What is a carding moment? 1

[EdClymer]

Greetings

A new design code for plastic tanks (EN13121-3) uses the term 'carding moment' - for moments applied to item in question.

The item in question, is a nominal 600 dia, about 250 long tube; fixed at one end (built into tank shell) and free at other. It is a manhole, with flange, gasket and bolted cover plate. It is constructed of polypropylene with substantial external GRP(FRP). Dead weight mass of branch is some 128 kg.

I have found a reference to 'carding moment' related to a bridge and bridge deck. But without an explanation.

I am unfamiliar with the term 'carding moment'. Can someone explain? Ideally in context of a short cantilever - which is in effect a cylinder.

If it helps, the original (native format) word was 'krempelmoment (German); then translated into English.

Many thanks

Ed



Ed Clymer
Resinfab & Associates
England

 

[ornerynorsk]

This came up in my online German tech reference. Not sure if it applies accurately to your application.

"Restraint against torsion around the linking axis of the nodes"

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[RPMG]

I google this and saw a picture, so obviously I became an instant expert.

If you have an S-shaped bridge, the far left and right sides create a carding moment. That moment must be resisted by the torsional strength of the bridge. If there is half of an S-shape, say C shape, designers can do some pretty fantastic things like place supports on only one side of the bridge, using the carding moment to balance things out.

So, with manhole and O-shape, I would guess it's the radial or transverse moment in the top shell. But then the carding moment, which is bridge torsion, is tank moment, and a dumb term to use in any case.

 

[EdClymer]

My thanks to ornerynorsk, Lomarandl and RPMG for their help.

I fear something got lost in the translation from German to English (not the first time!).

I can see two possibilities.

1) Dead gravity load of branch, flange and bolted cover-plate back to shell junction - as a moment (but it does not fit bridge description).

or,

2) Resistance of branch and connection to shell of the load applied by torque wrench to the flange/cover-plate bolting
- this would be torsion to the branch.

The comment from RPMG.

Do you mean Airy points? As in support pitch = Length/sq root 3 - for two supports. As in bookshelf uniformly loaded using two brackets? This uses cantilever ends to achieve balance between supports?

Comment form ornerynorsk.

I also saw this reference during a search, but I can't relate description back to a vertical 3 m dia tank with a 600 mm branch protruding.


Regards

Ed


Ed Clymer
Resinfab & Associates
England

 

[JStephen]

I'll leave it to others to translate, but this page:

http://www.cae-wiki.info/wikiplus/index.php/Axisymmetrie

Seems to be using it for the moment in Figure B:

 

[EdClymer]

JStephen

Very many thanks. The diagram B would be an explanation (but at a point much lower down the shell). The vertical load to the manway branch would pull shell outwards at top of branch, and force shell in at bottom of branch (and be neutral at the equator). This confirmed in practice and FEA model. Which is why the shell/branch connection is heavily compensated (to make sure etc).

My thanks to all who helped - another piece of the puzzle has been solved.

Regards

Ed

Ed Clymer
Resinfab & Associates
England