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Composite Beam Repair

Composite Beam Repair

Composite Beam Repair

(OP)
I have a theoretical question in regards to composite beam and deck design based upon a problem that recently popped up in the field.

We had a beam located at the perimeter of a building that was designed to act compositely with the slab above. During the shop drawing review process the distance from center line of beam to edge of slab was changed which required a 3/8” bent plate to be welded on the top flange of the beam. The fabricator mistakenly detailed the bent plate such that it covered the entire top flange of the beam. The shear studs ended up being welded to this plate rather than the beam top flange. The fabricator is now requesting a repair detail for the beam.

I don’t usually design these systems. The short answer would be to make sure the weld of the plate to the beam is sufficient to transfer the maximum shear force per shear stud (distributed across the length of the beam). Would this be an acceptable method?

RE: Composite Beam Repair

That is what I would do, provide as much weld as needed to match the shear stud capacity/spacing. I would also toss a bunch of weld at the ends becasue it feels right to me. Any splices in the edge plate?

RE: Composite Beam Repair

(OP)
dcarr

Anchoring the end of the plate seems right to me too (because it is done all the time when reinforcing beams) however I don't think it is necessary with the theory used in composite beam design (might do it anyway). I dug out the old AISC (14 edition because that one was within reach) and it appears as if I need to comply with equation I3-1c.

I know there are minimum thickness requirements for the material you attach the studs to. Do you know where they are in the AISC?

RE: Composite Beam Repair

I don't remember where the min thickness lives but I'm fairly certain that it's stud diameter/2.5. If you're developing the capacity of each stud reasonably near to each stud, you should be fine. As an edge beam, chord forces might be at play as well which makes a capacity matching scheme desirable.

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.

RE: Composite Beam Repair

(OP)
I wrote a spreadsheet for this about 10-15 years ago based upon the 9th edition AISC. In the spreadsheet I have the minimum flange thickness as the stud diameter/2.5.

I'm not quite sure what the beams are doing. Some of them are located in braced bays and are skewed to the orthogonal axis of the building. They almost look like they are being used for collectors but it is hard to tell.

RE: Composite Beam Repair

The relationship between stud diameter and flange thickness is given in Section I8.1 of AISC 360-10. The Qn term in Equation (I3-1c) is tabulated in Table 3-21 in case you are not familiar with it. Are you the Structural Engineer of Record?

RE: Composite Beam Repair

(OP)
Hokie,

I saw the table and it looks pretty straight forward. Unfortunately the AISC doesn't address phi or omega for this instance so I would need to need to be conservative with the weld size.

I am not the EOR. My client, the fabricator, asked me the question and if I would help them as the EOR is refusing to offer advice. I originally said no but they are continuing to ask for help and they are a very good client.

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