A deterministic–stochastic hybrid model of downbursts and its impact on a cantilevered structure

Thunderstorm downbursts, which are sources of extreme wind loadings in nature, have caused numerous structural failures around the world. It is essential to build some applicable, though approximate, model for these loadings under which structures can be assessed. In this paper, a deterministic–stochastic hybrid model of downbursts is presented. In this model, downburst winds are the summation of a deterministic mean and a stochastic fluctuation. Wood’s velocity profile for the vertical profile and Holmes’ empirical model for the time function are utilized to model the mean wind. The fluctuation is modeled as a uniformly modulated evolutionary vector stochastic process. Time histories of downburst wind speeds over slender structures, such as tall buildings, can be simulated by the spectral representation method. Using the simulated downbursts as input, the dynamic responses of structures are obtained in the time domain. As a numerical example, the dynamic response of a cantilevered structure to simulated downbursts is computed and their sensitivity to the coherence function is discussed.