Material lift. Where will the pick points fail?

[chadjans]

Hey guys, I just finished this material lift platform that can be used with a telescope fork lift, regular fork lift or a crane. The four pick points for the crane use are in the corners. What I need to know is what you guys think the fail point would be with the pick points. I followed similar designs I found on similar platforms. With one exception the anchor hole I drilled in the corner of the 2.5 by 2.5 by .250 wall box tube and not either of the flat sides. They are fully welded to the 2 by 2 by .188 wall box tube with approx 20 inches of weld. The entire main section of the platform is made of 2 by 2 by .188 wall and the x bracing is made of 1.5 by 1.5 by .120 wall. Hole size is 1 5/8 throught the dead center of the corner.


http://www.pirate4x4.com/forum/attachment.php?attachmentid=198846&stc=1

http://www.pirate4x4.com/forum/attachment.php?attachmentid=198847&stc=1

http://www.pirate4x4.com/forum/attachment.php?attachmentid=198848&stc=1

Chad

[pmurf1]

I don't think anything would fail if loaded reasonably, looks strong. It would take a hell of a lot of weight to shear your holes clean through to the point of failure. We routinely lift 4000# chillers with holes cut in 1/8" c channel frames. We tipped a 26000# forklift over once, but the chiller never came undone or ripped the holes. I might have made the holes a little smaller for more material since if you craned it you would probably use 4 shackles and they are usually 1" holes for the cross pin. It's a pain to keep hooks attached especially by yourself, shackles are set once they're on.

[chadjans]

My concern is that the corner would split and then two pieces of flat bar would be left and we all know how flat bar fails.

Chad

[NotHardCore]

Looks quite stout, what do you expect the max load carried might be?

We used to (and still do) use baskets of this type for light lifts say <500 lb, but for all our heavier lifting baskets & frames we have an alternate design (offshore oil & gas construction industry)

Our heavy lift baskets use padeyes welded on the inside of the vertical members, but rotated 45 degress about the vertical axis so they are pointing at the center of the basket.

Reason we do this is because, when you are lifting with 4 point slings from a single crane hook, your loading of the eyes will not be in plane. Its kinda hard to describe but the angle iron that form the lifting eyes will want to bend inwards as the slings load up. Having the padeyes on the inside and pointing at the center of the basket has loading in plane only and is much stronger (at the expense of interior space).

Additionally, the shackles will not sit properly on the eyes when they are loaded up.

In summary, should be fine for light loads, but if youre really stacking it heavy, or snatch loading the lifting points you might want to think about a redesign or extra beef.

Deano

[Toyota_Jim]

I would have used a heavier angle.

[PAToyota]

The problem that I see is that with a crane, you are going to pull the attachment points toward the center of the lift platform with the central attachment point. That will bend the angles inward over time and possibly fatigue the metal. With the large holes, I can see cracks eventually forming.

[edit] Reading back through things, I think I'm saying the same thing as NotHardCore and agree with his suggestion of rotating the attachment points 45 degrees.

[EMG7895]

At the least I would add more angle to the points and stagger them (long piece on the outside, short on the inside)

[BumpyDodge]

The short version: *Looks plenty stout. I wouldn't be scared to get in it.*

But I'm unemployed until tomorrow morning and not busy, so here's my lengthy editorial version should you care to read it.......


Over the long term,If it were to fail it could fatigue cracking in the top corners where the angle iron joins the top railing - from the top of the angle iron pick point wanting to fold inward if it's overloaded (as previously mentioned by several others) If you mentally fold the top of that piece of angle iron towards the center of the platform, the legs of the angle iron will want to buckle outward slightly where it meets the top rail. There are several combined forces working in unison on three seperate imaginary planes that are all welded solidly together, so any weak area will affect the entire weld. Torsional forces twisting the top outer corner + tension from the angle iron trying to bend inwards, pulling the weld apart at the top outer corners of the angle iron/top railing joints + shear between the vertical corner post vs. the angle iron pick point + compression on the inside corner "pocket" made by the angle iron. Note* -This analysis only applies if the rigging/slings/chains form a pyramid shape. This point's been well covered by PAToyota and NotHardCore and I agree with them.

Bust out the mind-altering substances, or put on your thinking cap now........

After you imaginarily bend the pick points towards the center, using the above make-believe rigging, you can now theretically consider the top portion of the welds cracked- thereby allowing the top of the angle iron to bend the direction it "wants to bend" - using the top railing corner point as the bend vertex. The remaining lower portion of your weld is now almost completely under a "the-weld-is-nicely-inline-with-the-direction-of-pull-and-it's-as-strong-as-it'll-ever-be" position. This part would probably never crack even subjected to extreme overloading... unless the crack had already propagated downwards after it started at the top. *Note -That's why in engineering specs there's usually a maximum limit to the length of fillet welds when opposite side fillets can't fully fuse together ,- you can't prevent a stress riser on the side of the weld you can't reach- should one weld start to crack, it will stop cracking when it reaches a gap between welds. The next fillet weld in a less-stressed position on the joint will continue to hold(at least temporarily). It also has a fringe benefit of making the part much easier to cut out/repair/replace should that section of a structure ever be seriously damaged. If water entrapment between the metal is a concern - just add a dab of sealer to the unwelded area of the joint before paint. Smear the sealer flat and smooth so it does not appear to be a "covered up" weld to anyone checking later. A couple plug welds would have been a real nice touch since you were cutting a few holes anyway.

Now it's time to go off on a wild tangent..........

Welds are stronger when they are positioned to hold loads parallel with an imaginary plane *along* their lengthwise axis, but they usually won't tolerate much bending *around* their axis unless it's a completely-perfect-on-both-sides-full-fusion-butt-weld. The horizontal position welds at the bottom of the pick point material would have been better if the angle had been cut/welded at a 45 degree taper instead of terminated at a 90 deg angle. Not only would it be stronger in this case, but it also looks nicer and doesn't really add any time to the job. You would have 1.4 times more weld holding the same load (remember middle school geometry?) + more nicely distributed stress, all using the same amount of raw material ( I know - technically only true if you add another 1/2x the angle leg width to the overall length and don't count the triangular cutoff scraps as waste). Or you could have been lazy and just left the end open, that weld is not adding any *significant* strength. Look at a commercial truck frame splice for an example. They don't weld any reinforcement on a perpendicular angle to the frame rails (If they do it right) it really only adds an unecessary stress concentration point (stress riser) for cracks to start. If the frame rails are spliced w/ a perdendicular weld, the weldor will usually at least cut the channel's legs at an angle, or they sometimes add a "diamond patch" for reinforcement. Look at how some motorcycle frames position "runoff" beads and gradually taper the ends of any highly stressed weld-on mounts for good ideas to protect against fatigue cracks. Or just look at an old tapered barn door hinge - same general concept of doing the same job, while using less unecessary material/lighter weight/cheaper/+looks pretty too.


Yet another dandy illustration......

There's a Ford Truck commercial on TV where they lift an entire truck with one bed bolt, but they rig the bolt in the shear position with a clevis - not in tension, like how it is loaded when holding the actual pickup bed on the truck. Serves as a good illustration of how easy it is to forget how different loads applied from different directions will affect the ultimate yield strength of the same object.

To summarize my 2 cents......

If I built the platform I would have drilled a hole in a piece of 1/2" thick bar stock or flame-cut plate steel, and bolted it through the vertical members from the outside. Then I'd heat/bend the top to a "natural angle" and attached a forged clevis or chain connection link to the pick point/lifting hole - If the bar stock bends or twists a bit, that's OK - you'd crumple the rest of the platform before it would ever break. Bolts add a solid "mechanical" attachment too, especially in shear position. You could alternately cut a long rectangular shape with a hole at one end from plate, and slot the square tube upright so the entire piece would slip in diagonally (from a vertical view), then you'd have twice the weld , at a less stressed angle, and your slings/clevises are at a much more happy angle.
You could alternatively forge what amounts to half of a a big long strap hinge from flat stock relatively easily, then sandwich a forged D-Ring in the "hinge" hole if you really want to show off your skills. Bolt that along the corner vertical members with 1/2" grade 8 hardware going through welded-in round spacer mounting bosses, and it'd be too damn cool for words to express. I'd gladly bring a case of beer to your shop for the pleasure of watching such fine fabrication. Seriously though, bolts are easy to check through paint, welds aren't. Bolts also have a much more narrowly definable breaking point than welds. White paint shows cracks best, and wont heat up the steel when it's out in the sun, so that's what I'd shoot it with.

Out of curiosity...

Do you work with/around shipping containers? They're the first thing that popped into my head when I saw your picture. That platform would stack nicely.

On my personal adventures with lift platforms.......

the work platforms I used at my old job used the really fancy threaded swivel mount D-rings attached at the base, large 360 degree swivel mount D-rings cost a small fortune (over $100 apiece x 4) . I think a well thought-out and bent piece of 5/8" mild steel rod welded on correctly + $7 farm store clevis would have been every bit as safe. We always used the POS with a forklift anyway.

If you have any doubts on the current version of this thing..........

Sticking one long 1/2" bolt horizontally *through* both the angle iron and each corner vertical member and welding the bolt/nut solid (to prevent loss /tampering/or questions like "WTF is that bolt for?") would cover your ass and prevent total seperation in a lift point weld failure scenario on what you have pictured - Just in case you're paranoid. I won't lose sleep over it.

Now everyone else can argue.......... :flipoff2:

[chadjans]

Thanks Bumpy Dodge. I appreciate the canded discussion. Now go to work.

Chad

[WideBody]

Why not make a mount that looks simular to this made out of 1/2 or 3/4 plate.
http://www.hi-lineperformance.com/lift-tab.jpg
Or mount some large eye-bolts or fabricate a mount made to attach some high-end shackles.

There is a whole section on rigging here::

http://www.all-lifts.com/