Collaborative Research: Characterization, Modeling and Uncertainty Analysis of Tornado Wind and Its Effects on Buildings

2011年密苏里州乔普林和阿拉巴马州塔斯卡卢萨以及2013年俄克拉何马州摩尔市最近龙卷风造成的破坏突显了全国对这些风暴事件的脆弱性。由于龙卷风的不可预测性和破坏力，很难直接测量地面附近的龙卷风风速。目前的做法是使用增强型Fujita(EF)标度根据观测到的结构和非结构破坏来估计风速，该标度在气候学研究、风险分析和关键设施设计中被广泛接受。然而，这种基于损害的方法具有很大的不确定性。关于地面附近风流的空间和时间分布，以及风流如何与地形和结构相互作用，存在着关键的知识空白。为了解决这些知识空白，这项研究将对龙卷风及其对建筑物的影响的不确定性进行表征、建模和分析。这项研究将有助于更好地了解龙卷风和地形参数对近地风场结构的影响，龙卷风对建筑设计的瞬时气动力，以及龙卷风作用下建筑性能的不确定性。这些知识将有助于开发基于性能的建筑规范条款，以减轻龙卷风荷载对建筑的影响。本研究旨在取得以下三个方面的知识进步。首先，通过对龙卷风的影响和地形参数的系统研究，提高对龙卷风风场的理解知识。这项研究将填补龙卷风高空结构和地面破坏之间的一个重要空白，并将为更新EF等级提供至关重要的基于物理的证据。将开发易损性函数，以重新校准EF等级中破坏程度的预期风速、上限风速和下限风速。其次，随着瞬变气动力模式的发展，对包括龙卷风和雷暴在内的非天气风的压力和负荷影响的理解将得到加强。这些模型不仅能够更好地描述非静止涡旋下的负荷效应，而且还将建立一座桥梁，将数十年来对静止边界层风的研究成果积累起来。第三，将开发一个新的框架，用于表征和量化建筑物上的龙卷风载荷链的不确定性，并通过有限元模型和风暴后破坏调查进行验证。这一框架将允许在评估建筑脆弱性时纳入不确定因素，包括建筑属性和建筑质量的不确定因素，从而为龙卷风建筑法规中基于性能的规定奠定基础。这项研究是在龙卷风模拟、数据采集和建模能力、龙卷风的全面研究、龙卷风的近地面测量以及非平稳性理论等方面的最新进展的共同作用下进行的，其中许多理论在几年前是不存在的。

The devastation from recent tornadoes in Joplin, Missouri, and Tuscaloosa, Alabama, in 2011 and in Moore, Oklahoma, in 2013 highlight the national vulnerability to these windstorm events. Direct measurement of tornado wind speed near the ground level is difficult to obtain due to its unpredictable nature and destructive force. Current practice is to estimate wind speed based on observed damage to structures and non-structures using the Enhanced Fujita (EF) Scale, which is widely accepted in climatological study, risk analysis, and design of critical facilities. However, such damage-based methods have a great degree of uncertainty. Critical knowledge gaps exist about spatial and temporal distributions of wind flow near the ground level and how wind flow interacts with the terrain and structures. To address these knowledge gaps, this research will characterize, model, and analyze uncertainties in tornado wind and its effects on buildings. This research will lead to better understanding of the effects of tornado and terrain parameters on near-ground wind field structures, the transient aerodynamic force of tornado wind on building designs, and the uncertainties in building performance subject to tornado wind. This knowledge will contribute toward the foundation for developing performance-based building code provisions to mitigate the impact of tornado wind loads on buildings.This research aims to make the following three knowledge advances. First, knowledge for understanding the tornado wind field will be advanced through a systematic study of the effects of tornado and terrain parameters. This study will fill an important gap between a tornado's structure aloft and ground level damages and will provide the physics-based evidence critically needed for updating the EF Scale. Fragility functions will be developed to recalibrate the expected, upper bound, and lower bound wind speeds for Degree of Damage in the EF Scale. Second, understanding of pressure and load effects of non-synoptic winds, including tornadoes and thunderstorms, will be advanced with the development of transient aerodynamic force models. These models will not only enable better characterization of load effects under a non-stationary vortex but also will build a bridge to results accumulated from decades of research in stationary boundary layer wind. Third, a new framework for characterizing and quantifying uncertainties of the tornado wind load chain on buildings will be developed and validated with finite element models and post-storm damage surveys. This framework will permit the integration of uncertainties, including those of building properties and construction quality, in assessing building vulnerability, laying the foundation for performance-based building code provisions for tornadoes. This research is enabled by a confluence of latest advances in tornado simulation, data acquisition and modeling capabilities, full-scale studies of the tornado vortex, near-ground measurements of tornado wind, and theories in non-stationarity, many of which were not available a few years ago.