Study On Wind Load Of Low-rise Buildings Under The Impact Of Downburst

Downburst is a type of local strong wind.Because of the strong downdraft and the radiant outflow caused by the wind shear after contacting the ground,which will cause huge damage to the building.It is particularly important to understand and study the wind field characteristics of downbursts and the wind load of buildings.In this paper,using the Beijing Jiaotong University Downburst Simulator to generate downburst wind field to study its characteristics,and the low-rise house model pressure test is carried out to study the downburst wind load.The main research work is as follows:1.Based on the impact jet theory,generate three different roughness downburst wind fields,and measure the spatial distribution characteristics of horizontal wind speed,vertical wind speed,turbulence and air pressure.The results show that in the center area of the downburst outflow,the wind speed is mainly vertical wind speed.The higher the distance from the ground,the greater the wind speed is and the maximum near the outlet;the turbulence is very small;the pressure is positive pressure,and the maximum positive pressure is near the ground.In the horizontal diffusion area of downburst,the wind speed is mainly horizontal wind speed.As the radial distance increases,the wind speed increases first and then decreases,and reaches the maximum when the radial distance is near the outflow diameter;the turbulence degree is large.The greater the roughness,the vertical wind speed,horizontal wind speed and air pressure are significantly reduced but the turbulence is increased.The horizontal wind velocity profile of the downburst generated by the experiment agrees well with the measured results and the theoretical model.2.When the downburst is in steady state,the wind load characteristics of the lowrise house model are studied by changing the radial distance and direction angle of the downburst and ground roughness.The results show that in the outflow area of the downburst center,the model is mainly affected by high air pressure,the surface wind pressure is all a large positive pressure,and the wind force is a large pressure;in the downburst horizontal diffusion area,the model is mainly affected by the horizontal wind speed.Near the radial distance double the outflow diameter,the maximum negative pressure appears on the front edge of the roof,and the maximum lift,side force and overturning moment of the wind force appear.The increase in roughness will increase these wind pressure coefficients and wind coefficients.3.When moving the downburst,the wind load characteristics of the low-rise house model are studied by changing the downburst's moving speed,direction angle,and distance of the moving path offset from the center of the model.The results show that the average wind pressure coefficient and wind coefficient on the model surface are basically consistent with the steady-state situation,but the maximum and minimum values will be significantly reduced.When the moving speed of the downburst increases,there will be a significant "lag" phenomenon,and the peak value of the wind pressure coefficient and wind coefficient on the model surface will also slightly decrease.When the offset distance of the downburst increases,the wind pressure coefficient on the model surface decreases significantly;the lift force,the lateral force in the vertical offset direction and the bending moment in the offset direction gradually decrease;the torque,the lateral force in the offset direction and the bending moment in the vertical offset direction increase first and then decrease.The torque reaches its maximum in the wind shear region,and the other two winds reach their maximum near the outflow diameter offset by one.