Thunderstorm response spectrum: fundamentals and case study

Thunderstorms are transient phenomena characterized by short duration. Engineering is usual to evaluate the structural response to such phenomena, most notably to earthquakes, by the response spectrum technique, a method extensively applied in both the scientific and technical fields. This paper represents the first stage of a research project aimed at introducing a "new" method that generalizes the "old" response spectrum technique from earthquakes to thunderstorms. In such a framework, it establishes the fundamentals of the structural response of ideal point-like Single-Degree-Of-Freedom systems subjected to thunderstorm wind actions perfectly coherent over the exposed structural surface. A general definition of thunderstorm response spectrum is introduced, which allows a straightforward evaluation of the maximum structural response and the equivalent static force. A new definition of thunderstorm base response spectrum is also provided. Several forms of representation and parameterization of these response spectra are studied, showing the merits and the shortcomings of each of these. The general properties of the response spectra are investigated, pointing out some relevant analogies with the seismic case and the classical analysis of synoptic events. In particular, while wind engineering is usual to express the wind loading starting from wind velocity models, the method proposed herein, similarly to seismic engineering, involves the use of real thunderstorm records. The records adopted in this paper to illustrate the new method come from the wind monitoring campaign conducted for the European project "Wind and Ports". Despite the application to this case study, the methods and the definitions presented are fully general and may be applied in any context.