Effects of turbulent wind on exposed flexible structures

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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.