Appears that the expected multiple support response spectra (MSRS) and the uniform response spectrum analysis results are not as expected in an AutoPIPE model, why?
For a specific model the results of R3 should between R1 and R2 values. (ie. R1< R3< R2).
Comments below reference node points to a specific model (imaged above) but may apply to other AutoPIPE models:
1. In a response spectrum analysis the applied spectrum is used to simulate the effect of seismic movement of the “Ground”.
However, in MSRS multiple input spectra can be applied to different supports in separate groups and all of them need not necessarily be connected to ground.
2. In this model the V-stop at F11M is connected to beam ID =‘1000’ and not ground. The uniform response spectrum applied in R1 & R2 would be modeling the motion of the supports/anchors connected to ground : F00,F20,SU29. It is therefore understandable that anchor at SU29 will see the vertical force and moment due to the portion of the model above it (upto F11).
3. In the MSRS cases R3 & R4, the V-Stop at F11M and the anchor SU29 have been placed in the same group S1. For MSRS, supports are to be grouped based on different floor levels or buildings. The user may want to review and make sure placing F11M and SU29 in the same group. If this is indeed the desired grouping of supports, it means that the modeling intent is to represent that these two supports will move in phase with each other. Thus, it would not be surprising to see that V-stop at F11M does not cause force & moment at the anchor SU29.
4. The program help provides the following information about MSRS
It cannot be mathematically inferred that the results for R3 should be in between R1 & R2. The MSRS results can be different depending on the model and applied input spectra.
5. With regard to the quote from the help "This means if a uniform spectrum case modeled as an MSRS, with a single support group for all the supports in the model, then the results for both analyses should be the same."
This model has two support groups. Thus it is not conflicting with this statement to see that results for R4 are not the same as R1.
Dynamic "Response Spectrum" Analysis