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

Photo courtesy of W. Kam

> 60% of Multi-story Reinforced Concrete Buildings Demolished

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

First Cordon February - March 2011

August - October 2011

June 2013

CBD Outline

Cordon

4

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

Demolition Decision Framework (Marquis et al 2015)

Traditional engineering focus

Case Study Buildings

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%

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

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)

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?

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

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

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

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

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

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

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

Effect of moderate-level loading cycles

No change in deformation capacity!

CYC

CYC-NOEQ

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

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

Thank you!

[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

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)

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)]

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

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

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

JBDPA Guideline (Nakano et al., 2004)

Previous work - JBDPA

Previous work – FEMA 306

FEMA 306 (ATC, 1999)

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

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

Concrete Building Performance

Tagging statistics for RC buildings (12 June 2011) – Kam et. al (2011)

Beyond the Code Residual Capacity?

June 13

Feb 22

Now what??

Demolish? Repair? OR

Central Business District (CBD) March 2011

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

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

Study Buildings

CBD Outline

Demolish

Repair

Unknown

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.

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

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)

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

[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