| Applies To | |||
| Product(s): | AutoPIPE, | ||
| Version(s): | ALL | ||
| Area: | Reports | ||
| Original Author: | Bentley Technical Support Group |
Problem:
At a pipe end point, actually a weld neck flange (A00), I have added concentrated forces (and moments) and made it an anchor point. When I list the results for Restraint Reactions the concentrated forces are included, but when I list the results for Global Forces & Moments in the same point they are excluded. I was expecting to see the same values but with opposite signs. Can anyone explain?
Solution:
Sub-reports "Forces & Moments" and "Restraint" (anchor) results may not always agree, each report maybe looking at a different side of the cutting plane.
In AutoPIPE, Pipe forces and moments are reported at one side of the cutting plane at a point. For calculations of Forces & Moments, all piping from the beginning of the segment up to a given node point will be removed and a free-body calculation performed on the remaining piping. Forces acting at a point would appear on one cutting plane, but not the other. See the following online help section: Help> Contents> reference information> results interpretation> Pipe Forces and Moments: Global Option for more information.
This is a limitation, reporting one side of the cutting plane for pipe points. In AutoPIPE XM and higher we have a new Reference Point report that reports forces on both side of a node point (use Insert> Reference Point command).
Output Report options:
Support Report
Report section which lists support forces and displacements (local, and global) for each active load case and Other combination.
Restraint Report:
Report section which lists anchor and support forces (and moments) at restrained points for each active load case and Other combination.
For a better understanding of reported result values please see the following AutoPIPE help section:
Help > Contents> Contents> Reference Information> Results Interpretation> :
- Support Forces: Hangers and V-stops
- Support Deformations: Hangers and V-stops without Gaps
- Support Forces for Guides and Line Stops without Gaps
- Support Forces: Guides & Line Stops with Gaps & Friction
Suggestion #1:
When models are symmetrical and an anchor is at the exact point where one would expect zero rotation and a reversal in moments direction. As there is no rotation to resist at the anchor, the moments applied at the anchor would be zero.
Every time net Moments = 0 for symmetrical systems, AutoPIPE reports zero moments. The question is what loads should be used to design the Anchor?
Answer, suggest to take largest +/- Global moment from each side of the anchor. Or, model the actual anchor more realistically in AutoPIPE, where there are no zero points of rotation.
Example: Per the following pipe anchor support, model 2 anchors separated by dimension F
There should be no pipe node points between the 2 anchors.
Suggestion #2:
Some supports located near anchor points have no forces for a response spectrum case. Those support points are in the ranges which are only excited at frequencies higher than the cut-off frequency. Therefore, there will be no forces and moments displayed for lower cutoff frequency analysis.