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FEMA 310 (302)

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Kenneth Tarlow wrote:

>Does anyone know how to use table on page 37.Ss is the short
>period acceleration from the curv (.2 sec).  when i get my information
>from the maps i get
>2% 50 years
>pga          83.93%
>.2 sec sa   188.3
>.3 sec sa   183.2
>1. sec sa   73.6

>For site class E, I should get 2.5.{from past experience I would guess

>Ss is defined as the maximum spectral acceleration at short periods. 
>how do I use this table to get my answer. I want to solve equation

Your short period acceleration Ss is 188.3, which translates to 1.88 g.  In
table, 1.88 is greater than 1.25 so the far right column of the
table is used.  If the site is really soil type E, the footnote to the table
indicates that you need a site-specific geotechnical investigation.

If on the other hand the soil is type D, the table gives a value for Fa of
1.0.  This value is used along with the 1.88 g for Ss to be used in equation

The values for equation are determined in a similar manner using
S1 and table

I hope this helps.
Brian Kehoe, SE
Wiss, Janney, Elstner Associates, Inc.