Existing Attachment to Concrete Encased Beam

[Teguci]

I am designing a support structure that will be attached to a modified concrete slab. I have raised concerns with the existing slab conditions (I am not the EOR and it is specifically exempted from my review), but wanted to get other opinions as well.
1. Do you think this is an effective detail for anchoring into the side of concrete encased beams? If not, what is the failure mechanism that should be checked.
2. Would you have a problem putting another 2,000 lbs of load through this connection? What numbers would you check?
2. What detail have you utilized to support into concrete encased beams?

The modified decking is upside down B-deck with lightweight concrete that is reinforced with WWR. No rebar is developed between the two slabs. The existing flat slab is 4" deep with a 2" topping conventionally reinforced with #4 at 6". The observed concrete encasement, with notable exceptions, is in decent shape.

 

[jayrod12]

I would be requiring removal of the encasement to make a real connection between the steel members. I don't like that detail one bit.

 

[KootK]

I don't love it but, for smallish loads, I'd be inclined to try to justify it as is so as to keep costs in check. I imagine that the concrete encasement currently is, among other things, the fire proofing for the steel beam. Possible concept below.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

@KootK - I'm with you on the smallish loads, I just can't put my finger on why properly substantiated large loads wouldn't also be acceptable.

The bolted connection to the W8 is slotted, so no axial load should be expected from the beam. However, the lateral restraint could come from the supported slab?

The anchors are expansion anchors.

 

[jayrod12]

I may be wrong in how I see it but wouldn't there have to be an ability to have axial loads through the new connection. Otherwise the loading scenario would have to be so low that the stress in any tension ties must be lower than the tensile capacity of the concrete encasement.

 

[KootK]

The anchors are expansion anchors.

I didn't realize that the stuff between the two beams was existing too. My bad.

I just can't put my finger on why properly substantiated large loads wouldn't also be acceptable.

I was actually thinking that 2kip was a comfortably smallish load.

The bolted connection to the W8 is slotted, so no axial load should be expected from the beam. However, the lateral restraint could come from the supported slab?

I may be wrong in how I see it but wouldn't there have to be an ability to have axial loads through the new connection. Otherwise the loading scenario would have to be so low that the stress in any tension ties must be lower than the tensile capacity of the concrete encasement.

There are a few possible path available and none is particularly wonderful or easy to asses.

1) Weld the connection so that axial can be transmitted.

2) Use the slab above in compression as Teguci suggested.

3) Take the lateral "kick" back into the beams/slabs via some version of anchorage / concrete in tension (sort of jayrod's concept I think).

4) Deal with things as straight torsion in the steel and/or concrete beam. Much depends on the torsional capacity of beam end connections of course.

5) Deal with things as torsion in the beam that quickly becomes moment in the slab. The suggested detailing isn't great for that unfortunately.

If any of that appeals to you, let me know and I'll help work it through.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.