Concrete Pier Foundation Cracking 5

[acer49]

What can cause this type of cracking? My first guess is lack of adequate shear reinforcement or some eccentric loading based on the anchor bolt/column configuration. The piers were constructed in 2009 and designed by someone else. Piers are 5'-0" in diameter with #4 ties at 12" O.C. vertical reinforcement is (8) #7 rebar equally spaced.

Also, have no concrete pour data, break reports, foundation specifications, or soil data available.

 

[acer49]

I forgot to add that the shear reinforcement is a single #4 tie 3" from top of concrete.

 

[WARose]

Piers are 5'-0" in diameter with #4 ties at 12" O.C. vertical reinforcement is (8) #7 rebar equally spaced.

That's not even 0.5% steel. Not good. (In fact, it's just below min. temperature steel.)

I forgot to add that the shear reinforcement is a single #4 tie 3" from top of concrete.

I typically have 2 close to the top. Also not good.

 

[Michel60]

Check for construction joints/cold joints near the top of the pier. That looks like the vertical reinforcing is being developed.

 

[acer49]

@WARose yes, I provide (2) #4 for shear reinforcement and just checking the 0.5% what they provided is 0.727 in^2/bar and what is required is 1.01 in^2/bar.

Is this foundation repairable or should it just be replaced?

 

[WARose]

Is this foundation repairable or should it just be replaced?

I'd say can it. I don't see how it can be justified. (Especially considering the anchor location.)

 

[KootK]

Another idea to add to the heap for consideration. Such a short piece ought not accumulate much thermal strain and I'd have hoped for a little slack in the bolts. Of what can be seen, that beam at the bottom is the only thing that strikes me as odd.

What is this thing? Why does it have such a beam at the bottom?

 

[acer49]

There are (6) in total with this double column configuration and all are cracking similarly.

 

[Ron247]

Is that an electrical ground wire?

 

[acer49]

Yes, that is an electrical ground wire. This is in a electrical substation.

 

[hokie66]

KootK has the answer. This is essentially unreinforced concrete trying to resist prying by the steel base connection.

 

[wiktor]

What are the loads on the steel columns? And how deep are the piers?

 

[acer49]

Wiktor, I'm trying to get the column loads and the piers are 13'-0" deep.

 

[KootK]

Sweet... I've been trying to earn a star from an Aussie for the better part of a month now.

 

[hokie66]

Don't call me an Aussie, I just live here.

 

[acer49]

All, so the vertical reinforcement is actually (18) #8 rebars spaced equally. But, only a single #4 tie for shear reinforcement. Which meets the 0.5% so do you think the thermal expansion is still the case because of inadequate shear reinforcement?

 

[KootK]

1) I don't see the ties helping much at all IF thermal expansion is the issue.

2) Depending where you're at, I sort of imagined things unfolding like this:

a) develop initial cracks that let water in.

b) water freezes and gradually jacks the crack apart wider and erodes the edges smooth at the top.

 

[azcats]

What's the rest of the structure look like above where you've shown?

Depending - I'm on board with that short beam acting like a fulcrum to jack the two sets of anchor bolts apart.

 

[Brad805]

How large is the bent atop the foundation and is the thermal loading plausible? That looks like about a W6x15 near the bottom, and the columns do not appear much larger. What might be the anticipated temp change? Some of those cracks look like they are 3/8" wide.

I would be curious to know if someone might have been doing their own thing with the rebar, or if something changed and we have a cap region with much different reinforcement near the top. It would not be uncommon to pour a cap region since setting anchor bolts accurately on a pile is not as easy.

 

[jayrod12]

Also, and this information may not be available, when was the steel erected and when were the cracks first present.

Because it would really lend confidence to thermal expansion causing this if it was installed when cold and the cracks showed up when warm.