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.

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  • 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



  •      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.

  • 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.