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Hello everyone. I have 3 X 3 X 3/16"' box mild steel and I want to store
my boat on crossbeams supported only on the ends. I have enough steel that I could double the beams by welding.

I was wondering if anyone could tell me the dead load capacity of this steel.
For a good ball park idea of span I haven't figured it out yet, but it will be anywhere up to 140 inches across or less to allow the trailer to pull out and leave the boat on jack stands.

Thanks.
 

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2x3x3 at 144 inch welded to make a 3x6 should hold 10 ton
We've all been gotten by a ghost thread or two, so I thought you might like to know that the last post on this thread was Discussion Starter · #1 · Oct 7, 2013
 

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Farr 11.6 (Farr 38)
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We've all been gotten by a ghost thread or two, so I thought you might like to know that the last post on this thread was Discussion Starter · #1 · Oct 7, 2013
As noted we've all replied to a dead thread, not to mention from a long lost member. The last time that the original poster was on SailNet was in 2016.

But out of curiosity, when you say that it can hold 10 tons is that as a point load at mid-span in bending?

Jeff
 

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As noted we've all replied to a dead thread, not to mention from a long lost member. The last time that the original poster was on SailNet was in 2016.

But out of curiosity, when you say that it can hold 10 tons is that as a point load at mid-span in bending?

Jeff
I'd like to see the math myself. Perhaps we are seeing a different images, but I get a SWL many, many times lower than that. Perhaps his 10 tons is the failure load, which is not what the poster needs.

The point is no engineer will touch this sort of thing without far more detailed information.
 

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I'd like to see the math myself. Perhaps we are seeing a different images, which is VERY likely, but I get a SWL many, many times lower than that. Perhaps his 10 tons is the failure load, which is not what the poster needs.

The point is no engineer will touch this sort of thing without far more detailed information.
 

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Farr 11.6 (Farr 38)
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I'd like to see the math myself. Perhaps we are seeing a different images, but I get a SWL many, many times lower than that. Perhaps his 10 tons is the failure load, which is not what the poster needs
I would like to see the math myself. Assuming A36 steel (since the grade of steel was not specified), and ignoring that AISC does not show a 3x3x3/16 square tube, I ran a quick calc assuming that the Section Modulus would be the S for a 3x6 rectangular tube, plus the section modulus for a 3/8" thick plate 3" long centered on the neutral axis, with a 12 foot span and the point load on center, I come up with a point load around 8400 ponds. Even with A60 steel I don't quite make 14,000 lb capacity.

Jeff
 

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You don't need to do the math, you just need to find the book. Problem for me is that it would take longer for me to find the book than it would be for you slide rule guys to do the math.
 

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You don't need to do the math, you just need to find the book. Problem for me is that it would take longer for me to find the book than it would be for you slide rule guys to do the math.
I understand that you should be able to look at a span table if this was a conventional steel section. But its not, its two 3x3 3/16 square tubes that have been welded together.

Jeff
 

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I understand that you should be able to look at a span table if this was a conventional steel section. But its not, its two 3x3 3/16 square tubes that have been welded together.
Depends more on who did the welds than the fact that they are welded. Structural Welds are common in steel construction.
 

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Depends more on who did the welds than the fact that they are welded. Structural Welds are common in steel construction.
My comment was not commenting on the welding. I agree that structural welding happens routinely. My comment was referring to the fact that there are two layers of 3/16" steel that occur on the neutral axis that increases the section modulus above that of a 3"x3x3/16" section. Plus neither a 3"x3"x3/16" nor a 3"x3"x3/16" section actually exist.

Jeff
 

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My understanding is that the OP was referring to stacking the tubing for extra rigidity which it would accomplish. I believe the better option if that is the case would be to make the beams as a truss which would give it significantly more rigidity. I think the 10 ton statement was more of a figurative statement than a load bearing calculation. A 12' x 3/16" piece of square tube used a spreader bar to lift 10 tons would bend like a wet spaghetti noodle.
 

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Farr 11.6 (Farr 38)
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3x3 x3/16" square tube is common. perhaps were talking about different things.
The structural properties for neither 3x6 x 3/16 nor 3x3 x3/16 are actually listed in AISC.I understand that the material exists. My earlier post inelegantly failed to say what I was thinking, which was that published values do not exist for those sections, In any event I calculated the section module for the two tubes stacked over each other using standard methods. To get the full structural property for the stacked tubes, I chose to include strength contribution of the the combined 3/8" thickness of the two 3/16:" faces of the tube that are against each other where they meet.

The only reason that I bothered to respond to this long dead thread is that the post "2x3x3 at 144 inch welded to make a 3x6 should hold 10 ton" appears to be a grossly misleading statement, especially in the context of the OIP's question. The actual number is roughly half of that for conventional steel and maybe 3/4 of that for high strength steel.

Jeff

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