Effects of turbulent wind on exposed flexible structures

目前的结构工程实践仍然广泛地依靠静力分析方法进行设计。近年来引入的基于性能的设计方法仍然严重依赖于过去的方法，基本上接受传统的极限状态设计解决方案作为可接受的解决方案，并将安全性和完整性问题留给设计师来解释。大多数极端环境荷载都会对暴露结构产生动力效应，在预测结构响应时，考虑破坏或逐渐倒塌的情况通常不能忽略这些动力效应。在结构抗震设计中，人们普遍认为，真正的性能化设计是建立在可靠的、合理准确的响应预测基础上的，而简单的静力分析方法是很难实现的。相当复杂形状的暴露结构上的风速廓线和压力载荷很难预测，这就解释了为什么直到最近，边界层风洞试验中的物理测试一直是评估复杂几何形状和部件结构上风载荷的首选方法。现场风压监测也用于重要的民用工程，世界上各种电力公司对架空线路导线进行了大量的试验研究，但在大多数现代规范和标准中，物理风洞试验结果是结构阻力计算的主要参考资料。

Current structural engineering practice continues to rely extensively on static analysis methods for design. The performance-based design approach introduced in recent years still relies heavily on past methods, essentially accepting traditional limit-states design solutions as acceptable solutions, and leaving the issues of security and integrity to the interpretation of designers. Most extreme environmental loads have dynamic effects on exposed structures, and consideration of failure or progressive collapse scenarios cannot generally ignore those dynamic effects when predicting structural response. As widely acknowledged in seismic design of structures, true performance-based design is based on reliable and reasonably accurate response prediction that is rarely feasible with simplified static analysis methods. Wind velocity profiles and pressure loads on exposed structures of rather complex shapes are difficult to predict, which explains why until very recently physical testing in boundary-layer wind tunnel tests has been the preferred method to assess wind loads on structures of complex geometry and components. In situ wind pressure monitoring is also used on important civil projects and numerous experimental studies have been conducted on overhead line conductors by various electric utilities in the world, but it is fair to state that physical wind-tunnel testing results are the main reference material of drag force calculations on structures in most modern codes and standards. The goal of this research program is to assess the accuracy/adequacy of (and eventually improve) the simplified static load methods described in various codes of practice and design guidelines to predict the response of exposed structures to environmental load effects such as turbulent wind, atmospheric icing, and combined wind and ice effects. Canadian regulations are targeted in the process, such as those of the National Building Code of Canada (NBC) - Commentary I Wind Load and Effects and in Canadian Standards Association CSA S37 on Antennas, Towers and Antenna-supporting structures, but the scope is extended to encompass similar methods used in international OHL design standards and for exposed transportation signage structures. The scientific approach will combine a critical review of available experimental results (from wind-tunnel tests and/or monitoring, old and modern-era) and advanced computational mechanics techniques using structural dynamics and fluid dynamics. In particular, fluid-structure interactions will be examined, both for bare and iced flexible structures in simulated realistic turbulent wind conditions. The impact and significance of the research program are far reaching. The immediate results of the research will eventually lead to updating (or confirmation) of the NBC recommendations, which will impact on other national and international design practice.