The building seismic base shear, V (kip) in a given
direction is calculated as follows:
where
| W | = |
effective seismic weight of the building (kip) |
| Cs | = | seismic response
coefficient, which is defined as follows:
| (12.8-2) |
|
where
| SDS
| = | the design spectral response acceleration
parameter in the short period range. This is determined from Section
11.4.5 |
| R
| = | the response modification factor defined in
Table 12.2-1 |
| Ie
| = | importance factor defined according to Section
11.5.1 |
The seismic response coefficient, Cs is subjected to the following conditions:
| (12.8-3 & 12.8-4) |
And Cs shall not be
less than:
| (12.8-5) |
And for structures with S1 ≥
0.6g, Cs cannot be less than following:
where
| SD1 | = |
the design spectral response acceleration parameter at a period of 1.0 s, as
determined from Section 11.4.5 or 11.4.6.
|
| T | = | the
fundamental period of the structure determined in Section 12.8.2 |
| TL | = |
long-period transition period(s) determined in Section 11.4.6 |
| S1 | = |
the mapped maximum considered earthquake spectral response acceleration
parameter determined in accordance with Section 11.4.2 or 11.4.4
|
In calculation of
Cs, the terms
SDS
and
SD1 are needed. These terms are related to the
short-period site coefficient,
Fa, and the
long-period site coefficient,
Fv, which are
available in Table 11.4-1 and 11.4-2, respectively. The following special
conditions are enforced in the program in using these tables:
- Table 11.4-1: If site class
is E and Ss ≥ 0.1, Fa is taken as
equal to that of site class C (See Section 11.4.8, Exception 1)
- Table 11.4-2: If site class
is E and Ss ≥ 0.1, Equivalent Lateral Force (ELF) procedure is
not allowed (site-specific response analysis needs to be conducted).
