Parametric study on the along-wind response of the CAARC building to downbursts in the time domain

A primary investigation on the along-wind responses of tall buildings to thunderstorm downbursts is presented in this paper. Related characteristics of downbursts are first reviewed. By assuming that downbursts are fully correlated over the building height, a simple model is applied for downburst wind speeds. As a representative, the CAARC building is modelled as a linear 2-D cantilever beam and a base-pivoted single degree of freedom rigid body as well, and subjected to non-stationary conceptual, actual, and wind tunnel-simulated downburst velocity time histories. For comparison, a typical stationary wind speed record is also applied to the building. The maximum dynamic magnification factor (MDMF) is introduced as a non-dimensional variable to measure and compare the effect of non-stationary downbursts on the building. The definition of MDMF is the ratio of the maximum dynamic response to the corresponding maximum static response. Relationships between MDMF of the first normal coordinate and MDMFs of responses are derived. For the parametric study, MDMFs of the first normal coordinate for all the time histories are obtained as functions of the building first circular frequency and the first modal damping ratio. Effects of gust profiles and building characteristics on MDMFs and structural along-wind responses are observed theoretically and by the parametric study. The characterizing period for downbursts could be 36 s. Differences between MDMFs from the downbursts and those from the typical wind are noted. In practice, the procedure and the results presented here may be used to estimate the maximum dynamic response of a tall building subjected to severe downburst winds. © 2004 Elsevier Ltd. All rights reserved.