Help on setting up a combinations for support load in operating condition

Hi, for a pipe stress model I'm currently reviewing, I need to know the support load in the operating condition when it is also subject to a snow load. As I have friction on some axial guides, I suspect a lot of friction forces.

In my model, I have defined all thermal sets and occasional loads such as wind and snow. If I look at the default output/result, AutoPIPE provides loads at supports for individual loads like Gravity{1}, Wind{1}, Snow{1}, ETC. and some combinations, like GW1{1} and GT1P1{1}. The combination Im looking for, isnt there.

I have tried making both a new Code combination (say EXTRA1), and a new Non-Code combination (say EXTRA4). Only the latter case showed up when I reviewed the Support Loads. (side question; why arent new Code combinations not showing up in results, and only non-code combs?)

My first guess at a proper combination was wrong, as it had 0 movement and 0 lateral forces due to friction. My second attempt is below.

Would this be a correct definiton for a new combination, in order to find the support load when my piping system is subject to a snow load in the operating condition? Assuming snow load is first, so before lateral movement takes place, the friction force needs to be overcome.

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  • Hello,

    There are a few parts to this question so I will address them in bullet points below:

    • The Code Combinations tab displays the combination sets defined for piping code compliance, which will be used to check code stress results.  Some default combinations are will already be created, based on the active load cases and the code associated with the current system.  The Non-code Combinations tab displays the active load case combination set defined for any purpose other than code compliance (e.g. displacement and support results).  In both tabs, any default combination may be modified, deleted or reset and any new user combination created and modified in the same grid. User-defined sets can also be defined.
    • The snow load currently has a limitation in which it can only be applied for a linear analysis.  This means that gaps and friction on supports will not be considered for the snow load case.  There is currently an enhancement request for this (Enhancement 139512) and I can add your name to the list, if you'd like.
    • Friction can be considered for the Wind Load Case but should not be considered for the Snow Load Case.  Therefore, you should create two Static Analysis Sets if you'd like to include friction for your Wind Load Case.
    • Analysis Set 1 can include, Gravity, Temperature, Pressure and Wind.  It should also have the Gaps/Friction/Soil checkbox checked on to include friction.  Pressure Extension can be included if necessary.  In the Nonlinear Analysis dialog, make sure to select the Initial case for Occ. loads correctly.

    • Analysis Set 2 can include, Gravity, Temperature, Pressure and Snow case.  It should not have the Gaps/Friction/Soil checkbox checked on to include friction.  Pressure Extension can be included if necessary.

    • Once these Analysis Sets are set up correctly, on the Non-Code Comb. tab of the Load Combination dialog, you will see your combinations automatically created.  You should have a GT1P1W1({1} case or a GW1{1} case, depending on what was set as the Initial case for Occ. loads. for Analysis Set 1.  You should also have a GT1P1+SN{2{} case for the snow results.  This is not automatically combined for you because the Snow load is correctly analyzed with a linear analysis.

    I hope this helps you to understand.  Remember that using the Help Button in any dialog box will open the context help and will also be useful in understanding these topics.

    Thanks,

    Jessica Alegre

       
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  • Hi Jessica, thanks, your reply helped a lot. I will go around messing with my model to see if it works.

    As to your comment "The snow load currently has a limitation in which it can only be applied for linear analysis.  This means that gaps and friction on supports will not be considered for the snow load case.  There is currently an enhancement request for this (Enhancement 139512) and I can add your name to the list, if you'd like."

    1. Is there more info in the help regarding the current limitation on linear analysis of Snow load?

    2. Yes, please add my name on the enhancement list, I've been using Snow loads more often lately and we will continue to do in the future.

    3. Why do I need to set the "Initial case for occ. loads" to OP1 in the 1st analysis set? This is not required for analysis set 2 (where snow is included)?

  • 1. The limitation just means that gaps and friction on supports, and soil yielding cannot be considered with Snow Load.  So they should not be included in any Analysis Set where snow load is included.

    2.  It appears that your company's name is already on this enhancement request list.

    3. My response to question 1 should help to answer this.  A non-linear analysis means that you are including gaps and friction on supports, and/or soil yielding in an analysis set.  While Wind/Earthquake can be considered in a non-linear analysis, Snow cannot be.  So they have to be applied in separate analysis sets if you wish to consider non-linear for the wind/earthquake loads.  When you run a non-linear analysis set including occasional loads, load sequencing applies.  With load sequencing, an initial state for occasional loads has to be set up.  This does not have to be set as OP1, but it does have to be set and understood.  The main question is... are the occasional loads occurring in the gravity state or in an operating state?  Please review the information at this WIKI page: https://communities.bentley.com/products/pipe_stress_analysis/w/pipe_stress_analysis__wiki/8403/06-non-linear-load-sequencing-explained 

       
    This is a test

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  • 1. The limitation just means that gaps and friction on supports, and soil yielding cannot be considered with Snow Load.  So they should not be included in any Analysis Set where snow load is included.

    2.  It appears that your company's name is already on this enhancement request list.

    3. My response to question 1 should help to answer this.  A non-linear analysis means that you are including gaps and friction on supports, and/or soil yielding in an analysis set.  While Wind/Earthquake can be considered in a non-linear analysis, Snow cannot be.  So they have to be applied in separate analysis sets if you wish to consider non-linear for the wind/earthquake loads.  When you run a non-linear analysis set including occasional loads, load sequencing applies.  With load sequencing, an initial state for occasional loads has to be set up.  This does not have to be set as OP1, but it does have to be set and understood.  The main question is... are the occasional loads occurring in the gravity state or in an operating state?  Please review the information at this WIKI page: https://communities.bentley.com/products/pipe_stress_analysis/w/pipe_stress_analysis__wiki/8403/06-non-linear-load-sequencing-explained 

       
    This is a test

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