Diferent style jib crane pole is an I beam

Bill D · Jan 23, 2021

I saw this jib crane on craigs list. It looks like a standard wall or vertical support post mount. But it comes with an I beam vertical post welded to a base plate with gussets like a regular pole type. It only swings 180 degrees or so.
Seems like the vertical post is less critical since the bolted on hinges could be shimmed level if needed? I mean if the base settles uneven over time.
Bill D

gbent · Jan 23, 2021

I think that is a home made unit from steel that was laying at hand. No engineering in evidence.

Mark Rand · Jan 23, 2021

Probably a H-beam/universal column rather than an I-beam/rolled steel joist. As in larger flanges and smaller web than the RSJ, so it has similar stiffness front/back and site/side,

Bill D · Jan 23, 2021

I would think a I-beam would be cheaper to buy the a round column for an equal strength. Just seems harder to roll land weld a tube. For steel a solid round is the cheapest form and other shape seems to cost more per pound. Of course the round pole has equal strength in all directions. The I-beam would be different strength at 90 degrees
Bil lD

DDoug · Jan 23, 2021

Bill D said:
I would think a I-beam would be cheaper to buy the a round column for an equal strength. Just seems harder to roll land weld a tube. For steel a solid round is the cheapest form and other shape seems to cost more per pound. Of course the round pole has equal strength in all directions. The I-beam would be different strength at 90 degrees
Bil lD

But it's not "Equal strength"....I've seen many commercially avail I-beam job cranes, however the vertical portion turn on the hinges, keeping the bending momement in line with the web.

gbent · Jan 23, 2021

Bill D said:
I would think a I-beam would be cheaper to buy the a round column for an equal strength. Just seems harder to roll land weld a tube. For steel a solid round is the cheapest form and other shape seems to cost more per pound. Of course the round pole has equal strength in all directions. The I-beam would be different strength at 90 degrees
Bil lD

The material in the center of a pillar adds nothing to the bending strength. Its not the cost per pound that matters, its the cost/lb of useful material.

I don't think you can find a wide flange beam that is any stiffer in the weak axis than 1/2 the strong axis, where some are less than 1/30 the stiffness.

Open sections such as a I/H beam have very poor torsional stiffness. Torsional stiffness has to be considered with jib cranes with powered rotation.

Bill D · Jan 23, 2021

gbent said:
I think that is a home made unit from steel that was laying at hand. No engineering in evidence.

I think you are correct. The square plate looks larger then I would expect. Fewer triangle braces then normal. I think there is a welded angle brace half way up the pole. It might be a gib brace instead.
Bill D

Mark Rand · Jan 24, 2021

It does look as though there are two braces at the front and one at the back, but it's hard to see what held it on to the ground.

magneticanomaly · Jan 24, 2021

You could no doubt make something good out of it, but as-is, much weaker as the boom swings out of the plane of the I-beam. Bad accident waiting to happen

wippin' boy · Jan 26, 2021

i dont like it

Cole2534 · Jan 27, 2021

wippin' boy said:
i dont like it

Me neither.

DDoug · Jan 27, 2021

magneticanomaly said:
You could no doubt make something good out of it, but as-is, much weaker as the boom swings out of the plane of the I-beam. Bad accident waiting to happen

Wack the ends off, and make a nice logsplitter with it.
Or a building column....

Bill D · Jan 29, 2021

More research has shown some good companies using an I beam for a column crane bolted inside a building. The jib seems to be bolted solid to the vertical beam, But there is a bearing top and bottom on the I beam so that avoids the different loading on the web.
Bill D

gbent · Jan 29, 2021

Bill D said:
More research has shown some good companies using an I beam for a column crane bolted inside a building. The jib seems to be bolted solid to the vertical beam, But there is a bearing top and bottom on the I beam so that avoids the different loading on the web.
Bill D

Very different scenario. The building column is not cantilevered, it is attached at each end. The columns I'm familiar with the upright is faced with a heavy piece of c channel, leg in, to withstand the forces when the beam is swung perpendicular to the rafter.

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