IBC SEISMIC LOAD CALCULATION
Contents:
1.
Determine weight of building, W.
2.
Determine 0.2 second response spectral acceleration, Ss from Figure 1615 (1)
3.
Determine 1 second response spectral acceleration, S1
from Figure 1615 (2)
4.
Determine Site class from Table 1615.1.1
5.
Determine site coefficient, Fa, from Table 1615.1.2 (1)
6.
Determine site coefficient, Fv, from Table 1615.2 (2)
7.
Determine adjusted maximum considered earthquake spectral response acceleration
parameters for short period, SMS and at 1 second
period, SM1.
SMS = Fa
Ss
(Eq. 16-16)
SM1 = Fv
S1
(Eq. 16-17)
8.
Determine deign spectral response acceleration parameters for short period, SDS
,and
at 1 second period, SD1.
SDS =(2/3) SMS
(Eq. 16-18)
SD1 =(2/3) SM1
(Eq. 16-19)
9.
Determine Important factor, IE, from Table 1604.5
10.
Determine seismic design category from Table 1616.3 (1) and (2)
11.
Response modification factor, R. from Table 16.17.6
12.
Determine seismic response coefficient from Eq. 16-35
Cs= SDS
/ (R/IE)
13.
Determine approximate fundamental period from Eq. 16-39
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. 16-36
Csmax= SD1
/ [(R/IE) T]
15.
Determine minimum seismic response coefficient
from Eq. 16-37
Csmin= 0.044 SDSIE
16.
Determine Seismic design category from Table 1616.3.2, if it is design category E
or F, or S1 is equal or grater than 0.6g, calculate minimum seismic response
coefficient from Eq. 16.38
Csmin= 0.5 S1
/ (R/IE)
17.
Determine Seismic response coefficient based on result of steps 10 to 14 and
calculate seismic base shear from Eq. 16-34. 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: Building frame system with concentrically braced frame
Given:
Code: IBC 2000 Equivalent lateral force procedure
Design information:
Weight of building, W= 100 kips
0.2 second response spectral acceleration, Ss=0.5
1 second response spectral acceleration, S1
= 0.2
Soil profile class: D
Building category I
Building height: hn = 50 ft
Building frame system with concentrically braced frame
Requirement:
Determine seismic base shear
Solution:
Site coefficient, Fa = 1.4
Site coefficient, Fv = 2.4
Design
spectral response acceleration parameters
SMS = Fa
Ss = 0.7
(Eq. 16-16)
SM1 = Fv
S1= 0.48
(Eq. 16-17)
SDS =(2/3) SMS
=0.467
(Eq. 16-18)
SD1 =(2/3) SM1
=0.32
(Eq. 16-19)
Seismic
design category C from Table 1616.3 (1) and category D from 1616.3(2), Use
category D
Important factor, IE=1
(Table 1604.5)
Building
frame system with ordinary steel concentric braced frame
Response
modification factor, R = 5
Building
height limited to 160 ft > 50 ft O.K.
Seismic
response coefficient (Eq. 16-35)
Cs= SDS
/ (R/IE) = 0.093
Fundamental
period, T = CT hn0.75 = 0.376
Maximum
seismic response coefficient (Eq. 16-36)
Csmax= SD1
/ [(R/IE) T] = 0.17
Minimum
seismic response coefficient (Eq. 16-37)
Csmin= 0.044 SDSIE
= 0.021
Seismic
base shear
V = Cs W = 93 kips
Seismic
base shear in service load
Vs = 0.7 V = 65 kips
Example
2: Moment resisting frame system with Ordinary moment resisting frame of
steel
Given:
Code: IBC 2000 Equivalent lateral force procedure
Weight of building, W = 1000 kips
0.2 second response spectral acceleration, Ss
= 0.75
1 second response spectral acceleration, S1=0.3
Soil profile class: E
Building height: hn=30 ft
Moment
resisting frame system with Ordinary moment resisting frame of steel
Requirement:
Determine seismic base shear
Solution:
Site coefficient, Fa = 1.2
Site coefficient, Fv = 2.8
Design
spectral response acceleration parameters
SMS = Fa
Ss = 0.9
(Eq. 16-16)
SM1 = Fv
S1= 0.84
(Eq. 16-17)
SDS =(2/3) SMS
=0.6
(Eq. 16-18)
SD1 =(2/3) SM1
=0.56
(Eq. 16-19)
Seismic
design category D from Table 1616.3(1) and (2)
Important factor, IE = 1.
(Table 1604.5)
Moment
resisting frame system with Ordinary moment resisting frame of steel
Response
modification factor, R = 4
(Table
16.17.6 limits maximum height to 35 ft)
Seismic
response coefficient (Eq. 16-35)
Cs= SDS
/ (R/IE) = 0.15
Fundamental
period, T = CT hn0.75 = 0.449
Maximum
seismic response coefficient (Eq. 16.-36)
Csmax= SD1
/ [(R/IE) T] = 0.312
Minimum
seismic response coefficient (Eq. 16-37)
Csmin= 0.044 SDSIE
= 0.026
Seismic
base shear
V = Cs W = 150 kips
Seismic
base shear in service load
Vs = 0.7 V = 105 kips
Example
3: Moment resisting frame system with Ordinary moment resisting frame of
concrete
Given:
Code: IBC 2000 Equivalent lateral force procedure
Weight of building, W = 1000 kips
0.2 second response spectral acceleration, Ss = 0.25
1 second response spectral acceleration, S1
= 0.1
Soil profile class: B
Building category I
Building height: hn = 40 ft
Moment resisting frame system with Ordinary moment resisting frame of concrete
Requirement:
Determine seismic base shear
Solution:
Site coefficient, Fa = 1.0
Site coefficient, Fv = 1.0
Design
spectral response acceleration parameters
SMS = Fa
Ss = 0.25
(Eq. 16-16)
SM1 = Fv
S1= 0.1
(Eq. 16-17)
SDS =(2/3) SMS
=0.167
(Eq. 16-18)
SD1 =(2/3) SM1
=0.067
(Eq. 16-19)
Seismic
design category B from Table 1616.3(1) and (2)
Important factor, IE = 1.
(Table 1604.5)
Moment
resisting frame system with ordinary moment resisting frame of concrete
Response
modification factor, R = 3
(Table
16.17.6 limits maximum height to 35 ft)
Seismic
response coefficient (Eq. 16-35)
Cs= SDS
/ (R/IE) = 0.056
Fundamental
period, T = CT hn0.75 = 0.557
Maximum
seismic response coefficient (Eq. 16.-36)
Csmax= SD1
/ [(R/IE) T] = 0.04
Minimum
seismic response coefficient (Eq. 16-37)
Csmin= 0.044 SDSIE
= 0.007
Seismic
base shear
V = Csmax W = 40 kips
Seismic
base shear in service load
Vs = 0.7 V = 28 kips
Example
4: Building frame system with special reinforced concrete shear wall
Given:
Code: IBC 2000 Equivalent lateral force procedure
Weight of building, W = 1000 kips
0.2 second response spectral acceleration, Ss
= 1.0
1 second response spectral acceleration, S1 = 0.3
Soil profile class: D
Building height: hn = 60 ft
Building category: II
Building frame system with special reinforced concrete shear wall
Requirement:
Determine seismic base shear
Solution:
Site coefficient, Fa = 1.1
Site coefficient, Fv = 1.8
Design
spectral response acceleration parameters
SMS = Fa
Ss = 1.1
(Eq. 16-16)
SM1 = Fv
S1= 0.54
(Eq. 16-17)
SDS =(2/3) SMS
=0.73
(Eq. 16-18)
SD1 =(2/3) SM1
=0.36
(Eq. 16-19)
Seismic
design category D from Table 1616.3(1) and (2)
Important factor, IE = 1.25 (Table
1604.5)
Building
frame system with Special reinforced concrete shear wall
Response
modification factor, R = 6
(Table
16.17.6 limits maximum height to 35 ft)
Seismic
response coefficient (Eq. 16-35)
Cs= SDS
/ (R/IE) = 0.153
Fundamental
period, T = CT hn0.75 = 0.755
Maximum
seismic response coefficient (Eq. 16.-36)
Csmax= SD1
/ [(R/IE) T] = 0.099
Minimum
seismic response coefficient (Eq. 16-37)
Csmin= 0.044 SDSIE
= 0.04
Seismic
base shear
V = Csmax W = 99 kips
Seismic
base shear in service load
Vs = 0.7 V = 69.3 kips
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