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#76061 - 12/03/21 09:43 AM Friction vs Frictionless
Michael_Fletcher Offline

Registered: 01/29/10
Posts: 1025
Loc: Louisiana, US
Could someone shed some light on this topic?

My understanding from a pipe stress webinar some time back (I think Dave was presenter?), that we shouldn't (or can't) take credit for friction to rescue our pipe and equipment.

Some client stress specifications call for this.

It's specifically a code requirement (B31.3) to consider the harmful effects of friction.

However, I think I might be misremembering whether or not frictionless is strictly a code requirement. However, I do not see that it is, unless I'm missing something.


#76063 - 12/03/21 10:27 AM Re: Friction vs Frictionless [Re: Michael_Fletcher]
danb Offline

Registered: 04/22/05
Posts: 1453
Loc: ...
I see the things as you mention. I can not see frictionless as a code requirement, more over the para.319.4.3 specify that restraint introduced by
support friction, shall be recognized (I see here that you may say you can take credit and none should say no you can't). I think that however, one may say that us as engineers, need also to see that friction is transitory in nature and we should not take credit from friction. In addition, if client ask to consider also the frictionless, well this is an additional requirement, that not negotiated at bid phase will bring some extra headache.

#76067 - 12/03/21 03:50 PM Re: Friction vs Frictionless [Re: Michael_Fletcher]
Richard Ay Offline

Registered: 12/13/99
Posts: 6226
Loc: Houston, Texas, USA
I agree with Dan's statement that "you can't take credit for friction". We've always advocated to err on the side of caution, especially with friction. Most people can't agree on a friction coefficient, let alone sliding versus static versus dynamic effects.

This is why we added the "friction multiplier" in the static load case setup. You can run:
a) ope w/ expected friction
b) ope w/no friction
c) ope w/ +25% friction
d) ope w/ -25% friction

All without changing the model input. I'd use the restraint summary and take the worst case - individually for each restraint.
Richard Ay - Consultant

#76966 - 02/16/23 06:31 AM Re: Friction vs Frictionless [Re: Michael_Fletcher]
PVM Offline

Registered: 03/25/13
Posts: 1
Loc: Madrid
And what about stress?
Do we have to consider friction as "1" or "0" on friction multiplier for thermal expansion stress for Seismic Anchor Movements?

I just read "Treatment of Support Friction in pipe stress analysis" from Peng and still donŽt see how to deal with it.
To cover my back I think that IŽll set both, as for support/equipment loads, one case with and one without, and take the worst.
What do you think?

#76968 - 02/16/23 12:26 PM Re: Friction vs Frictionless [Re: Michael_Fletcher]
danb Offline

Registered: 04/22/05
Posts: 1453
Loc: ...
Actually it depend on you status. Yes, I think is strange but let go on. if you are an company employee you are covered by the stress specification. Otherwise if you have to produce the stress report without referencing a stress specification, you will have to think at all the worst scenarios.


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