Study On Wind Load Of Rectangular Flat Roof Building Under Physical-simulated Tornado

The probability of a building being hit by a tornado is very small.It is uneconomical and unreasonable to carry out anti-tornado design for general civil and industrial buildings;however,some important buildings,such as terminal buildings,high-speed railway stations,nuclear power plants and lifeline projects,are generally located in the suburbs,where the surface is empty and vulnerable to tornadoes.Once subjected to a tornado,it will cause serious loss of life and property.Therefore,in the active area of the tornado,correct and reasonable consideration of the impact of tornado load on such buildings,and grasping the weak parts of the building under active tornado,will be helpful to reduce the wind loss and damage caused by the tornado wind disaster.In this paper,the tornado was generated by the tornado simulator of Beijing Jiaotong University,and a series of pressure measurement experiments under the tornado were carried out on a rectangular flat roof building.Based on the results,the influence of different parameters on the tornado wind field and wind load characteristics was analyzed in detail.The main research works are as follows:(1)Using tornado simulator to generate tornado airflow under five swirl ratio conditions,the tangential velocity,radial velocity,vertical velocity and pressure drop in wind field were measured by a three-dimensional pulsating wind speed tester,and the distribution characteristics of the tornado wind field and pressure drop were obtained.The results show that the tangential velocity has the largest amplitude in the tornado wind field,and the maximum tangential wind speed and the radius of vortex core increase with the increase of the swirl ratio;the air pressure in the tornado wind field is less than the standard atmospheric pressure,the amplitude of which decreases as the radial distance increases.In general,the tornado simulator of Beijing Jiaotong University can effectively simulate the real tornado airflow,and the test results are in agreement with the theoretical model and the measured data.(2)Carrying out pressure measurement experiments of rectangular flat roof building under static tornado using the pressure scanning valve system.By setting five angles of the guide vane,fourteen relative distances and seven direction angles of the model,the distribution characteristics of wind pressure and wind force coefficents acting on the building model under different static working conditions were comprehensively analyzed.The results show that the wind pressure acting on the building surface is formed by the coupling of the pressure drop and the aerodynamic action between the tornado airflow and the building model.Around the center of tornado,the pressure drop dominates the distribution of wind pressure and wind force coefficients.At the vortex core radius,the tangential wind speed is the decisive factor.(3)Carrying out model pressure measurement experiments under moving tornado.By setting three swirl ratios,five translation speeds of the tornado simulator,four direction angles of the model,and six offset distances of the model away from the tornado moving path,the characteristics of wind pressure and wind force coefficients under different mobile working conditions were studied.The results show that compared with the static tornado condition,the mean value of the wind pressure and wind force coefficients are unchanged at the points where the gradient of change is small in the time history curve,and decreases at the points where the gradient of change is large.The magnitude of the extreme value decreases as the translation speed increases.The amplitude of wind load decreases or increases first and then decreases with increasing of the offset distance.