Dependence Of Wind Effects Upon The Temporal And Spatial Variation Of Air Density For Highrise Buildings

With building structures being taller,softer and more complicated,wind load has become one of the main controlling loads for the structural design of highrise/super highrise buildings.In order to ensure the safety,comfort and durability of buildings under the strong wind/typhoon,the control of wind load and wind-induced response is of great importance.Wind load is closely related to air density which is affected by temperature,air pressure,relative humidity,tropical cyclones(TC),and altitude.However,in the field of wind engineering,air density is usually assumed to be a constant and the influence of its variation on wind effect of buildings is ignored.Based on the measured data from meteorological stations,the paper studies the temporal and spatial characteristics of air density.Meanwhile,a data-driven model for the height-dependence of TC air density in the eye-wall region of a TC is established.According to the model and wind tunnel pressure test,the dependence of wind effects upon the temporal and spatial variation of air density for highrise buildings is analyzed in detail.Base on the field data over 1/3 month duration at near-ground levels from five national weather stations in China for 30 years and measured data of 3 surface meteorological weather stations with different terrains in Hong Kong for nearly 14 years,the paper systematically analyzes the variation of air density with latitude,season and terrain.It is shown that air density is basically increases with increase of latitude,with obvious seasonal and annual cycles.Air density gets much larger in winter than in summer.Compared with the standard value at z=0 in the wind code of China,measured air density can vary by a factor of 8%～10%.Air density of urban and marine terrains is almost the same while that of mountainous terrain is obviously lower.In addition,based on field measurements from radiosonde balloons released at inner regions of three TCs that have triggered the issuance of Hurricane Signal No.10 by Hong Kong Observation during the past twenty years of the 21 st century,a data-driven model for the heightdependence of TC air density in the eye-wall region of a TC is established.Through comparison with the wind load codes of China and the USA,it is found that the measured profile of TC air density is agree well with the profile of the minimum air density stipulated in ASCE 7(2005)and the background air density profile in summer.In general,the profile of air density in GB50009-2012 and ASCE 7-16,the mean and maximum air density stipulated in ASCE 7(2005)are all conservative,with the magnified factor of 9.0%～9.8%、2.8%～7.6%、7.1%～7.6% and12.4%～15.6%.In summary,site-specific and season-specific values of air density should be adopted in the wind resistance design of engineering structures.In order to study the dependence of wind effects upon the temporal and spatial variation of air density for highrise buildings,wind tunnel pressure tests of square and four rectangular super highrise buildings with different aspect ratios are carried out.According to the random vibration theory,TC air density profile and evaluation method of constant density,the wind pressure and load distribution,peak displacement and acceleration response as well as the equivalent static wind load of buildings are compared and analyzed.The main conclusions are as follows:(1)As for the square highrise building with the high of 600 m,the wind-induced response of across-wind is much larger than that of along-wind.After considering the vertical variation of TC air density,the wind pressure and load,base internal force,acceleration,displacement and equivalent static wind load of buildings will be reduced by ～12%.(2)As for four rectangular highrise buildings with different aspect ratios and the same high of 500 m,depth-to-width ratio has few influences on the wind pressure distribution on the windward surface when the short side of the building is in the windward direction.As the depth-to-width ratio decreases,the peak displacement and acceleration response at the top of the building gradually decrease.After considering the vertical variation of TC air density,the wind pressure,wind load and wind-induced response of buildings will be reduced by 11%～12%.(3)Combined with the wind effect analysis of square and rectangular highrise buildings,it is concluded that particular buildings in specific sites do not need to be equipped with damping system after considering the vertical variation of TC air density,which will effectively improve the economic efficiency of structural design.On the basis of above research content and related results,the master thesis has important engineering practical significance for improving the economic efficiency of structure design,which can also provide a theoretical basis for the revision of relevant codes.