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

2011年在密苏里州乔普林和亚拉巴马塔斯卡卢萨以及2013年在俄克拉荷马州摩尔发生的龙卷风造成的破坏突出了国家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，很难在地面附近直接测量龙卷风的风速。目前的做法是根据观测到的结构和非结构的损坏，使用增强型藤田（EF）规模，这是广泛接受的气候研究，风险分析和关键设施的设计来估计风速。 然而，这种基于损伤的方法具有很大程度的不确定性。关于近地面气流的空间和时间分布以及气流如何与地形和结构相互作用，存在着关键的知识差距。为了解决这些知识差距，本研究将描述，建模和分析龙卷风风及其对建筑物的影响的不确定性。该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，龙卷风风对建筑设计的瞬态气动力，以及龙卷风风对建筑性能的不确定性。 这些知识将有助于为制定基于性能的建筑规范条款奠定基础，以减轻龙卷风风荷载对建筑物的影响。首先，通过对龙卷风和地形参数影响的系统研究，加深对龙卷风风场的认识。这项研究将填补龙卷风高空结构和地面破坏之间的重要空白，并将提供更新EF量表所需的物理学证据。将开发脆弱性函数，以重新校准EF等级中损害程度的预期风速、上限风速和下限风速。其次，随着瞬态气动力模式的发展，将进一步了解非天气风（包括龙卷风和雷暴）的压力和载荷效应。 这些模型不仅能够更好地描述非定常涡下的载荷效应，而且还将为数十年来定常边界层风研究积累的结果搭建桥梁。第三，将开发一个新的框架，用于表征和量化建筑物上龙卷风风荷载链的不确定性，并通过有限元模型和风暴后损害调查进行验证。该框架将允许在评估建筑物脆弱性时整合不确定性，包括建筑物属性和施工质量的不确定性，为基于性能的龙卷风建筑规范规定奠定基础。这项研究是由龙卷风模拟，数据采集和建模能力，龙卷风漩涡的全面研究，龙卷风风的近地面测量和非平稳性理论的最新进展的汇合，其中许多是几年前不可用的。

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.