Skirt Base Block Check for Two Lugs

[abuanaselmasry]

It is agreed that Roark's formula (7th edition) Table 9.2 Ref. No. 1 is not applicable for base block check in case of single tailing lug. Ref. No. 20 is the one that is commonly used by design software packages.

But, in case of 2 tailing lugs, what should be the case? Ref. No. 4 is used by PVElite, however, this looks like wrong. It is similar to Ref. No.1 in case of single lug.

Since, I'm preparing some excel sheet for the several cases of the base block configurations, I'm confused with the above.

If Ref. No. 4 is not correct, can we make a supper positioning by considering (Ref. 4 - Ref. 20) will realling represen the case?

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer

 

[abuanaselmasry]

No reply!

Hope some one to help

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer

 

[r6155]

Search in the web "Tower Lifting lug calculation", one is"Bechtel Riggind Handbook"

Regards
r6155

 

[abuanaselmasry]

Thanks for the reply. Unfortunately all those rigging books care only about the lifting equipment and accessories. The safety of the vessel during lifting is the responsibility of the vessel design engineer.

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer

 

[dhengr]

Abuanaselmasry:
I do know what a tailing lug is, but I don’t have Roark’s 7th Ed., as might be the case with some members here at E-Tips. Now, reread your original question, and realize that we can’t see what you are looking at, from here; either your references and their references or your actual details. Then ask if most people would have any real idea what you are talking about or what your details look like, given the way you’ve asked your question. So, you’ve already eliminated 70 or 80% of the people who might have tried to help you. If you would have included a few of the free body diagrams you must have drawn to start analyzing your problem, and/or some actual drawings of the vessel, the tailing lugs and the lifting scheme, people might have had some idea what you are talking about, and been able to help.

 

[abuanaselmasry]

dhengr,

Ok, thanks. You are absolutely correct. Since Roark's formula is the reference that many PV software packages like COMPRESS & PVElite are using for such calculation, I have assumed that many engineers have already verified this ans subsequently had the book to do so. What you have said was overlooked by myself. But, how to re-ask the question then .

Regarding the lifting diagram it is similar to this case:

http://www.heavyliftspecialist.com/...ifting-pressure-vessel-main-crane-tail-crane/

pictures of 2 loading cases is under below link. But ignore the 2 beams shown in second case.

https://www.dropbox.com/s/eaavkk43u7e3a96/Cases Photo.zip?dl=0

Let's generalize the question and ignore Roark's Formulas as of now till I find a way to solve this. Does someone has a good practice to follow while designing the case of 2 tailing lugs?

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer

 

[r6155]

See
1)"Pressure vessel design manual", by Dennis Moss
2) "Stress from local loads in pressure vessel" , by Bijlaard

Regards
r6155

 

[abuanaselmasry]

Thanks @r6155 for your cooperation. The procedure in Dennis Moss is simplified and doesn't have reference/base. Dennis Moss book is very great, no doubt. But, when we have references or derivation of the used equations, it becomes better.
COMPRESS & PVElite use Roark's formulas but they provide limited configurations. That's why my intention was to locate the proper case or case combination that will serve the purpose.

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer

 

[AWDMIKE]

Abuanaselmasry,

I have seen the exact derivation for the case to which you are referring. The derivation I have seen uses cases from Krupka's book, along with the assumption that the struts are rigid. If I am not mistaken, the derivation I have seen was used for the basis of the information in the Pressure Vessel Design Manual. The PVDM makes reference to Roark, 3rd Edition, Case 25, however, I do not have that version of Roark to check Case 25.

If you can find the Krupka book, it will be an excellent place to start. Unfortunately it is not in English; it is in Czech.

Vypocet Valcovych TenkoStennych Kovovych Nadob a Potrubi
Krupka
1967

 

[richard15]

Abuanaselmasry,


Roark's formula (4th edition) Table VIII Ref. No. 19 is what you need for 2 tailing lugs.

Richard

 

[AWDMIKE]

It turns out that Roark, 3rd Edition, Case 25 seems to be the same as what's in the 4th edition, for which I do have the circular ring section.

In the 4th edition, Case 25, I believe this is to what the PVDM is referring. This case would apply when the load is carried by tangential/circumferential shear. If you wish to account for internal stiffening members within the base ring you will have to superimpose additional cases.

In the 4th edition, Case 19, this loading would be the case where you have the entire weight concentrated uniformly around the circumference of the ring.

You have to ask yourself which case most similarly mirrors what you have and if it is an acceptable representation.

If you wish to derive the formulas, note that a closed ring is statically indeterminate so you may 1) calculate the bending moment over some section (maybe a quadrant if the loading is symmetric), 2) calculate the strain energy, 3) use Castigliano's theorem. Alternately, Roark lists his references so you may always look there.