post-earthquake demolition decisions in christchurch, new ......ken elwood quakecore research...
TRANSCRIPT
![Page 1: Post-Earthquake Demolition Decisions in Christchurch, New ......Ken Elwood QuakeCoRE Research Director Dept. of Civil and Environmental Engineering University of Auckland . Photo courtesy](https://reader035.vdocuments.us/reader035/viewer/2022071214/6042f0e896c6176b0c60a832/html5/thumbnails/1.jpg)
Post-Earthquake Demolition Decisions in Christchurch, New Zealand
and the Role Of Insurance
Ken Elwood
QuakeCoRE Research Director Dept. of Civil and Environmental Engineering
University of Auckland
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Photo courtesy of W. Kam
> 60% of Multi-story Reinforced Concrete Buildings Demolished
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Christchurch Damage Statistics
Significant number of RC buildings with relatively low damage were demolished.
223 RC Buildings over 2 stories (Kim et al. 2015)
9
17
24
11
5 0
8 8
2 0 0 0
1 3
0 0 0 0
18
28 26
11
5 0
0
5
10
15
20
25
30
0-1% 2-10% 11-30% 31-60% 61-99% 100%
# o
f B
uild
ings
Moment Frame Buildings
10
18
11
5 5 0
21
13
5
0 1 0 1
8
0 1 0 0
32
39
16
6 6 0
0
5
10
15
20
25
30
35
40
45
0-1% 2-10% 11-30% 31-60% 61-99% 100%
Shear Wall Buildings Demolish
Repair
Unknown
Total
Damage Ratio ≈ repair cost ⁄ replacement cost Damage Ratio ≈ repair cost ⁄ replacement cost
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First Cordon February - March 2011
August - October 2011
June 2013
CBD Outline
Cordon
4
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Cordon
2
35
3
38
5
55
6
39
0 8 0 12 0 7 2 1 0 10
8(4%)
81(36%)
5(2%)
47(21%)
5(2%)
77(35%)
0
10
20
30
40
50
60
70
80
90
100
0 Up to 6 7-12 13-18 19-24 25-28
# o
f B
uild
ings
Number of Months in Cordon
Duration in Cordon
Demolish
Repair
Unknown
Total
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Demolition Decision Framework (Marquis et al 2015)
Traditional engineering focus
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Case Study Buildings
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Case Study Buildings Design ductility (R or q)
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
Dam
age
Rat
io
De
sign
Du
ctili
ty
Design Ductility Damage ratio
Demolish Repair
0-1%
2-10%
11-30%
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Case Study Buildings %NBS (~ %Code)
Dam
age
Rat
io
Pre
-EQ
%N
BS
Pre-EQ %NBS Damage ratio
Demolish Repair
0-1%
2-10%
11-30%
20-33%
34-66%
67-80%
81-100%
Earthquake -prone
building
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Case Study Buildings Insurance
• High insurance penetration • Recovery in hands of
insurance/owners
• Reinstatement policies • “to condition as …when new”
• Typically underinsured for reinstatement. • “Uneconomic to repair”
• Cash settlements • Preferred by owners and insurers
• Faster and more flexible
0%
20%
40%
60%
80%
100%
Canterbury,NZ (2011)
Chile(2010)
Tohoku,Japan(2011)
L'Aquila,Italy (2009)
Turkey(2011)
Eco
no
mic
loss
es
cove
red
by
insu
ran
ce
(Data source: SwissRe 2012)
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Case Study Buildings Insurance
• High insurance penetration • Recovery in hands of
insurance/owners
• Reinstatement policies • “to condition as …when new”
• Typically underinsured for reinstatement. • “Uneconomic to repair”
• Cash settlements • Preferred by owners and insurers
• Faster and more flexible
→ A concrete wall repaired with epoxy,
while structurally sound, is it ‘new’ ?
→ How to address reinforcement
experiencing strain hardening?
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Case Study Buildings Insurance
• High insurance penetration • Recovery in hands of
insurance/owners
• Reinstatement policies • “to condition as …when new”
• Typically underinsured for reinstatement. • “Uneconomic to repair”
• Cash settlements • Preferred by owners and insurers
• Faster and more flexible
$-
$20
$40
$60
$80
$100
$120
$140
$160
$180
Mill
ion
NZ$
Sum insured
Estimated Replacement Value
Building ID
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Case Study Buildings Insurance
• High insurance penetration • Recovery in hands of
insurance/owners
• Reinstatement policies • “to condition as …when new”
• Typically underinsured for reinstatement. • “Uneconomic to repair”
• Cash settlements • Preferred by owners and insurers
• Faster and more flexible
0
10
20
30
40
50
60
70
80
90
100
South Island North Island OverseasP
erc
en
tage
(%
) Number ofbuildings
Net lettablefloor area
Owner profile for Christchurch before Feb 2011
(Data source: Ernst and Young 2012)
Owner’s home
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Case Study Buildings Insurance • High insurance penetration
• Recovery in hands of insurance/owners
• Reinstatement policies • “to condition as …when new”
• Typically underinsured for reinstatement. • “Uneconomic to repair”
• Cash settlements • Preferred by owners and insurers
• Faster and more flexible
Building demolition more convenient than financially risky building repair option.
Paradoxical role of insurance in recovery… - Individual building owner vs. community perspective
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Impact of Uncertainty in Structural Assessments
Damage Ratio 0 10% 30% 20% 40% 60% 50% 70% 80% 100% 90%
Engi
nee
r h
ired
by
insu
ran
ce c
om
pan
y
Engi
nee
r h
ired
by
bu
ildin
g o
wn
er
Uncertainty in Post-EQ Assessments w/o guidance
Uncertainty in Post-EQ Assessments with guidance
≈ repair cost ⁄ replacement cost
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Draft Post-EQ Assessment Methodology
• What do cracks tell us about peak drift demands in damaging earthquake?
• Do prior cycles impact drift capacity?
• Estimate of reduced stiffness due to prior cycles?
Peak drift demand
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Beam tests
~2.6m
Complies with ACI 318 SMRF and NZS 3101:2006 ‘ductile’ beam
Type CYC Type LD-1 Type LD-2
Type CYC-NOEQ Type P-1 Type P-2
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0
0.5
1
1.5
2
2.5
3
3.5
4
0 2 4 6 8 10A
bso
lute
val
ue
of
pea
k d
rift
bef
ore
mea
sure
men
t (%
)
Number of cracks wider than 0.2mm
Crack width vs peak drift demand
Existing post-earthquake assessment guidelines use the maximum residual crack width as a key damage indicator
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10Ab
solu
te v
alu
e o
f p
eak d
rift
bef
ore
mea
sure
men
t (%
)
Maximum residual crack width (mm)
Extent of cracking more useful than width of cracks
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Effect of moderate-level loading cycles
No change in deformation capacity!
CYC
CYC-NOEQ
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Stiffness reduction
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5 6
Mea
sure
d s
ecan
t st
iffn
ess
to 8
0%
of
max
imu
m b
ase
mo
men
t no
rmal
ized
to i
nit
ial
mea
sure
d s
ecan
t st
iffn
ess
Absolute maximum displacement ductility prior to reloading
Post
-EQ
sti
ffn
ess
/ In
itia
l sti
ffn
ess
Displacement Ductility prior to reloading
𝐾𝑟𝐾𝑦
=1
𝜇
Circular columns - after previous shake table tests
Beam specimens - after initial earthquake loadings
Inverse of displacement ductility
Conservative estimate for low ductility demands
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Repair Triggers
Repair Limit
Co
mp
on
ent
Beh
avio
ur
Damaged Building
Repairable Design Details Systems Drift Limits/R
Residual Capacity
Repaired Capacity
Syst
em
Perf
orm
ance
Repaired Building
Repairability of Current Designs
Test Data
Tools
MSA Analysis
Component Models
System Validation
Implementation
P58 Analysis
FEMA 306/352 updates?
ATC 145 – Guidelines for Repair and Designing for Repairability
Repair not needed Repair needed Repair technique
ineffective Damage
Index Repair Limit
Repair trigger
Post-EQ Performance Objectives
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Thank you!
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[s/db = 6]
For large strain cycles, strain ageing can reduce remaining
cycles to failure by ~50%.
Loporcaro and Pampanin (2017)
2ea
Reduction in Low-Cycle Fatigue Capacity
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Stiffness – repaired beams
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6
Sec
ant
stif
fnes
s to
yie
ld r
atio
(rep
aire
d s
tiff
nes
s /
und
amag
ed s
tiff
nes
s)
Approximate maximum displacement ductility prior to repair
French et al. (1990) Lee et al. (1976) Celebi and Penzien (1973)
Lehman et al. (2001) Cuevas and Pampanin (2017) Marder et al. (2018)
Recommended design stiffness
ratio for epoxy-repaired plastic
hinges in beams
Only specimen with
axial load
(~0.07Agf ’c)
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Does decreased stiffness matter?
But does this hold for: • Irregular (torsional)
structures? • Performance in wind?
Kajiwara, Kang, Kabeyasawa et al., 2019
Stiffness change does not matter. [Consistent with observations by: Cecen (1979) and Laughery (2016)]
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Christchurch Earthquake - Lessons and Challenges for RC Buildings
• Impacts on Code • Amendment • Ongoing
• Beyond the Code • Demolitions • Why? • What now?
• Future directions and opportunities
185 fatalities ~$NZ 40B loss
(~ 20% NZ GDP) CBD closure
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Building Characteristics Statistics
41
24
53
15 5 11 11 20 15 8 11 2 4 2 1
63(28%)
37(17%)
77(35%)
32(14%) 14(6%)
0
50
100
150
200
Pre 1965 1965-75 1976-91 1992-03 Post 2003
# o
f B
uild
ings
Construction Year
Demolish
Repair
Unknown
Total
17
121
12
53
6 14
35 (16%)
188 (84%)
Heritage Nonheritage
Heritage Status
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Logistic Regression Analysis
Variable Type Variable Name Notation
Dependent Decision Outcome y
Independent
Footprint Area x1
Construction Year x2
Heritage Status x3
SFRS x4, x5
Occupancy Type x6
Number of Floors x7
Duration in Cordon x8
Placard x9, x10
Damage Ratio x11
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JBDPA Guideline (Nakano et al., 2004)
Previous work - JBDPA
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Previous work – FEMA 306
FEMA 306 (ATC, 1999)
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GROUND MOTION & STRUCTURAL DRAWINGS OBSERVABLE DAMAGE
BEST ESTIMATE OF PEAK DEMANDS
CALCULATE RESIDUAL STIFFNESS, STRENGTH, & DEFORMABILITY FOR DAMAGED COMPONENTS
CREATE BUILDING MODEL AND PERFORM ANALYTICAL
ESTIMATION OF PEAK BUILDING RESPONSE
GROUND MOTION & STRUCTURAL DRAWINGS OBSERVABLE DAMAGE
BEST ESTIMATE OF PEAK DEMANDS
RE-CONDUCT ANALYSIS USING UPDATED MODEL
CALCULATE RESIDUAL STIFFNESS, STRENGTH, & DEFORMABILITY FOR DAMAGED/REPAIRED COMPONENTS
UPDATE BUILDING MODEL TO ACCOUNT FOR DAMAGED/REPAIRED COMPONENTS
CRACK DISTRIBUTIONS CRACK WIDTHS RESIDUAL DRIFT
ETC...
CREATE BUILDING MODEL AND PERFORM ANALYTICAL
ESTIMATION OF PEAK
BUILDING RESPONSE
IS REPAIR REQUIRED?
Proposed methodology
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Future challenges Risk-based assessment
• More holistic assessment of “condition as when new” • Repair to meet risk target of new building
MCE
Acceptable
Risk
Raghunandan et al 2015
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Concrete Building Performance
Tagging statistics for RC buildings (12 June 2011) – Kam et. al (2011)
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Beyond the Code Residual Capacity?
June 13
Feb 22
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Now what??
Demolish? Repair? OR
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Central Business District (CBD) March 2011
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CBD ~Sept 2012
X
X
X
X
X
X
X
X
X
X
X
X
What factors influence the demolition decisions on buildings?
Courtesy of W. Kam
X
X X
X
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Data Collection
• Conducted in collaboration with • Christchurch City Council (CCC)
• Canterbury Earthquake Recovery Authority (CERA)
• GNS Science
• Resilient Organisations
• Local engineers
• 223 Reinforced concrete buildings • 3-storey and higher
• Located within the CBD
• Represent ~34% of all RC buildings in the CBD
or ~88% of the 3-storey and higher RC buildings in the CBD
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Study Buildings
CBD Outline
Demolish
Repair
Unknown
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Building Damage Statistics
27
72
39 43
20 2 7 11 2
77(35%)
103(46%)
43(19%)
0
20
40
60
80
100
120
Green Yellow Red
# o
f B
uild
ings
Placard
20
43 43
19 12 1
32 24
8 0 1 0 3 13 3 1 0 0
55(25%)
80(36%)
54(24%)
20(9%) 13(6%)
1(0%)
Damage Ratio
Demolish
Repair
Unknown
Total
0-1% 2-10% 11-30% 31-60% 61-99% 100%
≈ repair cost ⁄ replacement cost (visual estimate)
Significant number of RC buildings with relatively low damage were demolished.
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Building Characteristics Statistics
66
49
7 16 18
40
4 3 4 10 4 2
88(39%)
99(44%)
15(7%) 21(9%)
0
20
40
60
80
100
120
140
MomentFrame
Shear Wall MomentFrame &Shear Wall
MomentFrame with
Infill
# o
f B
uild
ings
Seismic Force Resisting System
73
54
11
46
16 3 10 9 1
129 (58%)
79 (35%)
15(7%)
3-5 6-12 13-22
Number of Floors
Demolish
Repair
Unknown
Total
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Reduction in steel strain capacity
Str
ess
Strain Residual
strain after
EQ
Simplified cyclic
loading during
earthquake
Post-earthquake monotonic
behaviour
Virgin monotonic
behaviour
Simplified strain history
due to earthquake loading
Increase in reloading
strength due to strain
ageing + hardening
Reduction in uniform strain due to:
(a) Strain ageing
(b) Low-cycle fatigue
Adapted from Pussegoda (1978)
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Reduction in steel strain capacity - Strain ageing
Data: Restrepo-Posada et al (1994) and Loporcaro et al (2016) – grade 300
NZ Guidelines probable uniform strain
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[s/db = 6]
For large strain cycles, strain ageing can reduce remaining
cycles to failure by ~50%.
Loporcaro and Pampanin (2017)
2ea
Reduction in Low-Cycle Fatigue Capacity