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The DruckerPrager material model implemented in opensees is explained in the openseeswiki webpage: http://opensees.berkeley.edu/wiki/index.php/Drucker_Prager The elastic paramters are: k,G bulk modulus: k=E/(3*(1-2*ni)) Shear modulus: G=E/(2*(1+ni)) The yield surface parameters are: sigmaY,rho sigma...

I can suggest you to use the Drucker Prager material model. You can have fair estimations in case of monotonic analysis, whereas it is not suitable for cyclic analysis. Here you have the link to opensees wiki: http://opensees.berkeley.edu/wiki/index.php/Drucker_Prager With some colleagues, I have im...

The ShellNL is a Nine-node Lagrangian element. It does not include geometrical nonlinearity. It can be used with nonlinear material. I checked few lines of the code posted by jkbgbr and I found problems with node numbering that are sufficient to produce errors and need to be addressed. As an example...

I found an error in MembranePlateFiberSection.cpp
At line 372 it is written:

tangent(0,3) += -z*dd(0,1) ;

It sould be

tangent(0,4) += -z*dd(0,1) ;

This can lead to problems in executing opensees.exe due to the unassignment of the "tangent(0,4)".