That's a fairly complex engineering question (??)
Apart from in pure tension, the load limit is usually about when the
section will buckle - go unstable - or exceed elastic bending
(smallish) and plastic bend by large amounts to collapse.
Normally, when the service is not pure tension, closed sections -
SHS's - Structural Hollow Section - are much stiffer for the same
amount of material and will give a much higher load bearing.
The technical breakthrough of being able to economically manufacture
large amounts of Structural Hollow Section from good-specification
steel has been a transformation.
Other advantages with SHS's are eliminating rust-traps, with
hermetically-sealed internal volumes (no corrosion) and smooth
external sections advantaging paint systems to give good protection
against corrosion for long low-maintenance service.
Hence the return (?) of truss bridges.
You'll be wanting to study Second Moment of Area and the beam and
column calculations / equations.
The Euler column and the Euler-Bernoulli beam (both derived around the
1750's - about 250 years ago) which serve well for most applications
of beams and columns.
When I built a log splitter, sawmill and a hydraulic bucket loader for
my tractor I welded every joint that wouldn't have to be taken apart
to store or modify them. However structural steel design manuals say
to avoid field welding whenever possible, due to high cost. They are
more neutral about shop welding versus bolting. Why would field
welding be prohibitably expensive? Heavy construction equipment is
almost entirely welded.
Big difference between commercial and hobby, in all practical / real
That contention, "field welding expensive", would be true for typical
Commercially, you use MIG (GMAW) in a workshop, and SMAW on-site
* in a well-set-up fab-shop MIG (GMAW) is vastly faster than stick
(SMAW) applied in the same situation
* they'd be talking about bolted steel connections for buildings -
"rattle-gun" (impact wrench) a few bolts, rather than weld (SMAW)
(noting that at the ends of beams, where the bolts are, you only
have a small shear force, with all the serious big beam bending
stresses far away in the mid-length of the beam)
Hence, commercially, due to processes used and the majority
application, the statement is true.
In a hobby workshop, at best you still have a single-phase electric
power and you cannot pull those 15kW from the mains which makes
fabshop MIG so productive. Most MIG's are transformer and something
like 50% efficient, whereas many SMAW sets now are inverters and
high-90's percent efficient - so those 3.12kW (British 240V 13A max)
give almost twice the bang-per-buck and even up the productivity. No
loss of productivity outdoors with stick, which is one of the few
processes which is in reality rather tolerant of wind and rain.
Then you are going to have much more trouble making bolted joints that
in a well-set-up commercial shop, with all your marking tools,
benches, ironworker for punching holes, etc, etc, etc.
In summary - it's no wonder you see a different picture where for your
home fabs. welding is vastly easier and quicker.
It all makes complete sense - be assured of that.
So MIG indoors but stick outside. I though flux-core could stand a
breeze too. Does the time the crane spends holding the beam in
position figure in?
For reference, I do have a milling machine to locate and drill gusset
plate and beam end hole patterns, a 1 ton crane to lift steel, and my
welding and plasma cutting circuit is 240V, 100A which is half the
panel's capacity. I'm equipped to make and test prototype robotic and
aerospace components when I'm not sure what I want without seeing (and
modifying) the mental concept. The boss told me my parts looked like
they came from a Norden bombsight
The sawmill etc were retirement projects.
That's a lot of experience!
Need to only say what I can reasonably comment.
Gassless FCAW (Flux-Cored Arc Welding) can be used outdoors, yes.
Never met it - seen it in a welder testing ("Coding") centre once but
not watched what its like, running.
With shielding gas FCAW - not outside.
Crane time - yes, I would reckon - all times and use of resources add.
I think I have said as much as my experience permits.
works well outdoors as long as the wind isn't too bad . It does burn
hotter than solid wire , probably because the flux consumes the oxygen
in the weld zone (I think ...) . It does spatter more , and you do have
a little flux to clean off the weld , but the flux is usually pretty
soft and easy to remove - the spatter is harder to get off . The main
reason I use it is because it does burn hotter and I've been doing
repairs to thicker sections , right at the limits of my Lincoln 110V
Weldpak unit . If I need more power , I use either the 225A (AC only)
Tombstone or the TIG (AC/DC 250 amps) welder in stick mode .
Thanks. I've acquired a heap of galvanized tubing that might become an
upgrade to my 50' antenna mast, and was wondering if I'd missed a
reason why welding on a structure was discouraged, since it's how
ships are built.
* you'd burn the galv away around the weld - and the weld never has
any galv (spray with zinc-based paint - which will need periodically
reapiring / re-applying)
* you are not supposed to weld over galv. Zink toxicity & disturbs
arc (arc goes a lilac colour) & could affect weld strength and
We went over this a while ago, and I asked you what you paint on the
weld because the brush-on zinc-rich paint I have lets rust bleed
through after a year or three, even though I sandblasted the area
clean first. I then sprayed on waxy LPS-3 which kept the rust from
expanding, but it seems to need some existing rust to soak into or it
The goop that does last outdoors is Ox-Gard, for aluminium electrical
connections. The element and feed connections on my antennas remain at
a few milliOhms for many years after scrubbing them and quickly
applying it. I measure the resistance with a voltmeter while 1.00A
flows through the joint, 1mV = 1 milliOhm. I had to drill out the
rivets and install aluminium screws and nuts.
Our digital TV reception is much better than the old analog, and TVs
aren't taxed in the USA, however almost everyone prefers to pay
$150/month and up for cable. Antenna reception is pretty much a
do-it-yourself project with no repairmen to call. This British digital
receiver with the spectrum analyzer program is a great aid in aiming
the antenna to minimize multipath.
I'm just beginning to work with an RTL-SDR I picked up some time ago:
So far I've been pleased with it, works better than I thought it
would. Sure could have used this back when I was still working as a
Already considering a HackRF but the one you linked to looks pretty
good too. You could have used an RTL-SDR for your antenna job for ~$30.
So I figure you are using the RSP1A for other stuff too...
Happy with it, caveats?
Using Linux nowadays, so I have to check for software compatibility.
Looks like the RSP1A is probably supported.
I lived in the world of high-end precision measurement long enough
that I want at least 12 bits of accuracy; the RSP1A has 14. My
portable DVM resolves to 1mV in 22.000V. Back in the early 80's I went
to the trouble of designing and building a 4-1/2 digit multimeter
because I couldn't buy one.
I noticed that in its specs...
Early on I concerned myself with minor differences in voltages and
other bits of minutia. I soon learned this rarely had anything to do
with my need to fix something. Watch the relative values and go for the
likely failures. Like the old quote said, "round up the usual suspects".
Thanks for the explanation :)
I agree that repairs don't need it, but R&D requires not only high
accuracy but NIST-traceable calibration. I like it for hobby use
because it shows trends rapidly.
Inaccurate measurements and other poor lab technique have led to false
claims of room-temperature fusion etc.
Laser'ing is really the great thing - assume it's gone even more that
way in the States?
Avoid having to debur punched holes, flatten plates again, etc.
Holes all there laser'ed.
Get a pallet-load of plates with identities "etched" with defocussed
I've made big-ish platforms with bolted connections not needed for any
structural reason, solely so the broken-apart structure will fit on a
3~1/2 tonne flatbed truck.
Hi again Gunner, and anyone else who wants to join in...
So this thread - it's more of analysing structural performance -
strength / stiffness / load-bearing.
Something I find really exasperating here, in the UK. Is the same in
I think that with
* CNC plasma / laser cutting
* press-braking with a lot of software guidance
* high-strength tough thin plate
* highly-controlled welding - even if manual (GMAW processes)
* CRUCIALLY - Finite Element Analysis modelling easily done
you can make much higher performing structural assemblies from
plate, not assemblages of sections - various angles, box-sections,
etc. - for much nigher-performing steel fabrications.
Much stiffer, much more load-bearing to weight, well-predicted fatigue
resistance at high cyclic loads, etc.
Fairly-much - make in welded steel (cheap) for ad-hoc machine-chassis,
etc., to overall design strategy of riveted aluminum aircraft
Finite Element Analysis enables you to know under design loads the
stresses, deflections and likely fatigue resistance of the proposed
design which the fabricator "details" to the overall specification of
The thinking is so conservative here and there seems to be not a
single person in any engineering / leadership (none of that - is
"management") role with whom you can talk the absolutely obvious.
I spent about 30 days busting my brain around how to use a Finite
Element Analysis package, and went from zero to being show the
falacies in shoddy work with no effort put in by contracted-in
If you know FEA at all - "shell elements" enable you to model thin
plate structures very readily and economically. It is very difficult
to make a design for a single component which will take more than a
minute of a current personal computer's time to solve.
I did a web-page about this concept
It's so exasperating that what is obviously and readily done by
someone working "on the tools" is invisible by reason of unfamiliarity
to most in "leadership"...
It seems that there is a "lazy" assumption that progress is only being
made in "leading" endeavours like computing, bio-whatever and so on,
and no-one but those on-the-tools can see there's similar levels of
advancement possible in "traditional" (sic.) endeavours, as the
overall technological advancement lifts the "baseline" of what is
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