Reinforcing Existing Concrete by Bolting on Steel

Question

Reinforcing Existing Concrete by Bolting on Steel

fp23 (Structural)

(OP)

2 Aug 24 18:11

Can you bolt steel to existing concrete and use it as tension reinforcement? Or do you have to use something like FRP that is continuously adhered to the concrete? I don't do a ton of advanced concrete design but I'm wondering if there is code justification for something like the attached repair sketch when a concrete wall needs to be cut for a new window opening.

fp23 (Structural) · Answer 1 · 2024-08-02 18:18:17

A couple other thoughts: in this condition soil pressure is acting out of the page so the plate is on the tension face of the concrete, I would also have them fill the bolt holes in the steel plate with epoxy so that there's no space for the plate to slip before the bolts are engaged.

icebloom (Structural) · Answer 2 · 2024-08-17 01:38:19

You could try looking through texts or standards on composite structures - your situation looks analogous to a composite beam, i.e. steel beam below concrete slab with shear studs where the steel component is predominantly in tension and your concrete slab in compression. An approach would be to drill and epoxy some anchors into the concrete to provide the longitudinal shear transfer, however you'd encounter issue where the hole in your steel strap is oversized for the anchor installation, so you'd need to fill this hole somehow to get full engagement. HILTI filling washers or similar come to mind.

FRP is more commonly used for these kinds of things though as it avoids the issues above.

TRAK.Structural (Structural) · Answer 3 · 2024-08-17 14:55:36

I think you could run the calcs to justify this type of approach. I would do a transformed section analysis and make sure you have the shear flow accounted for, as well as providing adequate end anchorage and enough length to get beyond where you have high tension that you are trying to resolve.

cliff234 (Structural) · Answer 4 · 2024-08-17 15:15:35

I’ve reinforced walls in a manner similar to what’s shown in your sketch, however if this wall is an exterior wall with wind blowing in either direction, you’ll need that tension strap on both sides of the wall. Is that acceptable to the architect? (Otherwise the reinforcing will need to be more substantial than a tension strap.)

fp23 (Structural) · Answer 5 · 2024-08-20 19:40:40

Thanks for the responses!

Icebloom - The composite steel analogy is a good one that I hadn't thought of. I also didn't know about the HILTI filling washers but those look cool for future use.

cliff234 - Since there is soil up to the top of concrete I'm not too worried about wind loads in the other direction. There are some that need to be resisted but they are really light since there's only 2' of trib area and soil loads resisting them.

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Reinforcing Existing Concrete by Bolting on Steel