Square Steel Tubing Strength: Perforated vs Solid ?

I have an application where I know that 1 1/4" non-perforated square steel will carry the load.
But the perforated stuff (like on signposts) offers convenience in bolting things together.
Are the strengths the same or do I need to get some of the perforated stuff and test it ?
--
Pete Cresswell

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On 4/29/2016 12:47 PM, (PeteCresswell) wrote:

What type of load(s) are you most concerned with -- twisting, bending, tensile, etc.?
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On 04/29/2016 2:47 PM, (PeteCresswell) wrote:

1-1/4" isn't a complete spec; what thickness? Although if you're even comparing to the perforated stuff at all I presume you're really talking about gauge thicknesses rather than standard angle. But again, there still need to know that gauge to know the strength under various loading scenarios.
And, of course the perf angle isn't as strong as solid angle stock; particularly in side loading or compression as it will yield at a perforation far before the solid will simply from lack of local material creates stress concentrations.
If it's in tension so won't have a tendency to want to buckle it'll not show the effects as greatly as soon.
So, iow, "no and we don't know whether an unspecified piece will serve an unspecified purpose"... :)
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Per (PeteCresswell):

Here are some pix.
Essentially it is a small boat on a beach dolly. Max weight 220#.
We roll the boat/dolly up to the back of the trailer and then slide the whole thing up on to the trailer using the dolly beams as rails sliding on the trailer's 1" plastic-covered round crossbeams - which are actually Yakima roof rack bars.
Start here: https://picasaweb.google.com/108149798664924808733/AI#6279373270696420834 and keep hitting RightArrow to follow the loading process as the boat/dolly are hauled up on to the trailer.
The total span between the two white cradles is 69". Let's call it six feet...
So, while it is being cranked up on to the trailer, the maximum span that the two dolly beams have to endure is 3 feet- bearing on the trailer's rear roof rack bar.
Once the dolly is settled on the trailer, the spans are 8" to the rear cradle from the rear roof rack bar and 14" to the front cradle from the front roof rack bar.
I wedged a single length of non-perforated .065" 1 1/4" square SS tubing in such a way that I could hang my entire body weight of 215# on it with 3' of overhang ("Cantilever" ?) and there seemed to be no problem - maybe 2-3" of deflection.... and that's double the load because it was only 1 piece.
Intuitively, the Gotcha comes as the dolly beams slide across the 1" roof-rack crossbeams on the trailer. i.e. a highly-concentrated load.
For that reason, I think you may have already talked me out of the perforated stuff... so it probably comes down to 1 1/4" vs 1 1/2" tubing.
--
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wrote:

Since this is going to be outside, I would lean toward 2x2 aluminum square tube (.125" or greater) ... but that may just be a Florida thing.
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Per snipped-for-privacy@aol.com:

Alu was calling out to me - if only because of weight... but, although I know there are many types/qualities of alu, I am too clueless to make an informed choice as to type.
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wrote:

If you can get a wholesaler to sell it to you, a 20 or 24 foot stick of 2x2 is not that expensive but for structural I would go with 1/8" wall.
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Per snipped-for-privacy@aol.com:

Seems like my intuition about alu's weight was wrong.
To Wit:
- 8' length = 96"
- Alu 2x2x.25 = 2*.25**96*4 = 192 cubic inches of alu
- Steel 1.5x1.5x.065 = 1.5*.065*96*4 = 37.44 cubic inches of steel
- Steel = .28356 pounds/cubic inch
- Alu = .097986 pounds/cubic inch
= Steel Total Weight = 37.44 * .28356 = 10.6 pounds
= Alu Total Weight = 192 * .097986 = 18.81 pounds
A downside of alu is rub resistance. I had an alu boat trailer where a line on the boat was left loose so that it rubbed against one of the alu trailer's members during a 7-hour trip. The rope had actually worn a visible valley in the alu.
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wrote:

You should be putting some kind of plastic runners on this anyway.
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Per snipped-for-privacy@aol.com:

The roof rack bars that it rides on are plastic-coasted - and enveloped in schedule 40 PVC tubing for good measure.
Does that count? Or would you attach strips of plastic to the two dolly members?
Right now, using 2x4's the breadboard layout slides like butter over that PVC.
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wrote:

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On 04/30/2016 11:22 AM, (PeteCresswell) wrote: ...

It is, yes, essentially a point mid-span load that will be limiting...

I found some Unistrut literature that shows a reduction in allowable bending moment for 1-1/4" 12 ga (0.105") perforated of 25% less than for the solid. This reduction went to about 15% as the stock size increased to 2-1/2" which make sense as the fractional area of the holes decreases the solid web fraction increases which makes for a stiffer section.
I'd guess from this, the likelihood is it'll work w/ the size if you go to slightly heavier material. I'll see if I can find the time this evening to do a rough moment estimate for your loading but I've got stuff have to go do at the moment...
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On 04/30/2016 12:43 PM, dpb wrote: ...

OK, I found another table -- as I presumed likely, the same percentage reduction is given for 10 ga material as well so it is, indeed related to the perforation fraction essentially alone, not the thickness (again this is a percentage reduction, not an absolute value so the difference ratios out unless it is an effect as well).
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