Study on unsteady air force on low-rise buildings and numerical methods for prediction of wind load for wind resistant design

研究了低层建筑抗风设计中近地层的风特性和风荷载预测的数值方法。对2.4m立方体周围湍流统计量的空间变化进行了评估，并对墙体和屋面上的相关风压进行了研究。结果表明，风向分量随高度H、立方高度、距立方水平距离0.9H的上风向速度脉动与上风墙和屋面上风部分的压力有较强的相关性。另一方面，我们还对台风和龙卷风袭击日本造成的强风破坏进行了现场调查。研究了2001年发生的几起巨灾、2004年0314号台风袭击冲绳县宫古岛县、2004年0418号台风袭击广岛县宫岛县造成的损失。极端的损坏，如完全损坏的房屋，正在减少，但屋顶或覆层的损坏并没有减少。飞来的瓦片、玻璃、碎石等飞来的碎片造成的二次破坏和人员伤亡仍然很大。通过以上研究，正确预测临近地面的风和城市地区的风特性，对于低层建筑的抗风设计具有重要意义。给出了一些引入地表粗糙度影响的数值方法，如k-ε方法和大涡模拟方法，用于预报大风条件下城市地区的风场。采用PSU/NCAR MM5数值预报方法对台风大风进行预报。

We studied the wind characteristics of surface layer and the numerical methods for the prediction of wind load for wind resistant design of low-rise buildings.For the beginning, the wind characteristics of surface layer was studied using field experimental data. The spatial variations of turbulence statistics around the 2.4m cube were evaluated during rather strong winds and the correlated wind pressures on the wall and the roof was investigated. The results show that the upwind velocity fluctuations of streamwise component at a point with the height H, height of the cube, and the horizontal distance 0.9H from the cube have a rather strong correlation with the pressures on the upwind wall and the upwind portion of the roof.On the other hand, we also conducted field investigations of strong wind damage caused by typhoons and tatsumaki, tornado, struck Japan during the period of this study. The damages caused by some tatsumakis in 2001, by Typhoon 0314 struck on Miyakojima Island Okinawa prefecture in 2004 and by Typhoon 0418 struck on Miyajima Island Hiroshima prefecture in 2004 were studied. The extreme damage, such as completely failed houses, is decreasing but the damage on the roof or claddings is not decreasing. The secondary damage by flying debris, such as piece of broken roof tile or glass or gravels and so on, and the human damage are still large in number.Following above mentioned studies, it was resulted that the proper prediction of approaching wind and of wind characteristics in the urban areas near the ground is important for the wind resistant design of low-rise buildings. We showed some numerical methods using turbulent models introducing the effect of surface roughness, such as k-ε method and LES, for predicting the wind flow in the city areas for strong wind condition. Also the numerical method using PSU/NCAR MM5 was adopted to predict the strong wind caused by typhoon.