square tube strength

[StokedMotorSport]

buddy wants me to make a rack for him. 8'Lx2'Dx6'H. with four shelfs evenly spaced. each shelf needs to hold 400 lbs. dont know what size square stock to use
any help greatly appreciated

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[Wild bill]

10 gauge 1.5"

[atomicjoe23]

What are you gonna use for the shelfing? Are there gonna be supports under that material? How far apart are the supports going to be?

All of that will affect this. . .but 1.5" x 10G (should be about 0.135" WT) should be plenty.

You could get all crazy and figure out what you need though. . .figure out the surface area of the shelves (LxW. . .96" x 24" = 2304 sq. in.), then figure out what the load is on the shelves (400 lbs/2304 sq. in = 0.174 lbs./sq. in.); that's not inculding the weight of the structure and the shelf material itself. . .figure out what tubing will meet your strength requirements. I will post a link for you later today that lists the strength of different tubing diameters and wall thicknesses. . .

. . .this is more like teaching a man to fish rather than giving him the fish.

[StokedMotorSport]

this is prelim design. probly use ply wood for a base of shelf. didnt model a tube for the shelf front to back in between uprights
trying to build as cheap as possible

[StokedMotorSport]

looked for charts on square tube strength couldnt find any good info
easiest project ive ever done but have no idea where to start ha

[StokedMotorSport]

now wants a 6 foot to go along with the eight footer but dosnt want the center upright. Think i can get away with out it
Looks like im going into rack business now taking orders

[atomicjoe23]

I will have to look the values up, but if you have a copy of the Machinery's Handbook you can figure out the strength of the tube by using the section modulus and the physical properties for the steel (more than likely 1018 or 1020 would be my guess as to what you are using).

[StokedMotorSport]

the whole start to the problem is i can find any info on square tube strength

[atomicjoe23]

the whole start to the problem is i can find any info on square tube strength

The basic strength of the steel is the same regardless of the shape. . .you can use the section modulus to determine the strength of the steel in that particular shape. After I get done with some very time consuming work that I'm already behind on I will post up the formulas and information for you.

[atomicjoe23]

I did some calculations for you. . .I don't have time to type at all the formulas, etc. at the moment, but here's the basic assumptions and the results:

Assumptions
- You are using 1018 or 1020 mild steel
-Ultimate Tensile Strength: ~65,000 psi
-Yield Strength: ~48,000 psi
-Modulus of Elasticity: 29 x 10⁶ psi
-Section Modulus: .15625 IN³
- I'm using 1" x 1" x 0.120" square tubing for the horizontal tubing and 1.5" x 1.5" x 0.120 square tubing for the vertical columns
- You are making a 6 ft. shefl and an 8 ft. shelf; the 6 ft. shelf has no center support so the distance between supports is 6 ft. while the 8 ft. shelf has a central support so the distance between supports is 4 ft.
- I'm assuming the load is uniformly distributed on the shelf
- I'm using a relatively standard safety factor of 2 (you could easily go down well below this since we are talking about a static structure. . .but that is up to you, the designer/builder).

Based on the above data and assumptions. . .

Each 6 ft. shelf could support a maximum of 833 lbs (no safety factor. . .this is at yield strength of the material), but each shelf would support 417 lbs. with a safety factor of 2.

Each 8 ft. shelf could support a maximum of 2500 lbs (no safety factor. . .once again this at the yield strength of the material), with a safety factor of 2 each shelf would support 1250 lbs.

If you used 1.5" x 0.120" square tubing the Section Modulus would change to .556 IN³. . .so,

Each 6 ft. shelf could support a maximum of 3000 lbs (no safety factor) or a safe working load of 1500 lbs while the 8 ft. shelves would support a maximum of 8900 lbs. and a safe working load of 4500 lbs.

The actual load would be minus whatever the weight of the material you use to create the shelf itself, this is just what the structure would support. . .using 1.5" x 0.120" tubing for the vertical columns would be more than strong enough in bending and compression to support these loads.

I lied slightly, here is the basic formula used to calculate the maximum load the shelf could support. . .

W = 8sZ/l where: W = maximum load, s = maximum stress of the tube (yield strength), Z = Section Modulus (accounts for the shape of the member), and l = distance between supports (either 6 ft. or 4 ft. depending on the shelf).

I hope this helps. . .all of this data and the formulas came straight out of the Machinery's Handbook (28th Edition. . .current edition is the 29th).