Moments Calculation for Branch Connections

[SOROURA]

In the B31.1 Code, Para. 104.8.4(c) states the following:

"(c) For reduced outlets, calculate the resultant moment of each leg separately in accordance with (A) above. Moments are taken at the junction point of the legs, unless the designer can demonstrate the validity of a less conservative method...."

My question:
How can I determine the resultant Moment for each leg separately and -at the same time- take the moments @ the junction point? (If I take the moment at the junction point, it would make no difference calculating the resultant for each leg individually, because they would be all equal)

I think I am a little bit confused, so I need someone to clarify what the Code means in the above paragraph.

Thanks in advance for your help

 

[DSB123]

Soroura,
You are not correct. If you conduct a piping flexibility analysis of the piping system the software (Caesar, Autopipe etc) provide the moments and forces in each of the legs at the juction point for branch connections. The sum of the "internal" forces and moments sum to zero but each leg will have different values normally.

 

[SOROURA]

Thanks DSB123 for your reply.

So when the Code says "Moments are taken at the junction point of the legs..." what I understand is that it tells you to take the resultant moments of each leg at the vicinity of their junction to make the analysis more accurate.

Is my understanding correct?

Thanks again

 

[saplanti]

I guess the discussion goes into the stress analysis modelling and evaluating the results by respectable softwares. In case you use the loading/stresses at the intersection point of run pipe centreline and branch line centreline, the loads/stresses at this point are to be a lot larger than the run pipe shell-branch connection loads/stresses for the branch pipe.

The problem becomes how much extend the model. If I were you I would check with the simple model. If pases there is no problem. If it does not, I would add another node at the run pipe shell-branch intersection point and re-evaluate the loads and stresses at this point.

Regards,

Ibrahim Demir

 

[MJCronin]

Sorouda....

Consider posting your question on the COADE CAESAR-II discussion seminar

http://www.coade.com

-MJC