Research On Aerodynamic And Self-excited Wind Loads Of Squared High-rise Buildings

As the use of lightweight and high-strength building materials and the increase of building height in civil engineering,high-rise buildings show the characteristics of low frequency and low damping,and they are more sensitive to wind.Wind-induced vibration of highrise buildings can cause problems such as safety and comfort,so reasonable evaluation of wind-induced vibration is one of the key scientific and engineering problems.Considering that an accurate evaluation of the wind load acting on high-rise buildings is the basis for a reasonable evaluation of their wind-induced response,Firstly,the aerodynamic wind load caused by flow turbulence and characteristical turbulence acting on high-rise buildings for long term is studied in this paper;Secondly,the problem of crosswind induced response of high-rise buildings is more prominent than that of alongwind and torsional response,when there is aeroelastic effect in the crosswind response,considering the aerodynamic wind load only will seriously underestimate the crosswind response of the structure.Therefore,this paper also studies the self-excited wind load induced by the motion of the structure itself.Square-section is the most widely used for high-rise buildings,the research on wind load of square section high-rise buildings is also abundant.However,for the aerodynamic wind load,the pasted studies paid more attention to the aerodynamic load itself,but ignored the quantitative relationship between the aerodynamic load and the incoming wind speed;In addition,the pasted studies paid more attention to the influence of parameters(such as wind field,building height,etc.)on aerodynamic load,but relatively ignored the more basic analysis of time-frequency characteristics and mechanism of aerodynamic wind pressure and load.Based on the above,firstly,the aerodynamic wind pressure and wind force on the squared-section high-rise building are measured by the rigid model pressure test in wind tunnel in this paper,characteristics of aerodynamic wind pressure and force in time and frequency domain have been analyzed,and its timefrequency relationship with the incoming wind speed are quantitatively investigated.Then,in order to clarify the time-space correlation structure of the wind pressure field on the surface of high-rise buildings,the proper orthogonal decomposition,reconstruction and prediction of the wind pressure field in time and frequency domain have been carried out.For the self-excited wind load,the pasted research mostly focused on the crosswind response of high-rise buildings with aspect ratio of 6 ～ 12 and the aerodynamic damping characteristics characterizing the self-excited wind load.However,it is worth noting that the aspect ratio is far greater than 12 in the actual high-rise buildings,so the experimental research is delayed compared to engineering;moreover,considering the location of actual high-rise buildings,the influence of wind field on crosswind response and self-excited wind load also needs to be clarified.Based on the above,the free vibration wind tunnel test of aeroelastic models of squared-section high-rise building are further carried out in this paper,the aerodynamic damping is identified according to the measured displacement response probability density function,and the effects of aspect ratio and wind field on the response and aerodynamic damping are discussed.The main research contents are as follows:(1)This study performes the synchronously measurement of longitudinal wind speed and wind pressure on a high-rise building model under urban flow in a boundary wind tunnel,quasi-steady theory and aerodynamic admittance between wind speed and wall pressure/force is described in both time and frequency domain.Wind pressure characteristics,probability distribution spatial distribution and spatial coherence are clarified in detail.The correlation between the windward and leeward drag forces is analysed,and the difference and relationship between alongwind drag and quasi-steady alongwind drag are discussed.The correlation between the lift forces on two sideward walls is clarified,and the evolution of load in both time and frequency domain during the superposition of wall lift and crosswind lift is analyzed;The variation of time-frequency characteristics,(non-)Gaussian characteristics and cross-correlation characteristics of base moment with wind directions are clarified.(2)Based on the high-frequency pressure measurement of rigid models in the wind tunnel,the decomposition,reconstruction and prediction of wind pressure field are studied by both Covariance and Spectral Proper Orthogonal Decompositons(POD and SPOD).The certain mechanism and wind pressure/force reconstruction process of the surface wind pressure field on square-section high-rise buildings are studied by POD.Then,the dominant eigenmodes participate in the reconstruction process should be extracted in the variance proportion of the reconstructed time history and the original time history,when reconstructing wind pressure/force by POD.More orders should be evolved when predicting the wind pressures by POD.The SPOD method,which considering time-space coherence shows that the first-order dominant spectrual mode includes all of the frequency-domain mechanisms of aerodynamic pressure,which makes it clear that only the first-order dominant mode needs to participate in wind pressure reconstruction and prediction by POD,so it is more reasonable and accurate than POD which considering only spatial correlation.(3)Aeroelastic model wind tunnel tests of square-section high-rise buildings with different aspect ratios under suburban and urban terrain are carried out.The time history,probability density function,root mean square,kurtosis and other statistics of crosswind displacement response of high-rise structures under different wind speed and structural damping ratio are analyzed and discussed.Influenced by the influence of the above factors,the results show that the crosswind vibration of high-rise building appears random buffeting obeying Gaussian distribution,harmonic resonance obeying hardening nonGaussian and buffeting-harmonic mixed vibration.The crosswind vibration characteristics and statistics of high-rise buildings with slenderness ratios of 12,16 and 20 are studied,the results show that the crosswind response amplitude of the structure increases significantly with the increase of aspect ratio;The effects of the wind fields on the crosswind response characteristics and statistics of squared-section high-rise buildings are analyzed.The results show that when the aspect ratio of the structure is small(e.g.12),the increase of turbulence will suppress the crosswind aeroelastic effect;When the aspect ratio of the structure is large(such as 20),the increase of turbulence does not suppress the crosswind vibration,that is,the crosswind aeroelastic effect still exists when the turbulence is large.(4)The amplitude-dependent aerodynamic damping is described as the generalized Van der Pol-type(GVDP)model,and analytical probability density function(PDF)of the crosswind response which was derived based on equivalent nonlinear equation method is used to identify the aerodynamic damping by curve-fitting the PDF of the crosswind response.Next,the proposed identification method is validated by comparison with Monte Carlo simulation concerning the stochastic crosswind response of a square tall building.Using the above method,the displacement response of square section high-rise buildings based on aeroelastic model test is identified,and the nonlinear aerodynamic damping with amplitude dependence under different wind speeds is obtained.The effects of aspect ratio and wind field on the crosswind aerodynamic damping of squared-section high-rise buildings are further discussed.The results show that the crosswind negative aerodynamic damping of the structure under the same wind field increases with the increase of aspect ratio,and the crosswind negative aerodynamic damping of the structure under the same building basically does not change significantly with the increase of turbulence when the aspect ratio is large(such as 20).