Spalling Concrete

[CivilStructuralPE]

I have been asked to give a possible reason and repair for the concrete spalling in the attached photos. I have asked for the concrete reports, but do not have them yet. I am looking for some general thoughts on what might be going on here. This job is located in the north, and was winter construction. My first thought was freezing issues, or under consolidation or delamination. Thanks.

 

[hokie66]

The anchors seem to be very close to the edge of the wall. So temperature change resulting in shortening of the steel beams would highly stress the unreinforced concrete around the anchors, resulting in the spalling.

 

[jayrod12]

I'd tend to agree with hokie on this one.

 

[JAE]

I thought of that as well but hesitated because the spall is off to the right of the beam - the bearing plate below the beam would be the thing that would be pulled and it seems as though the distress would be at the bottom of the beam rather than the side.



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[jayrod12]

On the first picture yes it does not necessarily look like anchor bolt cover. However on the following pictures is consistent with hokie's thoughts

 

[KootK]

It appears as though these embedded plates have seen some welding. I have had issues in the past with limited cover studs when welds to the embedded plates have caused thermal expansion of the plates and subsequent spalling. This seems especially plausible for the second photo which appears to be of wet cast embed plates used for deck attachment.

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[JAE]

Well I failed to see the second and third photos - those do suggest some thermal pull from the beam or perhaps heat from welding popping off the cover.


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[EngineeringEric]

How would you guys detail this so it doesn't happen? Besides two anchor bolts in the center of the wall..

As for the repair. assuming you don't need the concrete strength for uplift you can probably just use a SIKA spall repair mortar mix. For shear you can look at each side working to transfer all the load, not as a group of embed four anchor bolts. if that doesn't work then you need to attach sleeves to the beam to (say angle with leg down on one side and plate on other both pressed against concrete wall) then through bolt the two sleeves tying it to the wall.

 

[CivilStructuralPE]

Thanks for the replies. I am going to specify SIKA for the spall repair, and add a channel toed out with a cap plate under the beams, with epoxy anchors into the wall below the spalled area. The beams are not girders, but secondary members, so the reaction is not high.

 

[KootK]

Much depends on whether or not you need to transfer axial loads in your beams to the walls. I like two anchor bolts centered in the walls.

For the beams, if axial loads do not need to be transferred, I like to bolt the beam to the embed plate with threaded studs. This eliminates field welding and gives you an opportunity to include long slotted holes to, hopefully, allow thermal stresses to dissipate through slip. If no axial loads need to be transferred, your beam connections are probably just simple bearing connections and the studs behind the spalling can be sacrificed. Just clean it up with SIKA as you've suggested.

For the connection between the deck and the the top of the wall, you can check to see if the embeds will transfer the deck shear using only the studs that have not spalled. If there isn't enough capacity, you could add a deck support angle to the face of the wall. Depending on whether or not your roofing is in place, you may have to connect to the deck from the underside. Either way, I'd ignore the capacity of the studs behind the spalling unless you're willing to chip out the concrete behind the stud and create a repair that is more than a cosmetic fix.

For all of the photos, it wouldn't have hurt to have had some wall rebar outboard of the studs. Maybe the walls are 8" with only one central mat, I'm not sure.

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[jike]

1st photo with the spall off to the side (ending at the vertical form mark) looks like it might be related to removing the form (insufficient form oil). I cannot see any microcracking under the beam bearing. Note also that bearing plate does not extend beyond face of wall. Unless the top of the wall is restrained by other construction, I doubt that shortening of the beam would cause this crack. It most likely would pull the top of the wall if the beam is sufficiently anchored.

2nd photo is that of exposed studs or anchors for deck bearing. Normally, we would like a layer of rebar between anchors and inside face of wall (none is evident in this photo).

3rd photo shows beam bearing plate hanging over edge of wall. I would suspect beam rotation putting excessive stress on the face of the concrete which would cause spalling. Note that there is, once again, no inside face wall reinforcement outside of the anchors.

 

[jike]

It does look like the depth of the pockets are not sufficiently deep. What is the thickness of the wall?

An alternate connection might be a vertical embed plate with anchors that beam clip angles can be welded to. Clip angles should have bolted slotted connections to the beam for field adjustment and reduction of eccentricity due to beam rotation.