| 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:
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.