低矮建筑龙卷风荷载特性及其模型研究

Tornado is one of the most destructive wind storm. Tornado-induced damages to low-rise buildings are so severe that the tornado wind load on low-rise buildings should be understood in order to take engineering measures against tornado. This project will study the tornado-induced wind loads on low-rise buildings and the modeling of tornado load. An independently-developed moving tornado simulator will be utilized in this project. There are many parameters that influence the wind pressures on both the interior and external surfaces of a low-rise building, which include various tornado parameters such as the swirl ratio, the wind speed and the convergence height, various building parameters such as the roof slope, the dominant opening size and ratio of air leakage, and the parameters to describe the relation between the tornado and the low-rise building such as the size ratio and the distances between them. In this project, a lot of tornado wind tunnel tests will be carried out systematically to investigate the effects of these parameters. Particular attention is devoted to the effects of the moving speed of the tornado on both the wind characteristics of the tornado and the wind pressure on the low-rise building. Meanwhile, a basic numerical model based on the Rankin vortex model will be assumed to describe the wind pressures on low-rise building, in which the tornado pressure on the building surface is divided into two individual parts, one is caused by the wind speed of the tornado while the other is caused by the pressure drop accompanying with the tornado, and the wind pressure on the building surface is the summation of these two parts. By comparing the results of pressure coefficients around the low-rise building predicted by the model with the experimental data, it can be expected to find the drawbacks of the model and modify it accordingly, in order to improve the prediction accuracy of tornado load model. The model after modification takes consideration of the aerodynamic interaction between the tornado and low-rise building so it is more reasonable than the original model. In addition, in order to obtain a general tornado load model applicable for the ground roughness categories A and B, which are more suitable for a tornado to be created, all the experiments and analysis will be conducted for these two ground roughness categories. This project is believed to satisfy the necessities to improve the science and technology related to the wind resistant design of wind sensitive structures and has obvious significance for both fundamental and applications to wind engineering field.

本项目研究低矮建筑的龙卷风荷载特性及其模型。利用自主研制的移动式龙卷风风洞，通过大量的系列龙卷风风洞模型试验研究龙卷风的各个参数（涡流比、移动速度、收束层高度等）、低矮建筑的各个参数（屋面坡度、壁面有无大开孔或背景孔隙等）以及相对于龙卷风涡核半径的低矮建筑代表尺度和龙卷风中心与低矮建筑之间的距离（即龙卷风路径）等对低矮建筑内外表面风压和风载荷特性的影响。在模型研究方面, 将龙卷风对低矮建筑的作用分解成旋转风速的直接作用产生的风压和伴随着龙卷风的压力降产生的风压, 以兰金涡模型为出发点建立低矮建筑龙卷风荷载的基础模型。通过与各种龙卷风参数和建筑模型参数条件下的风洞试验结果的比较修正基础模型并提出考虑了风与结构相互作用的龙卷风荷载模型。整个研究考虑易于龙卷风发生的A类和B类两种地面粗糙度。本项目适应我国从土木工程建设大国向防灾减灾强国迈进的迫切需要，具有一定理论价值和重大工程应用前景。

龙卷风具有旋转剧烈、突发性强、风速变化剧烈等特点，其导致的建筑结构风荷载不同于常规边界层下的风荷载，因此需要评估龙卷风对建筑结构抗风性能的影响。本项目以大量的龙卷风风洞模型试验为基础、研究低矮建筑的龙卷风荷载和其模型。考虑龙卷风的各个参数（涡流比、移动速度、收束层高度）、低矮建筑模型的各个参数（屋面坡度、壁面有无大开孔和背景孔隙）以及相对于龙卷风涡核半径的低矮建筑代表尺度和龙卷风中心与低矮建筑之间的距离（即龙卷风路径）对风压风力的影响。本项目的重要结果包括以下三个方面的内容：1）明确了龙卷风平均风速的垂直剖面、水平剖面以及风压降随涡流比的变化规律，揭示了龙卷风涡核附近湍流强度特性；2） 揭示了低矮建筑结构荷载随龙卷风涡流比、风向角、建筑结构高宽比和深宽比、屋盖角度、开孔类型和开孔位置的变化规律；和3）定量描述了常规边界层强风和龙卷风强风造成的风荷载的差异。研究表明直接采用建筑荷载规范进行抗龙卷风设计时，将会带来极大的不安全隐患。本项目满足我国从土木工程建设大国向防灾减灾强国迈进的迫切需要，具有一定理论价值和重大工程应用前景。. 在执行课题的4年期间在本行业最高水准的国际学术杂志上发表了标注本课题的SCI论文7篇。参加国际会议并发表标注本课题的学术论文3次以上。培养博士生1名和硕士生2名。