| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Area: | Report |
| Date Logged & Current Version |
April 2020 12.03.00.17 |
Problem:
Support Forces Report, why do local support forces on a global axis not match global forces in AutoPIPE's output report?
Example, see operating conditioning + Dynamic analysis (GrT1+R1, GrT1+S1). Notice how the global forces do not match the local forces. However, for operating condition (ex. GrT1) the global forces matches the local forces.
Solution:
Recall that all dynamic analysis results are can be either positive or negative, while AutoPIPE reports these as positive values (see WIKI here). With this in mind, support forces and displacements are calculated:
| Vertical axis Forces | ||||||
| Load case | Local | Global | Load Case | Local | Global | |
| GR | -1.40 | -1.40 | Gr | -1.40 | -1.40 | |
| T1 | -2.36 | -2.36 | T1 | -2.36 | -2.36 | |
| GrT1 | -3.76 | -3.76 | GrT1 | -3.76 | -3.76 | |
| S1 | -|0.22| | |0.22| | R1 | -|2.09| | |2.09| | |
| GRT1+S1 | -3.98 | -3.54 | GRT1+R1 | -5.85 | -1.67 | |
After reading the help reference in wiki page above, to include a -ve (negative) dynamic load case (ex. SAM, Response Spectrum, etc..), create a user combination and set the scale factor to -1.00, again as shown in WIKI page above.
Notice that the results are now flipped. Again this is due to the dynamic analysis load case results are now taken as a -ve value.
| Vertical axis Forces | ||||||
| Load case | Local | Global | Load Case | Local | Global | |
| GrT1 | -3.76 | -3.76 | GrT1 | -3.76 | -3.76 | |
| S1 | -(-|0.22|) | -|0.22| | R1 | -(-|2.09|) | -|2.09| | |
| GRT1-S1 | -3.54 | -3.98 | GRT1-R1 | -1.67 | -5.85 | |
Question #1:
Which results are correct:
a. Operating loads + dynamic loads
or
b. Operating loads - dynamic loads?
Answer:
They both are correct because dynamic analysis are oscillating / vibrating. Therefore, the stress analysis and structural people should know that both results are possible. Suggest to always add user load cases as mentioned above to correctly consider dynamic loads with operating loads.
Question #2:
When we look at the local coordinate system in AutoPIPE, local Y is usually aligned with global Y (i.e. upwards).
However, in the AutoPIPE report and MDB/SQlite database file, the support global FY corresponds to local FX. See the below example for the support at node A190. Do you know why the coordinate system is changing between the AutoPIPE model and the run results?
Answer:
To better grasp this concept, we should first consider the LocalXlabel direction. In your situation, it aligns with the vertical axis, indicating that Local FX is equivalent to Global FY. Therefore, the Local axis loads should be referenced relative to the LocalXlabel direction.
In the Result grid, LocalDir1 represents the vertical direction, indicating up/down orientation. Consequently, Force1 corresponds to the Global FY loads in this local direction. Similarly, LocalDir2 indicates the right/left direction, representing the lateral load of the pipe, which corresponds to Global FX. Lastly, LocalDir3 signifies the back/forward direction, corresponding to Global FZ in this case.
To ensure consistency between the result grid and the Results MDB/SQLite database file, the column names must be identical. Please review the existing IDEAs link here and cast your vote for the suggestion you support.