Acceptable Inward Bow in Basement Wall 5

[zero1238]

I have an 11 course masonry block basement foundation wall with a horizontal crack and it's bowing inward by 3/4". An engineer that I used to work for would suggest fixing any bow in a residential basement wall equal to or over 1/2" over its full height but I'm looking for where in the code books it discusses this. I've read online from multiple sources that the TMS 402 has a limit of 0.007h but I downloaded this text and can't seem to find this information anywhere in the book. Can anyone shed some light on this topic? 0.007h sounds correct but I can't seem to find it laid out in those figures in any of my code books.

 

[DoubleStud]

Let's forget about what the limit is for a minute. What are you suggesting to fix it? Most of the time the fixes people do are really to make the homeowners feel better, but it doesn't really fix the problem.

 

[zero1238]

Most times I recommend installing carbon fiber straps as well as redirecting runoff (grading/drainage) if hydrostatic pressure is the culprit.

 

[OldDawgNewTricks]

TMS 402 limits deflection to 0.007h under allowable stress level loads. The commentary says that a reason for this limit is that "a wall loaded in this range returns to its original vertical position when the lateral load is removed, because the stress in the reinforcement is within its elastic limit".

How old is the wall? Do you expect the problem will get worse with creep under sustained loading?

 

[zero1238]

It's from the 60's and was not built with vertical reinforcement so I do not see it returning to its original vertical position.

 

[Greenalleycat]

I think prescriptive limits aren't much use in a situation such as this. There is never a definitive answer as to what deflection is or is not acceptable. Context matters.

In this case, you've got an unreinforced vertical wall built in the 60s with a big crack across the middle and it's bowing 3/4"
Given that it's from the 60s this is not an "acceptable new construction yes/no" question
It's also presumably been accepted visually etc by the various occupiers as we are in 2023 and it's still like that

The question for me is more: is there a professional reason why we would recommend remediation?
Waterproofing could be a big concern but again, it seems that this crack is not new so presumably it's not pissing water or it would have been repaired by now
Structural stability is the other thing I'd be concerned about
An unreinforced basement wall with a big crack across it has very little reliable capacity and, while it has lasted 60 years so far, could just be one heavy truck or big rainfall away from a problem
Based on the limited info provided I would be recommending a structural repair and who gives a fuck what bow does or does not exist

 

[zero1238]

I completely agree with you. The reason for this post is that if a client's attorney wants calculations or evidence to back up my claim as to why I'm recommending repair, I want to be able to provide that.

 

[Greenalleycat]

Sounds like there is a lot of context missing that might help us to give more direct info.

I don't think there needs to be 'calculations' to back this up
An unreinforced whole section has a capacity based off concrete tension
This is unreliable and a brittle failure but is still a decent number
This wall has a big crack. An unreinforced crack section standing vertically only has capacity from axial load. This is very limited
A basement wall with low capacity is a potential life safety risk
Any engineer should recommend enacting a structural repair to the wall ASAP IMO

 

[zero1238]

That's basically what I'm getting at. The wall is 40' long, 11 courses tall with a crack 4 courses down from the top; 3/4" of inward movement over full height. It's got negative grading on the exterior side of the wall so it's more than likely a hydrostatic issue. No evidence of water intrusion but then again, it looked like it was recently painted. Flip house.

 

[Greenalleycat]

Are you acting on behalf of someone who purchased the property then found out that the flipper sold them a lemon?
I have no experience in how to approach that situation if so
My thoughts are, if you want to show them some numbers, run three cases

1) How you would design that wall now
2) What the capacity is of the unccracked wall vs case 1) - this may actually be higher but you can then talk about shrinkage etc as to why this is unreliable vs the reliable reinforced wall
3) What the capacity is of the wall after it cracks with no reo

At least that way you can demonstrate that you'll have like 5% of the capacity now that you had originally and that might put your client's concern into perspective
In terms of how it plays out legally though I have no idea
Was someone misled in terms of the sale or is this something that should have been picked up

 

[zero1238]

I'm working for the buyer and they are in the process of buying but they haven't closed yet; still doing their DD. And I think that's a good idea, I'm just not sure how to calculate the capacity of a wall after it cracks. Are there any resources for that?

 

[Greenalleycat]

Yea sure
The most basic would be just a gravity calculation with a lateral soil pressure on it
The bending moment at any point is just a rigid body rocking of two rectangles - above and below the crack
Your capacity comes from the self weight of the block above the crack
Axial load from the floor above etc could help too, but also could hinder if it's not able to load in a stabilising manner

If you require earthquake considerations then there are dynamic rigid body calculations out there but I think that would be getting too complex for this situation

 

[OldDawgNewTricks]

I wouldn't even go there. Not worth the risk, especially when attorneys are already involved. TMS says unreinforced masonry members shall be designed to remain uncracked. That should be evidence enough for the attorney.

 

[Tomfh]

Deflection limits are generally for serviceability and aesthetics. You have a more fundamental question which is whether the wall is structurally adequate. From the sounds of it it could be failing.

 

[SWComposites]

So, what does the buyer want to do?
And what is the bloody attorney going to do with calculations? Check them? Don’t think you want the calcs sent to the seller.
If the buyer wants the wall fixed, then they need to negotiate that before closing.

You could assume a conservative wall pressure load, then assume all the load is applied to the wall below the crack, as a pure cantilever with foundation base.

 

[zero1238]

All good points. I'm going to keep it pretty simple for the attorney's sake. I think less is more in this situation. Also, where in the TMS does it say that all unreinforced masonry members shall be designed to remain uncracked? I can't seem to find that in the text.

 

[OldDawgNewTricks]

8.2.2 for allowable stress design or 9.2.2 for strength design.

 

[zero1238]

I may have a different version. 8.2.2 in mine is flexural strength of unreinforced AAC masonry members and doesn't discuss anything about remaining uncracked...

 

[OldDawgNewTricks]

You seem to be using the 2011 edition? Is that still the legally adopted code in your jurisdiction? If not, I wouldn't recommend citing an outdated code to the attorneys.

In the 2011 edition, look at 3.2.1.3.

 

[zero1238]

Currently I’m using 2011 but I’m trying to get my hands on 2016. Not planning on citing anything until I’m able to get my hands on the latest digital version but I just wanted to make sure it was something that was covered in this text before I shelled out the money for a newer version. Thank you for the reference!