C8. PERIOD DETERMINATION. The fundamental period of the building, T in the direction under

consideration shall be defined using the structural properties and deformational characteristics of the

resisting elements in a properly substantiated analysis (FEMA 302, 5.3.3). Alternatively, T is permitted

to be taken as the approximate fundamental period, Ta determined in accordance with the following

requirements. The fundamental period, T shall not exceed the product of the coefficient for upper limit

on calculated period, Cu from Table C-4 and the approximate fundamental period, Ta determined as

follows:

3/4

Ta = CThn

(Eq C-24)

Where:

CT = constant = 0.0731 metric, (0.030 English) for cold-formed steel shear panels with

diagonal straps.

hn = the height in meters (ft - English) above the base to the highest level in the structure.

Design Spectral Response

Coefficient

Acceleration at 1 Second, SD1

Cu

SD1 < 0.1g

1.7

0.1g ≤ SD1 < 0.15g

1.7

0.15g ≤ SD1 < 0.2g

1.5

0.2g ≤ SD1 < 0.3g

1.4

0.3g ≤ SD1 < 0.4g

1.3

0.4g ≤ SD1

1.2

C9. VERTICAL DISTRIBUTION OF LATERAL SEISMIC FORCES. The vertical distribution of lateral

seismic forces, Fx (kN or kip), induced at any level shall be determined from the following equations

(FEMA 302, 5.3.4):

Fx = C vx V

(Eq C-25)

and

Wx h x

C vx =

(Eq C-26)

n

∑wh

i

i

i=1

Where:

Cvx = the vertical distribution factor.

V = the total design lateral force or shear at the base of the structure (kN or kip).

wi and wx = the portion of the total gravity load of the structure, W located or assigned to level i

or x.

hi and hx = the height (m or ft) from the base to level i or x.

The horizontal distribution of seismic story shear in any story, Vx (kN or kips) shall be determined from

the following equation (FEMA 302, 5.3.5):

n

Vx = ∑ Fi

(Eq C-27)

i=x

Where:

Fi = the portion of the seismic base shear, V (kN or kips) induced at level i.

C-7

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