brace figure optimization

[javidsharifi]

Dear all,

I am going to model a steel frame for optimization analysis of its braces. For this purpose, I shall firstly fill the supposedly braced bays with plane elements and then run the structure. Then, each time I run the analysis, based on some criteria, some elements will be eliminated until what remains will look like ordinary braces, and the elements will be substituted by proper equivalent steel profiles. My question is how should I model these primary elements which are to be eliminated analysis by analysis? Are quad elements with J2Plasticity nDMaterial correct to be used? Also, how shod I define the fixity conditions boundary nodes, i.e. those which will lie on the frame beams and columns? Should they depend on the displacements of the beams and column?
I truly appreciate your kind helps.
Waiting for your precious answers.

Behtash
SUTech