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

目前估计美国非飓风地区设计风速的方法没有区分起源于大风速和大风速的风扩大温带外气压系统和小但强烈的雷暴。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，不应像目前的情况那样使用单一(混合)分发来处理。从第一阶段的研究来看，看来在美国可能有许多地方的雷暴风主导了极端风气候(对于与传统结构设计相关的重现期)，而传统方法往往低估了设计风对风向分布的模拟过于狭隘。由于雷暴与大尺度温带风在风结构、风暴持续时间、频率、和方向性，这些差异可能会对未来设计风的编纂产生重要影响，结构的安全性，以及美国的风洞测试。第二阶段研究的目的，是评估把雷暴锋面风作为独立的独特的风荷载事件。综合研究计划包括三个基本任务：(1)建立雷暴时空特征的风工程模型阵风锋面；(2)分析选定地点的雷暴和非雷暴风速和风向统计；(3)评估雷暴对几类结构响应的影响。这项工作可能会在全国范围内产生影响，如果成功，影响美国和其他雷暴是极端天气重要贡献者的国家未来的风荷载设计标准风向频率。

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.