Study On Aerodynamic Characteristics And Wind-induced Responses Of Elliptical Arch With Length-to-short Axis Ratio Of 4:3

With the development of economy and society,the requirements for architecture are becoming higher and higher,and more and more novel structures are emerging.As a structure system which is easy to be compressed,arch structure h as been widely used in bridge engineering,from ancient stone arch bridge to modern large-span arch bridge.In addition,the aerodynamic characteristics of cylinders have been systematically studied in the field of wind engineering,but for elliptical cross-section,the aerodynamic characteristics of elliptical cross-section were not systematically studied because of many influencing parameters.In this paper,a 4:3 elliptical cross-section sightseeing arch was taken as an engineering background.The systematic pressure and force measurements of the elliptical cross-section and the arch structure were carried out in a wind tunnel.The aerodynamic characteristics of the elliptical cross-section and the arch structure were studied,and the wind-induced responses of the elliptical cross-section arch structure were analyzed.The main work is as follows:(1)An elliptical cross-section column with a ratio of 4:3 of long axis to short axis was fabricated,three circumferential measuring points were arranged,and end plates were installed on the top of the model.Wind tunnel tests were carried out to study the flow characteristics of the elliptical cross-section under uniform flow field.The experimental wind speed ranged from 5 to 22 m/s.Firstly,the circumferential distribution of the average wind pressure coefficient of the elliptical cross section at different wind direction angles is studied,and the influence of Reynolds number on the distribution of the average wind pressure coefficient is discussed.The results show that the distribution of surface wind pressure is consistent with that of the cylinder in the subcritical Reynolds number area when the long axis upwind angle is zero.When the wind direction angle is large,the distribution of the average wind pressure coefficient is significantly affected by Reynolds number.Then,the distribution of fluctuating wind pressure coefficient under typical wind direction is studied.The results show that the fluctuating wind pressure is greatly influenced by Reynolds number.Finally,the Reynolds number effects of average lift,drag coefficient and Strouhal number(St number)are studied.The results show that the average drag coefficient decreases with the increase of wind direction angle,and the St number of elliptic section is smaller than that of circular section.(2)Based on an elliptical sightseeing arch with 4:3 ratio of long axis to short axis,a rigid test model for measuring force and pressure of the structure is made.The geometric scales are 1:300 and 1:150,respectively.The wind tunnel tests for measuring force and pressure of the rigid model are carried out,and the aerodynamic characteristics such as the surface wind pressure coefficient,average aerodynamic coefficient and Strouhal number of the structure were studied.The results show that the airflow separation of each section of the arch structure is comparatively consistent;the average drag coefficient under the body axis is much smaller than that of the circular section;the St number corresponding to the shedding frequency of the cross-wind vortices is 0.124 under the 0 degree wind direction,which is less than the Strouhal number of the circular section(0.20).(3)Based on the wind tunnel test data of the rigid model of the arch structure,the wind-induced response of the arch structure is studied by using the frequency domain and time domain analysis method of Midas finite element commercial software,and the resonant wind speed under the typical wind direction angle is estimated.The results show that the average displacement response along the wind direction is much larger than the average displacement response along the cross wind direction,while the fluctuating displacement response along the cross wind direction is larger than the fluctuating displacement response along the wind direction,and the acceleration response in the cross wind direction is larger than that along the wind direction;the maximum displacement response in the arch axis direction occurs at the wind direction angle of 60 degrees;and the eddy vibration phenomenon does not occur in the design wind speed range of the arch structure.