Representation of a Structure by a Concentrated/Lump Mass Element

[struclearner]

When the weight of a structure is modeled by a lumped/concentrated mass element in FEA, the location of the lump mass element is cg of the structure, which it models.
When the analysis of this model is done for inertial loadings, for linear gravity loadings, this is ok.
When the structure is subjected to rotational acceleration, the lump mass element location will not be at radius of gyration.
Thanks for your input.

 

[jhardy1]

Correct.

Is there a question?

(Whether a simple lumped mass model is suitable depends on the nature and purpose of the analysis.):

http://julianh72.blogspot.com

 

[JoshPlumSE]

If the used lumped mass and mass moment of inertia at the CG, then this should be sufficient for both rotation and translation.

Now, it won't take any of the "accidental" torsion into effect (per ASCE7), unless the lumped mass & mass moment of inertia are offset by the % described in ASCE7.

 

[rb1957]

so why not apply body forces (and model density as mass/volume) ?

another day in paradise, or is paradise one day closer ?