Description and simulation of thunderstorm downbursts and their effect on civil structures

This document provides a simulation of the wind field produced by thunderstorm downburst and the effect of this over the structures. Downburst are categorized as a High Intensity Wind Event (HIW) and can be defined as a strong downdraft which induces an outburst of damaging winds on or near the ground. From an engineering point of view, downburst differ from the traditional synoptic winds inside the framework of the Atmospheric Boundary Layer model (ABL), because their statistical properties change with time i.e. the phenomenon is non-stationary. The studies available in the literature allow to describe downburst as slowly varying-uniformly modulated non-stationary phenomenon. To simulate the wind velocity field produced by the downburst it was implemented a Monte Carlo algorithm based on the Power Spectral Density of the signal. The model results inside this document were compared with the records of downburst available in the literature to verify the accuracy of the model, it shall be highlighted that the model developed is capable of reproduce the three-dimensional wind structure of the outflow. The aerodynamic effect of the downburst was applied to single degree of freedom (SDOF) and multiple degree of freedom (MDOF) structures to assess their structural response. For SDOF systems it was developed a finite element tool capable of solve the dynamic problem in the time and in the frequency domain, a parametric study to verify the consistency between the two analysis methods was performed by changing the natural frequency and the damping ratio of the structural system. Regarding the aeroelastic effects, specifically the aeroelastic damping component (which for the case of downburst is time-varying) a study on its effect on the overall structural response was made to verify if it was possible whether to neglect it or to use a constant value defining the contribution as it is for the synoptic winds. Finally, it is provided a methodology for the measure of the failure probability associated with downburst wind velocity fields for structures designed with the available design rules for ABL winds.