Recent Advances in Seismic Rehabilitation ofReinforced Concrete Buildings in Japan

Shunsuke SuganoGraduate School of EngineeringHiroshima University, Japan

NATO Istanbul WorkshopMay 30 – July 1 、、、、2005

Kobe Earthquake(Jan.17 1995)

State of Seismic Rehabilitation of Reinforced Concrete Buildings in Japan

Recent Advances in

ResearchDesignPractice

OUTLINE

・・・・ Most of severely damaged buildings were designed and constructed before 1981 when the design code (the building standard law) was revised to the present form.

・・・・ New buildings designed and constructed after 1981 generally behaved in a good manner.

・・・・ It was supposed that the damage would be significantly mitigated if seismic evaluation

and rehabilitation were advanced

Lessons Learned from 1995 Kobe Earthquake

Construction Year

Da

ma

ge

In

de

x D

100

80

60

40

20

0

1920 1930 1940 1950 1960 1970 1980 1990 2000

Major Damage

1981

Present Building Standard

Law

Damage Level

D≧≧≧≧50 D=10~50 D=5~10D<5

N=167

MajorMediumMinorLight

(Architectural Institute of Japan, 1997)

Damage to School Buildings in Kobe (1995)

Social Demands

・・・・ No disturbance to

building function

・・・・ No evacuation of

building occupants

・・・・ No change of building

design (facade)

・・・・ Short construction

period

Consideration when Selecting

Rehabilitation Techniques

・・・・ Effect on building function

(lighting, traffic line, usability)

・・・・ Hindrance associated with

construction (noise, vibration,

dust, chemical smell)

・・・・ Effect on foundation system (increased building weight)

・・・・ Construction cost and period

Demands for Seismic Rehabilitation

Seismic Strengthening Seismic Control

Seismic Isolation

Isolator

New

foundation

Damper

Brace

Shear wall orSteel brace

Type of Seismic Rehabilitation

Measures

(a) Sheet Jacketing (b) Strand Jacketing (c) Panel Jacketing

continuous fiber sheet

(carbon, aramid, glass)

existing column existing column

nonshrink mortar

carbonfiber

panel

carbon fiberstrand

connection sheet

existingcolumn

Column Jacketing with New Materials

8-Story Office BuildingSRC frame and wall structures

Constructed in 1967Strengthened with exterior

SRC frames (lower story) and steel braces (upper stories)

Construction 1996.3-1999.3

Strengthening by Exterior Structures

Seismic Isolation (Office Building)

Steel Frame with Damper

Column Jacketing and Steel Dampers

Steel Elasto-plastic Damper

Seismic Control

Recent Advances in Research

A Large Variety ofResearchers

Research ItemsPresentations

Response to Social DemandsConstruction under hard condition

Maintaining function of original structure

Accumulation of Research DataRehabilitation design

Design approval

Reinforced Concrete (RC)

Seismic Rehabilitation (SR)

SR/RC (%)

Research on Seismic Rehabilitation

Proceedings of Annual Convention ofthe Architectural Institute of Japan(AIJ)

（（（（%））））

0

50

100

‘98 ‘99 ‘00 ‘01 ‘02 ‘03 ‘04’66~

‘83

0

100

200

300

400

500

‘97‘96‘95

Nu

mb

er

of

Pa

pe

rs

M

P

R

h

R =δδδδ/ hM = PhDeflection angle R

Ben

din

gm

om

en

t M

My

Ry

Y

Mm

Rm

Point Y: yielding

N0.8Mm

Ru

Point M:maximum momentPoint N: ultimate displacement

M

Ductility factor µ =µ =µ =µ =Ru/Ry

Restoring Force Characteristics of Jacketed Columns

Building columnBridge columnBond failureShear failureLower limita/D ≦≦≦≦ 2.5a/D>2.5

Ult

ima

te d

isp

lac

em

en

t R

u (ra

d.) Ru=0.0040Vs/Vf+0.046

Strength Radio Vs(AIJ)/Vf

(Shear strength)/(Flexural Strength)

0 42 6 80

0.10

0.08

0.06

0.04

0.02

Continuous-fiber Jacketing

Ru=0.032Vs/Vf-0.001Ru=0.03(Vs/Vf-1)

Ductility of Columns Jacketed with Continuous-fiber Sheets (Japan Concrete Institute, 2000)

Survey of New Rehabilitation Techniques

l Answerers: General Contractors

Survey 1: 2000 38 (Buildings)

12 (Bridges)Survey 2: 2004 19 (Buildings)

21 (Bridges)

l Questions

1. Target (reduction of cost, work period, etc)

2. Object (column, pier, etc)3. Purpose of rehabilitation

(improvement of ductility,

etc)4. Outline of technique (what’s new,

how to evaluate, etc)

JCI Questionnaire Survey (2000, 2004)

Major general contractors have their

own R/D institute to develop design

and construction technologies.

Target of Technology Development(Buildings)

Survey 2000

1. Reduction of work term

2. Removal unnecessary3. Reduction of hindrance

(noise, vibration, fine particles, etc)

Survey 2004

1. Reduction of work term2. Removal unnecessary3. Reduction of cost

0

20

40

60

80

100

Designfriendly

Removal

unnecessary

Reduction of work space

Lightweight

Reduction

of noise,vibration,etc

Reduction ofcost

Reduction ofwork term

Others

Priority

Subject of Technology Development (Buildings)

Survey 2000

1. Isolated column2. Placing concrete wall3. Placing steel braces

Survey 2004

1. Placing steel braces2. Placing concrete wall3. Isolated column

Exterior structure

Placing steel

braces

Placing steelpanel wall

Placing

concrete wall

Shear wall

Beam

Column with

side walls

Isolated Column

Others

0

10

20

30

40

50Priority

Recent Advances in Design

Performance-based Design ApproachesTarget performance

Level of design earthquakesEvaluation of Performance

Accumulation of Research DataRehabilitation design

Design approval

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Seismic Structural Index Is (2nd Screening)

Da

ma

ge

Gra

de

In

de

x D

Architectural Institute of Japan, 1997

Iso=0.6

Observed Damage

by Inspectors

Collapse or major

moderate

minor

light

Seismic structural index Is

Is = E0xSdxTEo=CxFC:strength indexF:ductility index

Sd:structural designindex

T:time indexDamage Level

D≧≧≧≧50 D=10~50 D=5~10D<5N=167

MajorMediumMinorLight

Seismic Structural Index Is vs. Damage Level(Architectural Institute of Japan 1997)

Iso: judgment index

PML 20%

PML=Probable Maximum Loss

Building Price\ 10 billion

Repair Cost\ 2 billion

PML =Max. Loss by 10% / 50yr EQ

Rebuilding Cost

Probable Maximum Loss (PML)

0.4 0.6 0.8 1.0 1.20

10

20

30

40

PML50

35 35

40

45

40

30

20

10

50% 25% 15%

10%

5%

（（（（Min. Level））））

(30%) (15%) (7%)

(5%)

(2%)Min. Total Cost

(Target Performance)

Exp

ecte

d T

ota

l C

ost

(Co

nstr

ucti

on

Co

st

+ D

am

ag

e R

isk)

Seismic Structural Performance

Seismic Structural Index (IS)

Rehabilitation

Cost

Target Performance for Seismic Rehabilitation

2700 8000 7360 7360 36803680 7360 7360 8000 2700 5300

29100 29100

26 1225

24 3

23 4

22 5

21

620

19 7

8

9

10

9‘

1413

11

12

10‘

15

16

17

18

正面玄関方向

Seismic Isolation

As-built

Isolator

A Case of Buddhist Temple in Tokyo

Performance-Based Design for Seismic Rehabilitation

Historical earthquakes around Tokyo

l Target Performance: No damage against the 0.8g earthquake (return period 3000 years).

l Measures to improve performance: To install seismic isolation devices to reduce the response forces to 1/3 – 1/10.

1111

10101010

100100100100

1000100010001000

10000100001000010000

100000100000100000100000

0000 200200200200 400400400400 600600600600 800800800800 1000100010001000 1200120012001200 1400140014001400

3000yr

800

Seismic hazardAcceleration (cm/s2)

Re

turn

Pe

rio

d (

yr)

Seismic hazard of the site

Design Earthquake and Target Performance

Recent Advances in Practice

Increased Number of ImplementationsPublic buildings

Private buildings

A Large Variety of Rehabilitation TechniquesSeismic Strengthening

Response Control

Change of Consciousness and Awareness A large number of implementations

Increased number of private buildings

before Kobe EQ

after Kobe EQ0

1000

2000

3000

4000

5000

6000

7000

Publicbuildings

Evaluation Rehabilitation0

1000

2000

3000

4000

5000

6000 Privatebuildings

Evaluation Rehabilitation

7000

Public buildings

Private buildings

0

1000

2000

3000

4000

5000

6000

7000

after KobeEQ (1995)

Evaluation Rehabilitation

before KobeEQ (1995)

Evaluation Rehabilitation0

1000

2000

3000

4000

5000

6000

7000

Implementation of Evaluation and Rehabilitation

Japan structural Consultants Association (JSCA), 2003

A University Building

Seismic Rehabilitation Considering Building Facade

RC壁増設

外付増設フレーム

フーチング

新設杭

増打柱 480×500 増打梁 500×900

増打壁 W300開口閉塞壁 W250

Exterior Frame

Concrete Wall

Footing

New Pile

Concrete Wall (W250)

Exterior column 480*500

Exterior Beam500*900

Concrete Wall (W300)

Seismic Rehabilitation Using Exterior SRC Frames

Exterior FrameFloor Plan

Exterior Frame

Behavior of Rehabilitated Building

A Case of Kobe Yusen Building Survived 1995 Kobe Earthquake (M=7.3) without Any Damage

Kobe Yusen Building Use: Office Structure: Steel Encased with Concrete Designed: 1918Seismic rehabilitation for preservation (maintaining building facade)

Strengthening of concrete frames with steel framesStrengthening of brick walls with concrete walls

Extension of foundation slabs Construction for seismic rehabilitation: 1993.10 – 1994.3 Event during the earthquake: No damage

Why Seismic Rehabilitation Is not Spread?

1. Less attractive than building or rebuilding (backward business).

2. Hesitation to invest for long return period events (no budget) .

3. Hard job for designer and constructor because of time consuming work.

4. Rehabilitation is impossible(significant change of the building)

Change of Consciousness to Make Seismic Rehabilitation Possible

1. Attractive job to save human life, to secure properties and to maintain earth environment.

2. Necessary expenses to secure the building safety against earthquakes.

3. Advanced skill is displayed. 4. Advanced techniques make the difficult

seismic rehabilitations possible.

Column Jacketing

Steel-plate Jacketing

Carbon-fiber Jacketing

12.0

10.0

8.0

6.0

4.0

2.0

0.0 1.0 2.0 3.0 4.0 5.0

μμμμ =1.92 Vs/Vf + 2.45

R2=0.935

Strength Ratio Vs/Vf

(Shear strength)/(Flexural strength)

Du

cti

lity

fa

cto

r μμ μμ

0.0Concrete Jacketing

Ductility of Columns Jacketed with Concrete (Japan Concrete Institute.2000)

0.0 2.0 4.0 6.0

0.06

0.04

0.02

0.00Steel-plate Jacketing

Ru=0.055Vs/Vf+0.0261

Ru=0.0074Vs/Vf+0.0353R2=0.539

Strength Ratio Vs/Vf

(Shear strength) / (Flexural strength)

Ult

ima

te d

isp

lac

em

en

t R

u (

rad

)

Ductility of Columns Jacketed with Steel-plates(Japan Concrete Institute.2000)

Research

Application

Research

Application

Max. probable EQ Safety margin check

Recorded and/or artificial

50 cm/sec or more

Recorded and/or artificial

65 cm/sec or more

SuperstructureInterstory drift <1/400

No yielding

Interstory drift <1/200

Sufficient margin to failure

IsolatorLateral displacement

< 200%

Lateral displacement

< 300% or more

Superstructure

Interstory drift <1/200

Sufficient margin of safety

to member failure

Interstory drift <1/100

Margin of safety to

member failure

Damping system

Sufficient margin of safety

to energy dissipation

capacity

Margin of safety to energy

dissipation capacity

Level of ground motion

Seismic

control

Seismic

isolation

Max.velocity of

ground motion

Design Criteria for Response Control Buildings

Low friction isolation bearing Stable anchorage of isolator

Wall type viscous damper Full scale test of setting isolator

Back-up Technologies

ü Ministry of Construction, March, 1999.ü Specific building: The building which is used by many people such as office,

school, hospital, etc. and which has three or more stories and floor area

1,000m2 or more.

900 ( 0.5)300 ( 0.4)600 ( 1.6)Demolished

or rebuilt

4,100 ( 2.4)200 ( 0.2)3,900 ( 4.1)Rehabilitation

implemented

14,600 ( 8.6)500 ( 0.7)14,100 (14.9)Rehabilitation

necessary

28,100 (16.5)1,200 ( 1.6)26,900 (28.3)Evaluation

performed

170,000 ( 100)75,200 ( 100)94,800 ( 100)Surveyed

buildings

TotalPrivate

Buildings

Public

Buildings

Seismic Evaluation and Rehabilitation of Specific Buildings (Survey of 1999)

( ) %