Abstract Summary
Thunderstorms and extra-tropical cyclones provide significantly different wind conditions: extra-tropical cyclones, commonly referred to as Atmospheric Boundary Layer (ABL) winds, provide stationary wind conditions over time intervals of 10 minutes-1 hour and a wind velocity profile increasing with the height; instead, thunderstorms are responsible for nonstationary wind conditions and are characterized by a nose-shaped velocity profile. Furthermore, the two phenomena are characterized by different extreme distributions and high return period thunderstorm wind speeds can be higher than those corresponding to extra-tropical cyclones. Despite these remarkable differences, a shared model for the estimate of the maximum response and wind loading provided by thunderstorms is, to date, not available. The authors proposed a formulation generalized to thunderstorms of the gust response factor from Davenport for Single-Degree-Of-Freedom systems [1]. The objective of the present paper is to extend the approach to slender vertical structures and compare the effects of thunderstorm outflows and extra-tropical cyclones in terms of maximum alongwind dynamic response. Since thunderstorms are usually considered more dangerous for mid-low structures while ABL winds are considered as dimensioning for higher structures [2], two case studies with different heights are chosen: a steel lighting pole with height H = 15.76 m and a reinforced concrete telecommunication tower with H = 98 m. Different reference wind velocities with 50 years return period are adopted for thunderstorm and ABL winds, based on the results of a statistical analysis carried out on wind speed data collected by an anemometer located in the port of Livorno [3]. A literature nose-shaped profile is adopted for thunderstorms considering four different heights of the nose tip. The wind speed associated with the ABL wind is modelled through a logarithmic vertical profile assuming five different values of the roughness length. The gust response factor associated with the ABL wind is derived through the Davenport formulation, while for thunderstorms the generalized gust response factor is adopted. The comparison is performed in terms of ratio of the maximum response to thunderstorms and ABL winds. Such ratio is governed by three main factors: the reference wind velocity, the vertical profile and the gust response factor. Overall, for the two structures analysed, thunderstorms mostly provide a greater response also for the higher structure, especially when the tip of the nose-shaped profile is close to its top. References [1] Roncallo, L., Solari, G., Muscolino, G., Tubino, F., 2022. Maximum dynamic response of linear elastic SDOF systems based on an evolutionary spectral model for thunderstorm outflows. Journal of Wind Engineering and Industrial Aerodynamics. 224, 104978. [2] Sengupta, A., Sarkar, P.P., 2008. Experimental measurement and numerical simulation of an impinging jet with application to thunderstorm microburst winds. Journal of Wind Engineering and Industrial Aerodynamics. 96, 345-365. [3] Zhang, S., Solari, G., Yang, Q., and Repetto, M. P., 2018. Extreme wind speed distribution in a mixed wind climate. Journal of Wind Engineering and Industrial Aerodynamics, 176, 239–253.
