Determination and Limitation of Story Drifts per ASCE 7-16 §12.12

How does ideCAD determine story drifts and limitations according to ASCE 7-16?

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

• The condition given in 12.8.2 and the minimum equivalent lateral force condition defined in ASCE Section 12.9.1.4.2 are automatically considered.

Symbols

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

Story Drift Determination

The deflection at level x (δ_x) (in. or mm) used to compute the design story drift, Δ, is determined with the following equation.

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

Scaling of Drifts

Where the combined response for the modal base shear (V_t) is less than C_sW, and where C_s is determined by Eq. (12.8-6), drifts are multiplied by C_sW ∕ V_t.

DRIFT AND DEFORMATION

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 methods 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, does not exceed the allowable story drift (Δ_a) obtained from Table 12.12-1 for any story.

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Determination of Story Drifts per ASCE 7-16 with ideCAD

Related Topics

• Foundation Design per ASCE 7-16 §12.13

• Design Coefficients and Factors for Seismic Force-Resisting System per ASCE 7-16 §11.2

• Conditions Regarding Ductility Levels of Structural Systems per ASCE 7-16 §11.2

• Application of Overstrength Factor per ASCE 7-16 §12.2.1

• Application of Deflection Amplification Factor per ASCE 7-16 §11.2.1