Directional response of structures to thunderstorm outflows

Abstract

Due to the combined effect of the background wind, the translation of the downburst and the radial nature of the downdraft after the touchdown, a peculiar characteristic of a thunderstorm outflow as detected by an anemometer or experienced by a structure is the potential variation of the flow direction. The study of the wind-excited response of structures has habitually neglected this issue because, dealing traditionally with synoptic events, their direction is endowed with a regular pattern. This paper proposes two families of methods to take into account directional changes in the evaluation of the windexcited response of structures. The first one generalizes the method usually applied to downbursts, which by its nature implicitly assumes a non-directional response. The second one is based on a new directional decomposition strategy of the wind speed that represents a generalization to thunderstorm outflows of what is historically done for synoptic events. The conceptual aspects involved in and the results provided by these methods are critically discussed and compared both to each other and with regard to the traditional non-directional structural analysis of thunderstorm outflows.

A Refined Study of Atmospheric Wind Properties in the Beijing Urban Area Based on a 325 m Meteorological Tower

“…The peak wind speeds produced by thunderstorm events are sometimes relatively stronger than those produced by monsoon winds, while the duration of the thunderstorm outflows is much shorter and the 10-min mean wind speeds are relatively smaller [28]. Therefore, thunderstorm winds are also dominant for the structural design, and their main characteristics related to the wind loading of structures should be considered separately [29]. The Beijing Meteorological Tower, as shown in Figure 2a, located 2.7 km north of Deshengmen, 1 km away from the third ring road of Beijing city, was set up in 1978 for basic scientific research, with a height of 325 m. When it was built, the terrain was flat, with numerous low-rise buildings around the tower.…”

Thunderstorm Downbursts and Wind Loading of Structures: Progress and Prospect

“…The joint calibration and evolution of the first two methods led to substantial agreement (Solari and De Gaetano, 2018), confirming the efficacy of the thunderstorm response spectrum technique in structural design. A novel piece of research has been carried out on directionality effects on wind loading (Brusco et al, 2019). Research is also in progress to replace the classic wind loading by two loading conditions, one for cyclones and the other for thunderstorms, creating a novel set of partial and combination factors for thunderstorm outflows (Solari, 2014).…”

Structural Response to Non-Stationary Thunderstorm Outflows

“…where v is the wind velocity defined by Eq. ( 9) or (25), b is the reference size of the structure crosssection, CD is the drag coefficient evaluated neglecting the transient character of the wind field [11].…”

“…Within this framework, it is worth mentioning the first research [25] aiming to study the dynamic response taking into account the directional shift of the outflow due to the translation of the thunderstorm cell. It proves that such a shift often involves a relevant increase in the response.…”