Crack in non-load bearing block wall and out-of-plane movement
Crack in non-load bearing block wall and out-of-plane movement
(OP)
Please see the attachment which illustrates the following preamble and question.
A reinforced building built in the mid-1950's had a stair down to the parking garage floors added to it in the mid 1990's, by adding steel beams under the parking garage waffle slab floor and dry packing them tight to the ribs of the waffle slab, then the opening for the stair was cut into the floor, and then the block wall was built (I am assuming that is the order in which it was done).
Recent examination found that there was a vertical crack in the north block wall enclosing the stair, and there is out-of-plane movement across the crack (see attachment).
Examination of the crack with a magnifying glass did not reveal any paint in the crack, indicating that the crack was most probably not there at the time of the last painting, although we do not know when it was last painted. Unfortunately the wall was not examined before the current remedial work was started.
The crack is quite vertical. The crack is visible both sides of the wall. There is also cracking of the paint around the sides of the landing (the landing is the P1 floor itself) where the wall paint overlaps the landing floor paint.
The bottom course of back does have some diagonal cracking and spalling of the face shell on the stair landing side.
Recent remedial work to the garage floor involved removal of the existing 2" thick mastic and 1" thick concrete topping. A front end loader was used to push around the broken up mastic and topping and pile it up and take it away. There is no sign of the wall having been impacted though.
1. Would beam deflection result in a vertical crack, or is it more likely to cause a diagonal crack?
2. What would cause out-of-plane movement at the crack?






RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
Great question. If it were a longer wall and I didn't know the history, I'd probably be looking at shrinkage restraint cracking for a vertical crack. That doesn't make sense to me here though. There are cases where a flexural crack can be vertical. If the cantilever dimension is short enough relative to the height of the wall, the load can probably arch down to the nearest support and a common flexural-shear combination crack may be precluded.
I was thinking that the corner would have been lifted and dropped repeatedly via the mechanism depicted above.
The mechanism described above would lift the east wall and rotate the south wall as well. Is there anything to report at the west wall? And where abouts is the door into the shaft?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Crack in non-load bearing block wall and out-of-plane movement
The door into the shaft is in the west wall, at its north end.
The block cracking is only in the north wall.
My feeling is that the crack has something to do with deflection because the crack I believe gets a little narrower at the top of the wall than at the bottom. Also, if the wall deforms as per your drawing, I would expect that this would cause the the portion of the wall to the west of the crack to be displaced northward relative to the portion of the wall to the east of the crack. The opposite is what I see on site.
Other thoughts are that if they grouted the top of the wall tight to the underside of the first floor above when they built the wall, that some of the weight of the first floor eventually would come onto the wall due to creep, although perhaps not since the floor was 40 years old when the hole was cut. But the weight of added tile first floor finish etc. might have come onto it.
Also, the steel beams were connected with Hilti HSL bolts to the concrete columns. HSL bolts have a fair bit of play until the bolt shank come into bearing against the sleeve of the bolt.
Perhaps the out-of-plane movement is just due to instability of the wall once the crack forms.
Although it is the appropriate practice to find the cause of a problem before designing a repair, I am doubtful that a clear cause will be found in this case. Since the garage has to be put back into use by the end of the month, I have to get on with the repair. The owner's technical rep says to just repair and monitor. I don't know though if he will then blame us if it cracks again.
It seems to me that there are 2 options:
Option 1: Make good the masonry and monitor. Repair perhaps by taking the blocks each side of the crack out and rebuilding it. I would discuss with the contractor if he can do this neatly.
Option 2: Introduce a vertical control joint at the crack location and also make sure that there is a deflection gap at the top of the block by raking out any mortar there and installing a flexible caulking/insulation meeting fire barrier requirements. This would also require adding lateral support clips at the top of the wall. This too should be monitored I suppose.
What do you think?
RE: Crack in non-load bearing block wall and out-of-plane movement
Before doing anything, I'd be tempted to go stand inside the shaft while someone drives a heavy vehicle around it.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
Front end loader story seems perfectly plausible too though.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
RE: Crack in non-load bearing block wall and out-of-plane movement
Truly, it's not out of the range of possibility. Oil's over, I've been flirting with forensics for years, and there are some things that I just really miss about America. You just can't go back to CFL once you've had the real thing.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Crack in non-load bearing block wall and out-of-plane movement
But at least the localized damage to CMU right at the landing sure looks like it got hit to me, similar to what Ron has suggested. I see damage that looks very similar to this in street-facing CMU fence walls all the time where I live (drivers here suck).
RE: Crack in non-load bearing block wall and out-of-plane movement
Yes Mr Hershey I think you and the others who have suggested that the wall has been impacted are right. I looked along the length of the the base of the wall yesterday and the wall at the base can clearly be seen to have been displaced 1 mm± laterally southward. This is similar to the displacement that we saw across the vertical crack. Also the owner's rep said yesterday that the damage to the wall was not there before the current garage work started earlier in the year. Whether the vertical crack was caused by impact is a bit of a question, as it is narrower at the top than the bottom, but I suspect it was caused by impact, since beam deflection would most likely cause diagonal crack.
Since the wall relied on return walls at each end for lateral stability, and has a gap top and no lateral support clips, and lateral support clips are not easy to add at the top because the top of wall is accessible only from the stair flight side, what should we do with wall? If we scan the wall and find hor reinf like Blok-Lok in joints, can we just rout out the crack each side of the wall and fill it with a cementitious mortar? If there is no hor reinf, do we have to add lateral support clips at the top?