Carbon Fiber Reinforced Precast Panels 1

[mrengineer]

I am involved in a project where the design team is considering using carbon fiber reinforced precast panels. (One such product is "Carboncast". Just wondering if anyone has had any experience with this type of panel, good bad or indifferent. One thing we are pondering is whether cracking is ever a problem since the panels are so thin.

 

[rgerk]

Are you referring to GFRC (glass fiber reinforced concrete panels)? These consist of a light gauge steel frame with a concrete/glass fiber mix sprayed onto a form. The panels are typically 2" thick.

If so, they are subject to cracking, but the frame has to be sized and the supports located to minimize cracking due to wind, seismic, etc. It's not too hard to figure though.

We used to use staad to run our frames and the manufacturer had a typical spacing for the support rods.

Hope this helps.

 

[mrengineer]

This is different than GFRC. The carbon fiber reinforcing comes in flat sheets with a square grid pattern. In addition to using it in precast panels the literature says you can use it for double tee flange reinforcing in lieu of w.w.f.

 

[rgerk]

Sorry, I missed the CarbonCast reference in your original post. This is an excerpt from the website I visited, "CarbonCast is an innovative technology that uses C-GRID™ epoxy-coated carbon fiber composite grid for secondary reinforcing and shear transfer".

The way we design architectural precast is to limit cracking to 5*sqrt(f'c), so the reinforcement that we added to each panel was technically not required except for temp and shrink. Although we did design the bottom reinforcement for flexure and some of the vertical bars to distribute loads from the connections into the panel.

Seeing the statement above about using it as secondary reinforcement would make me uneasy using it for strength reinforcement. But for temp and shrinkage, I don't see why you couldn't use it.

Let us know what you end up doing, as this is a very interesting application.

 

[Qshake]

mrengineer - I refer you to ACI 440 for the appropriate commentary on failure mechanism with carbon FRP reinforced concrete. You will find that the controlling element is no longer tension as with normal reinforced concrete but compression failure of the concrete. For that to happen some cracking is expected in the tensile region.

It is therefore important to have some minimum acceptable thickness regardless of the high tensile strength of carbon reinforcing. It is also recommended that a fiber reinforced concrete can aide in crack reduction.

Good luck

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[dbuzz]

I have seen Sika CarboDur carbon fire strips installed before for some rehabilitation/strengthening work.

See

http://www.sikaconstruction.com/con-repair-ss.htm

http://www.sika.com.au/cmc/Structural_Strengthening.htm