Wind spectrum properties at a typical canyon bridge site in the Jinsha River

Wind parameters used for the wind-resistant design of the bridges in western canyons remain an unsolved issue by the relevant standards and hence need to be investigated. In the report， based on the long-term observations from wind measurement towers， the characteristics of the wind field in the mountainous canyon where the proposed Fengke Jinsha River Bridge was located were analyzed， the average wind speeds， wind directions， and turbulence intensities at the bridge site were obtained by the statistical analysis， and the power spectral density functions were analyzed at wind speeds which was higher than a threshold of 10 m·s^-1. The results indicated that the profile of the average wind speed varied with height was generally consistent with the specifications， however， the profile of the peak wind speed deviated significantly from the specifications. The canyon topography had a significant influence on the wind direction distribution and turbulence characteristics. The turbulence intensities of the wind samples along the canyon direction were significantly lower than that of the wind samples from the other directions， which exhibited the clear anisotropy. Along the canyon direction， the turbulence intensity of the flow was minimum in northwest direction（120°~165°）， the overall crosswind turbulence intensity exceeded the values suggested by the specifications. The von Karman and Harris spectra were the closest to the measured along-wind spectrum， but still lower than the measured along-wind spectrum in the high-frequency region. The peak values of both the Panofsky and Lumely-Panofsky spectra were difference slightly from the measured vertical spectrum， the latter showed a higher deviation than the former. In the low-frequency region， the values of both the Panofsky and Lumely-Panofsky spectra were lower than that of the measured vertical spectrum. In the high-frequency region， the values of both the Panofsky and Lumely-Panofsky spectra were higher than that of the measured vertical spectrum. Compared with the Lumely-Panofsky spectrum， the Panofsky spectrum was more coincide with the measured spectrum. Our findings can be sued as the references for wind-resistant design of the bridges cross over western canyons.