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 220.127.116.11.2 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
Story Drift Determination
The deflection at level x (δx) (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 (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 by Eq. (12.8-6), drifts are multiplied by CsW ∕ Vt.
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 (Δa) obtained from Table 12.12-1 for any story.
I or II
Structures, other than masonry shear wall structures, four stories or less above the base as defined in ASCE Section 11.2, with interior walls, partitions, ceilings, and exterior wall systems that have been designed to accommodate the story drifts
Masonry cantilever shear wall structures
Other masonry shear wall structures
All other structures