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 differently and have various advantages and disadvantages. Illustrations of these two stack accessories are shown above.

 

Spoilers (strakes)

As the name indicates spoilers also called 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, thus preventing any stack vibrations at or above critical wind speeds.

 

Tuned Mass Damper (TMD)

The tuned mass damper works by creating a resistance to stack movement or vibrations from wind speeds at or above critical wind speeds. The damper is mounted at or 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 hangers on pendulum style hangers, so it is free to move. Between the ring mass and the stack shell is mounted 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 weight (mass). The ring or mass is held in place by gravity.