Page 480 - Design of Reinforced Masonry Structures

7.42 CHAPTER SEVEN

The seismic response coefficient C is determined from Eq. (7.50):
s

C = S DS (7.50)
⎛ R ⎞
s
⎝ I ⎠
where S = the design spectral response acceleration parameter in the short period range
DS
R = structural response modification factor for the seismic force–resisting system
as listed in ASCE 7-05 Table 12.2-1 (discussed in the next section).
I = importance determined based on the occupancy category of the building
= 1.0 for buildings in Occupancy Category I and II
= 1.25 for buildings in Occupancy Category III
= 1.5 for buildings in Occupancy Category IV.
The value of the seismic response coefficient C determined from Eq. (7.50) is subject to
s
an upper limit and a lower limit. Its value need not exceed the value given by Eqs. (7.51)
or (7.52) as applicable:

C = S D1 for T ≤ T (7.51)
s ⎛ R ⎞ L
T
⎝ I ⎠
D1
C = ST L for T > T (7.52)
s ⎛ R ⎞ L
T 2
⎝ I ⎠
The value of C given by Eq. (7.50) may not be less than the value given by Eq. (7.53)
s
(ASCE 7-05 Suppl. 2):
C = 0.044S ≥ 0.01 (7.53)
DS
s
In addition to the lower limit for C given by Eq. (7.53), there is an additional lower limit for
s
C for structures located where the spectral parameter S is equal to or greater than 0.6g:
s
1
05 . S 1
C = (7.54)
⎛ R ⎞
s
⎝ I ⎠
where S = the design spectral response acceleration parameter at a period of 1 s

D1
T = fundamental period of the structure, to be determined as follows
T = long-period transition period (seconds) as given in Figs. 22-15 to 22-20 of

L
ASCE 7-05

S = the mapped maximum considered earthquake spectral parameter at a period
1
of 1 s as given Figs. 22-2, 22-4, 22-6, 22-8, 22-10, 22-12, and 22-14 of
ASCE 7-05
The design spectral parameters S and S are determined from the Eqs. (7.55) and (7.56):
DS
D1
S = /3(S ) (7.55)
2
DS MS
2
S = /3(S ) (7.56)
M1
D1