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Need Box Steel Specs for Boat Support

1K views 13 replies 6 participants last post by  Jeff_H 
#1 ·
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.
 
#9 ·
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
 
#14 ·
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

.
 
#13 ·
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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