AutoPIPE Wiki 01. Non-Linear Analysis - Gap Support review in AutoPIPE

01. Non-Linear Analysis - Gap Support review in AutoPIPE

	Applies To
	Product(s):	AutoPIPE,
	Version(s):	2004, XM, V8i, CONNECT
	Environment:	N/A
	Area:	Analysis
	Original Author:	Bentley Technical Support Group
	Date:	May 2016

The Non-linear method is a sequence of applied load cases as defined on the initial states dialog. For example, a guide support with 0.2" gap left / right, non-code combination GT1E1, is analyzed by:

1. First applying the Gravity weight load case to the system and calculating the deformation based on modeled restraints.

2. Next, the thermal expansion load case (T1) is applied to the deformed model, and again a new deformation is calculated.

3. Finally, the Seismic load case (E1) is applied to the deformed model, and again a new deformation is calculated.

4. Based on Non-Linear analysis load sequence, each individual load case is added to the existing pipe deformed location. Therefore it is easy to understand how one individual load case can have a gap movement greater that the indicated gap support.

However, the total operating condition movement (Gr+T1+E1) is correct.(dx = 0.105").

Note:

1. When reviewing an AutoPIPE output report

In the output report, users should only look at the operating conditions (i.e. GT1E1, GT1W1, etc..) and not the individual load cases (i.e. Gr, T1, E1). Why?

The individual load case(s):

A. could have displacements that are larger than a gap on a support allows (ex. seismic E1 load cases above moves 0.306" in a +/- 0.2" gap support)

B. could indicate a load on a support. However, when looking at the actual operating conditions, the pipe has moved with in its gap distance and is not touching the support in the gap direction. Therefore there is no load on the support for the respective operating condition.

Again, the results from non-linear analysis that considers Gaps/Friction/Soil settings are correct when reviewing the operating conditions. Best to use the individual load cases to understand how the individual load case contribute to the overall operating conditions total displacement, forces, moments, stresses, etc...

2. Confirm results are on based on Global or Local axis

When reviewing the different sub-reports of the output report, be sure to confirm which axis is being used for the printed results: Global or Local. See the following example for a common mistake

Example: In the image below, the guide support at node F04 was set to 20.98mm left / right.

When reviewing the Displacement sub section of the output report, Gravity load case movement was measured = 27.354 mm.

This clearly exceeds the gap setting above, clearly AutoPIPE must be wrong, correct? NO not correct, AutoPIPE is functioning correctly !!!

Recall from your official AutoPIPE training that a guide bearing springs are always perpendicular to the pipe orientation (both horizontally and vertically), and note in the image above that the pipe is not oriented on a global axis. Also recall from the training that the Displacement sub-report and Displacement tab of the Results Grids has values that are based on Global axis movement, and NOT Local axis movement.

Therefore what is the local movement at this support perpendicular to the pipe?, Which AutoPIPE sub-report has the Global and Local moments results printed automatically?

That is correct, the Support sub-report. Therefore, create and review the Support sub-report, (see image below):

Note that the Local movement is exactly the same as the support gap setting (ex. 20.98 mm), meaning that the Load cases has caused the support gap to close completely and that the pipe is now exerting a force on the support.

Again do not be fooled by the movement exceeding the gap setting; the Global displacement results = 27.354mm, but the true local distance movement was 20.980 mm.

01. Non-Linear Analysis - Gap Support review in AutoPIPE

Note:

1. When reviewing an AutoPIPE output report

2. Confirm results are on based on Global or Local axis

See Also

Non-linear Load Sequencing Explained