Comments, Questions, and Answers
Items #1:
In the end both AutoPIPE and CAESAR perform the same task of providing the user with stress analysis results based on load cases applied to a geometric model of a piping system. However, there is a fundamental difference between both applications on how load combinations are combined.
The following will provide insight into AutoPIPE's approach vs CAESAR's:
First, please read the following document installed with AutoPIPE:
C:\ Bentley\ AutoPIPE V8i SELECTseries\ Load_Sequencing.pdf
OR, search your hard drive for "Load_Sequencing.pdf"
As you have read in the above document, one of the major fundamental differences between AutoPIPE and CAESAR, is load sequence verses load vector superposition. This is clearly shown on the first and very last page (Summary) of this document. Referring to the last page of the document, results can differ for calculating individual load cases (ex. E1) by using superposition (ex. [C-B]).
If you consider the following example:
L1 W+P1+T1(OPE) – equivalent to AutoPIPE GRT1P1
L2 W+P1(SUS) – equivalent to AutoPIPE GR + Max P
L3 T1 (EXP) – thermal only, no mass etc, intermediate step for calculating hot sustained (L5) – no AutoPIPE equivalent
L4 L1-L2(EXP) – equivalent to the AutoPIPE T1 case
L5 L1-L3(SUS) – Hot sustained
Note that both L1 and L2 are operating conditions, and L4 is CAESAR's superposition method of adding load vectors to achieve an individual load case T1. Whereas in AutoPIPE, T1 is an individual load case added in a load sequence to correctly calculate the operating conditions.
Furthermore, understand that CAESAR needs intermediate equations like L3 to calculate equations like L5 - hot sustained. However, as you now know AutoPIPE load sequence approach does not need intermediate equations like that found in CAESAR. Thus reducing the complexity of load combinations and length of output report.
In addition, what is the difference between L2 and L5, where:
L2 = W+P1
L5 = L1-L3 = (W+P1+T1) - T1 = W+P1
Appears that L2 = L5.
Furthermore, what is the difference between L3 and L4, where:
L3 = T1
L4 = (W+P1+T1) – (W+P1) = T1
Appears that L3 = L4.
In conclusion, AutoPIPE has more advanced non-linear analysis engine with load sequencing and as a result users can expect more accurate non-linear results than from other programs.
If one must compare an AutoPIPE model with CAESAR, highly recommend comparing true operating conditions (ex. L1 to GRT1P1, L2 to GR+MaxP) instead of all the individual load case (ex. L3 & L4 to T1) as the fundamental different approach of adding vectors / load cases use by the two programs may present dissimilar results for individual load cases and respective combinations where such individual load cases are used.
Furthermore, see the following WIKI here for details on Reviewing 3 General methods used by Stress Analysis computer programs:
One final note, be sure check that all of AutoPIPE's Tools> Model Options> General, Edit, & Results settings match CAESAR's settings.
Item #2:
CAESAR CII has a ‘H’ load variable which represents the hanger pre-loads…AutoPIPE doesn't seem to have a hanger variable…does AutoPIPE somehow automatically incorporate the hanger pre-loads?
Answer:
When inserting a typical variable spring in AutoPIPE the user is asked to enter 3 key values: Cold Load, Spring rate, and number of hangers. These values are considered during the analysis.
Otherwise, the user can specify that the program correctly size the spring based on load and movement of the node point on the pipe. See online help for " Hanger Selection Procedure" in AutoPIPE.
A spring hanger cold load is applied to the Gravity (GR) load case. For each combination that contains (GR) spring cold load is applied.
Item #3:
CAESAR has a ‘D1’ load variable which represents the inclusion of a user-specified displacement….does AutoPIPE incorporate something similar?
Answer: Yes, Insert> Xtra-Data> Imposed Support Displacement, see online help for complete details on this AutoPIPE option.
As mentioned in the online help and apparent on the dialog screen, an imposed support displacement can be assigned to any number of load cases (GR, T1-T100, E1-E10, W1-W10, P1-P100, U1-U140, S1-S10) or configured to span a selection of load cases. When that load case is used in a code / non-code combination, the specified imposed support displacement will be applied accordingly.
Example, the following support displacement is applied to load case U1, and will only be applied when U1 is included in a combination.
Item #4:
CAESAR has a ‘F1’ load variable which represents the inclusion of a user-specified external force…does AutoPIPE incorporate something similar?
Answer: Yes, Insert> Xtra-Data> Concentrated Force, see online help for complete details on this AutoPIPE option.
As mentioned in the online help and apparent on the dialog screen, an concentrated force can be assigned to any number of load cases (GR, T1-T100, E1-E10, W1-W10, P1-P100, U1-U140) or configured to span a selection of load cases. When that load case is used in a code / non-code combination, the specified concentrated force will be applied accordingly.
Example, the following concentrated force is applied to load cases U1-U4, and will only be applied when U1, U2, U3, or U4 is included in a combination.
Item #5:
Comprehensive Automatic Code Combinations.
VCR buttons allow fast navigation to sorted multiple maximum stresses across multiple stress categories including maximum sustained stress, thermal range and all occasional stress combinations which Caesar does not calculate automatically.