Flat walls with ribs 1

[Konrad]

Hello,
How do you calculate flat walls strengthened with ribs? U-2(g)?
Konrad

 

[Konrad]

Of course, I mean SecVIII-1, but this applies also to SecIV.
Konrad

 

[ijzer]

By pure mechanics. Devide the bending moment by the moment of resistance.
A standard handbook on mechanic's will show it

 

[Konrad]

Right, that's pretty obvious. The problem is how do you justify it in a pressure vessel's calculations? Does adding ribs to a flat head remove it from "unstayed flat heads", and exempt from UG-34?
Konrad

 

[metengr]

Review ASME Section VIII, Div 1, Mandatory Appendix 13 regarding vessels of noncircular cross section. examples of stayed walls are provided.

 

[Konrad]

Thank you, metengr, this is right. But it does not apply to a flat head, which closes a circular shell. What would you do with it, when you need to reinforce the head with ribs?
Konrad

 

[metengr]

Konrad;
Review UG-32 and UG-47.

 

[Konrad]

Yeah, but I can't use stays. It must be ribs. What do you think, am I free to go to U-2(g) without bothering with UG-34? What about, say a honeycomb plate?

Konrad

 

[metengr]

But it does not apply to a flat head, which closes a circular shell. What would you do with it, when you need to reinforce the head with ribs?

You need to perform your own stress analysis with calcs to assure the AI that you have adequate strength if your head design does not follow any of the rules in Part UG. Why can't you use formed heads, why do you need to use a flat plate???

 

[Konrad]

The reasons for using ribbed flats are various. Sometimes I use rare and expensive materials, sometimes it's too thick to form, sometimes the design gets more compact with flat, sometimes it's just a pretext not to use UG-34's heavy wall thickness.
Konrad

 

[metengr]

Konrad;
That is fine because the ASME B&PV Code is either design by rule or design by analysis. Be aware you better have a detailed stress analysis for your design to fly (not literally, ).

 

[Konrad]

Well, I'm not setting stresses to 99% of the Yield Point of the piece of material actually used, like some suiciders do

Konrad

 

[GenB]

You can use ribs or can actually reinforce the flat plate with another flat plate add-on smaller piece.
I will look for the calcs and advise.
genb

 

[Konrad]

GenB, As a matter of fact, I most often do bursting test of a ribbed structure. The disadvantage is that BPVC provides for parts, not connections between them. This leaves an open discussion what to do when during a bursting test some welded/brazed joint breaks. Looks like some requirements are missing...
Konrad

 

[wjp123]

Konrad,
Sorry for this late rsponse, but you look at rib stiffenend flanges "FLANGES THAT WON'T FAIL" by Alexander Blake.
This may help you.
Cheers.

 

[arto]

wjp123 - is there more reference info on where to find that?

 

[GenB]

Arto, I checked up on-line and it is $250.Dlls book,
"FLANGES THAT WON'T FAIL" by Alexander Blake.