For any column or wall in the earthquake direction, storey drifts expressing the displacement difference between two floors, ∆i, is automatically obtained by Section 12.8.6.

The condition given in 12.8.2 and also the minimum equivalent lateral force condition defined in Section are taken into account automatically.


Cd = Deflection amplification factor in Table 12.2-1
δxe = Deflection at the location required by this section determined by an elastic analysis
Ie = Importance Factor
Δi = According to any column or wall earthquake, the relative displacement difference between two consecutive layers expressing reduced drift
δi = Story drifts

12.8.6 Story Drift Determination

The deflection at level x (δx) (in. or mm) used to compute the design story drift, Δ, is determined with eq. 12.8-15.

Eq. (12.8-15) is used to estimate inelastic deflections (δx), which are then used to calculate design story drifts, Δ. These story drifts must be less than the allowable story drifts ,Δa, of Table 12.12-1. Scaling of Drifts

Where the combined response for the modal base shear (Vt) is less than CsW, and where Cs is determined in accordance with Eq. (12.8-6), drifts is multiplied by CsW ∕ Vt.

Reference: ASCE 7-16


12.12.1 Story Drift Limit

The drift, Δ, is calculated according to the procedures of Section 12.8.6. (Sections 12.9.2 and 16.1 give procedures for calculating displacements for modal response spectrum and linear response history analysis procedures, respectively; the definition of Δ in Section 11.3 should be used).

The design story drift (Δ) as determined in Sections 12.8.6, 12.9.1, or 12.9.2 is not exceed the allowable story drift (Δa) as obtained from Table 12.12-1 for any story.