When the MOT site class is different from the Site Classes B to C boundary, site amplification effects shall be incorporated in peak ground accelerations and spectral accelerations. This may be accomplished using a simplified method or a site-specific evaluation (Section 3103F.4.2.5).
For a given site class, the following procedure from Chapter 1 of FEMA 356 [3.1] presents a simplified method that may be used to incorporate the site amplification effects for peak ground acceleration and spectral acceleration computed for the Site Classes B and C boundary.
Fa = site coefficient obtained from Table 31F-3-3 Fv = site coefficient obtained from Table 31F-3-4 SS = short period (usually at 0.20 seconds) spectral acceleration value (for the boundary of Site Classes B and C) obtained using Section 3103F.4.2.2, or at the period corresponding to the peak in spectral acceleration values when obtained from Section 3103F.4.2.3 S1 = spectral acceleration value (for the boundary of Site Classes B and C) at 1.0 second period SXS = spectral acceleration value obtained using the short period Ss and factored by Table 31F-3-3 for the site class under consideration. SX1 = spectral acceleration value obtained using the 1.0 second period S1 and factored by Table 31F-3-4 for the site class under consideration. PGAX = peak ground acceleration corresponding to the site class under consideration.
- PGAX, SXS, and SX1 constitute three spectral acceleration values for the site class under consideration corresponding to periods of 0, SS (usually 0.2 seconds), and 1.0 second, respectively.
T = Period corresponding to calculated Sa T0 = Period at which the constant acceleration and constant velocity regions of the design spectrum intersect
VALUES OF Fa
|< 0.25||0.5||0.75||1.0||> 1.25|
VALUES OF Fv
|< 0.1||0.2||0.3||0.4||> 0.5|