Compute Base Shear(V) using ASCE 7-05
●Obtain ground motion parameters using SAMPH
for NCR map. The response acceleration
parameters(interpolated). (Ss & S1)
●Soil Classification
○When the soil properties are not known
in detail to determine the site class, Site
Class-D shall be used unless the
authority's jurisdiction determines.
●Determine site coefficients, Fa and Fv, based on
soil classification.
Fa
SS
≤ 0.25
= 0.5
= 0.75
= 1.0
≥ 1.25
A
0.8
0.8
0.8
0.8
0.8
B
1.0
1.0
1.0
1.0
1.0
C
1.2
1.2
1.1
1.0
1.0
D
1.6
1.4
1.2
1.1
1.0
E
2.5
1.7
1.2
0.9
0.9
F
See Section 11.4.7
Fv
S1
≤ 0.1
= 0.2
= 0.3
= 0.4
≥ 0.5
A
0.8
0.8
0.8
0.8
0.8
B
1.0
1.0
1.0
1.0
1.0
C
1.7
1.6
1.5
1.4
1.3
D
2.4
2.0
1.8
1.6
1.5
E
3.5
3.2
2.8
2.4
2.4
F
See Section 11.4.7
●Site coefficient
○Sms = (Fa)(Ss) >short period
○Sm1 = (Fv)(S1) > period of 1s
●Design response acceleration parameters (Sds &
Sd1)
○SDS = Sms
2
3
○SD1 = Sm1
2
3
●Approximate structure fundamental period
○Ta = (Ct)(ℎ)𝑥
Structure Type
Ct
x
Steel moment resisting frames
0.0724
0.8
Concrete moment resisting frames
0.0466
0.9
Steel eccentrically braced frames &
Steel buckling-restrained frames
0.0731
0.75
All other structural system
0.0488
0.75
●Structures NOT EXCEEDING 12 STORIES in
height
○Ta = 0.1(N) N is # of storey
●Tmax per Section
○T = (Cu)(Ta)
Design Spectral Response
Acceleration Parameter at 1s (SD1)
Coefficient (Cu)
≥ 0.4
1.4
0.3
1.4
0.3
1.5
0.15
1.6
≤ 0.1
1.7
●Seismic Design Category, SDC
○S1 ≤ 0.74 … SDC F
●Seismic Importance Factor (I)
Occupancy Category
I
I or II
1.0
III
1.25
IV
1.50
●Structural System and System Parameters: R,
Cd, Ω𝑜
○R = response modification coefficient
○Cd = deflection amplification
○= system overstrength factorΩ𝑜
●
●Redundancy Factory ( )ρ
○SDC F = 1.0
ρ
○SDC D,E,F = 1.3
ρ
●Base Shear [V = (Cs)(W)]
○Cs = 𝑆𝐷𝑠
(𝑅𝐼)
○
○
○
●Distribute Vertical Lateral Loads
○Fx = (Cvx)(V)
○Cvx = 𝑊𝑥(ℎ𝑥)𝑘
Σ 𝑊𝑖(ℎ𝑖)𝑘
