8 th International Colloquium on Bluff Body Aerodynamics and Applications Northeastern University, Boston, Massachusetts, USA June 7 - 11, 2016 BBAA VIII Non-synoptic wind-induced effects on linear bluff-body aerodynamics Jianming Hao, Teng Wu Department of Civil, Structural and Environmental Engineering, University at Buffalo, Buffalo, NY, USA, Email address: jhao2@buffalo.edu tengwu@buffalo.edu SUMMARY: This study focuses on the non-synoptic wind-induced effects on linear bluff-body aerodynamics. More specifically, the transient nature of the downburst and tornado events and its effects on the aerodynamic parameters are investigated. Since an additional time scale is introduced in the wind-structure interaction system due to the time- varying transient nonstationarity in the non-synoptic winds, the conventional 1-D indicial response function needs to be extended to a 2-D case. Buffeting response of a bridge deck and a transmission line conductor based on the time- domain linear analysis framework associated with 2-D and 1-D indicial response functions, representing non- synoptic winds and corresponding synoptic equivalents, was carried out. The results highlighted the important effects of the transient nature on the non-synoptic wind-induced structural response. This study could facilitate more appropriate design of flexible horizontal structures considering non-synoptic wind loads. Keywords: Non-synoptic winds, transient effects, suspension bridge, transmission line, buffeting analysis 1. INTRODUCTION The non-synoptic wind events including downbursts and tornadoes have violent impacts on the earth’s surface, which may cause significant human fatalities and huge economic losses. Compared with vertical structures like residential buildings, the line-like horizontal structures such as the transmission lines and long-span bridges have a higher probability to meet the downbursts or tornadoes (Tamura, 2009). Actually, 80% - 100% of the weather-related failures of the transmission line systems due to high-intensity winds are associated with tornadoes or microbursts (Dempsey and White, 1996). While the synoptic winds are typically characterized by a constant mean wind speed, the non-synoptic winds possess a time-varying mean wind speed that generates a transient nature. Understanding the effects of transient nature on the bluff-body aerodynamics of horizontal bluff structures is important for more accurately assessing the structure performance under non-synoptic winds. In this study, the transient feature of non-synoptic wind events, which may significantly change the bluff-body aerodynamics well understood under conventional synoptic wind conditions, is mainly focused. The semi-empirical linear model in the time domain is applied to simulate the aerodynamic and aeroelastic forces (moments) on the long-span bridge and transmission line subjected to downburst and tornado events and their equivalent synoptic winds. Since an additional time scale is introduced in the wind-structure interaction system due to the transient nature in the non-synoptic wind, the conventional 1-D indicial response function needs to be extended to a 2-D case. The results from this study suggest the importance to consider the change of aerodynamics due to the transient nature in the non-synoptic winds.