Manufactured Home Foundation Wall 1

[Jerehmy]

There's a manufactured home that's being relocated. They want the new location to have a full basement.

There will be 5 steel beams to support the chassis beams. These steel beams will sit on pilasters integral with the a 6" thick concrete foundation wall. Since there is no way to easily attach the floor framing to the top of the foundation wall, I was going to use the steel beams ends to restrain the top of the foundation wall. I also was going to use concrete beams integral with the wall to span between the steal beams.

I lack concrete slab design software as I feel I could be much more efficient modeling it in say SAFE. But, I must make do without.

That said, is there a limit to the width of the concrete "beam" at the top of the wall even though it's integral with the wall? With this width be similar to a column strip? I have attached some sketch details of my ideas. Any input is welcome.

Thanks!

 

[Jerehmy]

Details

 

[jayrod12]

generally what I've seen is the W8x21 beams are removed on site. In fact, all of the steel gets removed once in place.

There are many options to connect the floor system to a new foundation wall assuming the floor is wood.

 

[XR250]

Sometimes with manufactured homes, it is best make the basement walls freestanding, such as cantilevered retaining walls or spanning between buttresses. Your floor diaphragm will have to resist loads in both directions and my experience has not been too positive in counting on this or even making a less than sketchy attachment.

 

[Jerehmy]

jayrod,

I'm requiring the installation of the W8x21s. Our issue is how does someone toenail the floor joists to the foundation wall when everything is already built? Also, this ensure the home can be move in the future.

The home is currently supported on piers at 14' on center so we need the W8s to support the chassis beams.

 

[jayrod12]

Don't use toe nails for starters. Use something like a simpson strong-tie H4 connection. It will nail into the side of the floor joist and into the side of the sill plate. Much more robust connection and can be done well after the fact.

Let the next guy who wants to move it worry about the logistics of picking it up and moving it. Most home movers I've dealt with have their own stock of beams they use to lift and move the homes, rarely do they purchase new beams.

 

[Jerehmy]

I need 505 pounds per foot at the top of the wall for restraint. H4 (which are now H2.5 and H3) only provide 110 to 160 pounds lateral restraint, and thats for wind. For earth, its more like 62 pounds and 90 pounds (Cd form 1.6 to 0.9). In addition, the floor joists are covered in a heavy vapor barrier that we'd like to maintain.

 

[oldestguy]

In some areas in Wisconsin local building codes wouldn't allow 6" basement walls. You may need to justify and satisfy an inspector.

 

[jayrod12]

If you think that toe nails are more competent than even the cheapest connector, then you need to go look at their installation more often.

But I digress, if this is the way you must go then so be it. I would agree with XR then about making the wall free standing, and since you're already providing pilasters they could act as your buttresses. I wouldn't worry about putting a "beam" in the top of the wall, just analyze the wall as spanning horizontally between pilasters.

 

[XR250]

At the end walls, are you going to span the top horizontally as well? FWIW, your system does not really work unless the backfill is equal +/- on the front and back of the building ( walls perp. to i-beams) unless you put some cross bracing in to bring the loads into the side walls or use the floor diaphragm.

 

[KootK]

I think that it's a pretty solid concept. Some thoughts:

- I'd think that your effective width could be taken pretty aggressively here. Span/4 maybe, similar to T-beams.

- I feel that 6" is pretty thin to really be calling anything in there an integral "beam". I'd probably look at it as three sided plates using the Moody coefficient charts etc.

- Keep an eye on punching shear where the steel beams will want to pop through the walls laterally.

- Take care that you've got the beams braced sufficiently for the axial loads that they'll see.

- It's just my gut saying this but I'd like it better if the axial in the beams could transfer through the anchor bolt connection rather than the end bearing connection. I realize, however, that you may have went the way the way that you did because the load was too much for the anchor bolt connection. I feel that the anchor bolts would deliver your shear / punching shear closer to the interior of the pilasters which feels good to me. I also feel that the end bearing connection would require either grout or welding in order to be constructable and achieve positive load transfer. It might be nice to run the pilasters full height and then attache the beams to the interior face of the pilasters.


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.

 

[KootK]

And gorgeous sketches by the way. As last week's Eng-Tips MVP, I hereby award you an honorary PhD in effective question asking. Spread the word. We'll get dhengr's blood pressure down to a solid 120/80 yet.

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.

 

[Jerehmy]

Jayrod,

I understand what you are saying, I was just trying to say the loads are prohibitive for that approach and I shouldn't have said toenails. I'd likely have used an HGA10 or something similar its just installation is the issue. Maybe spanning between pilasters is the way to go.


XR250,

Haven't addressed the endwalls yet as they also need bracing at the top. I like the cross-bracing idea


Kootk,

I'm not sure what else to call it, column strip I guess?

I'd love to use both anchor bolts and end bearing since they're there, might as well use them. I'm just skeptical of cast-in-place anchors and the bolt holes in the beam lining up properly without one side slotted. Thoughts?

I initially wanted to grout the space between the beams and the foundation wall. Either with epoxy or non-shrink grout. I just worry about durability so I was thinking infill the area with steel shims prior to backfiling. Once backfilled it should make it nice and tight and the shims shouldn't go anywhere. Thoughts?




Cost is an issue here which is another reason I don't want to use cantilevered retaining walls (maybe can't is the better word). They got it for a song at a sheriffs sale or something. They're likely going to balk at what I already have.

I appreciate all your comments.

 

[KootK]

I'd love to use both anchor bolts and end bearing since they're there, might as well use them. I'm just skeptical of cast-in-place anchors and the bolt holes in the beam lining up properly without one side slotted. Thoughts?

Field welding. Although I'd understand if you were trying to avoid this if you're not welding anything else.

Once backfilled it should make it nice and tight and the shims shouldn't go anywhere. Thoughts?

Not much beyond what I mentioned before. My money says that back-filling doesn't actually close any gap initially. That means that, sort of by definition, the shims would be sitting in there kind of loose until some hydrostatic pressure kicks in or a firetruck parks out back. I don't love that.







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.