Consideration of relaxation in pipes

My doubt is related to calculation of support forces in Caesar.

Ref: Eqn.(9) and Eqn. (10) of B31.1 2007

Let us consider an hypothetical case:

At a particular support,

Dead weight, WT= 2000 N

Relaxation (cold spring), C =1 (100%)

Eh/Ec = 0.9

Reaction for full expansion range, R = -1000 N

So,
Rh=(1-2/3)(0.9*-1000) = -300 N

Rc= -CR= -1*(-1000)= 1000 N

WT+Rh= 2000+(-300)= 1700 N and

WT+Rc= 2000+(1000)= 3000 N -------- (a) .

Please correct me if I am wrong but, for this case, Caesar will give output as:

WT= 2000 N
OPE= WT+R = 2000+(-1000) =1000 N
EXP= -1000 N
So, MAX= 2000 N -------- (b)

Shouldn't Caesar consider 3000 N (as per eqn.(a) above) as the MAX force possible instead of 2000 N (as per eqn.(b) above)?

Also, isn't EXP= WT+Rh the correct choice rather than EXP= WT+R?

Regards,
ASA

Hello everyone,

I am eagerly waiting for your responses. Is there something ambiguous about my question?

If some information is missing, please let me know.

Regards,
ASA

You have made so many erroneous assumptions, I doubt I would want to take the time to make a complete listing. Here's a start.

1. Equations (9) and (10) could only be used to calculate adjustments in support loads if (a) the supports were both anchors, and (b) all the cold spring was between those two anchors.

Go back and reconsider your work with this in mind, and perhaps you will be able to clarify your thinking on some of the secondary issues. My advice to you is to find a senior engineer knowledgeable in pipe stress analysis and learn from him directly before you kill somebody (perhaps yourself).

This is not a child's game, you can't buy another life either for yourself or others. You live in India, are you old enough to remember Bhopal?

Mr. CraigB,

I respect your advice but please be rest assured that I am not working on any system critical enough to cause "Bhopal II", or may be kill someone.

Though I am new to stress analysis, I do understand the seriousness of the subject, and if I am not wrong then "everyone starts small".

I would be grateful to you if you could explain where and how Eh/Ec ratio is considered in Caesar support-load calculations.

Also, How does a load combination like W+P+T (T being only Hot Case) take care of Cold Reactions (Rc value) of eqn.(10) of B31.1?

Regards,
ASA

The Eh/Ec ratio is not considered in the support loads. c2 does not implement equations 9 and 10.

Mr. Richard,

Could you please explain how in c2 the requirement of B31.1 (2007) code will be fulfilled without using Eh/Ec or eqn.(9) & eqn.(10).

Regards,
ASA

ASA,

You are not thinking about what I posted earlier. Equations 9 and 10 have no relevance to supports EXCEPT for two anchors with a cold spring in between them.

Please spend more time thinking and consulting with your senior engineer, and less time whining.

The Code permits "more rigorous methods of analysis". In your case running the model with the hot modulus in the operating case and cold modulus in the installed case, with the cut short in both, would be more rigorous.

Those equations 9 & 10 were "slide rule" simplifications.
I would suggest using both 2/3's and 4/3's of the design cut short in your analysis.

These analyses are used only for load calculations; not stresses.

Do not discount CraigB's advice.

Thankyou Mr. Richard, Mr. Diehl and Mr. CraigB for sharing those fundamentals.

Regards,
ASA