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.
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
RE: Horizontal CMU Cracking
RE: Horizontal CMU Cracking
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
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
Mike McCann, PE, SE (WA)
RE: Horizontal CMU Cracking
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
The sound will be lower at grouted cells.
Mike McCann, PE, SE (WA)
RE: Horizontal CMU Cracking
Vertical reinforcement can be retrofitted. I would consider this over having an epoxy crack repair to resist future seismic events.
RE: Horizontal CMU Cracking
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
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
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
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
RE: Horizontal CMU Cracking
Mike McCann, PE, SE (WA)
RE: Horizontal CMU Cracking
RE: Horizontal CMU Cracking
RE: Horizontal CMU Cracking
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
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
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
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