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AutoPIPE Wiki 06. How to automatically find the MAX load case from a group of load cases in an AutoPIPE model
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              • 05. How to change the order / sequence of listed combinations in AutoPIPE?
              • 06. How to automatically find the MAX load case from a group of load cases in an AutoPIPE model
              • 08. Why on the Non-Code combination tab does the initial case for occasional load not change in AutoPIPE?
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    06. How to automatically find the MAX load case from a group of load cases in an AutoPIPE model

    Applies To
    Product(s): AutoPIPE,
    Version(s): All
    Area: Combinations
    Original Author: Bentley Technical Support Group

    Problem:

    In order to evaluate the total load from operating conditions and worst case scenario from 6 Static Earthquake load case. The following combinations were created in a model.

    Static Earthquake load cases: 

    E1           User                      0.6280   0.0000   0.0000

    E2           User                      0.3830   0.0000   0.0000

    E3           User                      0.0000   0.0000   0.6280

    E4           User                      0.0000   0.0000   0.3830

    E5           User                      0.0000   0.2160   0.0000

    Create user combinations to evaluate all possible scenario of Static Earthquake cases:

    Trans1 = E1+E5

    Trans2 = -E1+E5

    Trans3 = E1-E5

    Trans4 = -E1-E5

    Trans5 = E3+E5

    Trans6 = -E3+E5

    Trans7 = E3-E5

    Trans8 = -E3-E5

    Create user combination to find worst case (MAX) scenario from above cases

    TRANS(POS)= sign Max  ( TRANS1… Trans4)

    TRANS(NEG)= sign Max  ( TRANS5… Trans8)

    TRANS = sign Max  [ TRANS(POS), TRANS(NEG)]

    Create user combination to evaluate normal operating conditions

    Func = Gr + T1 +P1

    Create user combination to total the loads of Operating and Worst case Seismic load cases 

    TRANSPORT = TRANS + FUNC

    Is this listing of combination correct, why or why not?

    Solution:

    NO, this set of combinations is NOT correct.

    The problem is because of load sequence, the results of Trans1 - Trans12 cannot be added into other user combinations to find the worst cases scenario.  

    Help topic explains AutoPIPE generates combinations based on the non-linear load sequence only

    Please see the following AutoPIPE help section: 
    Help > Contents> Search Tab> enter "Add default Non-Code combinations" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information.

    Non-linear analysis:

    For non-linear static analysis results, the program will automatically generate combinations based on the load sequences only. For example, if GR is the initial state of T12, and T12 is the initial state of P12, and P12 is the initial state of W10, then the program will generate the combination, GT12P12W10 or GT1P1E10.

    Combining 2 or more Seismic load cases in a combination is not valid.

    The seismic cases have to be explicit in different +/- directions.\

    For now using a non-linear analysis looks like for 12 'seismic' loads they will need 2 models where the seismic loads are defined e.g. E1 = trans1, E2 = trans 2, etc..

    Otherwise they could run as linear analysis with their existing combinations which would be valid and evaluate TRANSPORT load combination for worse loads and contributing load cases then go back and run a non-linear analysis for this load sequence only

    Then envelop the linear and non-linear results to capture final maximum. Some users do this for true seismic loading.

    Based on the setting s above, recommend the following corrective procedure:

    A. Update the defined Static Earthquake cases to match the intention of Trans1...Trans8, as followed:

    E1           User                      0.6280   0.0000   0.0000

    E2           User                      -0.6280   0.2160   0.0000

    E3           User                      0.6280   -0.2160   0.0000

    E4           User                      -0.6280   -0.2160   0.0000

    etc..

    B. Because the load case scenario will be evaluating, Gravity + Press +Temp + Seismic, change the default load sequence:

    Load> Static Analysis Set> open analysis set to confirm all pertinent load cases are checked ON, "Gaps / Friction / Soil" setting is checked ON, press OK button, and change "Initial case for Occ. loads" from GR to OP1 (see online help for details on this setting), and press OK button to close dialog screen.

    C. Run analysis

    D. Select Tools> Combinations> 

    i. Code Combination Tab:

    After opening this tab, noticed that AutoPIPE had automatically created the following operating load cases GRTP4+E1, GRTP4-E1, etc.. In order to configure AutoPIPE to evaluate a group of load cases (10 max per combination) and determine which one is the worst case, create the following user combination:

    Note: each of the load cases has M/S = S (stress), this combination would not be valid if one or more combination had M/S = M (moments). 

    Create as many grouping combinations (ex. Max Stress 5-8) as necessary to evaluate all the combinations, max 10 at a time. The following is an example of the next group to be evaluated:

    Finally, evaluate the actual group combinations as shown below:

    ii. Non-Code Combination Tab:

    After opening this tab, noticed that AutoPIPE had automatically created the following operating load cases GT4P4E1{4}, GT4P4E2{4}, etc (see online help to understand why GT4P4-E1(4) type comb. are not created for non-linear analysis). In order to configure AutoPIPE to evaluate a group of load cases (10 max per combination) and determine which one is the worst case, create the following user combination:

     

    Note: the different Combination method used for non-code combinations, Res. Max, see online help for details on this option.

    E. After all the correct combinations have been created, Press OK button to close the combination dialog screen

    F. Review the combination results in the Results grids or Output report.

    Note: a new enhancement has been logged, TFS-E239855 to help with generating this type of information. 

    See Also

    "Non-Code Comb." tab

    Bentley AutoPIPE

    • Load Case
    • Non-Code
    • code
    • AutoPIPE
    • COMBINATION
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    • Mike Dattilio Created by Bentley Colleague Mike Dattilio
    • When: Wed, Mar 19 2014 10:33 AM
    • Mike Dattilio Last revision by Bentley Colleague Mike Dattilio
    • When: Fri, Jul 12 2019 5:30 PM
    • Revisions: 9
    • Comments: 0
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