Laterally Supported Foundation Wall- Part 2

[BigBakwas77]

I posted a query two years ago regarding concrete foundation walls which are not considered laterally supported if the top end is not reaching the floor diaphragm. (

https://www.eng-tips.com/viewthread.cfm?qid=451821

) I have just thought about a solution where by the wall studs are extended up to the top of foundation wall as shown in the attached sketch. If the wall studs are designed to carry lateral force exerted by the foundation wall, will it then be considered laterally supported? If yes, then the would the stud to floor joist connection be acceptable as shown in the sketch?

 

[jimstructures]

What part of the word Hinge do you not understand. There is a pinned hinge located at the top of the masonry foundation and the bottom of the stud wall.


Jim

 

[phamENG]

I see what you're getting at, and no - that floor to stud connection is not sufficient as shown. Of course, you haven't shown much. I'm assuming the wall stud is meant to go from top of foundation wall to roof/floor diaphragm. You would need a competent tension connection from your first floor diaphragm to the wall which you're not showing. I'm not a fan of it myself anyway.

There are other considerations here, too. Fire blocking being a big one. This also relies on detailed sequencing to make sure everything goes just right. If they build the wall and backfill before you've built the house and made all of the connections, your wall could rotate in.

For the kind of building that would typically use this kind of detail, it's more trouble than its worth.

 

[jayrod12]

Any contractor I know would screw that detail up royally. They'd build it platform framed like typical. Don't do this.

 

[BigBakwas77]

@jimstructures
Your reply is quite rude, especially when you don't know who I am. See the image below and if you rotate it 90°, then you must have done many structures like that.
@phamENG
You are correct in assuming that the studs will extend from top of concrete wall to the second floor level or it could be roof at that level. So, in my structural model, the stud will be a simply supported beam with a cantilever (free) end where a concentrated load is applied which is due to earth pressure from the top of wall. I have done a couple of calculations and it appears that this works in principal. My reason for the question here is to find out if it is a practical solution, especially connecting the floor joists to the side of studs. Please note that the stud wall will be above grade.
@jayrod12
I am just floating the idea here. I haven't suggested this to anybody or any contractor.

 

[jayrod12]

Understood, but I'm pointing out that even if it works in theory, it will never get to construction. And if it does, it will get framed wrong. And by then the concrete is poured and cured and not designed as a cantilever, so at that point you're struggling to find a fix that doesn't require them to tear out work already done.

I don't understand the issue with designing the concrete wall as a cantilever and framing this the same way 95% of the bi-level houses around my area are built. Essentially only requires you to put the reinforcing on the outside face instead of the inside.

 

[BigBakwas77]

@jayrod12
Before I moved to North America, I never designed a retaining wall that wasn't a cantilever retaining wall. I still design cantilever retaining (CIP concrete) walls which is not part of any building. These walls usually have larger footings and heavier rebar requirements. It took me long to develop confidence in using retaining walls which has 24"x8" thick footings with minimum rebars and 8"x120" tall concrete walls with one layer of rebars. But this is how houses with basement are built where I live now. This concept assumes that the main floor diaphragm provides a pin support at top end of wall. (This is why the main rebars are placed on the face away from earth.) Problem arises when, due to site conditions, the while retained earth could be at full height of concrete wall on one side of the residence but on another side it may be at much lower depth. In such cases, the contractor or even architect decides not to raise the concrete wall up to main floor level. So, the space between the top of concrete wall and bottom of main floor joists is filled with a load bearing stud wall. This short stud wall cannot be considered as providing lateral support to the concrete wall. (This was my original question in the previous post). Unfortunately, I have come across houses built in this manner. (and fortunately they haven't collapsed! ). I believe the local authorities in our area are also waking up to such situations and questions plans submitted to them w.r.t laterally unsupported foundation walls.

 

[jayrod12]

I practice just a couple provinces over. These are constructed all the time. In fact the AHJ here has typical details for this construction specifically where they show the rebar on the appropriate outside tension face.

Welcome to Canadian construction.

 

[phamENG]

Welcome to Canadian construction.

Yeah, but when there's a dispute I bet the contractors are a lot nicer than they are down here...

 

[jayrod12]

Ha, to your face. As soon as you leave, they're just as douchy

 

[BigBakwas77]

@jayrod12
This is regarding your comment about the location of tension face of the foundation wall. The sketch below shows why I show rebars on the face away from earth in a residential foundation wall. But when it comes to a cantilever retaining wall, it is near the earth side. Does this make sense?

 

[jayrod12]

Yes, For your information, I've attached the detail from the Manitoba Building code for that type of construction.