The cracked behavior of shear walls and other shell objects may be modeled in ETABS by using property Property modifiers to adjust their stiffness. When local axes correspond with default settings, modifiers, and their associated properties, are as follows:
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ACI 318-05, Section 10.11 recommendations are associated with slenderness effects and governing flexural deformations, in which case, users should modify EI, which correlates with f11 I33 or I22 for frames and either f11 or f22 for shells.
ACI 318-08, Section 8.8 provides modification factors. No recommendation is made for shear, though users should modify GA when shear walls is expected to experience stiffness degradation upon cracking.
Default settings align shear walls such that their 1-axis is horizontal and their 2-axis is vertical. As a result, the flexural modifier EI should be applied to f22 for wall piers and f11 for spandrels. For columns usually I22 and /or I33, and for beams usually I33 assuming default orientation.