Design Spectral Response Accelerations SDS / SD1 (ASCE 7-16 11.4)
Site-adjusted design spectral accelerations, SDS and SD1.
Example
You enter
- Mapped Ss (short-period, fraction of g) 1
- Mapped S1 (1-second, fraction of g) 0.4
- Site coefficient Fa (Table 11.4-1) 1.1
- Site coefficient Fv (Table 11.4-2) 1.9
You get
- SMS = Fa Ss (MCER short) 1.100g
- SM1 = Fv S1 (MCER 1-sec) 0.760g
- SDS = 2/3 SMS (design short) 0.733g
- SD1 = 2/3 SM1 (design 1-sec) 0.507g
Checked against published worked examples from: FEMA.
Details, formula, and sources
ScopeSite-adjust the mapped MCER accelerations (SMS = Fa Ss, SM1 = Fv S1) then take two-thirds for design (SDS = 2/3 SMS, SD1 = 2/3 SM1) -- the ASCE 7-16 procedure; ASCE 7-22 reads SMS and SM1 from the USGS multi-period data instead of Fa and Fv. Ss 1.0, S1 0.4, Site Class D (Fa 1.1, Fv 1.9) -> SDS 0.733g, SD1 0.507g, the exact inputs a seismic base-shear calculation consumes. A design aid; the engineer of record governs.
Formula or tableSMS = Fa Ss; SM1 = Fv S1; SDS = (2/3) SMS; SD1 = (2/3) SM1.
Source and editionThe ASCE 7-16 11.4 site-adjusted MCER and design spectral response accelerations, by name (ASCE 7-22 replaced the Fa / Fv site coefficients with USGS multi-period SMS and SM1).
Free accessThe ASCE 7 site-coefficient adjustment and two-thirds design reduction are the published seismic-load procedure; the mapped Ss/S1 come free from the USGS seismic design maps.
What governsEstimate. AHJ and licensed professional govern.
API field namesss, s1, fa, fv, sms, sm1, sds, sd1
- Site adjustment SMS = Fa Ss, SM1 = Fv S1ASCE 7-16 11.4.4
- Design reduction SDS = 2/3 SMS, SD1 = 2/3 SM1ASCE 7-22 11.4.5
- Site coefficients Fa/Fv from Tables 11.4-1/11.4-2 by Site ClassASCE 7-16