Dear All ,

I have following query regarding response sectrum analysis of earthquake .

If I am applying Independent Support Motion response spectrum for my piping system , Then how should I calculate the value of seismic anchor movement as avaialble in spectrum load case option.

(a)Should we allow Caesar to calculate this value automatically without specifying any value in Anchor Movement column of Spectrum Load case tab .

(b)As a second option , Should i carried out static analysis for each ISM spectrum separately .then calculate the maximum value of displacement for each support group . The value for anchor movement will be the difference of displacement between support groups

Thanks in advance !

Richard /Dave ,

Please provide your comments .

Thanks & Regards ,

Item a), I would certainly check the number calculated by CAESAR II if you take this route. Depending on your spectrum definition, I am often surprised at the magnitude of this displacement.
Item b), Displacements from each support group are evaluated independently so do not use relative motion, enter your calculated displacement.

Dave thanks for response !

So i will better go for second method for defining the anchor movement .In this i will calculate the static equivalent seismic coeficient factor from the response spectrum & finally static load. I have a doubt regarding the application of static load for a piping system . For example i am considering the model of Caesar example file " CRYISM.CAESAR II" . I have two option for applying the static load .

1. In the same caesar file i will apply the different static load for ground & building supports simultaneously and in this case i will disconnect the piping at node 60 by cnode concept & specifying the anchor stiffness as 0 . So that each support group will show their anchor movement with respect to ground .The maximum displacement of each support group will be anchor movement .This anchor movement will be specify in spectrum load case tab.

2.In the second case ,firstly I will only apply static seismic load for ground supports and in this case piping is not disconnected as mentioned in point 1 . The maximum displacement of ground support will represent the anchor movement for ground support . The same procedure will apply separately for building supports fo calculation of maximum displacement/anchor movement.

As per my view the first approach is more accurate because in this piping is disconnected and one support group's piping weight has not any effect on the movement of other support group . Please confirm & correct me if i am wrong .

Thanks & regards

I don't think the Codes are clear in this area. Perhaps someone with more practical (nuclear?) experience can comment.

I believe most seismic considerations treat the structure as independent of the pipng - the pipe gets pulled along with the structure no matter where it goes. You can decouple the piping from the structure and, as we suggest, specify support movement as Independent Support Motion (ISM).

But te approach to use where piping and structure affect each other is not clear. So when mass and stiffness are similar, the combined system should be evaluated as a single system. In which case that ISM is no longer a defined part of the analysis.

Dave thanks for your response !
As mentioned above in my post , can i use second method for calculation of seismic anchor movement for a particular support group like in CRYISM.CAESAR II . In my case i have to consider the anchor movement because Ground & building supports are subjected to different shocks or response spectra . As an alternative i may use the envelop approach in which i need not to specify the anchor movement.I think this envelop spectra will act as Uniform support excitation for all support group and in most of the cases this approach is conservative .Please tell can i use my second approach as stated in earlier post to calculate the seismic anchor movement if i am using ISM response spectra .

In my opinion...
You are illustrating my point - that the piping interacts with the structure. By analyzing the entire system (piping & structure together) you need not pull the support displacements and apply them as ASMs in a second analysis of the piping alone.
But if you have to run a piping-alone analysis with ASM, I would guest your second approach is sensible. But I would not expect the results for the [spectrum for pipe plus ASM] response to match the [spectrum for everything] response.

Thanks Dave !

Dear all,

I need your help one more time. I'm analyzing a pipeline that is subject to earthquake. I have a doubt about displacements of anchor. I'm using CAESAR II 5.30.02 to do this analysis while another engineer is in charge of use another software. Both loads are almost the same but anchor displacements are very different. In my analysis all displacements of pipe have a cumulative value, that is: first anchor moves X mm and the rest of pipe have a displacement following this first anchor. In another analysis, the displacement of anchor is considered zero. My doubt is: in the middle of pipeline for example, the displacement is "pipe displacement + displacement of first anchor" or the displacements are independent?

If someone have some material for more understanding of earthquake results and solutions, I'll be glad.

Thanks in advance,

Miyamoto