Beam bearing by chipping 1½" into concrete column 1

[ajk1]

Is it safe to restore the connection of a rebuilt concrete beam in a parking garage, by chipping 1½" into the column for the 22" width of the column? The beam is lightly loaded (about 4000 pounds factored reaction) and spans 17 feet single span. The column continues above and supports a 8 storey building.

If we wanted to place a bond breaker on the 1½" horizontal surface, I suppose the surface should be first parged smooth, but what should be used as the bondbreaker (polyethylene sheet?), and how would it be held in place?

The concrete beam has been totally chipped out for its full length.

 

[JStructsteel]

I would say not the best detail. What will you accomplish by doing this?

 

[ajk1]

I agree with your comment, but the owner's technical director, who is a structural engineer and used to work for a structural engineering firm, has directed us to do this. I suppose he feels that the 1½" bearing of the beam on the column is a more reliable way of taking the beam reaction than Hilti adhesive anchors, and the slip sheet is presumably to prevent any concrete shrinkage movement of the beam from pulling off the column concrete from the 1½" wide supporting ledge.

 

[jayrod12]

is 1" of bearing enough, because that would be all I'm accounting for if they chip in 1 1/2". Either way that's a terrible detail.

 

[BAretired]

The detail is not a good one.

1. The column reinforcement is not protected from corrosion in the event of water ingress.

2. The concrete cover can break off from vertical load alone. It is unreinforced and cannot be considered an adequate bearing for a beam.



BA

 

[KootK]

I'd go with:

1) the bearing ledge, verified numerically.

2) no bond breaker as, unless you go with a fancy PTFE movement joint, it won't work worth a damn.

3) use copious drilled and epoxy dowels to keep the beam from pulling away from the column.

Client PM's that used to be structural engineers are the worst. I've got that on two projects at the moment. You'd think that they'd be structure friendly but, instead, they often just use their fading, arcane knowledge to bully the structural EOR extra hard.

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.

 

[ajk1]

To Jayrod12, BAretired, and Kootk:

You have all said it very well. Kootk's comments about the situation are what I am finding is happening. It seems not the wisest thing to retain a well known firm of professional engineers, and then direct us how to design. But that's life.

For client relations, I think I have to do what this man wants, but not rely on it; I will take all the load on dowels. Thanks for the moral support. It's nice to know from the 3 people on here whom I have come to trust the most, that I am not thinking completely irrationally and not senile (yet).

 

[KootK]

I recently stumbled upon this from Hilti Europe: Link. As far as I'm concerned, it's heads and tails above anything else I've seen with regard to how to design these connections rigorously.

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.

 

[wannabeSE]

KootK,
Thanks for the link. I will read it when I get a chance (or next time I need to post-install bars for a job). I was curious so I looked to see what Hilti USA had to say and found

https://www.us.hilti.com/rebar

 

[KootK]

And thanks for you contribution WannabeSE. I just got around to checking it out. Silly me, I had always assumed that post installed rebar would be equivalent to CIP rebar given the same development/anchorage lengths etc. If that was ever truly in question, I'm sure glad that someone got around to sorting it out.

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.