1 1/4" sq 14 ga versus 1 1/2" 16 ga sq tubing

[tpcollins]

For the load experts here - I'm going to build a tripod hunting stand that will use (3) 12' long sq tubing up to the seat with leg angles somewhere between 20 - 25 degrees. With a maximum top load of 250 pounds, would 1 1/4" 14 ga sq tubing be just as strong as 1 1/2" 16 ga sq tubing in this situation? I will add some bracing but would really like to minimize it. Thanks.

[socoj2]

For the load experts here - I'm going to build a tripod hunting stand that will use (3) 12' long sq tubing up to the seat with leg angles somewhere between 20 - 25 degrees. With a maximum top load of 250 pounds, would 1 1/4" 14 ga sq tubing be just as strong as 1 1/2" 16 ga sq tubing in this situation? I will add some bracing but would really like to minimize it. Thanks.

the larger your diameter the better if you can get away with it 1.75x 16ga would be almost 40% better than 1.25 14ga

[DSW]

Larger dia. tube is less likely to buckle than thinner dia. tube generally with everything else being equal. With your application buckling is more important than how much load the material will take. Either one would support that weight if the legs were only say 2' long. As the length increases, the leg usually fails in buckling before the material fails in compresion. Braces reduce the effective column length as far as buckling is concerned.

My table shows...
1 1/4" 14 ga sq tube to be 1.32 lb/ft.
1 1/2 16 ga is 1.27 lb/ft.
2" 16 ga is 1.88 / ft
2 1/2" 16 ga is 2.13 lb/ft.

2 1/2" would add about 30 lbs to the total weight, but be signifigantly stiffer than the 1 1/4" or 1 1/2" tube. The 2" tube would add about 20 lbs total if you chose that instead. ( they also have 2" in .063 wall and you would only add about 12 lbs with that.)


There's an equasion that will tell you how each of these tubes will react under load, but I don't have the basic data on hand to plug in and run the calcs unfortunately.

[socoj2]

I have this for round tube but square isnt that far off.

1.25 14 ga - moment of inertia is .048
1.50 16 ga - moment of inertia is .070
1.75 16 ga - moment of inertia is .114
2.0 16 ga - moment of inertia is .172
2.5 16 ga - moment of inertia is .342

[DSW]

Do you have E handy as well?

Doing the math ( assuming I did it right...) using those numbers for I given above.

1 1/2" will take 1.4 times the load before buckling that 1 1/4" will over a 12' length.
1 3/4" will take 2.3 times the load before buckling that 1 1/4" will over a 12' length.
2" will take 3.6 times the load before buckling that 1 1/4" will over a 12' length.
2 1/2" will take 7.1 times the load before buckling that 1 1/4" will over a 12' length.

http://www.engineersedge.com/column_buckling/column_ideal.htm

[socoj2]

Depends on the steel usually 27-31

29.5 would be fairly safe

[tpcollins]

Thanks for the help on this. I'm basing my project on a quad pod that has 4 legs using all 14 gauge sq tubing. Their design has about 2' of 1 1/2" sq tubing at the seat/platform area, probably 8' of 1 1/4" that sleeves into that, and 1" that goes into the bottom of that. So they really only have 6' of 1 1/4" exposed and about another 4' of 1" exposed ( about 10' to the platform) - and I realize there are four legs but they use no bracing.

For my tripod, I have to use 1 1/2" sq at the top because that's what the upper platform is designed for. I have a heavy duty one piece "climbing stick" to use for one of the legs, and I'm thinking of 8' of 1 1/2" 14 ga for the top and sleeve 6' of 1 1/4" for the bottom and let it extend 4' out the bottom - this gives me adjustment to allow for uneven ground. It also makes it easier to transport and set up.

If this doesn't work out, I'll through it away and start over . . .

[socoj2]

Can you toss up a drawing or something.

[tpcollins]

I bought the top platform and seat section from this site. He's uses 1 1/2" 16ga 10' long for the tripod legs. I was going to use 8' of 1 1/2" 14 gauge for the top section and 6' of 1 1/4" 14 ga sleeved into that for a total of 12' (2" of 1 1/4" sleeved). This allows me to adjust for eneven ground. Thanks.

http://jackstradeshack.weebly.com/

[DSW]

...and I realize there are four legs but they use no bracing.


Actually the tube inside a tube is considered a "brace" in this case as it reduces the unsupported length of the single tube.

If anything I'd reverse the idea and go up in tube size rather than down. The larger tube can be longer without needing to be braced. I'd probably use straps to keep the legs from spreading though.

[jrose]

Some angle bolted in a cross in between the legs is a must for a tripod. It will really sturdy it up.