Stiffness modification for fiber elements.

[alima2065]

Hello everybody,

I have my experimental data for a 2-story Rc frame. I built its model in OpenSees based on different assumptions as follows:
Model #1: Used zero length spring for the plastic hinges and an internal elastic element between them that its stiffness modified for cracking.
Model #2: Used zero length Fiber section for the plastic hinges and an internal elastic element between them that its stiffness modified for cracking.
Model #3: Used fiber element without any modification for cracking.

After analyzing (Transient analysis) Models 1 and 2 verified experimental data but model 3 is stiffer and responses are smaller than real responses. I have to mention that in both Models 2 and 3 I used confined concrete (Concrete02) for core (based on Mander model) and cover. Also in all models, I applied Joint2d to consider the effect of the joints based on Altoontash model (MCFT).

My question is that Fiber elements have to be modified for cracking, or fibers can consider this effect inherently based on material model (Zero tension)? If it cannot how I can modify it for cracking?

Many thanks