the grade 8 bolts where stronger than the steel!

[Mace Canute]

Not really hard to believe at all if you look at the math. Look at the "area" of the steel pieces.

The perimeter of that tubing would be about 6" at 1/8" thick. But it broke where the bolt holes were, and assuming 1/2" holes (times 2) take another inch off. So 5" at 1/8" thick is only 5/8" total area.

A 1/2" bolt has an area of over 3/4", AND you have two of them. Not to mention the fact that the grade 8 bolts have about twice or better the tensile strength of the steel. So the bolts would be easily 4x's stronger than that tubing.

Channel iron should fare better but I wouldnt mount it like you have with bolts through the flange. If you insist on mounting it that way, go back to tubing but upsize it. Perhaps some 2x2 x 1/4" wall

I think your math is off; the formula for area of a circle uses radius squared, not diameter squared (and I know it was just a brain fart, we all get them every now and then). I get just under .2 square inch cross sectional area.

 

[LD1]

Yep. Brain fart. I am suprised no one caught it....

But even at .2 sq in, @ 150,000 psi tensile for grade 8, thats still almost 30,000lbs of tensile strength per bolt.

At 5/8" square for the tubing, which is likely just A36 steel with 36,000 tensile strength, thats only 22,500lbs.

Bolt is still stronger

 

[sparc]

Bolt is still stronger

Looking at just the areas of the two maybe, but the shape of the tube steel would make it stronger I think, even for a pure tensil load. From a bending perspective it should be much stronger. You can probably bend a length of 1/2" diameter round stock by hand, but I doubt you could even flex a piece of 1x2" tube steel of the same length with a 1/8" wall thickness.

 

[lloyd430]

Yep like I said before this was stock I had left over from another project, it took #4K to bend it the 1" dimension then........I was just surprised the 3/8" grade 8's where fine!

Looking at just the areas of the two maybe, but the shape of the tube steel would make it stronger I think, even for a pure tensil load. From a bending perspective it should be much stronger. You can probably bend a length of 1/2" diameter round stock by hand, but I doubt you could even flex a piece of 1x2" tube steel of the same length with a 1/8" wall thickness.

 

[SPYDERLK]

I think your math is off; the formula for area of a circle uses radius squared, not diameter squared (and I know it was just a brain fart, we all get them every now and then). I get just under .2 square inch cross sectional area.

Yep. Brain fart. I am suprised no one caught it....

But even at .2 sq in, @ 150,000 psi tensile for grade 8, thats still almost 30,000lbs of tensile strength per bolt.

At 5/8" square for the tubing, which is likely just A36 steel with 36,000 tensile strength, thats only 22,500lbs.

Bolt is still stronger

I caught it. Just didnt say anything. If I corrected all the stuf I see Id have 20K posts counting rebuttals.

Looking at just the areas of the two maybe, but the shape of the tube steel would make it stronger I think, even for a pure tensil load. From a bending perspective it should be much stronger. You can probably bend a length of 1/2" diameter round stock by hand, but I doubt you could even flex a piece of 1x2" tube steel of the same length with a 1/8" wall thickness.

Bolts are employed in tension and/or shear. Shape, as long as its regular [avoiding stress risers], will not change tensile or shear strength. -- And, the steel in that bolt has 2 to 4 times the tensile strength of that in the tubing. That bolt could withstand the force needed to collapse and bend the tubing even without a hole in it.-- There were no forces bending the bolt and very little shear.
larry