Dynamic wind effects on buildings with 3D coupled modes: Application of high frequency force balance measurements

Contemporary high-rise buildings with complex geometric profiles and three-dimensional (3D) coupled mode shapes often complicate the use of high frequency force balance (HFFB) technique customarily used in wind tunnel testing for uncoupled buildings. In this study, a comprehensive framework for the coupled building response analysis and the modeling of the associated equivalent static wind loads using the HFFB measurement is presented. This includes modeling of building structural systems whose mass centers at different floors may not be located on a single vertical axis. The building response is separated into the mean, background, and resonant components, which are quantified by modal analysis involving three fundamental modes in two translational and torsional directions. The equivalent static wind load is described in terms of the modal inertial loads. The proposed framework takes into account the cross correlation of wind loads acting in different primary directions and the intermodal coupling of modal responses with closely spaced frequencies. Wind load combination is revisited in the context of modeling of the equivalent static wind loads. A representative tall building with 3D coupled modes and closely spaced frequencies is utilized to demonstrate the proposed framework and to highlight the significance of cross correlation of wind loads and the intermodal coupling of modal responses on the accurate prediction of coupled building response. Additionally, delineation of the proper role of the correlation between integrated loads, modal response, and respective building response components in the evaluation of wind effects on coupled buildings is underscored.