| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | Combinations |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Dec. 2016 10.01.00.09 |
Problem:
Is Longitudinal Pressure stress included in my Code combinations when using AutoPIPE? Why?
Example:
-
GR+P1
-
Sus+E1
-
Gr+P1+(LONG)
Where:
Gr = Gravity
P1 = Pressure Load Case #1
Sus = Maximum sustained stresses
E1 = Static Earthquake Load Case #1
(LONG) = Maximum longitudinal pressure stress
Solution:
Yes Longitudinal pressure is added in the following combinations:
- Sus+E1
- Gr+P1+(LONG)
No Longitudinal pressure is NOT added in the following combination:
- GR+P1
To answer the question Why, lets look at each combination in detail:
Note: the CAE development team has created a set of default combinations to meet the code requirements for the selected piping code in a given model. Some of these default combinations include (LONG) and some do not. Again, default combinations are only meant to meet the requirements of the respective codes. The user can add additional Code combinations as needed. Under certain modeling approaches (ex. modeling non-metallic pipe) it may be suggested to add User defined combinations to see stresses in the pipe not covered by default combinations.
GR + P1
For code combinations the pressure is divided in 3 parts
LONG = Longitudinal stress due to pressure (PD/4t or so)
HOOP= Hoop stress (PD/2t or so)
P1 = Stress from imposed forces/displacements and from forces and moments under P1 load case
In this combination, GR+P, only those imposed forces/displacements, forces, and moments under P1 load case are considered. There is no Longitudinal stress added to this combination.
Sus + E1
building on the information from the previous combination, E1 does not include any longitudinal component, but what about (SUS). What is (SUS)?
As mentioned before, (SUS) is the maximum sustained stresses. Therefore the program will use the results from a Sustain category combination that has the maximum value. In some cases there is only a single sustain category combination. See Example below:
In this case, (SUS) is the results from GR+MaxP. This GR+MaxP combination represents sustained stress due to Gravity bending stress + maximum longitudinal pressure stress.
Hence, longitudinal stress is included in this combination.
Gr + P1 + (LONG)
This combination is a little more involved. It can be viewed as 2 individual components: 1. Gr+P1 and 2. P1+(LONG).
The first part, Gr+P1, this would combine the forces and moments from these 2 load case to calculate a stress. In the 2nd part, P1+(LONG), the actual longitudinal pressure stress would be calculated based on the pressure in the specified case (ex. P1). In the end these 2 stresses are than added together to get a total stress value for the combination.
For more information on combinations that include (LONG), (SUS), etc.. please see the following AutoPIPE help section (be sure to read the notes):
Help > Contents> Search Tab> enter "Case/Combination List (Standard)" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information.