When the bond law is considered along a bar, the slips are calculated and the load transfer can be reproduced, including the anchoring regions. Therefore, there is no need to consider such a formula in your ATENA model (however, on the other hand, you can make a parametric study with ATENA to verify if/under what conditions this formula is a good design guideline...).

If the background behind the lambda is something different, please refer to the exact code and page (copy-paste if possible), such that we can look at its meaning and possible influence in nonlinear FEM.

Regards.

Does the ATENA implementation of the CEB-FIP bond-slip model consider the reduction parameter (lambda) given by the code?
(lambda: reduction parameter for those parts of the reinforcement that are a distance x<=5 times the rebar diameter).

Thanks for the answer,

Kind regards,

Valentina