Cylindrical Wood Tower

[Bozzo]

I am a licensed Civil Engineer (Structural)with numerous years of experience designing wood residential homes in Southern California. I am attempting to laterally design a wood tower attached to a house. The tower is about 25ft tall and approximately 15ft in diameter and is at the Entry of the home. This type of tower is very common in California. In the past we have always wrapped the entire tower with 3/8" shear panel with 6/12 8d common nailing and left it at that without providing calculations. However, now I am having to design the Tower because the lateral forces at the tower cannot be transferred to the main part of the home. A plan checker has suggested designing for the Hoop & Radial Stresses in the plywood, but I do not think designing the tower in that aspect is accurate. I believe I will be limited to designing the tower with Cantilevered Columns out of the Foundation to resisit the 2 main orthogonal directions. Does anyone else have experience or suggestions in this area? Thanks for your response!!!!!

 

[SacreBleu]

Just to reduce a difficult/fuzzy design problem to sensible approximation, why not assume it is actually an enclosed square in plan (enclosed within the diameter of the full circle)?

 

[DaveAtkins]

I agree with you, Bozzo. I don't think hoop stresses have anything to do with the lateral analysis of this tower. In fact, I don't think there are any hoop stresses in this tower (it's not like it's filled with fluid or grain).
I would analyze it on a 3D structural analysis software, as a cylinder, with reactions around the base. Then you will see what forces the plywood must take, what reactions the anchor bolts must take, etc.

DaveAtkins

 

[skier1578]

In the houses we have designed in Southern California, towers like this have typically been very tall and narrow. This pushed us to use either cantilever columns with a grade beam or to design a moment frame because of the height to width ratio limitations of a plywood shear wall. The owner/contractor always cries when they see steel, but that is the cost of these turrets.

 

[Bozzo]

Thanks Everyone,
We already gave in and designed cantilevered columns with grade beams at the base.

Thanks,