Field Measurement Of Wind Properties At A Bridge Site Near A Canyon Deep-cut To Hilly Land

With the development of Chinese economic construction,more and more cross-canyon bridges will be built on the mountainous region in Western China.In order to ensure the safety of the structures and comfort of driving during the construction and operation,it is necessary to conduct detailed research about the wind characteristics at the canyon terrain where bridge are located.However,the existing China Wind-resistant design specification of Bridges does not specify clearly the wind field characteristic parameters at complex mountainous terrain,such as the the wind angles of attack,the distribution of turbulence intensity,turbulence integral length,and the longitudinal and cross wind spectra,etc.Without sufficient investigations,it would be difficult for designers to predict accurately the wind response of structures.Therefore,it is of practical significance to study the wind field characteristics on mountainous valleys in western China.The main research contents of this paper are presented as follows:Firstly,a field observation station is built for wind properties at the Jiangdihe valley in northern Yunnan province.Wind data have been collected by a wind observation tower for nearly two years.After that,the collected data are processed by computing software.Based on statistical analyses,random vibration theory and Aerodynamics,the data are analyzed to obtain the wind field characterist ics and laws at the bridge site.Main findings are listed as follows: 1)By comparing the hourly maximum wind velocities and wind directions of those obtained by the field observation and those collected from a local meteorological station,a phenomenon of wind direction locking is found at the canyon,on top of accelerating the wind speeds;2)The range of wind angles of attack is from-7° to 10°,higher than that typical of plains;3)The relations between the turbulent intensity and the mean wind speed are obtained by fitting with inverse example functions,resulting in good fitting effects;4)The along-wind turbulence intensity in high wind speeds is close to the those specified in the China Wind-resistant design specification for highway bridges,while the vertical-wind turbulence intensity is significantly higher than those specified;5)The integral length scales calculated from the observed turbulence are found to be of large discreteness;6)The wind spectra of the measured winds are quite different from the Kaimal spectrum,but in good agreement with the von Karman spectrum;7)A new formula of power spectral density is proposed based on known experiences and characteristics of the measured power spectral density;8)The wind spectra of the vertical wind fluctuations are close to the von Karman spectrum;9)The attenuation coefficient obtained by fitting the coherence function is smaller than that obtained in relevant literature;10)the attenuation coefficient obtained by the coherence function fitting increases with the height above the ground.