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Re: FRP Reinforcing

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Thanks for the reply Mike. My responses are in [ blue ].
 
I write:
 
Dave,
I think you're right about the difficulty of obtaining large increases in stiffness with FRP.  Taking a step back, what is causing the large deflections you have?  Is the slab deteriorated?
 
[ Slab is not deteriorated. I have not seen it yet, however, previous reports are that cracking is minimal. I believe the design may not have been correct in this area as drop panels would seem to be required. ]
 
And, is there a reason you can't jack the slab past level (at risk of some cracking), apply the FRP, let it settle to where it's going to settle to, and then apply a topping to level it and cover the cracks you just made?
 
[ My concern is the amount of stress that is going into the FRP (and how to accurately define the value)..if jacking beyond relieving DL then we would be putting bars into compression where they are normally in tension. The FRP would then be supporting a significantly higher portion of the load.  FRP is not ductile in any way and when it fails it just snaps. ]
 
One of the significant problems with FRP reinforcing, especially on the bottom of slabs, is fireproofing.  If the FRP installers start talking about fireproof paint, ask a lot of questions. 
 
[ This is also a concern of mine. We have used intumescent paint with steel before however it is always based upon a certain m/d ratio of the column (if my memory is correct). I have not heard of any research with respect to this and bonded FRP reinforcement.  Perhaps spray fireproofing would work better. The underside is presently sprayed with some kind of insulation for thermal concerns. ]
 
On the shear strength, we have added capitals to existing columns.  The columns we had were round; we bush-hammered all around the top foot or so of the column to a depth of 1/4 inch or so (make sure this is more than just surface abrasion--break into the concrete a significant depth), put rebar hoops around the columns, and cast conical capitals to within about 3 inches of the underside of deck.  Then wait a week for cure and grout the 3 inch space.
 
[ This sounds like a good method. Much simpler than the addition of drops, however. ]
 
The length of capital needed is determined by the shear force to be transferred (your judgement as to whether the capital takes all of it or the slab shares some) and the allowable stresses based on shear-friction.  Then the hoops are sized as if they were corbel reinforcing.  The hard part is to develop a hoop detail that can be installed, that gives you the strength you need.  I would suggest small rebar (#3 or #4) made up into spirals that the contractor then winds on the column, much like a key is put onto a keyring.
 
There is a reference article for what I describe, but I don't remember details (this was at a previous job).  Perhaps someone else remembers this, or it can be found by a search.
 
[ Any hints on a search for this would be appreciated. I tried several keywords and nothing like you talked about was found. ]
 
HTH,
Mike Hemstad
MBJ
Minneapolis, Minnesota