Seismic Design Story Drift and Allowable Limit (ASCE 7-22 12.8.6 / 12.12)
Amplified seismic story drift against its allowable limit.
Example
You enter
- Elastic story drift delta_xe (in) 0.5
- Deflection amplification Cd (Table 12.2-1) 5.5
- Importance factor Ie 1
- Story height hsx (in) 144
- Allowable drift coefficient (default 0.020) 0.02
You get
- Design story drift delta_x = Cd delta_xe / Ie 2.75 in
- Allowable drift delta_a 2.88 in
- Util 0.955
Checked against published worked examples from: FEMA / BSSC.
Details, formula, and sources
ScopeAmplified drift delta_x = Cd delta_xe / Ie against the allowable delta_a = drift coefficient x story height (commonly 0.020 hsx). Cd 5.5, delta_xe 0.5 in, 144 in story -> 2.75 in vs 2.88 in allowable, OK at 0.955 utilization; a softer frame at 0.6 in fails. A design aid; the engineer of record governs.
Formula or tabledelta_x = Cd delta_xe / Ie; delta_a = drift_ratio x hsx; util = delta_x / delta_a.
Source and editionThe ASCE 7-22 12.8.6 amplified design story drift and the 12.12 allowable story-drift limit, by name.
Free accessThe Cd amplification of the elastic drift and the tabulated allowable drift are the published ASCE 7 drift-check procedure.
What governsEstimate. AHJ and licensed professional govern.
API field namesdelta_xe_in, cd, ie, hsx_in, drift_ratio, delta_x, delta_a, util
- Design drift delta_x = Cd delta_xe / IeASCE 7-22 Eq. 12.8-15
- Allowable drift delta_a = drift coefficient x hsx (commonly 0.020 hsx)ASCE 7-22 Table 12.12-1
- Single-story check does not run the analysis or check torsional amplificationscope of this tile