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Re: How to Retrofit a Concrete Beam

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Eric,
 
        We had similar, but smaller magnitude, problems in the recent restoration of our heritage building.  In our case we were not limited by existing dimensional constraints and we needed wider beams to reduce the spans of the slab between beams.
 
        Our solution was to build new composite beams completely encasing and utilizing the original beams.  We developed a special mix that was very fluid, high strength, and contained a shrinkage compensation admixture.  We were able to pump/pour the concrete through a series of 4" diameter holes in the slab above and achieve 100% contact with the slab above the beams.  The contractor liked working with this mix so well that he proceeded to use it for underpinning footings, and every other difficult concrete placement situation on the project.
 
        You should chip away some or the concrete cover to assess the main reinforcing, get a pacometer survey to find all of the ties and/or stirrups, and roughen the full surface of the existing beams to get a complete bond with the new concrete.
 
        Hope this helps.
 
Regard,
 
H. Daryl Richardson
----- Original Message -----
To: seaint
Sent: Thursday, May 20, 2010 11:03 PM
Subject: How to Retrofit a Concrete Beam

Existing structural plans show "pre-cast concrete beams by others" (which are above grade, not in the soil) running 25 ft O.C. and the dimensions are approximately 24"wi X 36" deep.  These beams run approximately 50 ft to hold up a building on top.  Below is a parking garage underneath the building.  We cannot find the existing plans that show the existing reinforcement  in the concrete beam, so we cannot analyze the existing beam with the new live load.  The reason why we are adding more live load onto the concrete beams is due to an architectural remodel. 
 
I guess I have a few questions.  First, how would someone go about analyzing an existing concrete beam and not knowing the reinforcement.  How can we find out what the reinforcement is?  Can we xray the concrete beam?  Or is there any other procedure to figure this out?
 
Also, i'm assuming the worst and i cannot figure out what reinforcement is doing inside the concrete beam.  Is there a way to retrofit these concrete beams without knowing the existing reinforcement?  How would you retrofit the concrete beams? Please go into detail as much as you can with the procedure.
 
Thank You,
 
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