2/3 of MCE can only be made on a site-specific or
performance objectives is described in Paragraphs 4-
regional basis. However, the authors of the FEMA
7, 4-8, and 4-9, and is summarized in Tables 4-3 and
302 provisions have indicated that, in many areas of
4-4.
b.
Design Spectral Response Accelerations. The
the U.S., the new ground motions corresponding to
spectral response design values, SDS and SD1, adopted
2/3 of MCE will be comparable to those specified by
prior codes. It was also considered that, for most
in FEMA 302 are defined as:
structural elements, the design criteria in FEMA 302
SDS = 2/3 SMS
provided adequate reserve capacity to resist collapse
(3-3)
at the MCE hazard level.
SD1 = 2/3 SM1
(3-4)
d.
Site Response Coefficients.
For all
structures located within those regions of the maps
For regular structures, 5 stories or less in height, and
having a period, T, of 0.5 seconds or less, the
having values of short-period spectral acceleration,
SS, greater than 0.15g, or values of the one-second
SMS # 1.5 Fa
the site shall be classified according to Table 3-1.
(3-5)
Based on these Site Classes, FEMA 302 assigns Site
SM1 # 0.6 Fv
Response Coefficients, Fa and Fv, as indicated in
(3-6)
Tables 3-2a and 3-2b. The adjusted MCE spectral
response acceleration for short periods, SMS, and at 1
c.
Seismic Response Coefficients.
second, SM1, are defined as:
(1)
Equivalent
Lateral
Force
(ELF)
SMS = Fa SS
(3-1)
Procedure. For this procedure the seismic base shear
is represented as V=CSW and the seismic response
SM1 = FV S1
coefficient, CS, is determined in accordance with the
(3-2)
following equation:
3-2.
Design Parameters for Ground Motion A
S DS
(FEMA 302).
CS =
(3-7)
R
a.
General. Ground Motion A is the basic
where
design ground motion for the FEMA 302 provisions.
The design parameters for Ground Motion A are
R = Response modification factor defined
those used in this document for Performance
in Section 5.2.2 of FEMA 302.
Objectives 1A (Life Safety) and 2A (Safe Egress for
Special
Occupancy).
The
combination
of
The value of CS need not exceed the following:
performance levels and ground motions to form
3-2
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