Investigation of Thunderstorm Winds with Respect to Wind Load Design Criteria and the Safety of Structures

目前估算美国非飓风地区设计风速的方法不能区分源自大尺度温带气压系统的风和小而强的风雷暴。这两种不同的气象现象有不同的统计分布，根据第一阶段的结果，不应像目前那样使用单一（混合）分布来处理。从第一阶段的研究来看，似乎在美国可能有许多地点雷暴风主导极端风气候学（与传统结构设计相关的回归期）和传统的方法往往低估了设计风，过于狭隘地模拟风向分布。由于雷暴在风的结构、风暴持续时间、频率和方向等细节上与大尺度温带风不同，这些差异可能对未来设计风的编纂、结构的安全、以及在美国进行风洞测试。第二阶段的研究目的是评价将雷暴阵风锋风作为一个单独的、不同的风荷载事件来处理的重要性和优点。综合研究计划包括三个基本任务：(1)建立雷暴阵风锋时空特征的风工程模型；(2)选定站点的雷暴和非雷暴风速和风向统计分析；(3)评价了雷暴对几种结构响应的影响。这项工作可能具有全国意义，如果成功，影响未来的风荷载设计标准，在美国和其他国家，雷暴是极端风频率的重要贡献者。

Current methods for estimating design wind speeds in non-hurricane regions of the United States do not distinguish between winds originating from large-scale extratropical pressure systems and small but intense thunderstorms. These two different meteorological phenomena have separate statistical distributions and, based on the Phase I results, should not be handled using a single (mixed) distribution, as is currently the case. From the Phase I study, it appears that there may be many sites in the United States where thunderstorm winds dominate the extreme wind climatology (for the return periods relevant to conventional structural design) and that the traditional approach tends to underestimate the design winds and too narrowly models the wind directionality distribution. Since thunderstorms differ from large- scale extratropical winds in the details of wind structure, storm duration, frequency, and directionality, these differences could have an important influence on the future codification of design winds, the safety of structures, and wind tunnel testing in the United States. The objective of the Phase II research is to evaluate the importance and merits of treating thunderstorm gust front winds as a separate and distinct wind loading event. The integrated research plan includes three basic tasks: (1) develop wind engineering models of the spatial and temporal characteristics of thunderstorm gust fronts; (2) analysis of thunderstorm and non-thunderstorm windspeed and direction statistics at selected sites; and (3) evaluate the effects of thunderstorms on structural response for several categories of structures. The work could have nationwide significance and, if successful, influence future wind load design criteria in the United States and other countries where thunderstorms are important contributors to extreme wind frequencies.