Concrete beam reinforcement

[milkshakelake]

Let's say I have an existing concrete beam that I want to reinforce. If I add a layer of concrete under it with new reinforcement, the depth will increase. Let's say I dowel the new concrete into the existing beam with some epoxy and rebar. Can I analyze this as a regular concrete beam with the new rebar and depth?

I don't have a sketch or anything, and it's not a real situation. Just a thought bouncing around in my noggin.

 

[KootK]

We got into this a fair bit earlier in the year:

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Some of the salient issues to consider:

1) Stresses and deformations locked in at the time the reinforcing is undertaken.

2) Do the dowels connecting the new pour actually need to be lapped with the stirrups effectively.

But yeah, it can be done.

 

[BridgeSmith]

This is typically accomplished with post-tensioned bars or strands, so that the existing and new reinforcement both contribute substantially without yielding the existing reinforcement (and severely cracking the existing concrete) before the new mild reinforcement is contributing substantially. Otherwise, the beam has to be shored up while the new reinforcement is added, which is a tricky process. (How do you support the beam while casting new concrete on the bottom of the beam?) As long as you're doweling stuff in, why not just dowel in anchors for PT bars?

 

[milkshakelake]

KootK and HotRod10: Thanks for the ideas! It seems a lot more complicated than I thought, but those are good suggestions. Looks like I need to brush up on post tensioning.