2x2 square tube strength

[mobilesport]

I have a box van with 2x2 inch square tubes that stick out of the rear bumper barely , there's 2 of them , i made 2 ( 1.75x1.75-----12 inch) long square tubes and stuck one inside of each of the vans 2x2 square tubes, I only stuck them in 6 inches so there's 6 inches sticking out of each one as you can see in the picture , I plan to put a 7 inch wide 5 foot wide plate going across the back of the van sitting on top and mounted to the 2
( 1.75x1.75-----12 inch) tubes.
Do you think this is strong enough to haul a 300# motorcycle?

 

[BukitCase]

Looks like your wall thickness is at least .120" - I have one of harbor freight's cargo carriers

500 lb. Steel Cargo Carrier

Amazing deals on this 500Lb Deluxe Steel Cargo Carrier at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

They rate it at 500 lbs (I always cut their numbers in half to be safe) - I wanted a bit of "up-tilt" so I cut their 2" tube (about HALF as thick as yours) and re-welded it - my first test was to stand on the carrier and jump up and land on it as hard as I could - I weigh 180, and it never budged - this, with just ONE tube about HALF as thick walled as your TWO.

Dunno how you intend to tie down, but I'd be more concerned with THAT... Steve

 

[firebirdparts]

Jump on them and go by that. If you can't bend that structure jumping on it then go with it.

 

[laser3kw]

the weak point will be where they are welded to the motorcycle carrier. Gusset that area for sure.
Neither post will carrier the entire 300lb of static load BUT, it's the bouncing and road conditions that may exert more than 300lb of dynamic load.

 

[vavet]

What you have is a cantilevered beam.
Deflection of a cantilevered beam is calculated with:

Force * length^3 / 3* modulus of elasticity * moment of intertia


Force is half of the total load since you have 2 of these supports (150 lbs)
length is the center of loading (let's use 6 inches to add a margin of safety)
modulus of elasticity is 29,000,000 PSI for A36 steel (guessing at the alloy, but most steels are similar)
moment of inertia is calculated by (a^4 - b^4)/12 where a is the outer dimension and b is the inner dimension of the square tubes. I'm assuming 1.75 and 1.5 inch of a and b, which calculates to 0.360 in^4.
Put it all together and you have a deflection of 0.001 inch.

But that's not enough. You need to know if the stress exceeds the maximum stress in the material.
stress = distance to neutral access (half of the tube height) * moment divided by moment of inertia
moment is the the force * arm. Worst case scenario = 300lb * 6 inches = 1800 in-lb
moment of inertia is the same as above
You end up with about 4400 psi.
Max stress of A36 steet is ~60000 psi. You're well below the max stress.

I'm pretty sure all of the above is right, but it's been a while since i did these calculations.

 

[brownbagg]

yes , thats a piece of HSS. hollow structrual steel. its design to hold up a building

 

[Jarwop]

plan to put a 7 inch wide 5 foot wide plate going across the back of the van sitting on top and mounted to the 2
( 1.75x1.75-----12 inch) tubes.

Unless you can bend a lip on the plate, I'd use two pieces of angle. I think that would be cheeper, lighter and stronger.

 

[GaryM909]

Make sure you check out what the 2" sq tubing is welded to. About 30 years ago I welded a receiver on to a travel trailer bumper for a bike rack. I made it about 10 miles before the welds ripped off from the bumper. Had to replace both wheels and tires on one of the bikes.

 

[WNYflyer]

Make sure you check out what the 2" sq tubing is welded to. About 30 years ago I welded a receiver on to a travel trailer bumper for a bike rack. I made it about 10 miles before the welds ripped off from the bumper. Had to replace both wheels and tires on one of the bikes.

^^^
Yup