| As the frequency of tornadoes increases year by year,the destruction mechanism of buildings under tornadoes has become one of the important topics in the wind engineering field.However,unlike conventional large-scale strong winds,tornadoes are small-scale cyclones,and building scale has an important impact on tornado-induced loads that buildings experience.Therefore,it is necessary to study the difference of tornado-induced loads for the two situations where the building scale is completely within and beyond the vortex core,which can be helpful to analyze the characteristics of tornado damage of different scale buildings,and corresponding suggestions for wind disaster prevention can be proposed to further reduce the life and property loss in the tornadoes.Based on the tornado simulator of Beijing Jiaotong University,this paper conducted a series of experimental studies on the characteristics of the tornado field and the difference in tornado-induced loads of low-rise buildings in different scales under physical-simulated tornado.The main research works and results are as follows:1.Using tornado simulator to realize the physical simulation of tornadoes in the laboratory,and by setting three swirl ratios and three ground roughness densities,the effects of swirl ratio and ground roughness density on tornado wind speed and pressure distribution were studied.The results show that as the swirl ratio increases,the threedimensional wind speed and pressure drop will increase,but under high swirl ratio operating conditions,there will be a slight decrease.The introduction of roughness reduces the near-ground tangential velocity and vortex core radius.2.Pressure measurement experiments of rigid model of low-rise buildings was carried out under stationary tornadoes.By setting three swirl ratios,three orientation angles and fourteen relative radial distances between tornado and model,the effects of swirl ratio,orientation angle and relative radial distance on the distributions of wind pressure and force coefficient of the model were studied,and the effect of building scale on wind loads under stationary tornadoes were analyzed.The results show that the existence of the small-scale model force the tornado structure to change from a singlecelled vortex to a dual-celled vortex.In addition,when the relative radial distance exceeds 250 mm,the influence of scale effect is no longer obvious.3.Pressure measurement experiments of rigid model of low-rise buildings was carried out under translating tornadoes.By setting three translation speeds,six lateral distances and four orientation angles,the effects of translation speed,lateral distance and orientation angle on the distributions of wind pressure and force coefficient of the model were studied,and the effect of building scale on wind loads under translating tornadoes were analyzed.The results show that the horizontal movement of tornado affect the amplitude and time of the peak wind pressure and force coefficient,and the small-scale model is subjected to stronger tornado-induced load at any translation speed.In addition,the changes of wind pressure and wind coefficient with lateral distance and orientation angle are different due to scale effect. |
