What size of tube steel is needed for a 1500-2000 lb load on a 48 x 76 frame?

[xOttox]

Hello all! I am not the most well versed in engineering but my old man is attempting to build a slide out rail system for his pick up truck. The design we have in mind calls for a frame made of tube steel however what we have laying around the shop seems to be a bit overkill (or maybe not). The frame will be 48" wide and 76" long with 3 braces located on the inside of the frame. Based on rough weight estimate fully loaded the frame will itself will need to support between 1500-2000 lbs.

Any help figuring out what size rectangular tube steel to A) carry the load B) not sag under load or its own weight and C) be fairly easy to obtain would be greatly appreciated as this is neither of our specialty.

If more details on the design are needed I have a simple drawing I can share showing the use of track rollers to allow the frame to slide in and out of the truck bed.

Thanks, Otto

 

[Bystander]

You're trying to build a permanent steel pallet for "container" loading of a pick-up truck?

 

[xOttox]

We are attempting to build a frame that will rest on a set of rollers allowing all the tools to sit on this "pallet". The pallet will rest on the rollers letting the pallet be pulled out the back of the truck bed so no has to climb into the bed to get the items at the front.

Something like this: http://www.pickupspecialties.com/Bedslide/bedslide.htm

 

[Bystander]

My inclination? Someone's already in the business and willing to accept the liability issues for the engineering and load limits, and probably cheaper in the long run than what can be done "by guess and by gosh." The killer on the design issue is going to be the bending moment at full extension plus bed anchors; a one ton load sticking four feet out the back end is putting a two ton load on the front rail anchor (non-trivial for most bed construction), and putting a monstrous bending moment on the frame just over the back edge of the bed floor. If you've got to do this thing, try mocking up with 2 x 4s first and just see what sort of loads it takes to break them, or that they can support.

 

[berkeman]

Something like this: http://www.pickupspecialties.com/Bedslide/bedslide.htm

I would just try to duplicate the construction of those items. Unless you have a very strong ME/design background, and probably access to some FEA software, it doesn't make sense for you to try to come up with this on your own (even with "help" over the Internet).