Whenever a static analysis load set includes Gaps/Friction/Soil it is calculated using a non-linear analysis. As a non-linear analysis, individual load cases (i.e. Gr, T1, P1, E1, W1, etc..) are applied one at a time in a sequence. This specific sequence does affect the calculated combination results.

For example, see Analysis Summary output report:

Here one case clearly see that the Load Cases analyzed are Gr, T1, E1, and W1. Also that the load sequence was:

1st, analyze load case GR. 

2nd, from the displaced pipe location due to Gravity, add load case T1.

3rd, again, from the displaced pipe location due to Gravity, add load case E1.

Lastly, again, from the displaced pipe location due to Gravity, add load case W1.

Conversely, pipe displacement and support load results can be significantly different if the Wind loads were applied to a piping system that had already been displaced by operating conditions, example OP1:

Here one case clearly see that the Load Cases analyzed are Gr, T1, E1, and W1. Also that the load sequence was different than above:

1st, analyze load case GR. 

2nd, from the displaced pipe location due to Gravity, add load case T1.

3rd, again, from the displaced pipe location due to Gravity + T1, add load case E1.

Lastly, again, from the displaced pipe location due to Gravity + T1, add load case W1.

How to perform a Non-Linear Analysis?

On the Static Analysis Sets dialog screen, check boxes in the  "Non-Linear" column 

.

OR

Select an Analysis set and press the modify button to open the dialog below.

Enable setting for "Gaps/Friction/Soil" and press OK button. 

How to define Non-linear options?

As mentioned above, enable to the setting "Gaps/Friction/Soil" and press OK button. Now the Non-Linear Analysis options dialog will appear. See online help for details on this dialog screen.

Note:  Why does NonLinear Analysis provide the following options on the dialog above:

“Ignore friction GR”

"Ignore friction E”

How to control load Sequence?

There are 2 settings to control load sequence both options are accessed by Non-Linear Analysis options dialog mentioned above.

1.Initial case for Occ. loads

2. Use default sequence

For more complicated load sequence, uncheck the "Use Default Sequence" box to modify the Load sequence and press OK button as shown below:

Now manually adjust the load sequence as needed. There are some limitations to load sequence:

1. Initial state for occasional load cannot be another occasional load case.

2. Initial state for occasional load cannot be a User load case.

3. Initial state for User load cannot be another User load case.

etc... 

 Attention:

1. Please see the following AutoPIPE help section:

Help > Contents> Search Tab> enter "Understanding Load Sequencing" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information select the hyper link for "Understanding Load Sequencing".

2. Open the PDF file directly from the AutoPIPE folder, search for "Load_Sequencing.pdf"  or "Non_Linear_Load_Sequencing.pdf" on your computer.

3. Additional documents:

a. Non-linear_Guide_explained

b. Understanding Non-Linear Load Sequencing

c. Treatment of Support Friction in Pipe Stress Analysis

d. Nonlinear Effects in Piping System Analysis

e. Improved Iteration Strategy for Nonlinear Structures

f. Advanced Nonlinear Analysis - Linear vs. Non-Linear analysis in AutoPIPE 

g. Discussion of AutoPIPE Advanced Non-Linear Analysis Engine

Note: 

V-stop lift-off message is displayed by AutoPIPE when a pipe is resting on a V-stop in sustained/dead load condition i.e. gravity (which means that the support force displayed in the grid in the Global vertical axis would be negative, meaning that force is acting downward on the v-stop), but the pipe lifts-off from the support (Zero force acting on the support in global vertical axis, displacement of the point would be positive in global vertical axis) under operating loads i.e. Pressure or temperature.

The maximum possible frictional force that can be developed for a support depends on the bearing (vertical) force applied to that support point, forces applied in the orthogonal direction to bearing and the friction coefficient.

Item #1: Example Systems:

01. Non-Linear Analysis - Gap Support

02. Non-Linear Guide vs Inclined Supports Explained  in AutoPIPE

03. Non-Linear Analysis - Wind Load

04. Non-Linear Analysis - Pipe / Support Friction Force

Item #2: When looking at the output report

Item #3: Review of 3 General methods used by Stress Analysis computer programs

See Also:

Loads and Load Sets - AutoPIPE

Bentley AutoPIPE

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