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Difference between different loadings



I am trying to build my container model and running a static analysis on it. The requirement is that I need to show stresses and deflection of the container and equipment while it is at tiedown provision state. The situation for tiedown is 2G at transverse, 4G longitundinal and vertical. The question is that do I:


1) model the equipment as MASS element (kg), giving them various mass and running the analysis with 4 times the BODY LOAD (9810mm/s2 X 4) vertical or longitundinal or 2 times (9810mm/s2 X 2)the BODY LOAD transverse?


2) model the equipment as LOAD (Newton), giving the equipment 4 times the load (load X 4) or 2 times the load (Load X 2)?


Thanks for your time.


Re: Difference between different loadings

I've seen a lot of analysts apply a 1g load in each direction, then in FEMAP, use output set combinations to combine them with any factor you want.  I am assuming you're doing a linear analysis, where a linear combination of results will be acceptable.  In v11.2, there's virtual linear output set combinations where everything is done on the fly, you just specify the factors on the base output sets.

Re: Difference between different loadings

Dear Mattz,

The approach to use to model the equipment as mass or equivalent force is depending of your needs, and the type of analysis to perform:

  • If you want to see the effet of the container located at the tip of the full crane, then the crane will not more stiff not matter you mesh the container as mass or load.
  • But if you want to compute the natural frequencies of the crane, then the container mass value and location is critical, you will need to define a mass element at the Center of Gravity of the container and use an spider RBE3 element to attach to the crane. Here the use of a force loading is not possible, do you see the difference?.

I always suggest to use mass elements instead forces, this is more efficient, and give you freedom to run static & dynamic analysis using the same FE model.
Best regards,Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
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