Comparison of Gust Factor Data from Hurricanes

The relationship between short-duration gusts and a average wind speed (the gust factor) is important in the determination of the magnitude of wind loads that are experienced by structures in high wind events. Currently, engineers and meteorologists in the United States use relationships established by Durst (1960) and Krayer and Marshall (1992) to calculate the ratio of a gust measurement of a short duration to the corresponding mean wind speed. In both studies, the mean hourly wind speed is used as the basis of comparison.

The Krayer and Marshall curve was derived from the 11 wind records taken from 4 different hurricanes and is used to standardize wind speeds taken from hurricane landfalls. It represents an upward adjustment from the Durst curve that may be associated with increased turbulence in convective regions of the hurricane. Current engineering practice assumes that at high wind speeds, the boundary layer profile can be considered neutrally stratified, i.e. that mechanical turbulence dominates over convective turbulence. However, the latest research suggests that hurricanes contain regions of high wind speeds that correspond to unstable or even irregular boundary layers where current standardization procedures will not apply.

For the last 2 years, Wind Engineering researchers at Texas Tech have carried out research into the hurricane boundary layer by way of mobile, multi-level instrumented towers that are placed in the path of landfalling hurricanes. The high-resolution data obtained from this experiment can be used to construct wind speed averaging curves similar to Durst and Krayer and Marshall. This paper presents the results of this analysis and compares it to Krayer and Marshall’s findings on hurricanes.