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FEMA Tier3 Analysis - Seismic Factor

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Perhaps you've gotten an answer or discovered it yourself.  The Commentary for FEMA 310 5.2.1 (page 5-2) states that the 0.75 factor "applies to the evaluation of the building only.  Any mitigation or rehabilitation as a result of the evaluation must use the full seismic force for design."

Best regards,




Dan Morrow, P.E.

Swenson Say Fagét Structural Engineers

2124 3rd Ave. Suite 100

Seattle, WA  98121

206-956-3745 (direct)

206-443-4870 (fax)

email: dmorrow(--nospam--at)




Original message:




I wanted a clarification on one of the issue mentioned in FEMA 310 which =

is currently the ASCE standard 31-03. =20


Referring to sec5.2.1, it states that 75% of the calculated seismic =

force can be used for a Tier 3 analysis. =20

Q1. Is this only for the evaluation or the retrofit design which =



It suggests that FEMA 356 be used for this evaluation.  It says that the =

75% force is taken since the documents (FEMA356) are intended for ="">

design. =20


Q2. What force level should be considered when upgrading the structure - =



Suppose during evaluation, a few beams (say 10) do not meet the =

suggested criteria and were found 20% overstressed under the 75% seismic =

force level.  But while using 100% seismic level for the retrofit, =

several more members might fail?  How do you justify this unless you did =

a 100% analysis during the evaluation and reported the cost to the =



-  Aswin


Aswin Rangaswamy, P.E.

Jacobs Facilities Inc. ( )

(714) 503-3772 (P); (714) 503-3865 (F)