Page 380 - Design of Reinforced Masonry Structures

WALLS UNDER GRAVITY AND TRANSVERSE LOADS 6.31

For all design purposes, each structure can be categorized into one of the four occu-
pancy categories: Categories I, II, III, and IV, which are based on the use of a building or
structure. The seismic importance factor I depends on (1) the Seismic Design Category
of a structure, which are designated as type A through F (ASCE 7-05 Section 11.6), and
(2) the values of S (defined above) and S , design earthquake, 5 percent damped, spectral
DS
1
response period acceleration parameter at 1 s. The values of spectral response acceleration
parameters at short period (S ) and at 1-s period (S ) for a given site can be found from
1
S
the internet. One such source is the California Geological Survey Web site (http://redirect.
conservation.ca.gov/CGS/rghm/pshamap/pshamap.asp). Given the longitude and latitude
of the site, the Web site provides values of these parameters. The site longitude and latitude
can be obtained from an internet site such as http://www.gpsies.com/coordinate.do by sim-
ply inputting the address.
Table 6.5 summarizes, for various occupancy categories, the relationship between the
values of short and 1-s spectral accelerations parameters, S DS and S , respectively, and the
1
SDC of a structure. The SDC of a structure is determined separately based on the its S and
DS
S values, which might be different; the structure is assigned the more severe of the SDCs
1
so determined, irrespective of its fundamental period.
6.5.3.2 Earthquake Loads on Nonstructural Walls and Parapets For the purpose of
calculating seismic force acting normal to a parapet, ASCE 7-05 considers it to be a non-
structural component. Poor performance and lack of redundancy requires parapets to be
designed for higher design loads than those for walls.
Provisions for determination of forces on nonstructural walls and parapets are covered
in ASCE 7-05 Section 13-5, which also covers seismic forces acting normal to a wide range
of architectural, mechanical, and electrical equipment. Architectural components include a
variety of components such as interior and exterior nonstructural walls, partitions, parapets,
chimneys, veneer, ceilings, cabinets, signs and billboards, appendages, and ornamenta-
tions, etc.
For design purposes, nonstructural components are assigned the same SDC as the struc-
tures they occupy or are attached to. In higher seismic design categories, almost everything

TABLE 6.5 Seismic Design Category Based on Short Period and
1-s Period Spectral Response Acceleration Parameter
(Adapted from Ref. [6.19]).
Occupancy category

Value of S DS I or II III IV
S DS < 0.167 A A A
0.167 ≤ S DS < 0.33 B B C
0.33 ≤ S DS < 0.50 C C D
D D D
0.50 ≤ S DS
I or II III IV
Value of S D1
S < 0.067 A A A
D1
0.067 ≤ S D1 < 0.133 B B C
0.133 ≤ S D1 < 0.20 C C D
D D D
0.20 ≤ S D1