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The elastic deformations calculated under reduced forces (see Section C12.8.6) are multiplied by the deflection amplification factor, C_d, to estimate the deformations likely to result from the design earthquake ground motion.

The application of the factor R/Ie I_e to the design response spectrum reduces not only design forces but also displacements. To compensate for this, ASCE 7 requires that the deflections at level x at the center of mass, δxδ_x, be determined in accordance with where Cd C_d is from Table 1112.7, Ie 2-1, I_e is from Table 111.5-1, and δxe δ_xe is the deflection determined by elastic analysis with seismic forces reduced by factor R/IeI_e. Using a value Cd C_d equal to R would result in the displacement δx δ_x being equal to δxeδ_xe, which would be consistent with the equal displacement rule.

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