumed wind loading distributions and/or correlations, which introduce inherent uncertainties associated with the inappropriate modelling of the actual wind loads influenced by the site specific characteristic of the surrounding proximity. This paper proposes a new HFBB analysis method independent of the information of the wind load distributions, referred to as the linear-mode-shape (LMS) method, to minimize the discrepancy in the estimation of generalized wind forces due to nonlinearity of mode shapes. The uncertainties of the translational components of the generalized wind forces prediction are eliminated by linearizing the three-dimensional (3D) coupled mode shapes. A series of wind tunnel pressure tests was conducted at the CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology to determine the distribution of wind loads on an example building, from which an “exact” wind-induced response was computed and used as a reference for the comparison of the LMS method and the conventional HFBB method. The accuracy of the generalized forces prediction, and hence the estimation of structural responses, for buildings with 3D coupled mode shapes was improved. In addition, a parametric study was carried out to examine the robustness and reliability of the LMS method for a range of practical mode shape power exponents. The detailed formulation of the LMS method is outlined in this paper.