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Horizontal CMU Cracking
3

Horizontal CMU Cracking

Horizontal CMU Cracking

(OP)
I have got a 20'x30' CMU building that has some significant horizontal cracking on the east wall. The walls are 7'4" tall and contain NO vertical reinforcement or grouted cells. There is a horizontal bond beam halfway up the wall according to the as-builts, but I have been unable to confirm this. According to the owner the cracking occurred all at once, around the time of a large earthquake. I had the foundation surveyed and confirmed that some foundation settlement has occurred at the east wall. My concern is that if I suggest the foundation be jacked to close the cracking and fix the settlement, the building still has no, or very little, ability to resist another seismic event. Is there an epoxy that could be used in the cracks that would increase the lateral resistance? Are there any other suggested fixes? Below are some more details on the cracks and there are a couple pictures attached.

The south wall at the east end of the building has a large horizontal crack, three courses from the top that wraps around to the window on the east wall. Crack starts in the middle of the block nearest the door latch and steps up to the corner, widening to approximately 3/8”. On east wall, crack remains horizontal to window with width varying from 3/8” to 1/4”. The top 3 courses at this corner have shifted between 1/8" and 1/4" to the south.

The east wall has a horizontal crack above the second course that spans most of the length of the wall with a width between 1/8” and 1/4”.

The east wall has another horizontal crack that starts above the fifth course near the middle of the wall. Crack increases in width to between 3/8” and 1/2” at the northeast corner and wraps around to the north wall.

RE: Horizontal CMU Cracking

An FRP exterior wrap could help, but I would also be concerned with the external un-tightlined (assumed) downspout and any undermining to the foundation that may have occurred prior to the seismic event.

Just for the record, where is this building, and how strong was the tremor?

And, being a restroom facility in possibly a remote area, it should have had an original importance factor of 1.5. (just kidding)

Mike McCann, PE, SE (WA)


RE: Horizontal CMU Cracking

(OP)
The back side of the building does not have a gutter and the downspout you are referring to doesn't lead very far away from the foundation. So it is possible that the soils have eroded away over time. It was built in 1980.

The building is located in the Oklahoma City area. At the beginning of September this year there was a 5.8 that hit about 75 miles away.

The general notes call for vertical reinforcement and grout filled cells at 32" O.C., but I was able to visually confirm that it was not done that way. I have a feeling that the whole thing was empirically designed.

RE: Horizontal CMU Cracking

Personally, I feel that the seismic force seen was just the straw that literally broke the camel's back.

Mike McCann, PE, SE (WA)


RE: Horizontal CMU Cracking

For the issue of whether there are vertical bars in grouted cells, sometimes simply drilling a series of small holes in the center of the cells (8" o.c.) can tell you at least what rhythm of grouted cells may exist.

If there are NO vertical bars, then perhaps there should be given the seismic activity but depending on the location it may or may not be required. You could simply do a design check to see if the empirical design meets code or not.

If you need reinforcement and there is none, then there is the technique of knocking out the face shells of the blocks every X inches o.c. and inserting vertical bars and grouting solid.
That might solve the wall flexural and shear conditions but you still might have problems with anchorage to the footing and roof-wall anchorage.

As far as the cracks go, you could use helical piling to stabilize and perhaps jack the footings back into place. Sometimes those cracks do close but if debris exists in some of the cracked areas the cracks may not close evenly or at all.

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RE: Horizontal CMU Cracking

You should be able to ping the cells with a hammer to see if they are grouted at 32 or not vertically.

The sound will be lower at grouted cells.

Mike McCann, PE, SE (WA)


RE: Horizontal CMU Cracking

GPR will tell you if the cells are grouted. If grouted, it will tell you if there is rebar in them.

Vertical reinforcement can be retrofitted. I would consider this over having an epoxy crack repair to resist future seismic events.

RE: Horizontal CMU Cracking

2
I just joined a team member on a project from another firm who had a small IR device that attached to an iPad and allowed you to see, and take IR photos of, masonry walls.
The IR image, depending on the current state of temperatures in the wall, can sometimes show you fully grouted cells as well.

The camera can be seen here: http://www.flir.com/flirone/ios-android/ and works also on Android phones. Only about $300.
(I'm not affiliated with this company at all...just was amazed at the cost here as most IR cameras can run $10k or more.)

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RE: Horizontal CMU Cracking

Mike beat me to it. Go old-school and use a hammer. I had to use my very technical umbrella to test for delaminations in a slab today - worked like a charm.

Ron is right as well - GPR would definitely tell if there's rebar. (To the tune of a crapton of money, unless they're available for rent!)

I like the drill a hole idea but if you miss slightly, then you don't know.

Either FRP (on both sides) or retrofitting rebar is also done a lot, but like folks said, get that foundation sorted out first.

And JAE - I'm totally getting one of those IR things! Cool!

Please remember: we're not all guys!

RE: Horizontal CMU Cracking

update - I just asked a friend who does IR stuff all the time and she seconds the FLIR thing. She's had one since 2008 and it works really well.

Please remember: we're not all guys!

RE: Horizontal CMU Cracking



This is an IR image we took of a masonry wall at Jacksonville Beach, FL. It shows the majority of the cells to be filled as specified, but some were not.

So yes...IR can be used to check the location of filled cells, provided it is done at the proper time to get a prominent temperature differential.

RE: Horizontal CMU Cracking

Quote (Ron)

This is an IR image we took of a masonry wall

What brand & model IR camera do you use, if you don't mind sharing?

OP - sorry for the 'hijack' of your thread.

RE: Horizontal CMU Cracking

The OP said he had determined that there was no reinforcement or cell grouting. Sounds like this is just stacked up blocks.

RE: Horizontal CMU Cracking

Correct Hokie. So I have to assume that since he determined that visually, he saw no vertical rebar or grouted cells in the horizontal cracks...

Mike McCann, PE, SE (WA)


RE: Horizontal CMU Cracking

Yes, Mike, I was just wondering why everyone was trying to help him determine what is inside the wall, when he already knows.

RE: Horizontal CMU Cracking

Nice. Can you distinguish the bars as well with IR, or only grouted/ungrouted cells?

RE: Horizontal CMU Cracking

Hokie66...yes, the OP knows the existing condition; however, he/she will need to remediate the defective condition and the noted methods would then be used to verify the repairs.

Ingenuity...I have a FLIR T360 IR camera. I've had it for about 8 years. Prices have come way down since then. You can get comparable FLIR model now for about $12k. Many smaller models available for $2k to $5k. Key to getting a good image is timing! Hitting the right temperature differential is sometimes difficult and also sometimes requires shooting at night.

RE: Horizontal CMU Cracking

(OP)
Yes, because of the size of the cracks I was able to look into every cell for a 5' section of wall starting at the corner and visually confirm that none of the cells contain grout or reinforcing. The attached picture is the corner cell.

I've had GPR done on some projects in the past with varying degrees of success. I like the idea of IR though. I'll have to check that out next time I need to locate rebar.

JAE, I like your suggestions. Use helical piles to bring the foundation up and close the cracks. Then knock the faces of the block off and insert reinforcing. I would think that while the wall is opened up I could dowel some bars into the footing. There is supposed to be a bond beam at the top course with anchors to the top plate. I should probably confirm that.

RE: Horizontal CMU Cracking

Question to Ron:

Some older CMU structures have cells filled with Vermiculite for insulation (for whatever it was worth).

That being the case, how would the infrared picture for the vermiculite filled cell vary from a mortar filled or unfilled cell?

Just wondering...

Mike McCann, PE, SE (WA)


RE: Horizontal CMU Cracking

M^2:

also vermiculite filled for fire resistance... often need 2 hours and 8" CMU only 1-3/4 in these environs... Vermiculite filled can give you 4 hours...

Dik

RE: Horizontal CMU Cracking

Mike....The cells filled with vermiculite will show differently than the the solid concrete fills....in short, can still determine the grouted cells.

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