Stress Analysis of Wall to Floor Joint, Without Trailer Supp

[jmedclay]

My 5x8 trailer will sit on an A-frame trailer like sqweaka's so I'm depending on good structural performance from the trailer box, particularly aft of the wheels. I'd like to retain interior headroom by having the walls sit on top of the floor but with that arrangement, bumps and other vertical loads will try to pull the floor laminations apart; so is that a wise design? If I attach the wall to the edge of the floor and the perimeter framework underneath then the wall laminations are in shear (better), the floor laminations won't see tensile loads and I'll loose 1-1/2" of headroom.

Have many folks killed the wall into the top of the floor like this, but without a supporting trailer underneath?
I could epoxy a scab around the perimeter to transfer the load from wall to the perimeter framework under the floor. Not pretty to me, but functional.
I could build up a substantial epoxy/fiberglass cloth overlay to take the load in the same way. Adequate?

Any other ideas or feedback welcome.
Thanks,
John

[Miriam C.]

First, you will be bolting the floor to the walls using something as a cleat, I hope.

Second the bolts should go all the way through and have good support from underneath. I used fender washers. Madjack used aluminum angle as a cleat. I used the same but turned it upside down. It has not rattled apart yet.

You do want to cover the end grain of the floor too..........and seal the end grain of the floor and sides first.

Most important is does 1 1/2" matter that much? If it does then you might need your td to be taller? You should end with at least 44"-45" depending on how you do the roof.

[kennyrayandersen]

My 5x8 trailer will sit on an A-frame trailer like sqweaka's so I'm depending on good structural performance from the trailer box, particularly aft of the wheels. I'd like to retain interior headroom by having the walls sit on top of the floor but with that arrangement, bumps and other vertical loads will try to pull the floor laminations apart; so is that a wise design? If I attach the wall to the edge of the floor and the perimeter framework underneath then the wall laminations are in shear (better), the floor laminations won't see tensile loads and I'll loose 1-1/2" of headroom.

Have many folks killed the wall into the top of the floor like this, but without a supporting trailer underneath?
I could epoxy a scab around the perimeter to transfer the load from wall to the perimeter framework under the floor. Not pretty to me, but functional.
I could build up a substantial epoxy/fiberglass cloth overlay to take the load in the same way. Adequate?

Any other ideas or feedback welcome.
Thanks,
John

John,
The vertical loads (which basically almost always act in a down direction – in the up direction they might go to nearly zero or something if you hit a real whoopty-doo) are reacted at primarily two locations:
1) The front wall/floor intersect
2) The axles
I did a quick sketch to show how the floor and the wall (basic) might come together. You can do it either way, but on the left it’s easy to see how you just drive a couple of lag-screws through the metal angles and into the wood ties everything together nicely. You could always biscuit/dowel the one on the right, so in the end I’m not sure there is so much difference – either one will work. The one on the left also allows the loads from the floor (which might be such things like propane, water, and an ice chest) to be reacted as a shear load rather than loading up the dowels or biscuits as the wall tries to resists those loads. It’s only a couple of inches in height, so I’d sacrifice it myself and go with the setup similar to the one on the left, but as long as you put plenty of biscuits/dowels the one on the right would also work. Frankly, I don’t think you will be able to tell the difference in utility between the two.



Additionally, at the front wall interface, if the vertical wall goes down over the outside of the floor, the attachment would be similar and there would be plenty of room to bolt from the trailer into the front floor cross member (which will probably be something like a 2x2.

YOu can also get and intermediate attachment from the trailer to the floor by using a puck (plywood) inset (burried) into the floor.

[jmedclay]

Thanks Kenny and Miriam,

I'm not sure the sketches are what I had in mind - maybe I'm missing something.
I was going to glue a full-perimeter 2x2 cleat around the perimeter of the floor (3/8" from the edge of the floor) to tie the wall to the top of the floor. When thinking about reactions at the rear 2' of the trailer, where there is no supporting steel trailer frame, I became concerned that reactions would put that rear perimeter of the floor in tension, thereby trying to lift the top veneer off. I figured I'd run deck screws up from under the plywood floor and into the 2x2 but still, glue would be the main structural connector, at least in my assumptions. I'm not so concerned at the front of the trailer since the A-frame provides support/punch, as does the 2' bunks (atop the axle mounting point) on each side. I was a little concerned about the front corners but so much of the reaction would seem to be at the A-frame, didn't worry too much.

Then I figured that gluing the 2x2 perimeter cleats flush with the floor edge, overlapping the walls and gluing them to them would put things into shear or compression. I'll use deck screws regardless. That seemed an innately better design but loses me 2" overhead. We can live with it but if there was a silver bullet that would keep the 2, and address the delam forces, so much the better. Whatever I do will have FRP cloth sealing and supporting the exterior edges but I can make that strong or stronger.

That making sense?

Behind schedule, I just finished clearing a workspace, and configuring the roof racks for the lumber pickup tomorrow. 4-day weekend coming up and I expect to get a lot done but I need to figure this out. I'm leaning heavily towards the "under-cleat", shear-version-joint, and loose the 2".

[kennyrayandersen]

how about a simple sketch?

[jmedclay]

[quote="kennyrayandersen"]how about a simple sketch?[/quote]

Sure. I'll have to use the scanner at the office tomorrow. Sketch challenged at home.

[jmedclay]

[quote="kennyrayandersen"]how about a simple sketch?[/quote]

Can't see how to attach/insert an image, so I put a sketch here...

http://www.flickr.com/photos/21624415@N04/?saved=1

The top arrangement would need substantial FRP edging for strength but is sano, the bottom would get it for sealing purposes but wouldn't rely on the strength it offers. At least that's how I see it. The bottom detail seems the safe way to go. What do you think?

[doug hodder]

My opinion, I like the bottom version, don't have to deal with a cleat on the interior of the trailer. If you use an epoxy for an adhesive, I'd think you should be fine. I seal the ply edges with epoxy, no cloth and all have been holding together fine. Doug

[jmedclay]

[quote="doug hodder"]My opinion, I like the bottom version, don't have to deal with a cleat on the interior of the trailer. If you use an epoxy for an adhesive, I'd think you should be fine. I seal the ply edges with epoxy, no cloth and all have been holding together fine. Doug[/quote]

Thanks Doug. I've decided to go with the bottom version. The lumber is on deck. I hope to have the floor framed up, and the walls shaped and well under way this weekend. Glue: I've read a lot of good info on Titebond II, so am planning to use that with deck screws. I'll probably end up glassing the entire box; top, bottom, sides - everything, to seal it up well for a long time

First step tomorrow will be to scab join two 48x62" pieces of 1/2 ply for the floor and build the framework underneath.

[kennyrayandersen]

My opinion, I like the bottom version, don't have to deal with a cleat on the interior of the trailer. If you use an epoxy for an adhesive, I'd think you should be fine. I seal the ply edges with epoxy, no cloth and all have been holding together fine. Doug

Thanks Doug. I've decided to go with the bottom version. The lumber is on deck. I hope to have the floor framed up, and the walls shaped and well under way this weekend. Glue: I've read a lot of good info on Titebond II, so am planning to use that with deck screws. I'll probably end up glassing the entire box; top, bottom, sides - everything, to seal it up well for a long time

First step tomorrow will be to scab join two 48x62" pieces of 1/2 ply for the floor and build the framework underneath.

Of those 2 I also like the bottom one as well, but either of those I think will be heavier than the sketch I drew (mind you it’s probably only the weight of the cleat – maybe 10-15 Lb). That concept does make it easier to install through-bolts than the one I sketched. It also puts the joint between the wall and the floor in shear, which is what you want. I think as long as you seal the bottom really well you could leave off the wrap plies as well, but as long as you are wrapping the whole thing… couldn’t hurt. Just remember to put some king of radius on the corner so you won’t break the plies and make it a bit more robust with regard to impact damage.

[planovet]

[Miriam C.]

Seems to me with the bottom picture the weight of the wall is supported by the cleat and nothing else. If you reverse that, and put the cleat on the top but hang the wall over the floor you will only loose the thickness of the floor but still have a cleat to screw into. The cleat and the floor are supporting. May not matter---but you will loose less of your height that way.

You can still come from under and screw in with deck screws.

[jmedclay]

[quote="planovet"][img]http://i278.photobucket.com/albums/kk112/planovet/3678482852_4908190eec.jpg[/img][/quote]

Thanks for adding the picture to the thread. How'd ya do it?

And thanks for the input - I appreciate the ideas. I ended up choosing the second of the two since the wall and front are supporting the floor, for the most part, particularly aft of the axle.

[Senior Ninja]

In the "for-what-it's-worth-department" I do have a frame around the perimeter, but I assembled the walls with wiring and insulation, then stood them up and over a cleat on each side. The walls were glued, stapled and siliconed (on the inside) to the cleats. The cleats were a tight fit and glued as well as screwed to the floor. It has made for a very rigid box. The floor was a single sheet of 4x8 3/4 plywood. I trimmed over the gap with wood slats to hide the joint. Makes for a finished look.

Steve

[kennyrayandersen]

Thanks for adding the picture to the thread. How'd ya do it?

And thanks for the input - I appreciate the ideas. I ended up choosing the second of the two since the wall and front are supporting the floor, for the most part, particularly aft of the axle.

Upload a picture into your personal album (link top of page click album, then personal album). Click on the picture you just uploaded. Copy the link to the picture from the address. Then in your post click img, paste the link to the picture, and the click img again. Done!

Even if you are going to do the floor/wall joint the way you say, I would still connect the floor to the side wall independent of the cleat. Maybe it’s not exactly necessary, but us stress guys like to see it not only light-weight, but robust. I would close out the floor with a perimeter 1x2 (2x2 at the front wall) and then I would glue and screw the side wall to the floor (with dowels or biscuits). That would be enough, but the cleat would be extra insurance and could be bolted every 12-18 inched with some ¼ inch dia bolts. That will leave you locked and loaded and FAR more robust than most commercial trailers are built (i.e. you’ll have your structural box).