Fabrics in karamba

Hi!
I'm exploring Karamba, trying to develop tensile models, and I have some doubts about working with meshes simulating fabrics.
With cables I'm turning the bending off with 'modify element' and prestressing them till having no compression forces (with a negative value as 'initial strain')
But, with meshes, is there any option to put hinges in the nodes attached to other rigid elements to let know karamba that we have there articulated nodes?
And, related to prestressing the mesh, I have noticed that it's done in both directions at the same time. The thing is that if we introduce negative values as 'inicial strain', the results obtained in 'von mishes stress' are tractions, but if we look the 'principal stresses' in directions 1 and 2, we have increasing compressions. Why is this?
Using positive values as 'initial strain' (which makes no sense) results in 'von mishes stress' are compressions, but 'principal stress 1 and 2' returns traction values...
I will be gratefull if anyone has advices about how to simulate fabrics properly.
Thanks a lot!
Cristina