Sample Problem
ASCE 7-05 Seismic Provisions
A Beginner’s Guide to ASCE 7-05
Dr. T. Bart Quimby, P.E.
Quimby & Associates
www.bgstructuralengineering.com
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
1
The Problem Definition
The wood framed
office building shown
here is to be
constructed in a
“suburban” area in
Juneau, Alaska out
near the airport. The
site conditions consist
of deep alluvial
deposits with a high
water table.
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
2
Other Given Data
 Roof DL = 15 psf
 Typical Floor DL = 12 psf
 Partition Load = 15 psf
 Snow Load = 30 psf
 Exterior Wall DL = 10 psf
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
3
Determine the Seismic Design
Category
 The building is in Occupancy Category II
 Get SS and S1 from the maps or online
Using USGS software with a 99801 zip code:
SS = 61.2%; S1 = 28.9%

 The building Site Class is D
 From Tables
Fa = 1.311; Fv = 1.822
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
4
Seismic Design Category
continued….
 Determine SMS and SM1
SMS = FaSS = 1.311(0.612) = 0.802
SM1 = FvS1 = 1.822(0.289) = .526
 Determine SDS and SD1
SDS = (2/3) SMS = 2(0.802)/3 = 0.535
SD1 = (2/3) SM1 = 2(0.526)/3 = 0.351
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
5
Seismic Design Category
continued….
 SD1 = 0.351
 SDS = 0.535
 Use Seismic
Design
Category D
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
6
Categorize the Plan Irregularities
 Categorize the Plan Irregularities

The building has re-entrant corners (type 2) since
the projection is more than 15% of dimension
0.15(40’) = 6’ < 10’ and 0.15(60’) = 9’ < 30’
 No Vertical Irregularities
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
7
Determine the Analysis Method
 Use ELF Method
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
8
Determine R, I, and Ta
 From Table 5.2.2, R = 6.5 for bearing wall systems
consisting of light framed walls with shear panels.
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
9
Determine I and Ta
 From Table 11.5-1, I = 1.0
 Determine the approximate fundamental
period for the building (Section 12.8.2.1)
Ta = 0.020(40’)3/4 = .318 sec.
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
10
Determine Cs
From section 12.8.1.1:
Cs = SDS/(R/I) = .535/(6.5/1) = 0.0823
lower limit = 0.01
TL = 12 (Figure 22-17)
Upper limit = SD1/(T(R/I)) = .351/(.318*6.5/1)
Upper limit = 0.169
USE CS = 0.0823
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
11
Determine Building Weight
Roof:
Unit
psf
Roof
Ext. Walls
Snow/4
Area
ft^2
2040
1120
2040
Unit
psf
Roof
Ext. Walls
Partitions
Area
ft^2
2040
2240
2040
Typ. Floor
Total Building
Level
Roof
4th flr
3rd flr
2nd flr
15
10
12.5
12
10
15
Weight
lb
30600
11200
25500
67300
Weight
lb
24480
22400
30600
77480
Weight
k
67.3
77.48
77.48
77.48
299.74
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
12
Compute the Base Shear, V
V = CsW = 0.0823(299.74 k) = 24.67 k
 This is the total lateral force on the structure.
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
13
Compute the Vertical Distribution
Base Shear, V =
24.67 kips
k= 1
wx
hx
wxhxk
(k)
(ft)
(ft-k)
Roof
67.3
40
2692
0.367
9.05
4th floor
77.48
30
2324.4
0.317
7.81
3rd floor
77.48
20
1549.6
0.211
5.21
2nd floor
77.48
10
774.8
0.106
2.60
Sum:
299.74
7340.8
1.000
24.67
Level
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
Cvx
Fx
(k)
14
Typical Level Horizontal Distribution
 Load is
distributed
according to
mass
distribution.
 Since the loading
is symmetrical,
each of the two
supporting shear
walls receives
half the story
shear.
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
15
Determine the Design Shear Force for the
Shearwall on Grid A and the 2nd Floor
 Story shear
from structural
analysis is
11.03 kips
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
16
Compute E
 There is no Dead Load story shear so
 E = DQE = 1.0 (11.03 k ) = 11.03 k


D = 1.0 since the stories resisting more than
35% of the base shear conform to the
requirements of Table 12.3-3 (other).
QE = 11.03 k
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
17
ASCE 7 Load Combinations
See ASCE 7-05 2.3 & 2.4
LRFD
5: 1.2(0) + 1.0(11.03) + (0) + 0.2(0) = 11.03 k
7: 0.9(0) + 1.0(11.03) = 11.03 k
ASD
5: (0) + 0.7(11.03) = 7.72 k
6: (0) + 0.75(0.7(11.03)) + 0.75(0) + 0.75(0) = 5.79 k
8: 0.6(0) + 0.7(11.03) = 7.72 k
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
18
ASCE 7-05 Load Combinations
 Combinations 3 & 4 have E in them.
 For the wall shear:


D=L=0
E = 11.23 k
 Design Wall Shear = 11.23 k
Seismic Provisions Example – A Beginner’s
Guide to ASCE 7-05
19