the modal period of vibration, in

at the base in the *m*th mode,

seconds, of the *m*th mode of the structure,

in the *m*th mode, induced at Level *x*, and

level of the structure when vibrating in its *m*th mode,

the structure, *W*, located or assigned to Level *x. *The

modal drift in a story, *) * m, shall be computed as the

and

difference of the deflections, ***xm, at the top and

bottom of the story under consideration.

level of the structure when vibrating in its mth mode.

(d) Design values. The design values for

The modal deflection at each level, ***xm, shall be

the modal base shear, each of the story shear,

determined by the following equations:

moment, and drift quantities, and the deflection at

each level shall be determined by combining their

(3-21)

modal values as obtained above. The combination

shall be carried out by taking the square root of the

and

sum of the squares (SRSS) of each of the modal

values or by the complete quadratic combinations

*g **T*m Fxm

2

= 2

(3-22)

* W *

(CQC) technique.

4*π *

where:

Table 3-2 in TM 5-809-10 assigns seismic zones to

selected locations outside the United States.

The

the deflection amplification factor

seismic zones in that table are consistent with the

determined from Table 7-1,

design values in the 1991 Uniform Building Code

(UBC). Table 3-3 in this document provides spectral

the deflection of Level x in the *m*th

ordinates that have been derived to provide

mode at the center of the mass at Level x determined

comparable base shear values.

by an elastic analysis,

(1)

Algorithms to convert UBC zones to

spectral ordinates. The UBC base shear equations

m/s2),

are as follows:

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