Strengthen Existing Concrete Column

[Jasonw567]

I am looking for the best way to strengthen some existing concrete columns. I am working on an existing concrete piperack with 1'-10" square columns. New equipment will be added to the existing structure. The wind loads introduced by this new equipment are causing the bottom 4 ft of the columns to require more reinforcing than they currently have. Bracing cannot be added to to clearance constraints. I was thinking of adding large channels to either side of the column and through bolting them. I was just wondering if anyone had some other ideas?

 

[swearingen]

Have you looked into carbon fiber wrapping? It's been done on many highway columns in California to strengthen them for earthquakes.

 

[Taro]

How about externally bonded FRP wrap? Look up ACI 440.2 and manufacturers such as Fyfe or Quakewrap.

 

[Jasonw567]

I have thought about that. I don't have much experience with FRP. Can you get a large increase in a column's moment capacity with an FRP wrap? It was my understanding that this was mainly done to increase ductility for earthquakes.

 

[JAE]

I would think that FRP wrap...or through bolting channels would have the potential to improve the bending capacity of the columns, but if its a non-braced pipe rack, aren't your columns cantilevering up to provide the lateral restraint? And if so, isn't your maximum moment at the base? Wrapping columns would have to stop at the base and not develop past the bottom of the column. Then your internal rebar would still be resisting the moment alone. Just trying to visualize it.

 

[Blackhorse007]

well, there due to space constrain, FRP would be the best way out, Fyfe have both Glass and carbon fibr which would be useful in this situation and i am quite sure that they would help u do the necessary calculations.

On top of ductility for earthquake ( which fyfe uses glass fabrics) it could also be used to increase the axial capacity. I have done some experiments on it and well for round columns, usually you would be suprise about the strenght that it could increase.

 

[Ron]

JAE nailed it as usual...it doesn't matter what you put above the base of the column if you don't connect the two.

I realize you have clearance constraints, but you'll likely have to dowel into the base or provide a supplementary steel collar as a base for your repair tie-in.

 

[Jasonw567]

I was planning on welding the channels to the existing base plate, and extending it if neccessary and adding new anchor bolts.

 

[UcfSE]

Can you increase the size of your column for those 4 or 5 feet where it is needed? That would increase your depth "d" for the rebar so that it works. You can epoxy dowels into the existing column to develop the composite section.

 

[J1D]

Jasonw567, how strong is the base plate? Is it a plate embedded into the foundation or just like the base plate of steel column? Welding channels to base plate sounds like a simple solution, but this may introduce big load onto the base plate (We designed concrete piperack columns with a angle at each corner all the way up, with Nelson studs into concrete, the angles were welded to a very thick base plate).