What is the Load rating of Aluminum rectangle tubing?

[studay]

Greetings, I will describe the problem and my proposed solution which leads me to the load bearing question..

Problem: Pickup camper cabover floor is compromised where it attaches to the driver side sidewall, i.e., separation of floor from sidewall due to some dryrot and a blowout doing 65mph with the camper on... not fun..

Solution?: Instead of rebuilding the front structure I propose to build supports (aluminum rectangle 6061-T6 tubing 4x2x0.125) that run underneath across (two 8 foot spans) and welded together with cross members (three 31 inch pieces). Attached page 1 gives an idea of the concept. Trying to keep the weight down as well as not go any more than 2 inches below the cabover floor (don't want it to hit the truck roof..)

They will be through bolted to the cabover frame where possible underneath and the panels you see in the second page of the attachment will hold it up via through bolts into the sidewall frame. I will have the panels (6061 aluminum plate 0.125) welded to the outer 4x2 pieces.

THE Question(s):

1) How much weight will 4x2x0.125 hold assuming there would be two full size adults and gear above (~600lbs total with 500 of that being in the middle 60% of the 8 foot span when sleeping)?

2) Do I really need 4x2x0.125 or can I use something smaller to save the weight and space (1x3, 1x4, 2x3, 2x2, or tubing? I was told that grating wouldn't work given the weight needed to cover that span)? Remember the floor is still firmly attached (i.e., as structurally sound as it can be given the damage on the one side) on 3 other sides and ~25% of the 'broken' side.

Appreciate any feedback offered. Thanks!

 

[nvn]

studay: It currently appears 101.6 mm wide x 38.1 mm deep x 3.175 mm thick Al 6061-T6 rectangular tubing would be adequate to support your stated loading.

However, because your 991 x 305 x 3.175 mm thick Al 6061-T6 end panels are only a flat, thin plate, it appears they might bend at the horizontal line in your second diagram between your rectangular tube cross member and the camper sidewall, unless you make these two aluminum end panels 7.1 mm thick.

 

[studay]

Thank you nvn. I was hoping I did not have to go that thick on the side panels. Does that hold true if I go with the 101.6 mm x 50.8 mm x 3.175 mm for the tubing (31 inch length welded to the two 8 foot spans)? I may be loosing it but your reply seems to have changed a bit since last evening

 

[nvn]

studay: For simplicity, we can say it would be the same with the 101.6 x 50.8 x 3.175 mm rectangular tubing.