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 ?
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
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"... :)
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.
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
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"
Seems like my intuition about alu's weight was wrong.
- 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.
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
Right now, using 2x4's the breadboard layout slides like butter over
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...
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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