Shoud we apply this is from ACI 318 in ETABS

[Kovan A.]

Hi

As i see rarely someone check wither the shear wall is cracked or not then apply stiffness modification accordingly for the shear wall, as you know we should apply F22=0.35 for cracked wall and F22=0.7 for uncracked wall (default axes orientation)?
we check this by creating a model and assume that wall is uncracked and apply f22 = 0.7 then analysis the model, create and envelope load combination for (0.9DL+E loads or all lateral loads combination) then check S22 stress of wall if it is greater than the modulus of rupture of concrete (fr), if the stress is greater than fr we consider the shear wall a cracked and apply 0.35 , this is effect checking of Story drift,Stability index and calculating fundamental period of the building. What do you think about this.

ACI 318-19 R6.6.3.1.1 "If the factored moments and shears from an analysis based on the moment of inertia of a wall, taken equal to 0.70Ig, indicate that the wall will crack in flexure, based on the modulus of rupture, the analysis should be repeated with I = 0.35Ig in those stories where cracking is predicted using factored loads."

 

[r13]

Your thinking is in the right direction. However, it seems the code language has changed since the time at my last practice. I could be wrong, but I recall 0.7 Ig was for cracked compression member, and 0.35 Ig for flexural member. Anyway, the difference between assigning every member to 0.7 Ig and 0.35 Ig is not too great, but when members within the same model with varying stiffness, the difference could be huge. Owing to the speed of today's computing power, you may want to perform the latter addressed approach to get optimum results through iterations. Please note that this is only my personal view, which may not be shared/agreed by others.

 

[Kovan A.]

thanks
This from ACI 318-19 R6.6.3.1.1, so i think we should apply it when we design according to ACI318-19 unless at another section it allowed us to ignore this section.