Sidewall strength

[Vanq]

Sidewall strength-How much is enough? I'm pondering the design of a light weight tiny toy hauler, and I'm afraid I just don't have the knowledge to complete this design. Although I'm no expert there is enough information around that I can make a guess at what I could get away with in terms of frame, but for sidewall I'm at a loss. I've looked at things where its ultra thin sheeting with a 1x1 frame which were deemed o.k. and builds where people were questioning if 1/2 inch was sufficient.

Can somebody point me to any sort of a reference where I can determine how much sidewall is enough? Since we are all pulling these things through the same medium at simmilar speeds my gut says there has to be some simple math that says for this much area you need this much strength...

[bobhenry]

I know little to nuttin' you can ask anyone. However I am not bashful.

A lot of the strength is needed to overcome the air pressure and road flex that occurs in the box. A rounded nose whether horizontal like a teardrop or vertical like a round nose horse trailer will redirect the air flow rather than fight it and thereby will need less strength to resist the force the air exerts on the nose. The hinge points are the weak points on the box. If the sidewall set on the deck it will flex, if it is glued and screwed into the side of a deep floor halo or the frame itsself it will add conciderable strength. The hing point at the roof is another weak point. Perhaps by cutting arched plywood gussets 6 inches or so deep and adding 2x material in between these two plys then utilize these as the roof spars would add greatly to the strength and further resist the corner to corner flex. By screwing thru the sidewall into this sandwiched "truss" this would eliminate a great deal of the road wiggle in the sidewalls. Even the rear doors should set in a recessed trough to help reinforce the rear and act as a shearwall when closed and latched. I don't think it is as much the material strength as it is intelligent design ideas that will make the build strong but light as well.

[Forrest747]

if you can give us a rough idea of where you want supports and things we can crunch numbers.

[angib]

I think you will find almost any sidewall is strong enough - the real test is whether it is durable enough. You could build a foam composite sidewall that is strong enough overall, but you could stab a finger through it. Similarly you could make a thin ply sidewall with wood stiffeners that could survive everything - unless you stumble nearby and shoulder-charge the side wall as you are falling over.

So the sidewall needs to be strong enough to satisfy you in the workshop - build a test panel and see if it feels tough enough.

Building the lower half of the front panel tougher than the rest, to withstand stone impacts, has always made sense to me.

[Woodbutcher]

Without knowing exactly what you are doing let me also say this. With it being a toy hauler the sides can be called on to be used for tie downs. This will make building a bit different then a Teardrop. Also things being loaded into a toy hauler could easily punch a hole in a side wall. If all the tie downs are located in the floor then this worry could go away some.

[Vanq]

I'm picturing something roughly dodge neon sized plus a couple inches for comfort. Basically 15x6ft 5 feet height in the middle with minimum size and weight so I don't bankrupt myself towing it. I think the teardrop profile looks cool, has some aero advantages and if one popped the hatch and rolled out a car that would be pretty slick. Add to that there would be more than enough room for 4 flip up bunks and I can cover accommodations as well.

I currently run an open trailer built on a 3500lb axel which runs 2800lbs when being towed in its current state. If I use that as the base of my teardrop toy hauler I need to build LIGHT, even if I modify or fab a new frame I still want to keep weight and size down which lead me to how heavy do I really need to build it.

[Forrest747]

an unsupported 4-ply sheeting of plywood will fail at about 407 lbs. they had an 8-ply at 1,009 lbs. this is an 8 foot length compressed unsupported.

Given your 5 foot hieght and desire to have a foldbale bunks. you could go with a 3/4 inch plywood with 3/4 by 2 inch supports every 24 inches on center and that should be enough. you will also need spars at the rood every 12 to 16 inches and attached to your floor every 12 inches.

that should give you a support of 1,564 bending force in a static condition.

[Vanq]

I pictured the bunks as boxes hinging on the floor so i could keep the walls light. The bunks I'm envisioning are basicly a 1x6 frame with particle board bottom thick enough to hold the bedding in. when open the particle board is fully supported by the floor and when closed the wall and particle board seal in the bedding.

[Forrest747]

I will take some strips i have and bring them into work tomorrow and put them to the test. let you know by the afternoon. plan is to do 4 foot long strips of various thicknesses.

[mezmo]

Hi Vang,

Don't use particle board for anything in your build, even if it is free to you.
it has no 'performance strength'. It is heavy, it crumbles. it's not durable.
Water destroys it, all it does is wait for water to come so that it can
disintegrate and rot. It is the epitome of a "cheap" material! [Can you tell I
don't like it?!] Use a plywood, preferably the Baltic birch type, for the bunks
as the more 'plys' per thickness, the better.

Cheers,
norm/mezmo

[Forrest747]

Ok testing is done

all samples were four feet long and compressed in an MTS test stand. each sample was 3 1/2 inches in width and thickness varied. with the exception of the 2x4 all samples were of baltic birch plywood. each sample was compressed until failure. no injuries were reported to operator or observers.

2x4 2917 lbs
1 1/2 inch 2647 lbs
1 inch 2169 lbs
3/4 inch 1658 lbs
1/2 inch 1291 lbs
3/8 inch 1046 lbs
1/4 inch 743 lbs
1/8 inch 215 lbs


Notes:
2x4 was a home depot average stud material. failure point was not specfic to any knot or joint.

1 1/2 inch was made from 2 pieces of 3/4 inch plywood glued together with gorilla glue to an approximate thickness of 4 to 10 mil clamped every 6 inches for 8 hours. Failure point was in plywood glue point 2 layers from aftermarket assembly joint.

1 inch was made from 2 pieces of 1/2 inch plywood glued together with gorilla glue to an approximate thickness of 4 to 10 mil clamped every 6 inches for 8 hours. Failure point was in plywood glue point 1 layers from aftermarket assembly joint.



test setup was a basic 3 point bend test fixture with the contact support points at 6 inches from end, load cell at 24 inches from end and contact support 42 inches from end. File picture of set up attached to notes. May not reflect actual test samples. File picture of test equipment used. May not reflect test location or setup. Extension supports used due to test samples lengths. See Engineer for any questions.

[Vanq]

so if I'm interprating this correctly this is basicly peak buckeling strength from vertical load on one wall support of the various material types?

[Forrest747]

so if I'm interprating this correctly this is basicly peak buckeling strength from vertical load on one wall support of the various material types?

Yes that would be correct this is just the material compressed until it failed and at what max load it achieved.

[Vanq]

As far as vertical load goes I don't think dynamic loading on the road is my biggest worry as much as static snow load while its parked in my backyard for the winter. Homes here are designed to ~35psf snow load... if I assumed a flat top 15x6 that means 3150lbs on the roof ( actually less because fron & back are sloped) if we go with a brace every 2 feet thats 210lbs per support. Looking at that even 1/4 inch supports on a1/4 inch sidewall is more than strong enough....

Looks like angib is right its more a durability queston than a strength one...

[Cdash]

It is really cool that you did this testing, but I think you said and what I see seem to be two different things.

all samples were four feet long and compresses in an MTS test stand

What I see in this picture is that you applied the load (and the supports) to the flat face of the plywood. If what I see is correct, this would test a bending load, which would be better indicator for the floor or roof.

It seems like the right test for a wall panel would be to - (this is the best way I can think to describe it) - would be to place a 4x8 sheet upright on the 8' edge and load it (on the thin edge) vertically until it fails. I know this wouldn't be practical due to the size and I don't think the test would scale well either since a small width of the material material size isn't braced the same by the rest of the material around it.

I wonder if anyone has an old teardrop that could be backed under the load cell.....