IBeam vs Tube for Gantry Crane Stilts

kramttocs

Member
Wasn't sure the best forum for this but I find that most of my google searches wind up here so figured I'd see what you all thought.
Apologies for my first post being an essay.

I recently picked up two identical gantry cranes/a-frames. The only downside to them is that they are short (7.5 feet from ground to bottom of ibeam). My plan is to raise then a few feet so that a trolley and hoist won't be dragging the ground. One will be used to lift items on occasion but the other will be turned into a swing/playset. 10" I beam and 8x8 square tubing.

I have two options available to me using material I have. My inclination is to use ibeam for the lifting one and round for the playset but I am all for overbuilding.

Ibeam:
I have a few lengths of ibeam: 37', 29', 29'. 1/2" web thickness, 10" flange width, 14" height, and 7/8" flange thickness
Cut into 5' chunks, weld top and bottom plates on them and bolt the existing foot of the crane to the top of the ibeam. The bottom plate will be anchored into a concrete pad or footer.

Steel Round Core:
I have quite a few hollow round cores. They are 4'4" tall, 9" diameter, and 1/4" thick.
Would weld plates to top and bottom same as the ibeam


Photo 1: crane before I disassembled and moved it
Photo 2: I beams
Photo 3: cores
Photo 4: proposed plan. NOTE: the dotted lines going horizontal are 3 places for tension chains/cables holding the legs together. The top 2 are already available from the gantry as is, the third is proposed to replace the second.

General Questions:
1. Would either of them not work well for this?
2. Which is stronger/better for this application and by how much? Not asking for numbers here as I know the math gets complicated fast. Really looking for simple terms like 'a lot', 'not much', etc :)
3. For the tension points - would above or below the stilt connection be best for the bottom cable/chain?

Ibeam Questions:
1. Web perpendicular or parallel to the ibeam (figuring perpendicular)?
2. Beneficial to weld some pieces of strap across the flanges on both side? So not a full box-in but more like ladders on either side

Core Questions:
1. Would filling them with concrete make a worthwhile difference?



Let me know if I haven't explained any of this very well. Thanks
 
Images:
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The concrete should be slanted inward at the same angle as the "legs" of the crane. If set as shown the spreading of the legs
under load will tip them outward. Extending the existing legs with the new material, at the same angle, then terminating them in
concrete at ground level is also operational. Jim
 

That was actually my first draft of the design but wasn't sure how critical that was as going straight down off of the existing flat pads would be 'easier'. I definitely realize there is merit to it (hence the A in A-frame). So is going straight down even with the two tension cables/chains on each leg asking for trouble?
 

To clarify some more, the rectangle over the new material (shaded in the drawing) is the bottom plate that is welded onto the existing material making a 1 inch thich 10"x6" pad.
 
I agree with you here, a bend will be very hard to engineer so the legs don't try to spread at the bend. Of course that depends on how much you plan to lift with it. For a 1 ton hoist they are enough over built that you could get by if you do it right. If your planning on lifting what those are designed to lift you will need the leggs to be straight and very well built.
 
Thanks guys. I appreciate the comments.

I doubt I will ever get close to how much this thing will lift but I am all for do it once, do it right. Plus, these will by far outlive me and I'd hate to have
people at my farm sale think I was crazy. I also have no clue how much this thing would lift in its current design. Would love to know their history.
For the lifting one my near future plans are a couple 460 Fords and some truck cabs (so nothing heavy). Our biggest tractors are 4430's so not sure if this would lift
the rear end or not but I am guessing that would be the absolute largest thing I'd ever have a need to lift around here.
For the playset one, who know's what monstrosity my 3 and 4 yr olds will want me to build on top of it someday but weight wouldn't be an issue there.

There's been comments from both sides and while I am leaning toward the bent-leg approach for a few reasons I want to make sure it's the right decision.
I really don't want to cut on the existing material (sentimental I guess) and I am not sure how I could make the straight leg work without cutting off the current
foot plate. I would also go with square tubing in that design and getting about 50' of that wouldn't be cheap (about 6ft x 8. 6ft for the hypotenuse since I'd still
like to vertically raise it at least 5ft).

I am all for hearing arguments against the bent-leg approach.

For the bent-leg approach, I know that crossmembers are vital. The existing material has nuts welded on where I have the top dotted line drawn. It also has keyhole
chain slots close to the bottom plate where I have the second dotted line drawn. There's no reason not to put a crossmember in the top location (although the least
essential) but for the other one would it be best served at the second or third line. My thoughts are telling me the second line to reduce the shear force on the
bolts attaching the extension piece.
 
If there's any doubt with going bent-legged with crossmembers, I could always add a reinforcement pipe/tube/web onto the outside edge of the extension that would continue on at the same angle as the legs. It would make my footing larger but a wider range of 'free' material would work for that and it's still a simple concept.

I can add a drawing of that if it isn't clear what I mean.
 
If you run a tie between the legs at one of your dotted lines then the straight legs will be fine, just make sure it is enough for the job. The only reason not to do this is so you can work through that area just as your trailer is in the pic. If you run a tie there you will be restricted to only driving through between the legs. If that works for you, then that is the best and strongest plan, even stronger than straight legs due to the shorter spread of the legs.

Use the round for the uprights rather than the I-beam as the beam will be flexible and is not a good choice for that.
 
(quoted from post at 23:31:08 02/20/17) ...

I've thought about that and I don't think it will be a problem (99% of the time at least). The top tie shouldn't ever have to come out and the bottom tie could be removed prior to backing whatever in, added back before lifting, and then the trailer driven out from underneath it. Most things could actually drive/back through from either direction of the ibeam.

Would adding the strap 'ladder' to tie the flanges of the ibeam together (or even boxing it in completely with 1/8) make a difference on using the ibeam over the round?
 
I'm not sure 1/8" would be good, but 1/4" would, then you will have basically the same thing as a tube
if you do it right. The pipe will still be better in this situation if you have enough.
 
(quoted from post at 09:09:12 02/21/17) I'm not sure 1/8" would be good, but 1/4" would, then you will have basically the same thing as a tube
if you do it right. The pipe will still be better in this situation if you have enough.

Gotcha. Yeah, we have plenty of those things around. Appreciate all of the input. Sounds like a plan I can proceed with.
 
Just remembered - if using the cores, what are your thoughts on leaving them hollow vs filling them with concrete before welding the top plate on?
 
Your "transverse stiffeners" could also be called buttresses. Very similar to cathedral design where the arches have a thrust force that is resisted in compression by the buttresses.

Provide a triangle shaped support with the vertical leg on the inside. This will resist that compression. Anchor the triangle to the ground to prevent sliding from the thrust forces. All your forces are then resolved into axial forces rather than bending.
 
(quoted from post at 17:53:21 02/21/17) Your "transverse stiffeners" could also be called buttresses. Very similar to cathedral design where the arches have a thrust force that is resisted in compression by the buttresses.

Provide a triangle shaped support with the vertical leg on the inside. This will resist that compression. Anchor the triangle to the ground to prevent sliding from the thrust forces. All your forces are then resolved into axial forces rather than bending.

You are describing what I mentioned earlier, correct? About the reinforcement pipe/tube/web on the outside edge of the vertical extension the would continue in the same path as the existing angled legs?

With all of these options, which is best in your opinion?
Core vs ibeam (with buttresses)?

If I go with the triangle at the base, would I need the cross ties?

Best selection for the triangle material? I doubt I have that much solid 1/4 plate to make a 8 webs but no problem with pipe or square tubing.
 

Yes, I was referring to your earlier post.

You wouldn't necessarily need cross ties because the thrust force would be resisted by the buttresses. The buttresses would just need to be strong enough to resist that force and be anchored at the base to something also strong enough to resist that force. You'd need cross ties if one of those isn't possible.

I would probably use square or rectangular tube sections if you have those available. They have good strength in both axes and are also good in torsion. You could get some funny, unexpected bending if things don't align well. Your I sections are pretty beefy, so they're probably OK as well.

You also need to think about creating a possible house of cards in the longitudinal direction (parallel to the crane beam) where all of your newly attached supports could topple. Something to think about.

Here is a somewhat similar setup. The geometry is a little different, but the concept is the similar:

http://www.advancedindustrialsolutions.com/top-running-knee-braced-crane-runway.html
 
It would take some significant anchoring at the base of both the main post and the buttress for that to work in this situation. It could certainly be done and with some bracing at the top to help it would be better, but you will still need to make them so they can't be pulled out of the ground.
 
(quoted from post at 15:05:14 02/22/17) It would take some significant anchoring at the base of both the main post and the buttress for that to work in this situation. It could certainly be done and with some bracing at the top to help it would be better, but you will still need to make them so they can't be pulled out of the ground.

Agreed. I am thinking no matter what I'll anchor at the top point and have a removable chain+boomer at the second point. Again so it would let me drive through, chain, lift, drive out under the chain. Once assembled if I feel like it needs more I can pour another pad, weld the hypotenuse to the upright, and bolt it to the new pad. Guessing at that point, the shear strength of the bolts would be the weak link more than anything.
 

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