Experimental Study On Galloping Characteristics Of Structures With Square Cross-Section

The square cross-section is commonly used in high-rise structures in civil engineering field.Square cross-section towering structure will happen galloping in a particular direction Angle,while its aerodynamic damping is negative.The structure has always absorbed the energy in the flow to produce the wind induced vibration,which caused more serious damage to the structure.In the past,scholars usually only study the aerodynamic characteristics of the square section under the vertical wind direction.However,the structure of the square cylinder in the actual project is often under the action of inclined wind.The distribution law and estimation method of aerodynamic force are not clear,and the characteristics of wind-induced vibration are not clear.The angle between the incoming flow direction and the incoming flow perpendicular to the axial component of the structure is defined as the wind deflection angle ?.The widely used square cylinders in engineering are commonly experienced oblique wind under which the aerodynamic characteristics and estimating methods are still unclear.In the present study,the wind pressure distribution on the yawed cylinder are tested in wind tunnel to illustrate the aerodynamic characteristics.The rigid section model pressure test was used to obtain the wind pressure on model with square cross-section cylinder.The variation of wind pressure distribution,aerodynamic force characteristics and galloping instabilities with the skew wind were analyzed.The vibration characteristics of the system are analyzed based on the normal assumption.Mainly include the flowing aspects.(1)When the flow and structure axial Angle are large,the traditional wind velocity decomposition method can only estimate the wind pressure before the separation point,and it is not applicable to the estimation of the complete aerodynamic force of the slant structures.(2)When wind angle is small,vortex shedding intensity weakens,wind pressure of square column lee decreases,and the force coefficient is basically the same with the change of wind Angle.When large wind deflection,the static aerodynamic characteristics differ with small Angle.The wind pressure and average drag coefficient are much larger than the vertical wind direction;(3)The vortex shedding intensity weakens with the wind declination angle.The strongest vortex shedding strength position moves from the upstream to the downstream,and the extreme value of the storroha number increases,and vortexinduced resonance is more easily induced.(4)Under the oblique wind structure,the unstable region of galloping increases slightly from the vertical wind,and the critical wind speed at which the galloping occurs also becomes smaller.Under the effect of oblique wind,the square cross-section structure is more likely to cause galloping.