wind pressure on silo
wind pressure on silo
(OP)
I am checking an existing barn silo which is being added to a building that I am designing. The silo will be empty (used a stair tower). Does anyone know how to check an empty silo for wind pressure. In particular I am concerned about localized bucking or cruching of a side, much like when you step on the side of a beer can.






RE: wind pressure on silo
RE: wind pressure on silo
RE: wind pressure on silo
The book "Formulas for Stress and Strain" by Roark, has formulas for circular rings that would give you the maximum concentrated or uniform load that would produce certain level of stress and/or deflection in the shell.
The formulas are based on the shell being perfectly circular, it is good practice to provide an additional safety factor for any imperfections.
If needed, the best way to reinforce the shell is using reinforcing rings spaced along the length of the cylinder.
Regards
AEF
RE: wind pressure on silo
The simple approach it to treat the whole silo as a pipe to check for localized buckling.
RE: wind pressure on silo
Assuming 36 ksi steel, you would be allowed a maximum compressive stress of about 16ksi with a tank diameter of 11'-3". That is the upper limit of allowed ratios.
The formula is Fa=(662/(D/t)) + .4Fy for (3300/Fy)<D/t<(13000/Fy)where D is the diameter and t is the shell thickness.
Because of irregularities in this type of section, it should be substantially reduced. I read somewhere (I'm sure it's in the ASD manual), that theorectical design will substantially (>200%) overestimate the buckling strength.
Unless AWWA helps you out in this, I would reduce my theoretical allowable stresses by a factor of 3.
Hope this helps.
Chip
RE: wind pressure on silo