Thunderstorm gust response factor: A closed-form solution

The Davenport gust factor technique is an efficient approach for the estimate of the wind loading on structures due to synoptic winds and the availability of closed-form solutions favoured its implementation in codes and standards. The gust response factor was generalized for thunderstorm outflows based on the definition of suitable equivalent parameters to account for the nonstationary characteristics of the wind velocity. Its sensitivity to the shape of the slowly-varying mean wind velocity was investigated, showing that it has a significant impact on the gust response factor, especially when the structure is lowly-damped. In order to simplify the derivation of the gust response factor the present paper outlines the derivation of a closed-form solution for the equivalent parameters, starting from the approximation of the time-varying variance of the response. The gust response factor derived through the closed-form solution proposed is compared with numerical solution and the existing formulation from literature. Results show that the proposed solution is very accurate and accounts for the transient dynamic effects neglected by the existing formulation, providing an efficient and handy tool for the structural design.