Duration of extreme synoptic wind speeds for North America in a changing climate and its engineering implementation

Abstract

In modern wind engineering practice, wind load effects are often defined as a function of a basic design wind speed, an aerodynamic force coefficient, several multipliers to consider surrounding terrain, topographic effect, and the directionality of the wind climate. Among these variables, the basic design wind speed is associated with an averaging time (also known as gust duration), e.g., 0.02-second, 3-second, 10-minute, or one hour. The design level aerodynamic force coefficients are defined as a specific percentile within a reference period, representing the generic time duration of wind events, i.e., wind duration, which is assumed to be one hour. A recent study showed that the hurricane wind duration could differ from this assumption. There has not been any study that investigated synoptic wind duration and its engineering implementations comprehensively. It is also unclear whether climate change impacts the synoptic wind duration. Historical records, often less than 50 years, are insufficient to calculate the wind duration for threshold wind speeds at a higher return period. Therefore, this study employed 15 long-term hourly wind speed simulations covering most of North America, each of which has 70 years in the past (1050 years in total) and 80 years into a future changing climate (1200 years in total), to investigate the wind durations in the current and future changing climate. It was found that the durations for winds of about 700-year return period are close to the traditionally assumed one hour and have limited effects on the wind loads for the strength design. However, wind durations can be much longer than one hour for the lower return period level wind speeds, which can impact the wind responses for serviceability limit state design and cladding and component (C&C) design.