Out of plane buckling in lifting lug

[ElCidCampeador]

Hi,

I'm designing classics lifting lugs for a pressure vessel (construction code ASME VIII div.1), like these:

https://mechanicalc.com/static/img/LugAnalysis/Theory/asme-lug-dimensions.png

In some other calculations (not so many) I found a sort of "out-of-plane buckling" check. Is it necessary? Because many people don't consider it in designing and I don't know why. Thanks

 

[ConstantEffort]

Out of plane buckling? Or bending?

For out of plane bending, the assumption is that an appropriate spreader beam is employed.

 

[ElCidCampeador]

Reference to this: "Design and construction of lifting beams" by David T. Ricker

There's something here:

https://mechanicalc.com/reference/lug-analysis

beff.2=4t This limit is intended to protect against dishing failure (once the lug thickness drops below 1/4 of the net width b e
be, the effective width is driven down). This limit can be ignored if the lug is stiffened or constrained against buckling.

Do I have to consider it? For a vessel that I'm designing, if I don't consider this "buckling", lifting will be 10mm of thickness; if yes, it shall be 30mm. This is strange.

 

[JStephen]

In the ASME BTH, they have a couple of limits on b-eff. It appears one of those limits is to eliminate that kind of buckling. But normally, you wouldn't make the lug thicker, you just analyze using that reduced bff, which is usually not the limiting factor.

 

[ConstantEffort]

I haven't considered it, but out of ignorance I suppose. It's not covered in the references I use. I stumbled across this on the internet though:

The fourth failure mode, dishing, is conveniently prevented by establishing a minimum thickness limit. It is suggested that plate thickness be not less than 0.25 × hole diameter​

--

http://www.engineerandbuild.com/lifting_beams.pdf

Most, if not all, of my designs have met this requirement. Sticking a 1" pin through a 1/4" lug doesn't sound right to me.

From the Crosby shackle catalog:

Point loading of Crosby shackle pins is acceptable as long as load is reasonably centered on the pin. Although point loading is acceptable, a pad eye width of 80% or more of shackle spread is best practice.​

If you come close to using 80% of the shackle spread on a 2130 shackle, the lug thickness is going to be much greater than 25% of the hole diameter.

All that said... I'm a vessel engineer not a rigging engineer.

 

[ColinPearson]

See "Pinned Connection Strength and Behavior" by Duerr (2006), and "ASME BTH-1 Pinned Connection Design Provisions" by Duerr (2008). Both of these address the issue, and, like JStephen said, BTH prevents this failure.

 

[TomBarsh]

An issue that concerns me, that I'm not certain is addressed by the standards that have been mentioned, is the possibility of lateral-torsional buckling of certain types of lifting lugs. Consider a vessel being lifted and rotated from horizontal to vertical. Typically it will have some lugs (or trunnions) near the top of the vessel, and a tailing lug near the bottom.

Some types of lifting lugs are placed near the top head (or at a transition) and project upward for some distance. In the horizontal position this makes the lifting lug act as a cantilever beam. It is conceivable that if the lug's span is long enough and the b/t ratio low enough then it could experience lateral-torsional buckling. I believe that paying attention to this possibility and designing the lug with a low b/t ratio should account for this condition. For instance, a "relatively thin" lifting lug might have plenty of strength to support the vessel in pure tension (vertical position), and even adequate bending strength in the horizontal position. But if the lugs are too thin then lateral buckling may be a failure mode.

 

[JStephen]

I believe in BTH, they do have design information for a rectangular bar in bending that would address that.

 

[r6155]

See examples in Pressure Vessel Design Manual 4th edit., by Dennis Moss

Regards
r6155