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AutoPIPE Wiki 04. Support report indicates a load on a support who's open gaps never closed during an AutoPIPE Analysis, so why is there a load on the support in open gap direction?
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              • -"Support" sub report using Results> Output Report in AutoPIPE
                • 01. What is the difference between the support and the restraint output reports in AutoPIPE?
                • 02. Why are Membrane or Local stresses from pipe supports not included in AutoPIPE?
                • 03. During animation of load-case in AutoPIPE, pipe support moved with pipe freely without any opposition, why?
                • 04. Support report indicates a load on a support who's open gaps never closed during an AutoPIPE Analysis, so why is there a load on the support in open gap direction?
                • 05. Support results on a vertical support in an AutoPIPE model does not change, regardless of "Weight of Contents" settings. Appears Weight of Contents is not considered in my model, how to verify?
                • 06. AutoPIPE FAQ Question 116: Why are membrane stresses from pipe support not included in AutoPIPE?
                • 07. AutoPIPE's Support sub-report results indicate little to no displacement at a Support that has large gaps all around, WHY?
                • 09. Support forces for Occasional load (i.e. Earthquake) are not evenly distributed among multiple supports in AutoPIPE model, why?
                • 10. How are a support's axial force due to xxx load case calculated in AutoPIPE's reports?
                • 11. Pipe displacement decreases as gap size increases in AutoPIPE, why?
                • 11. Support forces = 0.00 in AutoPIPE's results, why?
                • 12. Support Forces Report, why do local support forces on a global axis not match global forces in AutoPIPE's output report?
                • 13. Why are spring or rigid hangers on vertical legs showing large reaction loads in the Hydrotest load set case for AutoPIPE's reports?
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    04. Support report indicates a load on a support who's open gaps never closed during an AutoPIPE Analysis, so why is there a load on the support in open gap direction?

    Applies To
    Product(s): AutoPIPE
    Version(s): ALL
    Area: Report
    Original Author: Bentley Technical Support Group
    Date Logged
    & Current Version
    June 2015
    09.06.02.06

    Problem:

    When reviewing the load on a gaped support, there is a load in the same direction as a large gap. The pipe never closes the gap, so why is there a load on the support in that direction?

    Solution:

    If you are running a non-linear analysis, 9 times out of 10 the answer is due 1 of 3 reasons: Nonlinear analysis, Friction, or Dynamic analysis rules.

    1. Nonlinear analysis

    Problem is directly with Load sequencing (see WIKI here). Essentially do not consider individual load cases results (ex. Gr, T1, W1, E1, etc..), only consider the operating conditions (GrT1P1, GrE1, GrT1W1, etc...). Only consider the individual load case when trying to understand Why the results of an operating condition are what they are. 

    2. Friction

    Another reason for forces in gapped direction would be directly attributed to Friction. Perform the following test: for each support in question change the Friction to 0.00 for no friction. Now re-run the analysis and check the results. The force should now be removed in the gapped direction.  Why you ask? because one or more gaps may have closed. Example: guide support with the following gap settings:

    Stiffness = Rigid
    Gap Up = 100
    Gap Down = 0.00
    Gap Left and Right = 0.1
    Friction = 0.3

    Look at the Support output report for all operating condition (ex. GrT1P1E1)

    Force: fx = 944 (axial), fy  = 250 (up), fz =  2181 (left)

    Movement in local coordinate:  dx = 1.63 (axial), dy = 0.94 (up), dz = 0.1 (left)

    Because the left gap on the support closed there is a friction force as the pipe is moving up. However, when performing the test above, there is no friction and thus free to move up therefore force in the up direction would then be 0.00 as expected. 

    3. Dynamic analysis rules

    Remember that all dynamic analysis depend on Modal Analysis results and are subject to the rules of performing a Modal Analysis. 

    Note: if using a guide support where 2 opposite directions have large gap settings. Highly suggest to model using an Incline support instead of a Guide support.

    See Also

    "Support" sub report using Results> Output Report in AutoPIPE

    Bentley AutoPIPE

    • Forces and moments
    • AutoPIPE
    • friction
    • Gaps setting
    • support
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    • Mike Dattilio Created by Bentley Colleague Mike Dattilio
    • When: Tue, Jun 9 2015 6:16 PM
    • Mike Dattilio Last revision by Bentley Colleague Mike Dattilio
    • When: Tue, Aug 25 2020 9:23 AM
    • Revisions: 12
    • Comments: 0
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