Analysis of alongwind tall building response to transient nonstationary winds

Transient nonstationary extreme winds such as thunderstorm downbursts are responsible for significant structural damage and failures. This study deals with the frequency domain analysis of alongwind tall building response to transient nonstationary winds based on nonstationary random vibration theory. The transient wind fluctuations and associated wind loads are modeled as the sum of deterministic time varying mean and evolutionary random fluctuating components. The alongwind loads on buildings are determined through the approaching winds by using strip theory and taking into account the unsteady force characteristics in terms of aerodynamic admittance and joint acceptance functions. An analysis framework is developed to quantify the time varying mean, evolutionary spectrum, and time varying root-mean-square values of building response. The traditional analysis framework concerning stationary boundary layer winds serves as a special case of this novel framework. Applications of this general framework are addressed to the cases where the mean wind speed is characterized by a time-invariant vertical profile and a single time varying function that also serves as the modulation function for the wind fluctuations. The influence of time varying mean wind speed, mean wind speed vertical profile, and spatial correlation of wind fluctuations on building response is discussed using tall building examples.