friction stiffness reduction for non convergence

Hi All,

In my calculation , Friction(mu) value for the +y support is given as 0.3(steel to steel). But It is not converging . I gone through same topics posted in the forum, it says that one way is to reduce(alter)the friction stiffness in the config/stress computation control.
I followed the same way, it works out.My clarification is , if we do like ( i.e reducing the friction stiffness)

1. whether all client will accept this procedure?
2. I understand that there is slight change in result(I hope that it has an impact only in restrain summary). Hence I am not very sure whether this changes will be more if it is a big calculation
3.The stiffness given in the ceasar database is derived from where?this is for just to get the info only. I would like to know that where to use which stiffness?

I searched the forum list, but I could not find any such related answer for my queries.

Experts can guide me!!!!!!!

Regards

Sha...

Are you sure?... Im no expert but this doesnt need expertice to tell you to read not just one or two but read all discussion UNTIL YOUR SATISFIED!
This topic is very clear and I think 10% of the discussion here are related to friction. the best word I quote would be "STOCHASTIC"!

And also try to look at your Tech. ref., you will find a good article.

Please dont say things you have not done...

Regards!

One more thing, some of our good member in the forum post some technical paper of "TREATMENT OF SUPPORT FRICTION IN PIPE STRESS ANALYSIS"... I didnt have time to read it for now.

Regards!

Once you get results from C2 you can review those results to see how the model responds. If the node moves: Is the restraint resultant friction force equal to mu*N; Does the friction force vector line up with the displacement vector? If the node does not move, is the restraint resultant friction force less than mu*N.
Are your results sensible?
Quite a few years ago, we had a low value for friction stiffness. Jobs converged quicker (important with the PCs of the day) but lower stiffness allowed supports to slide before they actually would and that, then, walked the model a little farther from reality. Based upon those observed model results, we increased the default stiffness.
Friction is a very "sticky" subject. We include it in C2 to produce conservative results, maybe very conservative results. I, personally, do not expect an accurate prediction of system response. A much more sophisticated analysis algorithm would be required to attempt a better solution.
I usually try not to fool with friction parameters to find convergence. Instead, I work with nonconverging nonlinear restraints (+Ys or Guides with gaps) by making them linear (Ys or Guides with no gap, respectively). It's easier to evaluate the output for these points.

Hi Bom ,

i searched the forum to my level best. I have got the reply related only friction with converging/non converging. But I could not got the reply to related my queries. Pl read my queries again (3 points).
Thank you for your response

regards

Sha..

No comment!

Hi Dave Diel

Thanks for the reply.I will try to goahead with changing non linear restraints into linear restraints.

I am not able to get your points for the following

In the first paragraph of your reply "

If the node moves: Is the restraint resultant friction force equal to mu*N; Does the friction force vector line up with the displacement vector? If the node does not move, is the restraint resultant friction force less than mu*N.

Can you throw some little bit info about it.I understand that if node move only there is a friction force. if there is no node moves , means that it might be an anchor/semi anchor

and
"Friction is a very "sticky" subject. We include it in C2 to produce conservative results, maybe very conservative results. I, personally, do not expect an accurate prediction of system response. A much more sophisticated analysis algorithm would be required to attempt a better solution"

I understand from your statement that we can choose any friction stiffness from the configure/setup. But choosing the default or greater value would be more conservative !!!

Once again thx for responding immediately.

1. There is no industry-wide standard approach to friction. The client's opinion will play a role.
2. Changes in friction paramters may affect each job differently.
3. COADE has no indication that the default C2 stiffness value for non-sliding friction restraint needs to be changed.

Here is my opinion on friction and nonconvergence in Caesar II. It may differ somewhat from Dave's opinion, which just shows you that there is no absolute correct answer to this question. It is an engineering judgement issue.

By making +Ys into Ys, will that have an impact on running a hot sustained case as it may change the results of the temperature only load case?

I am still getting my head around the hot sustained load cases so apologies if this is a stupid question.

hi dude,

Try reading this article(sustain topic). This help me alot in understanding this lift-off things(hot sustain).

http://coade.com/newsletters/jan01.pdf

Regards!

Hi bom, that is an excellent article however I don't think it answers my query.

If +Ys are made Ys, would this affect the hot sustained stresses, as the OPE-T stress range may be different?

If the pipe rests during operation, but is non-converging at that point so is made a Y. What happens if the temperature only load case wants to lift off at that point, won't the OPE-T load case be affected?

Hi dude,

I dont understand Sir Dave's point, It realy deffer when you dont allow the lift-off's. I have'nt tried this one. there is a paper posted with some member addresses the software approach in solving convergence. If you have time to search for that..., it is quite a good paper. I forgot the topic but it's all about convergence.

Regards!