Concrete Pier Cracks at Beam Bearing

[RFreund]

I'm looking for ideas to what might be causing the concrete cracking seen in the photos below. There are near vertical cracks at the end of the beam, about 8" past the face of the support. I can see into the right side (worst looking side) and the faces of the concrete are very smooth. I'm assuming this is a construction joint. No bars can be seen crossing the joint. Some of the cracks appear to be somewhat fresh and others look older. The building was constructed about 10 year ago. However, they just observed these cracks early last spring. Although they admit that they may have been there before (not sure). I ran some rough numbers there is about 9.1kip /ft (factored) and the beam is about 20 feet long. The bearing area is about 8" x 14" (14" wide beam) which comes out to less than 1ksi 'bearing pressure'.
My thoughts (also see pdf notes in the link below):
It looks like this beam was poured after the walls were poured, so they are not integral with the pier. There is no horizontal reinforcment that extends into the adjacent wall. Therefore the beam shrinkage and thermal movement has caused the cracks. The vertical pier reinforcment on the left side of the pier extends up into the beam. This reinforcment is "going along for the ride" and contributing to some of the cracking at bearing. Water getting into the crack and freezing which is contributing to larger and larger cracks.
My issue with this is - why would it be cracking now? Why was this not an issue right away?
There is some sort of discoloration to the concrete near the bearing points. What would this be from?

PDF Notes HERE

Photos:

Thanks for any thoughts. I will try to pay it forward.


EIT

http://www.HowToEngineer.com

 

[XR250]

Overall foundation shortening due to shrinkage showing up at the weakest point?

 

[Ron]

Under-reinforced for shear and lack of spirals/spacing in the column.

 

[JAE]

The one on the right appears to me to be a concrete pier/ledge that the beam rests upon - but only for a short distance to the end of the beam.
The end of the beam is the very vertical joint.

The cracking below appears to be a classic concrete bearing failure - probably exacerbated by inadequate rebar - or incorrectly placed rebar as Ron suggests.

The problem also might be made worse by longitudinal beam shrinkage (is this prestressed?) which adds a horizontal force component to the bearing condition.

The discoloration on the left looks to be an old grout patch of some sort.

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[Agent666]

Looks like it's possibly a precast beam/lintel to me, most likely designed as simply supported & would be consistent with the fact that you think there is no reinforcement going further into the wall across the crack at the end of the beam, which you would expect if it was cast as being monolithic with the walls beyond.

As far as the crack on the right, agree with the others, it's either a bearing failure in the corbel supporting the beam (possibly made worse by a horizontal tension from the restraint of shrinkage or differential settlement) or alternatively the column may have been pushed outwards by a vehicle impact in the past. You could get it scanned to confirm the reinforcement that is present as this will no doubt aid in determining the cause and a likely fix (I assume the post is just a temporary measure by the looks of it).

While the average bearing pressure might be low, if it was a precast beam it could have been sitting on a shim with a much higher bearing stress combined with inadequately grouting any gap.

 

[Tomfh]

Shrinkage and bearing.

 

[RFreund]

Thanks I appreciate all the thoughts. We are getting it scanned.
Regarding bearing failure - I'm not sure the best way to check that. Meaning, there really is no corbel, so it wouldn't really be different than a point load on a wall. My understanding is that this is not a precast beam, or wasn't supposed to be according to the original drawings. But my inclination is that at some point it was likely changed to a PC beam. I'm thinking some that there should have been some allowance for horizontal movement at the bearing location. It just seems odd that this didn't show up earlier. Also, I'd have to beleive that the horizontal force is what cause most of the cracking in the pier and then the vertical bearing force just made things worse. If it were appropriately detailed for horizontal movement, I'm inclined to think that all would be well.


EIT

http://www.HowToEngineer.com

 

[TehMightyEngineer]

Look at PCA Notes on ACI 318-11 example 14.2: shear-friction design (inclined shear plane).

This is the exact failure you have.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)
American Concrete Industries

https://americanconcrete.com/

 

[RFreund]

@TME - thanks for the reference. Your exactly right. Given the loads though, it just seems odd that it's happening. But then again, I haven't gone through the calcs.
One way that I can justify it (intuitively), is considering the shrinkage and thermal forces. The only issue I have there, is that I would expect to see this almost immediately. And maybe it did occur immediately, but the cracks were much smaller.

EIT

http://www.HowToEngineer.com

 

[RFreund]

Some further notes for my future self if I refer to this:
Shrinkage force: Use PL/AE, with shrinkage calculated as 800x10^-6 in/in at the higher end, 300x10^-6 at the low end, as ball park. Refer to AM Neville
Coefficent of thermal expansion: about 5.5 x 10^-6, varies with aggregate though. Gravel is 6.0, limestone 3.8 (Here)
AM Neville gives 7.3 for gravel and 4.1 for limestone.
Use these lateral loads applied to the wall parallel to the beam. Then look at the issue similar to an anchor (bearing plate anchor) subject to the applied load as a shear force parallel to the beam. Or look at it as shown in ACI notes when evaluating the reinforcment design.

EIT

http://www.HowToEngineer.com