Steel stacks have relatively low inherent structural damping. Therefore, excessive top-of-stack deflection can result at critical wind speeds due to vortex shedding. To keep these deflections within acceptable limits, damping must be added to the "stack-foundation-soil" system.
A Fabreeka damping ring of preformed fabric pad material is placed between the stack base plate and concrete foundation. Fabreeka washers/pads are placed between steel washers/plates under the anchor bolt nuts.
Helical strakes and tuned dampers are other methods used to control top-of-stack deflection due to vortex shedding. However, the wind drag load can increase resulting in added costs for stack material and foundation size to resist this added load.