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Mass Modeling Problem

Hi Everyone,

    An error keeps coming up when trying to run a dynamic analysis of pedetrians loading. The error is "No unsupported massed entered- check densities.

  Try just about everything i know, can't seems to find the solution to the error. Will be glad if anyone can help.

7 Replies (Most Recent Reply)

  • Attached is the model of the structure for the analysis. Thanks
    STAAD SPACE.docx
  • In reply to piston:

    1) From load case 1, remove the command MODAL CALCULATION REQUESTED

    2) In load case 2, just before the line TIME LOAD, add the lines

    SELF X 1.0
    SELF Y 1.0
    SELF Z 1.0

    3) Change the CUT OFF MODE SHAPE value from 10 to 20.

    The modified file is attached.

  • In reply to NIHESH.N:

    Hi Nihesh,

       Thanks so much, I'm so glad I joined this community. You are a good man. Cheers!

  • Hellow,

    I am also facing the same problem for a simple cantilever beam with a dynamic load applied to it. I am not sure but the problem can be with the software lumping the mass to the support. But, I have no idea what to do with this idea in mind. Can anyone please help on this? Thank you

  • In reply to Philipose:

    Make sure that you have applied load items in the load case that includes the MODAL CALCULATION REQUESTED command. Make sure that they are entered in the form of forces rather than masses, and that the magnitudes are all positive. Make sure that the load items are specified in all global axis directions that you want the program to consider them as being dynamically active. Finally, if it is just a single member in the model, break it into a number of members, and then verify the loads. This will more closely approximate a uniform distribution of force representing the mass. Cheers, Chris

  • In reply to Chris Conrad:

         That was helpful to me as well doing spectrum seismic analysis. So, i entered forces rather than masses and made sure all magnitude is positive.  I'm a bit perplexed at the Modal calculation, sir could you elaborate further on this part... definition, procedure and other basics that we( begginer) needs to know.

  • In reply to etnickstudio:

    When MODAL CALCULATION REQUESTED is used, the software carries out an eigensolution and reports the modes and the frequencies. This command is typically used when you want to know the structural frequencies but do not need to get into a detailed dynamic analysis like a response spectrum or a time history. However when you are doing a response spectrum or time history analysis, the software automatically does the modal calculations and you do not need to use the MODAL CALCULATION REQUESTED command. You can find more details on this at section 5.34.2 of the technical reference manual titled Modal Calculation Command.  

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