Wind Load Characteristics Analysis Of The High-rise Building Under Downburst Over Topography

Thunderstorm downburst could cause an extremely high velocity generated close to the surface, which draws great attention of the scholars in structural wind engineering field. Currently, the research of the downburst mainly focused on the wind field characteristics of stationary downbursts over flat topography. But little study has been done towards the wind load characteristics of high-rise building under downburst flow over escarpment terrain, and the study about the influence of topographic parameters on wind load characteristics is more rarely. Therefore, in this article, the wind pressure distribution characteristics of building under stationary thunderstorm downburst over flat and escarpment terrain and the influence of topographic parameters on wind load characteristics are studied experimentally and numerically. The main works are shown as follows:(1)The wind load distributions of high-rise building under thunderstorm downburst flows over flat terrain and escarpment terrain are conducted. As for flat terrain, drag coefficients have similar changing rule along vertical direction. The maximum drag coefficient approximately locates at the 1/4 height of the building. Above this height, the drag coefficient decreases gradually. The maximum drag coefficients locates at the range of 1.0~1.25 D. With the increase of the radial distance, the drag coefficient of each layer decreases gradually. As for escarpment terrain, the drag coefficients of each layer is smaller than that of the flat terrain, and the height of the maximum drag coefficient is lower. Compared with the drag coefficient, the lift coefficient is relatively smaller.(2)The influence rules of escarpment terrain on the wind load distributions of high-rise building are accounted. It was found that there is no obvious amplification in the wind pressure coefficient of the windward side under downburst field over escarpment terrain. The topographic parameters have great influence on the magnitude of the wind pressure coefficient. Compared to that of flat terrain, the wind pressure coefficient of the windward side under escarpment terrain is somewhat reduced. As to the reduced mechanism of wind pressure on the windward surface, on the one hand, due to the existence of the escarpment terrain, the reduced horizontal wind velocity component leads to smaller impact force on the windward side of the building. In addition, the increased vertical wind velocity component contributes to the increase of dynamic pressure. For those two factors, which lead to the reduction of the wind pressure on the windward side under escarpment terrain.(3)The wind pressure distribution characteristics of building under unsteady-thunderstorm downburst are studied numerically by LES simulation. The results obtained from RANS simulation and LES simulation, under flat terrain or escarpment terrain, are shown to agree well with that of wind tunnel test. The reliability of the results of this study are verified by the three methods mentioned above. While the time-averaged surface pressure distributions around the test model are very helpful to reveal the global features of the microburst-induced mean wind loads acting on high-rise buildings, it would be very insightful and essential to take the turbulent nature of the microburst wind into account in order to assess its damage potential more accurately. It was found that the extreme wind loads are 2.2~2.5 times of the mean wind loads. In the engineering design, if necessary to consider the impact of thunder storm, this paper suggests that an appropriate amplification factor could be multiplied based on the mean wind loads.