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AutoPIPE Wiki 03. Non-Linear Analysis - Wind Load review in AutoPIPE
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          • 04. Results From Loads and Load Sets Not Answered By Piping Code Calculations
          • +05. Combination Load Cases (Tools> Combinations dialog)
          • -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?
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     Questions about this article, topic, or product? Click here. 

    03. Non-Linear Analysis - Wind Load review in AutoPIPE

    Applies To
    Product(s): AutoPIPE,
    Version(s): 2004, XM, & V8i
    Environment: N/A
    Area: Combination
    Original Author: Bentley Technical Support Group

    Let us consider this simple example: Let us assume you have vertical pipe with a horizontal support that has gaps of 1” on each direction.

    Let us also assume that under operating conditions (T1) the pipe moves 0.8” in the +X direction. That means the pipe can only move 0.2 inches for wind in +X and 1.8 inches for wind in –X direction. That is assuming the wind load acts under operating load. If however, the wind is acting under shutdown or ambient temperature, the displacements due to wind can be a full 1” in each direction. Let us assume W1 is in the +X direction.

    If you were to analyze using the nonlinear option:

    Initial case for Occ. loads: GR

    You will notice that depending on the wind case W1 amplitude, pipe displacements up to 1.8 inches could be obtained in +X direction when adding up load cases GW1 and T1 since GW1 is limited by 1 inch gap. So 1+0.8 for T1 will give 1.8 inches which is not true in the +X direction.
    To correctly analyze the nonlinear effect of wind and other occasional loads in AutoPIPE we recommend the following.
    (1) Analyze the system by applying occasional load under NON-OPERATING condition
    This can be done easily using the nonlinear analysis option:

    Initial case for Occ. loads: GR

    This is the default in most cases in AutoPIPE. AutoPIPE will automatically create code combination Sus+W1 for stresses. It also creates a consistent non-code combination GW1 for support forces and displacements. In this case displacements GW1 are limited to +1 inches for our wind example. If you manually create a user case GW1+T1 then this is not consistent with the selected initial state and would have displacements up to 1.8 inches. So DO NOT manually create GW1+T1. Instead do the following:
    (2) Rerun the analysis with occasional load under OPERATING condition:

    Initial case for Occ. loads: OP1

     

    AutoPIPE will automatically create code combination Sus+W1 for stresses. This W1 is different from the one obtained under the previous sequence or initial state since it is evaluated using GT1W1-GT1. The previous one was evaluated from GW1-GR. AutoPIPE also creates a consistent non-code combination GT1W1 for support forces and displacements. GT1W1 will correctly be limited to 0.2 inches in this case. In this case the displacements would not exceed specified gap limits for supports.

    NOTE: AutoPIPE will by default create for you non-code combinations that are consistent with the load sequence (i.e initial state) selected. In general if you manually create a user non-code case, it is very likely that it will have inconsistent forces or displacements. Please refer to the PDF files posted on April 17 2007 (understanding load sequencing) for more information.

    In order to capture nonlinear effects for wind under operating conditions in all directions we recommend the following:

    Define 4 wind load cases as follows:

    W1 for Wind in +X
    W2 for Wind in –X
    W3 for Wind in +Z
    W4 for Wind in -Z

    Analyze using the option

    Initial case for Occ. loads: OP1

    This will automatically create 4 occasional code cases (for stresses):

    Sus+W1
    Sus+W2
    Sus+W3
    Sus+W4

    And 4 consistent non-code combinations (for support forces and displacements):

    GT1W1
    GT1W2
    GT1W3
    GT1W4

    These load cases will be consistent with support gaps and friction limits.

    If you also want wind loads under non-operating conditions, you would need to do a separate run with initial state option changed to:

    Initial case for Occ. loads: GR

    The nice thing is that AutoPIPE does create for you the non-code combinations that are consistent with the initial state selected. It is just a simple switch.

    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

    See Also

    06. Non-linear Load Sequencing Explained

    Bentley AutoPIPE

    • Load Sequence
    • AutoPIPE
    • COMBINATION
    • Non-linear Analysis
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    • Mike Dattilio Created by Bentley Colleague Mike Dattilio
    • When: Mon, Nov 10 2014 11:49 AM
    • Mike Dattilio Last revision by Bentley Colleague Mike Dattilio
    • When: Mon, Jun 4 2018 2:42 PM
    • Revisions: 7
    • Comments: 0
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