Hy! Ussualy, the stifness modification, due to damages is modelled by changing the geometrical characteristics, and not the modulus of elasticity, although in reality is not true. With, regards, Alex Popescu!

Sorry about the "big" delay. Thanks for answering.
You say it is about the geometrical properties changing. The geometric properties reffer to:
- cross-sectional area (a)
- moments of inertia (i22;i33)
- torsional constant(j)
- shear areas(as)
Which one, in your opinion, is more appropiate to define the crack state?
From SAP2000 manual I get that:
-the axial stiffness of the section is given by (a*E)
-bending stiffness is given by (i*E).....and so on.
So (E=modulus of elasticity)...it is about the elasticity modulus. Or not?

Hey popauf
Instead of changing any thing in the existing model, simply split the member where the damage is.

Now the new node will be used to represent damaged portion of the member. You may be able do something on constrain of the node to represent the damage...like if it only transfers axial force...define constrains accordingly.

Or split the member into enough pieces so that the damage can be represented by modifying E as you have said    

I tried to split the element, but SAP2000 is stopping at "Creating analysis model" when I have too many nodes, and it's not responding anymore.
When you have 300 elements and 1000 nodes, it's not easy to split everyone/element and define the new ones with another E.
Thanks