Structural Engineer

Dear Mr. Fadi,

Thanks for your question.

This is defined in EN1992-4 section 4.7 "Determination of concrete condition". Basically if the sum of stresses due to internal concrete restraints (like shrinkage, creep etc.) and external stresses due to applied loads are lower (in the negative region of stress-strain diagram) than the admissible stress ( who's value is zero) , then we can consider the concrete as un-cracked concrete.
Please see the explanation below



Let me know if there is any question.
Regards
Muhammad Usman