FEMA site factors, *F*a and *F*v, are applied to the

1.25*S*

(3-24)

2

MCE ordinates *S*S and *S*1 in Equations 3-1 and 3-2.

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 *S*S and *S*1 values listed in Table 3-3. The

adjusted design values, *S*DS and *S*D1, 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 *R*w with allowable

Table 3-3 by the appropriate local site adjustment

stress design is comparable to the FEMA 302

factor, *F*a or *F*v, 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-

(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

(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. *C*z =

0.011x1). If an average value of 4.0 is assumed for

the *R *factor in Equations 3-7 and 3-8, then

Motion B are those used in this document for

(3-27)

Performance

Objectives

2B

(Safe

Egress

for

Hazardous

Occupancy)

and

3B

(Immediate

(3) Conversion to *S*S and *S*1. 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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