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Increase axial capacity of existing slender concrete column

Increase axial capacity of existing slender concrete column

(OP)
I am working on a project which involves an addition above an existing reinforced concrete building.  The top story has slender columns (14" Diameter, 14' long).  An increase of 110K will be added to each column (total gravity load of 185K).

I was thinking of using FRP to increase the axial capacity, but  ACI 440 - Chapter 11 only discusses the axial strength of nonslender members.  Does ACI have any other design guide which discusses slender members? If not, the other alternative I was considering was encasing the existing concrete columns in concrete and increasing capacity that way.  Are there any other options?

Lateral loads will be handled by the addition of shear walls.  

RE: Increase axial capacity of existing slender concrete column

Will the shear walls not decrease the effective length of the columns?

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Increase axial capacity of existing slender concrete column

(OP)
Yes, the shear walls will, but not enough for me to get the column handle the capacity.  

RE: Increase axial capacity of existing slender concrete column

You might want to talk to an FRP supplier...if you give them your column sizes and required capacity they will tell you if their product is appropriate (I've done this before). If there is anyway FRP can solve your problem they will happily let you know.

RE: Increase axial capacity of existing slender concrete column

Eng32,

I would suggest you do a google search on seismic retrofit, they do this sort of thing all the time. You may consider a steel jacket.

RE: Increase axial capacity of existing slender concrete column

Eng32: Ref- Structural Renovation of Buildings  by Alexander Newman. He has given several methods for strengthening concrete columns: 1) Section enlargement 2)Adding new columns 3)Reinforcing with structural steel 4)Reinforcing with fiber wraps
5)Reinforcing with fiberglass jackets 6)Shortening the length of the columns.
  

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