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Why always I beams for cranes?

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
Not "Always"
You make your crane the way you need, using what ever material you can get.
 

boslab

Titanium
Joined
Jan 6, 2007
Location
wales.uk
I beams have essentially a larger section modulus than a tube,
I have tinkered with a matterson gantry crane, it was the teeny tiny 500 ton version, I remember load testing with steel slabs, 1200 tons worth, the surveyor was on the top beam to check the deflection, it went from a positive camber to flat ( apparently going negative would be very bad) it’s still in service though the switchgear and motors have been changed, rope changed every 12 months, quite a job with 54 falls on each end of the lifting beam, quite a big spool of 2” cable.
Mark
 

johansen

Stainless
Joined
Aug 16, 2014
Location
silverdale wa
I beams are preferred for all the reasons mentioned but i can add one more, the rolling process of producing an I beam would have had an advantage in years past at producing the strength in the directions you want.

For pressure vessels, you want to roll the pipe along it's circumference and then roll it into a tube and then weld it somehow with no loss of strength. You can get tubing that is wound in a spiral and has a spiral weld, which is a compromise but it does work.

For structural tubing you can get square tubing and it will have more moment of inertia than round, for the same weight. Also preserves the torsional strength of a closed beam.


If you want torsional strength but the same moment of inertia in the strong axis as an I beam, then make your own.

You can add triangular gussets or stiffeners to an I beam to get the torsion you need. Vertical flange stiffeners don't add torsional stiffness.. Or you can take the top and bottom flange of equivalent thickness in steel, and weld a box beam using steel of half the web thickness of the equivalent I beam. (Two webs each half as thick provide the same sheer strength as one solid web, but only 1/8th each the crushing strength. Which is usually not a limitations) so it's the same strength, same weight, but now 100 to 1000 times the torsional stiffness of an equal weight I beam..


If the two webs are not set at the edges but in one inch from them, you can still make many gantry I beam trolleys work with your beam. Because the sheer stress is distributed, weld quality is not critical. I suppose if the gantry is used enough you could cause your welds to break due to fatigue.

Easier still is to make your crane from 2 I beams welded side by side to get your moment of inertia in the strong axis and get torsional strength and get your rolled flanges for your off the shelf trolly to ride on.
 
Last edited:
Joined
Apr 19, 2006
Location
Manchester, England
I beams have essentially a larger section modulus than a tube,
I have tinkered with a matterson gantry crane, it was the teeny tiny 500 ton version, I remember load testing with steel slabs, 1200 tons worth, the surveyor was on the top beam to check the deflection, it went from a positive camber to flat ( apparently going negative would be very bad) it’s still in service though the switchgear and motors have been changed, rope changed every 12 months, quite a job with 54 falls on each end of the lifting beam, quite a big spool of 2” cable.
Mark
They used to service the cranes from British Steel regularly. One I remember was a ten ton static hoist that only performed one lift every year. It lifted the lid off something and put it back again.
After that one lift it was sent back to “ Matterson “ and completely overhauled. New bearings throughout and a brand new rope. This happened every year. The price of failure was too great apparently.
They also made cranes for changing the engines in Royal Navy ships. The long travel drive was a rack and pinion and the cross shops crab drive was a lead screw. All to stabilise the lift. The couldn’t do anything about the ropes.
It was a great place to work but Mrs Thatcher and the asset strippers won out in the end.

Regards Tyrone.
 

metalmagpie

Titanium
Joined
May 22, 2006
Location
Seattle
I once read on rec.crafts.metalworking about a potential "gantry" design. Weld two pipes into a T. Do it again. These are the legs and feet. Take a 3rd pipe and weld 90 degree slip couplings to each end. Now lay the legs out flat on the ground and slip the top pipe over the vertical legs. Secure the feet and use a car to pull the thing upright, at which point you restrain it from coming over top dead center with ropes or chains. Now turn the legs 90 degrees and wa la it's a cheap gantry. No rolling trolley - just throw a short sling over the top pipe somewhere and hook your chain hoist to that. To take it back down and store it, reverse the procedure.

Pretty redneck, but I bet someone built it. You could lean the parts against the side of a barn and they wouldn't be much in the way.

metalmagpie
 

Toolmaker51

Cast Iron
Joined
Jan 13, 2009
Location
West MO
It’s quite simple. Most of the metal in the tube is not where you need it. Most of the metal in a I beam is exactly where you need it.
The I beam was revolutionary in development of high rise architecture. Pipe hardly goes beyond getting fluids where they belong.
 

Strostkovy

Stainless
Joined
Oct 29, 2017
Turns out pipe works totally fine, but I was quoted $2.20 per pound for tubing and $1.20 per pounds for I beams.
We normally pay around $0.59 for HRPO plate, but we buy a lot of that. I'm not interested in welding a gantry from plate.
 

garyhlucas

Stainless
Joined
Oct 17, 2013
Location
New Jersey
In order of cost increasing:
Flat Strip
Angle Iron
Channel
I-Beam
H Beam
Pipe (mostly made from flat strip)
Rectangular/Square tube (rolled from round tube/pipe)
Same for torsion strength in increasing order except Rectangular/Square is less not more.
 

Strostkovy

Stainless
Joined
Oct 29, 2017
In order of cost increasing:
Flat Strip
Angle Iron
Channel
I-Beam
H Beam
Pipe (mostly made from flat strip)
Rectangular/Square tube (rolled from round tube/pipe)
Same for torsion strength in increasing order except Rectangular/Square is less not more.
That makes sense but the tube rollers must be making bank, selling material for four times the cost of buying it for just rolling and welding it. This wasn't even pressure rated or certified material, and could likely be rolled cold.
 

johansen

Stainless
Joined
Aug 16, 2014
Location
silverdale wa
In order of cost increasing:
Flat Strip
Angle Iron
Channel
I-Beam
H Beam
Pipe (mostly made from flat strip)
Rectangular/Square tube (rolled from round tube/pipe)
Same for torsion strength in increasing order except Rectangular/Square is less not more.
If most square tube is made from steel pipe then I agree, it's going to cost more than steel pipe to get the same torsion stiffness. You get a small benefit in stiffness by weight from squishing a circle into a square but you loose some strength due to force concentration in the middle of the flats.

The difference between a square tube and a pipe of equal weight isn't particularly large, but a square tube of equal wall thickness compared to a pipe is significant difference because the square tube weighs 4/pi more and has more outer edges located 41% further away from the centroid, where their contribution matters (1.41^4) more.

There can be great differences between torsion stiffness vs strength, squishing a pipe into a rectangle of 2:1 length to width ratio would reduce it's torsional strength significantly but it's stiffness might be similar.

I believe the cheapest method to get sufficient torsion stiffness for an I beam gantry is to simply weld two I beams together to make a closed box section, let the gantry roll on the exposed flange. Or my other suggestion of make your own box beam with 4 flat bars welded into a sort of double web H beam
 

Strostkovy

Stainless
Joined
Oct 29, 2017
If most square tube is made from steel pipe then I agree, it's going to cost more than steel pipe to get the same torsion stiffness. You get a small benefit in stiffness by weight from squishing a circle into a square but you loose some strength due to force concentration in the middle of the flats.

The difference between a square tube and a pipe of equal weight isn't particularly large, but a square tube of equal wall thickness compared to a pipe is significant difference because the square tube weighs 4/pi more and has more outer edges located 41% further away from the centroid, where their contribution matters (1.41^4) more.

There can be great differences between torsion stiffness vs strength, squishing a pipe into a rectangle of 2:1 length to width ratio would reduce it's torsional strength significantly but it's stiffness might be similar.

I believe the cheapest method to get sufficient torsion stiffness for an I beam gantry is to simply weld two I beams together to make a closed box section, let the gantry roll on the exposed flange. Or my other suggestion of make your own box beam with 4 flat bars welded into a sort of double web H beam
I found in simulations that straight square tube is very good at resisting deflection, but but a bent square tube (mandrel bent or rolled, not kinked) is very bad at it because the large flat areas are unsupported and tend to cut the corner, and deflect to a broader radius at very little load that puts all of the stress on the side walls and corners.
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
I found in simulations that straight square tube is very good at resisting deflection, but but a bent square tube (mandrel bent or rolled, not kinked) is very bad at it because the large flat areas are unsupported and tend to cut the corner, and deflect to a broader radius at very little load that puts all of the stress on the side walls and corners.
Why not post up some screen shots ?
 

gustafson

Diamond
Joined
Sep 4, 2002
Location
People's Republic
If most square tube is made from steel pipe then I agree, it's going to cost more than steel pipe to get the same torsion stiffness. You get a small benefit in stiffness by weight from squishing a circle into a square but you loose some strength due to force concentration in the middle of the flats.



I believe the cheapest method to get sufficient torsion stiffness for an I beam gantry is to simply weld two I beams together to make a closed box section, let the gantry roll on the exposed flange. Or my other suggestion of make your own box beam with 4 flat bars welded into a sort of double web H beam
I think you want strength in bending, not torsion, no?
I would think the strongest beam would be stacked one on top of the other then welded rather than side by side. The load carrying of taller beams usually increase exponentially in height rather than width. IOW in wood a 4x16 carries more load than an 8x8
Not that welding beams together makes a lot of sense unless you already have a bunch of them
 

cyanidekid

Titanium
Joined
Jun 4, 2016
Location
Brooklyn NYC
Semi trailers have I beam chassis ,top and bottom plates are 3/4 or thicker ,the diaphragm is only 1/8"...........stiffeners are rarely used as they add to production cost........in any case the deck structure acts as. bracing.........if the frame does bend ,the trailer simply collapses..............back in the day ,trailers had a lower tension member ,similar to a railway wagon,except the railway wagon always had a turnbuckle that could be tightened to maintain the camber of the frame ........the trailer had a steel strap that could be tightened by cutting and rewelding.
depends... some flatbeds have I section frame rails, (BTW, top and bottom are called flanges, "diaphragm" is the web) but most new enclosed trailers use formed C section. they are formed from heat treated alloy for improved S/W ratio.

no stiffeners???

the the formed C alloy rails don't have welded stiffeners ( it says "DO NOT WELD" right on them ) but im sure ive seen bolted stiffeners.
the welded frame rails, I think are usually aluminum? and I think ive seen stiffeners on them too.
I don't think the cost of adding stiffeners is a significant factor, regardless.
 

johansen

Stainless
Joined
Aug 16, 2014
Location
silverdale wa
I think you want strength in bending, not torsion, no?
I would think the strongest beam would be stacked one on top of the other then welded rather than side by side. The load carrying of taller beams usually increase exponentially in height rather than width. IOW in wood a 4x16 carries more load than an 8x8
Not that welding beams together makes a lot of sense unless you already have a bunch of them
For some things you want both torsion and bending, and the cheapest way to get it in my opinion is either weld a double web I beam from flat plates (spacing the two webs as far apart as you can, or weld two I beams side by side. On top of each other wastes the material in the flanges in the middle. You might as well have made a castle beam from a single I beam. (Cutting the web in a truncated triangle pattern and then welding back together shifted a bit with a deeper web)


I do have to correct what I said earlier.

Expanding a circle into a square would result in greater stiffness in torsion. Squishing a circle into a square results in about a 20% reduction in torsion stiffness.
 

gustafson

Diamond
Joined
Sep 4, 2002
Location
People's Republic
But a crane needs little torsional strength. A crane needs strength as a point loaded simple beam.
Two I beams welded vertically, I would think, would be significantly stronger than two welded side by side
 








 
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