3. For periods greater than *T*s, the design

but shall not be less than:

spectral response acceleration shall be as given by

the following equation:

(3-9)

where:

(3-12)

The fundamental period of the

where the value of *T*s shall be as given by the

structure.

The

above

equations

are

shown

following equation:

graphically in Figure 3-1.

(2) Modal Analysis Procedure. The required

(3-13)

modal periods, mode shapes, and participation

factors shall be calculated by established methods of

structural, analysis assuming a fixed-base condition.

(b) Modal base shear. The portion of the

base shear contributed by the *m*th mode, *V*m, shall be

(a) General response spectrum. Where a

determined from the following equations:

design response spectrum is required in this

document, and where site specific procedures are not

(3-14)

used, the design response-spectrum curve shall be

developed as indicated in Figure 3-2, and as follows:

2

n

∑ wi f im

1. For periods equal or less than *T*o, the

1

(3-15)

∑ wi f i2*m*

given by the following equation:

where:

(3-10)

the modal seismic response

Where TO = 0.2TS and TS is defined by Equation 3-

coefficient determined below,

13.

2. For periods greater than *T*o and less

the effective modal gravity load

than or equal to *T*s, the design spectral response

including portions of the live load as defined in Sec.

5.3.2 of FEMA 302,

equation:

(3-11)

the structure at level i, and

3-7

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