moment redistribution 9aci section 8.4.30

huangyhg

moment redistribution (aci section 8.4.3)
section 8.4.3 states "redistribution of negative moments shall be made only when et is equal to or greater than 0.0075 at the section at which moment is reduced."
my question is, can anyone tell me how or point me to a reference on how to calculate the strain of steel to see if it's equal to or above 0.0075?  i know how to do it pre-flexural-failure, but i'm not sure how to do it post-flexural failure, which would be the case here.  
thanks.
pca notes on aci 318 have a good example of moment redistribution
i don't know why you say post flexure failure.  per section 10.3.5 the minimum et = 0.004 at nominal strength.  also se section 10.3.3
section 10.3.4 states that the tension-controlled zone begins when et is equal to or greater than 0.005.
et can be calculated using similar triagles, see the stress diagram in section r.10.3.3.
similar triangles.