Question:
How to calculate the code compliance results values reported?
Example:
Answer:
Example model has the following properties:
Calculations:
Combined stress calculations
Conclusion:
In summary, the majority of users tend to make basic mistakes in their calculations of Combined Stress due to the use of incorrect values.
For some examples, notice that both the Hoop and Longitudinal Stress values used in the Combined Stress calculation were not the same values shown in the output report. Furthermore, recall how the reported Longitudinal Stress was determined as the maximum value between Slmin and Slmax. At the same time, the Combined Longitudinal Stress applied in the combined stress calculations was derived from Slna. Lastly, it is important to remember notes about calculating combined stress, use the Milll (reduced) section properties.
Upon careful examination of the example provided above, one can readily comprehend the methodology used by AutoPIPE in calculating the reported values.
Question:
Is the negative value for axial force in the local coordinates indicates that it is a tensile force?
Answer:
AutoPIPE help states that tension is positive in the axial force term (Fa) when calculating stresses, yes
Question:
If a negative force indicates compression, it should not be additive with SLP. The way the formulas for sLmax and sLmin are calculated, a positive axial force (tension) would reduce the tensile stress due to the pressure load.
Answer:
This is a common misunderstanding.
Q. Where does the Faxl value come from? (hint see image reprinted below)
Answer: Correct, the Forces and Moments sub-report
Q. What does the Local Forces and Moments sub-report represent?
Answer: Reaction of the node to balance the force being applied. Therefore a -ve forces value is actually a Tensile load on the node point. Conversely a +ve force value represents a compressive force on the node point.
Conclusion: A +ve SLP value indicates tension on the pipe, while a -ve reported force value also signifies tension on the pipe. To combine these two tension values, one must subtract a -ve F/A term. Consequently, the two terms can now be accurately added together.
Question:
The only difference when using von Mises (octahedral) for the combined stress would be the equation, not the inputs?
Answer:
Yes and No..
Yes, the equation is different.
And No, the user must update the Results model Options setting for " Total stress (Oct/Max)" to indicate the type of stress reported.