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Strengthening RC beam with externally bonded plates.

Strengthening RC beam with externally bonded plates.

Strengthening RC beam with externally bonded plates.

My friends

I am looking for good design references/guides on the strengthening of RC beam (for flexure and shear) using externally bonded plates. Theory and practice if possible. While FRP is well-covered, this one seems not to be.

Thanks for your time.


RE: Strengthening RC beam with externally bonded plates.

FRP seems to be the preferred material for externally bonded strengthening; however, the principles would be the same for any externally bonded reinforcement, only the approach to providing shear bond between the concrete and the external reinforcement varies. Steel used as external strengthening is typically anchored into the concrete, rather than attempting to bond it to the surface. Most often, external steel strengthening takes the form of anchored end blocks connected with high-strength threaded bars, steel prestressing strand, or carbon fiber strands as post-tensioning, since it is typically more effective than unstressed reinforcement.

RE: Strengthening RC beam with externally bonded plates.

Fire rating would be a consideration.


RE: Strengthening RC beam with externally bonded plates.

When adding reinforcing externally that is of similar capacity to you internal reinforcement, you need to look closely at the strains in each layer allowing for the strain in the concrete at the time of the addition of the external reinforcement.

You normally will not be able to use the full capacity of the added external reinforcement as its strain will be limited to below the yield strain due to compatibility considerations.

This is not such a problem with CF as you are never using the full capacity of the CF due to bond considerations. And with external; PT, the steel is stressed to 60-70% of breaking before being bonded, so again normally not so much of a problem.

RE: Strengthening RC beam with externally bonded plates.

Now a somewhat dated publication by ACI is "SP-165: Repair and Strengthening of Concrete Members with Adhesive Bonded Plates ".

It is a collection of conference papers from 1992, printed in 1996. No longer in hardcopy print, but individual papers are downloadable here: Link.

Free if you are an ACI member.

RE: Strengthening RC beam with externally bonded plates.

There is also a publication T55 by The Concrete Society (UK): Design guidance for strengthening concrete structures using fibre composite materials.

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