Axial-moment capacity of concrete arch with external external CFRP wrap

[Enginerdad]

I'm in charge of load rating an existing reinforced concrete arch that has an external carbon fiber wrap along the bottom. I can easily determine the axial-moment interaction curves for the reinforced concrete section, but how do I account for the CFRP? Obviously it won't add any axial capacity in compression, but it will add flexural capacity when there's net tension on the bottom. Any thoughts?

 

[Celt83]

In general the analysis is the same as if the CFRP were a reinforcing bar, you maintain strain compatibility and then relate the strain in the CFRP layer to tension force via the stress-strain profile of the CFRP. See ACI 440.2R-17 for more info.

 

[rb1957]

Wow, I mean WOW ! Concrete wrapped with CRFP. Wow !

I'm not saying it's wrong, but more diverse structural materials I really can't think of.
And I can't stop thinking of issues with the CFRP ... how "wrapped" ? how cured ?? how bonded ?? how to verify the bond over time ?? how ...

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WesternJeb]

rb1957, at least where I am from, this is a pretty common practice..

enginerdad, I disagree with the compression comment. It is helping to "confine" your concrete at the bottom and strengthening it in compression. I have seen many instances that columns are given additional capacity from a CFRP wrap when detailed to do so. As Celt83 has already mentioned, ACI 440 is the hub when it comes to CFRP and strengthening.

 

[Enginerdad]

WesternJeb,
"Wrapped" may not be the most best term, that's just what the documents say. This is an arch with longitudinal strips running along the bottom. There's no confinement added in this application.

 

[SWComposites]

rb - CFRP is used a lot in retrofit situations for concrete structures. Including wrapping a lot of highway columns in CA to upgrade seismic capability. And reinforcing the undersides of concreate beams and panels. There have been lots of articles about it over the years at compositesworld.com

 

[SWComposites]

engdad - any chance you can get the original analysis for the arch for when they added the CFRP? Building dept have it? or can you find out what company performed the CFRP install and contact them?

 

[Enginerdad]

SWComposites
Yes, contacting the manufacturer is my next step. I don't have the design done by them, but I do have the plans for when the work was done. I'm also looking into ACI 440.2R as Celt83 recommended.

 

[Luceid]

rb1957 - There are many cases where FRP is wrapped around a column as previously discussed - in a manner where it provides confinement to the concrete so the bond actually isn't super critical to the design. In other cases where the bond is critical - there are splay anchors among other methods that are embedded into the concrete and splay out to join the FRP mesh.