FEMA site factors, Fa and Fv, are applied to the
1.25S
C=
(3-24)
2
MCE ordinates SS and S1 in Equations 3-1 and 3-2.
T
3
The design parameters defined by Equations 3-25
and 3-26 have been multiplied by 1.50 to obtain the
but C need not exceed 2.75.
equivalent SS and S1 values listed in Table 3-3. The
adjusted design values, SDS and SD1, for Earthquake
If the importance factor, I is eliminated in Equation
A, can thus be obtained by multiplying the values in
3-23, and if it is assumed that Rw with allowable
Table 3-3 by the appropriate local site adjustment
stress design is comparable to the FEMA 302
factor, Fa or Fv, and multiplying the product by the
reduction factor, R, with strength design, then by
2/3 factor indicated in Equations 3-3 and 3-4.
comparison with Equation 3-7,
Similarly, for Ground Motion B, the product is
multiplied by the factor indicated in Equations 3-
SDS = 2.75Z
(3-25)
28 and 3-29.
Where Z is the seismic zone coefficient from Table
(4) Use of available data. As indicated in the
3-4. Similarly, Equation 3-24 can be compared with
above subparagraphs, the spectral ordinates listed in
Equation 3-8 with T = 1.0 sec to yield:
Table 3-3 are derived from the data contained in the
current TM 5-809-10. These data are at least six
SD1 = 1.25Z
(3-26)
years old, and the conversion is approximate.
If
better data are available in more recent publications,
(2) Spectral ordinates for Seismic Zone O.
or from site-specific investigations, the data should
The Building Seismic Safety Council (BSSC) Design
be converted to the appropriate design parameters by
Values Group that developed the MCE maps
the procedures outlined in this chapter.
recommended that, regardless of seismicity, all
buildings should be designed to resist a lateral force
of one percent of the building weight (i.e. Cz =
3-3.
Design Parameters for Ground Motion B.
0.011x1). If an average value of 4.0 is assumed for
the R factor in Equations 3-7 and 3-8, then
a.
General. The design parameters for Ground
Motion B are those used in this document for
SDS and SD1 = 0.04
(3-27)
Performance
Objectives
2B
(Safe
Egress
for
Hazardous
Occupancy)
and
3B
(Immediate
(3) Conversion to SS and S1. The preceding
Occupancy for Essential Facilities). Performance
subparagraph
provides
the
basic
relationship
levels, ground motions, and performance objectives
between the design parameters in the UBC and those
are summarized in Tables 4-3, and 4-4. Criteria for
in FEMA 302. It should be noted however, that the
the seismic evaluation or design of essential military
Site Adjustment Factor, S, is applied directly to the
buildings have typically prescribed ground motion
UBC design values in Equation 3-24, while the
3-18
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