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Guidelines forSeismic Retrofit of Weak-Story
Wood-Frame Buildings ATC 71-1
FEDERAL EMERGENCY MANAGEMENT AGENCY
Michael Mahoney (Contracting Officer’s Technical Representative)
Cathleen Carlisle(Contracting Officer’s Technical Representative)
TASK ORDER CONTRACT MANAGEMENT
Christopher Rojahn(Project Executive Director)
Thomas R. McLane(Project Manager)
Jon A. Heintz(Project Quality Control Monitor)
William T. Holmes (Project Technical Monitor)
PROJECT
MANAGEMENT COMMITTEE
David Mar -
Project Technical DirectorDavid Bonowitz
Kelly CobeenDan Dolan
Andre FiliatraultJohn Price
Mike Korolyk
-
Analysis Consultant
PROJECT REVIEW PANEL
Chris Poland -
ChairBret Lizundia
Andrew MerovichLaurence KornfieldJoan MacQuarrieTony DeMascole
Tom Tobin
Daniel Shapiro (Subject Matter Expert)
Robert Hanson(Subject Matter Expert)
The Team
4,400 Dangerous Multi-unit Buildings: 8% of population
Create Seismic Retrofit Program for
Weak-Story Wood-framed Apartment Buildings
in Western US
Inexpensive to Construct(Work Only In Ground Story)
Inexpensive to Design(Unsophisticated Engineers)
Performs Well(Shelter-In-Place)
Inexpensive to Construct(Cheap)
Inexpensive to Design(Fast)
Performs Well(Good)
The Scope
Typically:
Non-Engineered
No Plans
Archaic Materials
Archaic Construction Practices
1989 Loma Prieta
earthquakeImage by Raymond B. Seed
National Information Service for Earthquake EngineeringUniversity of California, Berkeley.The Problem
San Francisco, CA, Loma Prieta
Earthquake 11/17/1989Beach and Divisadero
in the Marina District. U.S.G.S. by Nakata,
J.K.
FEMA News Photo FEMA News Photo
Northridge, CA: Northridge earthquake FEMA News Photo
Design for a Population of Buildings,
not an Individual Building
Pattern Recognition
Strong but Brittle Upper Structure
Weak and Brittle Lower Structure
Pattern Recognition
Limited Damage to Upper Structure
Damage Concentrated in Lower Structure
Pattern Recognition
0
50
100
150
200
250
300
0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%
Interstory Drift Ratio
Stor
y Sh
ear,
kip
s
Ground story fixed
Ground story with uplift
0
50
100
150
200
250
300
0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%
Interstory Drift Ratio
Stor
y Sh
ear,
kip
s
Second story fixed
Second story with uplift
0
50
100
150
200
250
300
0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%
Interstory Drift Ratio
Stor
y Sh
ear,
kip
s
Third story fixed
Third story with uplift
0
50
100
150
200
250
300
0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%
Interstory Drift Ratio
Stor
y Sh
ear,
kip
s
Fourth story fixed
Fourth story with uplift
Overturning Reductions
Overturning Reduction Factor Qot , for Upper Structure
Level Perpendicular to
Framing Parallel to Framing
Unknown or mixed
Two or more stories above
0.95 0.85 0.85
One story above 0.85 0.8 0.8
Top story 0.75 0.8 0.75
The Relative-Strength Method
0
50
100
150
200
250
300
350
400
0% 1% 2% 3% 4% 5% 6%
Drift Ratio
Elev
atio
n, in
.(E) Structure
Optimal-performance retrofit
Overly strong retrofit
Optimal-cost retrofit
Pattern Recognition
Can a Building’s Capacity be Determined from a Few
Parameters?
Epidemiology
Predict Risk of Heart Disease Based on a Few Indicators
Genetics
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Period, sec.
Spec
tral
Acc
eler
atio
n, g
Mean Median Geomean
Local Seismicity
Body Mass Index
Translational Weakness
Structural Use of Non-conforming Materials
Load-Drift Data for Wall Bracing Material
Standard Drift Ratio, aj
Material ID 0.5 % 0.7 % 1.0 % 1.5 % 2.0 % 2.5 % 3.0 % 4.0 %
Up to late 1940s
Stucco L01 333 320 262
Horizontal 1x wood sheathing
L02 85 96 110 132 145 157 171
Diagonal 1x wood sheathing
L03 429 540 686 913
Plaster on wood lath L04 440 538 414 200
After the 1950s
Stucco L01 333 320 262
Plywood panel siding, “T1-11”
L05 354 420 496 549 565
Gypsum wallboard L06 202 213 204 185 172 151 145 107
Plaster on gypsum lath L07 402 347 304
Wood structural panel 8d@6
L08 521 621 732 812 836 745 686
Wood structural panel 8d@4
L09 513 684 826 943 1,018 1,080 1,112 798
Wood structural panel 8d@3
L10 1,072 1,195 1,318 1,482 1,612 1,664 1,686 1,638
Wood structural panel 8d@2
L11 1,607 1,792 1,976 2,222 2,418 2,496 2,529 2,457
Wood structural panel 10d@6
L12 548 767 946 1,023 1,038 1,055 1,065 843
Wood structural panel 10d@4
L13 707 990 1,275 1,420 1,466 1,496 1,496 1,185
Wood structural panel 10d@3
L14 940 1,316 1,696 1,889 1,949 1,990 1,990 1,576
Wood structural panel 10d@2
L15 1,414 1,979 2,551 2,841 2,931 2,993 2,993 2,370
0
500
1,000
1,500
2,000
2,500
3,000
3,500
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00
Drift Ratio, %
Unit
Forc
e, p
lf
Stucco
Horizontal wood sheathing
Diagonal wood sheathing
Brick veneer
Plaster on wood lath
Plywood panel siding
Gypsum wall board
Plaster on gypsum lath
Wood structural panel 8d@6
Wood structural panel 8d@4
Wood structural panel 8d@3
Wood structural panel 8d@2
Wood structural panel 10d@6
Wood structural panel 10d@4
Wood structural panel 10d@3
Wood structural panel 10d@2
Structural Use of Non-conforming Materials
V1,y
1,y
Ground Story translationalload-deflection curve in they-direction, F1,y
Wall: 1 32 4
1,y 1,y 1,y 1,y
1,yf 2,yf
shea
r for
ce
drift ratio
3,yf4,yf
Drift ratio at which translationalstrength occurs
Translational strengthof the Ground Story
Translational Weakness
Smoking
Torsional Weakness
Ground Floor Plans Upper Floor Plans
eq.
eq.
L
0.2L
L
0.0
Lateral strength proportionalto building length in eachdirection
Edge of floor above
0.000.00
AW
0.600.80
C
0.330.33
0.600.80
0.670.67
0.600.80
1.001.00
0.600.80
T
Torsional Imbalance
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Torsion Coefficient, C T
Cap
acity
Red
uctio
n Fa
ctor
Ductile, Aw = 0.60AB
Ductile, Aw = 0.60R
Ductile, Aw = 0.80AB
Ductile, Aw = 0.80R
Brittle, Aw = 0.60AB
Brittle, Aw = 0.60R
Brittle, Aw = 0.80AB
Brittle, Aw = 0.80R
Dire
ctio
n of
drif
t as
sess
men
t
Torsional Imbalance
Stress
Low Displacement Capacity
-1.5
-1
-0.5
0
0.5
1
1.5
-6 -4 -2 0 2 4 6
Drift Ratio, %
Forc
e
Hysteresis of low displacement capacity material
High Activity Level
High Displacement Capacity
Hysteresis of high-displacement capacity material
-1.5
-1
-0.5
0
0.5
1
1.5
-6 -4 -2 0 2 4 6
Drift Ratio, %
Forc
e
Strength Degradation Ratio
0
200
400
600
800
1,000
1,200
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Drift Ratio, %
Uni
t For
ce, p
lf
Load-Deflection CurvePeak Strength, V
Strength at 3% Drift, V3%
Strength Degradation Ratio,C D = V 3% /V
Ground-story Strength
Upper-story Strength
Upper to Ground Strength Ratio
Toughness
Torsional Imbalance
Characteristic Structural Coefficients
s
s
Ni
N
ijj
xixU
W
VC
2
,, min
sN
jj
xxs
W
VC
1
,1,
TCT
x
xxD V
FC
,1
,1,
%)3(
xU
xsxW C
CC
,
,,
Create a Controlled Experiment
Determine the Influence of Each Characteristic
Analytical Engine:Surrogate Structure Concept
Ductile
Upper-story strength ratios, Au:(4) per mat'l form
Material forms:(2) total
0.1 0.2 0.4
Weak-story ratios, Aw:0.6 to 1.1 by 0.1(6) per upper-story strength
Retrofit strengths:Aw to 1.6(51) per upper-story strength ratio
TOTAL NUMBER OFBUILDINGS:
612
Time-historyseed records:
(22) Bi-directional records = (44) individual
Scaled so that median Sa( T = 0.3 sec ) = 1.0g
0.6
Brittle
0.1 0.2 0.4 0.6
(35) intensities per seedrecord varying from 0.1to 3.5 by 0.1
Given drift criteria, fitlog-normal CDF
Recover peak interstorydrift ratios for eachanalysis
Earthquake Intensity0 1.0 (Sa = 1g) 3.5
0
1.0
0.5
Simplified Building Model
W 50 in.H 100 in.L 111.8q 1.107 rad,
63.4 deg.cos(q) 0.447Astrut 1 in2
Mg 1 kip (total weight of building)
Perform Tool –Post Processing Utility
612 surrogate structures x 44 EQs
x 35 intensities
1 million nonlinear response-history analyses
Analytical Engine:Surrogate-Structure Concept
Analysis Results
Aw=0.6Aw=0.8
Aw=1.1
Aw=0.6
Aw=0.8
Aw=1.1
Aw=0.6
Aw=0.8
Aw=1.1
Aw=0.6
Aw=0.8
Aw=1.1
0.7
1.2
1.7
2.2
2.7
0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
Total Ground Floor Strength/Upper Floor Strength
Spec
tral
Cap
acity
, Sc
Au = 0.4
Au = 0.6
Au = 0.2
Au = 0.1
Analysis Results
Aw = 0.6
Aw = 0.7
Aw = 0.8
Aw = 0.9
Aw = 1
Aw = 1.1
Aw = 1.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Upper-Story Strength Ratio, A U
20th
Per
cent
ile In
tens
ity S
pect
ral C
apac
ity, S
c,20 48.0
,,20, 47.134.0 xUxWc AAS
Curve fit for Incremental Dynamic Analysis
Excel –Visual Basic Applications
Structural Capacity
48.0,,,1 5.0124.2525.066.0 xUsTxWxc AQCAS
60.0,,,0 5.0159.1122.060.0 xUsTxWxc AQCAS
xcDxcDxc SCSCS ,03
,13
, 1
CD
= 1.0
CD
= 0.0
for intermediate values
MSxc SS , if true –
no retrofit required
Onset of Strength Loss drift criteria, OSL
20% Probability of Exceedance, POE
Modifier for POE
= 0.2 Mean spectral capacity, Sm
Retrofit Strength Requirements
xUxUxr VAV ,,max, 22.111.0 upper limit
lower limit
31
31
32
32
, 11
DD
DDMSxre CYCX
CYCXSV
TsU CQAX 5.0148.00 01 48.1 XX 02 35.0 XX
TsU CQAY 5.016.00 01 96.0 YY 02 07.0 YY
Strength of Retrofitted Ground-Story
Spec
tral
Cap
acity
, Sc
Au = 0.4, Aw = 0.6
Maximum Strength, V r max
(Best Performance)Minimum Strength, V r min
(Adequate Performance)
Acceptable Retrofit Range
S c = S MS
Range of Retrofit Strength
xUxUxr VAV ,,max, 22.111.0 3
13
1
32
32
, 11
DD
DDMSxre CYCX
CYCXSV
Strength of Retrofitted Ground-Story
Spec
tral
Cap
acity
, Sc
Acceptable Retrofit Range
Au = 0.1, Aw = 0.6 Maximum Strength, V r max
Minimum Strength,V r min = 0.9V r max
S MS
Estimated Minimum Strength, V re
S c
2/3 S MS
Range of Retrofit Strength
xUxUxr VAV ,,max, 22.111.0
= 0.5
0.55
0.30
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Site-Specific Spectral Acceleration, S S
Prob
abili
ty o
f Exc
eeda
nce
ofSe
lect
ed D
rift C
riter
ia
Site-specific seismic intensity, S S ( = 0.521 in this example).
Fragility curve after retrofit identified by mean spectral capacity S . (S = 0.55 in this example)
Fragility curve before retrofit identified by mean spectral capacity S . (S = 0.30 in this example)
Log-normal standard deviation, , determines relavent set of fragiltiy curves. ( = 0.5 in this example)
0.47
0.87
Probability of exceedance before retrofit (P = 0.87 in this example)
Probability of exceedance after retrofit (P = 0.47 in this example)
Given Spectral Demand, Find Probability of Exceedance
WST IDA –Data Base Graphic Utility
Purpose: The Weak-StoryTool IDA application exists as an interface to query the raw IDA data.
Weak-StoryTool
IDA Application
Predictive Understanding