ASCE 7-98 SEISMIC LOAD CALCULATION
1. Determine weight of building, W.
2. Determine 0.2 second response spectral acceleration, Ss
from Figure 9.4.1.1 (a) or (c), (e), (f), (g-1), (h-1), (i), and (j)
3. Determine 1 second response spectral acceleration, S1
from Figure 9.4.1.1 (b), or (d), (f), (g-2),
(h-2), (i) and (j)
4. Determine Site class from Table 9.4.1.2
5. Determine site coefficient,
Fa, from Table 9.4.1.2.4a.
6. Determine site coefficient,
Fv, from Table 9.4.1.2.4b
7. Determine adjusted maximum considered earthquake
spectral response acceleration
parameters for short period, SMS and at 1 second
period, SM1.
SMS = Fa
Ss
(Eq. 9.4.1.2.4-1)
SM1 = Fv
S1
(Eq. 9.4.1.2.4-2)
8. Determine deign spectral response acceleration
parameters for short period, SDS
and at 1 second period, SD1.
SDS =(2/3) SMS
(Eq. 9.4.1.2.5-1)
SD1 =(2/3) SM1
(Eq. 9.4.1.2.5-2)
9. Determine Important factor, I, from Table 9.1.4,
10. Determine Seismic design category from Table 9.4.2.1
11. Determine Response modification factor, R. from Table
9.5.2.2 and
check building height limitation
12. Determine seismic response coefficient from
Eq.
9.5.3.2.1-1
Cs=
SDS
/ (R/I)
13. Determine approximate fundamental period from
Eq.
9.5.3.3-1
T = CT hn0.75
where
hn
is the height of building above base.
CT
is building period coefficient, 0.035 for moment resisting frame of steel,
0.03 for moment
resisting frame of
concrete and eccentrically braced steel frame
0.02 for all other building.
14. Determine Maximum seismic response coefficient
Eq.
9.3.2.1-2
Csmax=
SD1
/ [(R/I) T]
15. Determine minimum seismic response coefficient
from Eq. 9.5.3.2.1-3
Csmin=
0.044 SDSI
16. If it is design category E or F, or S1 is equal or
grater than 0.6g, calculate minimum seismic response coefficient from Eq.
9.5.3.2.1-4
Csmin=
0.5 S1 / (R/I)
17. Determine Seismic response coefficient based on result
of steps 12 to 16 and calculate
seismic base shear from
Eq. 9.3.2-1. for strength design or
load and resistance factor design.
V = Cs W
18. For service load design, multiply the seismic base
shear by 0.7
Vs = 0.7 V
Example 1: Bearing wall systems with ordinary
reinforced masonry shear wall
Given:
Code: ASCE 7-98 Equivalent lateral
force procedure
Design information:
Weight of building, W=500 kips
0.2 second response spectral
acceleration, Ss = 0.25
1 second response spectral
acceleration, S1 = 0.1
Soil profile class: E
Bearing wall systems with ordinary
reinforced masonry shear wall
Building category I
Requirement: Determine seismic base shear
Solution;
Site coefficient, Fa
= 2.5
Site coefficient, Fv =
3.5
Design spectral response acceleration parameters
SMS = Fa
Ss = 0.625
(Eq. 9.4.1.2.4-1)
SM1 = Fv
S1= 0.35
(Eq. 9.4.1.2.4-2)
SDS =(2/3) SMS
=0.42
(Eq. 9.4.1.2.5-1)
SD1 =(2/3) SM1
=0.233
(Eq. 9.4.1.2.5-2)
Seismic design category C from Table 9.4.2.1a, category D
based on Table 9.4.2.1b.
Use category D.
From Table 9.5.2.2, Bearing wall system with ordinary
reinforced masonry shear wall is NP (not permitted). Need to change structural system.
Example 2: Building frame systems with ordinary
steel concentric braced frame
Given:
Code: ASCE 7-98 Equivalent lateral
force procedure
Design information:
Weight of building, W = 500 kips
0.2 second response spectral
acceleration, Ss = 0.25
1 second response spectral
acceleration, S1 = 0.1
Building frame systems with
ordinary steel concentric braced frame
Building category I
Building height: 30 ft
Requirement: Determine seismic base shear
Solution:
Site coefficient, Fa
= 2.5
Site coefficient,
Fv = 3.5
Design spectral response acceleration parameters
SMS = Fa
Ss = 0.625
(Eq. 9.4.1.2.4-1)
SM1 = Fv
S1= 0.35
(Eq. 9.4.1.2.4-2)
SDS =(2/3) SMS
=0.42
(Eq. 9.4.1.2.5-1)
SD1 =(2/3) SM1
=0.233
(Eq. 9.4.1.2.5-2)
Seismic design category C from Table 9.4.2.1a, category D
based on Table 9.4.2.1b.
Use category D.
From Table 9.5.2.2, Building frame system with ordinary
steel concentric braced frame is 160 ft
Response modification factor, R = 5
Important factor, I = 1
(Table 9.1.4)
Seismic response coefficient
(Eq. 9.5.3.2.1-1)
Cs=
SDS
/ (R/I) = 0.083
Fundamental period
(Eq. 9.5.3.3.1)
T = CT hn0.75 = 0.0256
Maximum seismic response coefficient
(Eq. 9.5.3.2.1-2)
Csmax=
SD1
/ [(R/I) T] = 0.182
Minimum seismic response coefficient
(Eq. 9.5.3.2.1-3)
Csmin=
0.044 SDSI = 0.018
Seismic base shear
V = Cs W = 42 kips
Seismic base shear in service load,
Vs = 0.7 V = 29 kips
Example 3: Building frame systems with ordinary
reinforced concrete shear wall
Given:
Code: ASCE 7-98 Equivalent lateral
force procedure
Design information:
Weight of building, W = 1000 kips
0.2 second response spectral
acceleration, Ss = 0.5
1 second response spectral
acceleration, S1 = 0.15
Soil profile class: C
Building frame systems with
ordinary reinforced concrete shear wall
Building category II
Building height: 40 ft
Requirement: Determine seismic base shear
Solution:
Site coefficient, Fa
= 1.2
Site coefficient, Fv
= 1.65
Design spectral response acceleration parameters
SMS = Fa
Ss = 0.6
(Eq. 9.4.1.2.4-1)
SM1 = Fv
S1= 0.25
(Eq. 9.4.1.2.4-2)
SDS =(2/3) SMS
=0.4
(Eq. 9.4.1.2.5-1)
SD1 =(2/3) SM1
=0.17
(Eq. 9.4.1.2.5-2)
Seismic design category C from Table 9.4.2.1a, category C
based on Table 9.4.2.1b.
Use category C.
From Table 9.5.2.2, Building frame system with ordinary
steel concentric braced frame is 160 ft
Response modification factor, R = 5
Important factor, I = 1 (Table
9.1.4)
Seismic response coefficient
(Eq. 9.5.3.2.1-1)
Cs=
SDS
/ (R/I) = 0.1
Fundamental period
(Eq. 9.5.3.3.1)
T = CT hn0.75 = 0.318
Maximum seismic response coefficient
(Eq. 9.5.3.2.1-2)
Csmax=
SD1
/ [(R/I) T] = 0.104
Minimum seismic response coefficient
(Eq. 9.5.3.2.1-3)
Csmin=
0.044 SDSI = 0.018
Seismic base shear
V = Cs W = 100 kips
Seismic base shear in service load,
Vs = 0.7 V = 70 kips
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