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面层风特性及风荷载预测的数值方法。在此基础上，利用实测数据研究了近地层的风场特征。研究了在较强风条件下，2.4m立方体周围湍流统计量的空间变化，并研究了墙体和屋顶的相关风压。结果表明：在高度H、立方体高度、距离立方体水平距离0.9H处，迎风分量的迎风速度波动与迎风壁面和顶板迎风部分的压力有较强的相关性。另一方面，我们也在研究期间对台风和龙卷风袭击日本造成的强风损害进行了实地调查。研究了2001年、2004年袭击冲绳县宫古岛的0314号台风和2004年袭击广岛县宫古岛的0418号台风造成的一些辰俣灾害。极端破坏，如完全倒塌的房屋，正在减少，但屋顶或覆盖层的破坏没有减少。由飞散碎片造成的二次破坏，如破碎的瓦片或玻璃或砾石等，造成人员伤亡的数量仍然很大。通过以上研究表明，正确预测城市近地面区域的接近风和风特性对低层建筑的抗风设计具有重要意义。本文介绍了引入表面粗糙度影响的紊流模型的k-ε法和LES法等几种预测强风条件下城市风场的数值方法。采用PSU/NCAR MM5数值方法对台风引起的强风进行了预报。

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.