Help with SAP2000, Negitive Poisson's Ratio 1

[Mabon]

Hi there,
I have been asked to model an auxetic meta-material in SAP2000. Where an auxetic material is defined as a material with a negative Poissons ratio and some other interesting properties but this is the main one I'm focussing on. The cell structure is also more important than the material itself. The cell I'm modeling looks like this:

Where it can be infinitely replicated side by side or up and down. The part I am stuck on is defining the material as one with a negative Poissons ratio as SAP2000 doesn't allow this. Is there any other way to model this in the software?

 

[FEA way]

Some FEA software doesn’t allow negative Poisson’s ratio (PR) but most advanced codes let you define it. Anyway, if you model the auxetic cell geometry then you don’t have to specify the negative PR. Such cell can be made of any regular material such as steel and have positive PR. The thing is that thanks to its specific shape it will behave as auxetic and you can see this if you calculate the effective PR from strains. The only reason to define material with negative PR is when you have a homogenous geometry (like a simple cube) and want to get the deformation typical for auxetic structure.