Page 526 - Design of Reinforced Masonry Structures

7.88 CHAPTER SEVEN

(c) Eq. (7.50) [ASCE 7-05 Eq. (12.8-2)] is used to calculate the seismic response
coefficient, C .
s
(d) The diaphragms are rigid; or for diaphragms that are flexible, the distance between
the vertical elements of the seismic force–resisting system does not exceed 40 ft.
It is important to understand the significance of SDC of a building. ASCE 7-05 Table 12.2-1
(see Table 7.5 for shear wall SFRS) specifies the following compliance requirements for
different SFRS to be used in buildings:
1. No limit in height (NL) for building in specified SDCs.
2. Specific height limitations for buildings in specific SDCs.
3. Restrictions (not permitted) on using certain SFRS in buildings having different SDC (NP).
Example 7.15 presents the procedure for determination of seismic design category of
buildings. It illustrates and highlights the point that buildings of different occupancy cat-
egories but having the same site class and the same short-period and 1-s spectral accelera-
tion parameters (S s and S , respectively) can have different seismic design category.
1
It is noted that occupancy categories are defined in ASCE 7-05 Section 1.5 (Table 1-1)
and in 2009 IBC Table 1604.5. There are, however, some differences between the two
tables. In the following example, provisions of 2009 IBC Table 1604.5 have been used
(legal building code).

Example 7.15 Determination of seismic design category of buildings.
Determine the Seismic Design Category for
(a) A daycare facility with capacity greater than 250
(b) A police station
The following information applies to both structures: Site Class C, S = 1.76g, S = 0.81g.
1
s
Solution:
1. Determine the occupancy category for each building based on 2009 IBC
Table 1604.5.
(a) Daycare facility with capacity greater than 250: Occupancy Category III
(b) Police station: Occupancy Category IV
2. Determine S and S for the given buildings.
D1
DS
S = 1.76g
s
For Site Class C and S ≥ 1.25g, F = 1.0
a
s
S MS = F S = (1.0)(1.76) = 1.76
a s
2
S = /3 S = /3 (1.76) = 1.17
2
DS
MS
S = 0.81g
1
For Site Class C and S ≥ 0.5g, F = 1.3
v
1
S M1 = F S = (1.3)(0.81) = 1.05
v
1
2
S = /3 S = /3 (1.05) = 0.70
2
M1
D1