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RBE/MPC Formulation


Here's a strange question: I've seen presentations on the web that talk about RBEs being a specialized combination of MPCs between nodes.


Does anyone know of a reference that actually shows the MPC formulation for an RBE2? how about an RBE3?






Re: RBE/MPC Formulation

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Dear Tony,

The NX NASTRAN R-type elements are elements that imposes fixed constraints between components of motion at the grid points or scalar points to which they are connected. Thus, an R-type element is mathematically equivalent to one or more multipoint constraint equations. Each constraint equation expresses one dependent degree of freedom as a linear function of the independent degrees of freedom.

Although sometimes the R-type elements are referred to collectively as rigid elements, the name “rigid” is misleading. The R-type elements that are rigid consist of the RROD, RBAR, RBE1, RBE2, and RTRPLT. The RBE3 and RSPLINE are interpolation elements and aren’t rigid. The RBE2 and RBE3 elements are the most commonly used R-type elements in the NX Nastran element library.


To learn more about RBE2 vs. RBE3 you can visit my blog in the following address:


Best regards,


Blas Molero Hidalgo, Ingeniero Industrial, Director
Blog Femap-NX Nastran:

Re: RBE/MPC Formulation

Thanks Blas,

I've seen the presentation you reference, and I generally understand the concepts of the RBEs. However, what I'm looking for are the actual MPC equations for the RBE2 and RBE3. Do you have anything that shows what those are?

Tony D.

Re: RBE/MPC Formulation

Siemens Phenom Siemens Phenom
Siemens Phenom

Try this link:


If the link doesn't work, just Google "rbe3 formulation"


It covers RBE3 formulation pretty well.