Concrete cracking in basment wall corners

[shobroco]

I was asked to review an existing house basement (40 yrs old +/-) that has cracked full height vertically at the corners. I have never seen anything like it because they look like shrinkage cracks, but rather than occuring at the centre of the walls, or at some windows, they are in the corners. There is no displacement, there are no other cracks, I'm sure there is no reinforcement, and I can't come up with a reason for the cracks. The walls are not terribly long, 30' X40' or so. Any ideas?

 

[shobroco]

Sorry, should have previewed. I do know how to spell basement.

 

[rowingengineer]

How about a photo or two, without something more i would be guessing

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[rowingengineer]

Also is this a brick wall?

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[shobroco]

Sorry, photos are on another computer but attached is a quick sketch. The basement is poured concrete, the 2 storey dwelling is wood frame with brick veneer. The cracks are not the typical short diagonal cracks on the corners where the brick veneer breaks off the concrete because the dampproof course wasn't continuous around the corner, these are full height, through the wall cracks, appearing to be a result of shrinkage except that I've never seen them in the corners before, usually at mid-length, or from the corner of a window.

 

[hokie66]

Construction joints? Maybe they cast the walls separately?

 

[chicopee]

How much of a gap do you have? Do all corners have cracks? does it appear to be old cracks (check for sign of dust and debris to tell)? Was the second floor added later on?

 

[shobroco]

The cracks are not joints, although they are more or less vertical & within 4" or 5" of the corners for the full height. They are not new, probably more than 20 years old & possibly as old as the house. They pre-date the present owners. They occur at 3 of 4 corners (not at the garage) and the width is pretty consistent at 3-4 mm top to bottom. There have been no major alterations to the house; it was built as a 2-storey. Someone convinced them a few years ago to dowel into the walls & pour pilasters under the ends of 2 steel beams that sit on the long walls; for what I don't know. The walls are plumb & the cracks are nowhere near the beams, the beams are well-supported and they provide some lateral support to the walls. I think it was a case of "They'll pay for it & it looks like I'm doing something".

 

[cooperDBM]

If they're possibly as old as the house they could still be shrinkage cracks. They can occur at corners with the wall shrinking towards the center, particularly if the beams are holding the wall in place. Could the wide crack width just be near the surface due to deterioration and seasonal ground movement (drying or freezing)? In other words a tighter crack at mid-depth of the wall. Are they leaking? That could also widen a crack over a long time.

 

[a2mfk]

Based on the locations of the cracks, the consistent width of the cracks throughout the height of the wall, the length of the walls which have no control joints or reinforcement- not sure what else this could be but from shrinkage.

 

[grantstructure]

I'm going to vote shrinkage cracks, and theorize that the lack of reinforcement is what makes this crack location look odd to us. Corner bars and horizontal steel is probably what keeps all our walls from cracking right there.

 

[shobroco]

I believe from the appearance they are shrinkage cracks, but I thought maybe someone had a different idea or had seen something similar with a definite cause. Thanks.

 

[McSEpllc]

I have seen this type of crack in new residential masonry construction. The walls have no horizontal reinforcing. The contractor braced the top of the wall during back-filling - but not the corners, going with the assumption the wall braces itself at the corners. Even though the block is grouted solid, only 6'-8" high and back-filled with washed stone, the CMU cracked through every second block. A compactor was used to consolidate the washed stone.

Eric McDonald, PE
McDonald Structural Engineering, PLLC