Square Steel Tubing Strength: Perforated vs Solid ?

[(PeteCresswell)]

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

[Uncle Monster]

Are you referring to the right angle perforated steel? If you want something stronger, go to an electrical supply house and look at some Unistrut products. ^_^

http://www.unistrut.us/index.php?WP=MFProdOver&#M1

[8~{} Uncle Strutting Monster

[Oren]

On Fri, 29 Apr 2016 15:47:33 -0400, "(PeteCresswell)" <x...@y.Invalid>
wrote:

Pick your poison. My garage door has perforated angle iron - not
square box and it is still doing fine. Ceiling mounted to stabilize
the tracks. Bolted where needed.

What is the application? Just saying don't dismiss the perforated
metal.

[Don Y]

What type of load(s) are you most concerned with -- twisting, bending,
tensile, etc.?

[dpb]

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"... :)

--

[(PeteCresswell)]

Per dpb:

>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.

I was figuring the same wall thickness as the solid stuff I tested.

In this case, .065".

http://www.onlineconversion.com/gauge_sheet_metal.htm says that is
15 gauge for standard steel and 16 for galvanized.

http://www.mesteel.com/cgi-bin/w3-msql/goto.htm?url=/info/carbon/thickness.htm
says 16 gauge.

To my limited gray matter, at least, it's quite a complicated situation
and I think trying to explain it via text would muddy the waters.

As soon as some parts arrive (hopefully today, Monday latest), I will
make up a breadboard version using 2x4s and take some pix.
--
Pete Cresswell

[dpb]

That'd probably be bestest...the details of the load concentration in a
perforated tube are indeed more than a single beam calculation type
computation.

I'm sure there's probably some semi-empirical correction for general
loading capacity but I don't know of it specifically, unfortunately.
(Mechanical was a far-removed tertiary (or lower) concentration to the
nuclear/chemical primary/secondary and a quick "gargle" search didn't
uncover anything particularly helpful... :) )

Again, primarily the difference in weakness will be in bending in the
various modes altho while your posting clearly said "square tubing" I
was thinking more along the lines of the punched angle stock. Similar
concern but the square filling in the other two sides does stiffen it up
quite a bit so that the free leg isn't able to buckle nearly so easily
as an angle could.

But, just how much less I don't have any data on and don't have a FEM
modeling tool available currently to do a real calculation quickly.

--

[(PeteCresswell)]

Per (PeteCresswell):

>As soon as some parts arrive (hopefully today, Monday latest), I will
>make up a breadboard version using 2x4s and take some pix.

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.
--
Pete Cresswell

[gfre...@aol.com]

On Sat, 30 Apr 2016 12:22:55 -0400, "(PeteCresswell)" <x...@y.Invalid>
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.

[dpb]

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

> Intuitively, the Gotcha comes as the dolly beams slide across the 1"
> roof-rack crossbeams on the trailer. i.e. a highly-concentrated load.

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

> 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.

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...

--

[dpb]

On 04/30/2016 12:43 PM, dpb wrote:
...

> 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.

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).

--

[(PeteCresswell)]

Per gfre...@aol.com:

>
>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.

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.
--
Pete Cresswell

[gfre...@aol.com]

On Sat, 30 Apr 2016 17:26:43 -0400, "(PeteCresswell)" <x...@y.Invalid>
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.

[(PeteCresswell)]

Per gfre...@aol.com:

>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.

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.
--
Pete Cresswell

[gfre...@aol.com]

On Sun, 01 May 2016 12:03:55 -0400, "(PeteCresswell)" <x...@y.Invalid>
wrote:

You should be putting some kind of plastic runners on this anyway.

[(PeteCresswell)]

Per gfre...@aol.com:

>You should be putting some kind of plastic runners on this anyway.

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.
--
Pete Cresswell

[gfre...@aol.com]

On Sun, 01 May 2016 17:47:50 -0400, "(PeteCresswell)" <x...@y.Invalid>
wrote:

That will work.