Stack Features & Accessories
To prevent damage to a stack due to excessive or prolonged vibration from wind induced vibration forces several treatments may be utilized. The most common two methods used today are to employ Spoilers (strakes) or to utilize a Tuned Mass Damper (TMD). The two methods work entirely different and have various advantages and disadvantages.
As the name indicates spoilers, or strakes, spoil the effect of the wind forces acting on a stack structure by creating a disturbance at the stack wall, thus preventing the wind from creating a negative pressure on the downwind side and therefore preventing any stack vibrations at or above critical wind speeds.
Tuned Mass Damper (TMD)
The tuned mass damper work by creating a resistance to stack movement or vibrations from wind speeds at or above critical wind speeds. The damper is mounted near the top of the stack. The damper consists of a mass (weight) constructed by rolled plate several inches larger than the stack diameter. The weight is sized specifically for each stack. It is supported by three or more pendulum style hangers, so it is free to move. Mounted between the ring mass and the stack shell are a series of cable springs. As the stack tries to move from the wind forces, it is resisted by movement against the cable spring, which is held in place by the ring mass (weight). The ring or mass is held in place by gravity.