Control and prevention of transverse wind vibration effect in steel structure chimney design

When there is wind load on the steel chimney, alternating vortices will be produced behind both sides of the chimney, and one side will alternately fall off to the other side, forming the Karman vortex column. The occurrence of Karman vortex will make the pressure on the surface of the building change periodically, and its direction of action is perpendicular to the wind direction, which is called transverse wind direction vibration. As the vortex appears, the vibration creates a forced vibration. Once the vibration is enhanced, there will be a vortex controlled by vibration, and the steel structure will produce a violent resonance, showing the characteristics of self-excited vibration.

In practical engineering, the transverse wind vibration phenomenon of steel chimney often occurs, especially when the stiffness of the chimney is small, the critical wind speed is generally less than the designed large wind speed. Therefore, the probability of critical wind speed is higher. Once there is a critical wind speed, the frequency of vortex shedding is the same as the natural vibration frequency of the chimney, and the chimney will have a crosswind resonance.

The harm caused by transverse wind vibration is great :1) the inertia force generated by wind vibration causes additional stress in the structure; 2) Due to the high frequency of wind vibration response, steel structures may produce fatigue effects.

The transverse wind vibration will have a great effect on the chimney. Therefore, resonance phenomena should be avoided in the design as much as possible. If not completely avoided, the effect value of resonance should be small.

First, subcritical breeze resonance can occur when Remiao is 3.5×106 and vH>vcr, j. The critical wind speed vcrj is not less than 15m///, and anti-vibration measures or control structures can be taken in the structure. s, for example, measures can be taken to increase the vertical reinforcement plate and increase the stiffness of the chimney.

2) In the design process, it is also possible to increase the horizontal fulcrum of the chimney at an appropriate height by changing the natural vibration period of the steel structure chimney; The chimney vibration damper is used to properly reduce the influence of vibration and the damage caused by vibration, so as to weaken the transverse wind vibration. If it is difficult to achieve the purpose after adjusting the stiffness of the chimney, it is also an effective solution to set a wind breaker in the upper part of the chimney.

The chimney can use auxiliary support structures such as cable and tower to increase the stability of the chimney.