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AutoPIPE Wiki 06. Non-linear Load Sequencing Explained
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          • 04. Results From Loads and Load Sets Not Answered By Piping Code Calculations
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          • -06. Non-linear Load Sequencing Explained
            • 01. Non-Linear Analysis - Gap Support review in AutoPIPE
            • 02. Non-Linear Guide vs Inclined Supports Explained in AutoPIPE
            • 03. Non-Linear Analysis - Wind Load review in AutoPIPE
            • 04. Non-Linear Analysis - Pipe / Support Friction Force - Load Case GrP1T1
            • 05. Non-Linear Analysis - Pipe / Support Friction Force - Load Case GrP1T1E1
            • f. Advanced Nonlinear Analysis - Linear vs. Non-Linear analysis in AutoPIPE
            • g. Discussion of AutoPIPE Advanced Non-Linear Analysis Engine
            • i. Why does AutoPIPE provide an option to “Ignore friction GR” on the Nonlinear analysis dialog?
            • ii Why does AutoPIPE provide an option to “Ignore friction E” on the Nonlinear analysis dialog?
            • Item #3: Review of 3 General methods used by Stress Analysis computer programs
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     Questions about this article, topic, or product? Click here. 

    06. Non-linear Load Sequencing Explained

    Whenever a static analysis load set includes any Gaps, Friction, or Soil defined settings it should be analyzed as a non-linear analysis (recall Linear analysis ignores all Gaps, Friction, and Soil settings). 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 (note, linear analysis all load cases are applied all at the same time). 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 - GrT1P1

    05. Non-Linear Analysis - Pipe / Support Friction Force - GrT1P1E1

    Item #2: When looking at the output report

    In the output report only look at the operating conditions (i.e. GT1E1, GT1W1, etc..) and not the individual load cases (i.e. Gr, T1, E1). The individual load case(s): A. may have displacements that are larger than a gap on a support allows or B. support may have a load in a direction of a gap. However, when the individual load cases are added in a valid combination, the results of non-linear load sequencing are correct.

    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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    • Load Case
    • AutoPIPE
    • Non-linear Analysis
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    • Mike Dattilio Created by Bentley Colleague Mike Dattilio
    • When: Thu, Aug 22 2013 12:59 AM
    • Mike Dattilio Last revision by Bentley Colleague Mike Dattilio
    • When: Wed, Oct 6 2021 2:08 PM
    • Revisions: 46
    • Comments: 0
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