Structural Monitoring of the Akashi Kaikyo Bridge

Kiyohiro Imai

Honshu Shikoku Bridge Expressway Co. Ltd.

Japan and Honshu Shikoku Bridges2

Pacific Ocean

Hokkaido

Honshu

Kyushu

Japan Sea

Seto-Inland sea

Osaka

Tokyo

Shikoku

N

Naruto

SakaideImabari

Kojima

Onomichi

Kanmon Tunnel

Kanmon Bridge

Seikan Tunnel

Nagoya

Kobe

Okayama

Kurashiki

Akashi Kaikyo Br.

Ohnaruto Br.

Wakayama

Sumoto

Kobe

Osaka

Kansai International Airport

Awaji Island

NarutoTokushima

Sakaide

Takamatsu

Matsuyama

Imabari

Hiroshima

Onomichi

Kobe Naruto Route

Kojima Sakaide Route

Iwakurojima Br.

Hitsuishijima Br.

Shimotsui-Seto Br.

Minami Bisan-Seto Br.

Kita Bisan-Seto Br.

Kurushima Kaikyo Br.

Hakata Ohshima Br.

Tatara Br.

Ikuchi Br.

Innoshima Br.

Ohmishima Br.

Onomichi Imabari Route

Shin Onomichi Br.

Sanyo Expressway

Chugoku Expressway

Matsuyama

Expressway

Tokushima

Expressway

Kochi

Prefectural Capital

Honshu

Shikoku

Yoshima Br.

Outline of the Honshu Shikoku Bridges3

Honshu Shikoku Bridges contribute to the national highway network between Honshu and Shikoku Islands

19

75

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76

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77

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78

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81

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82

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83

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84

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85

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87

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88

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89

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90

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91

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97

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98

19

99

AKASHI KAIKYO BR.

OHNARUTO BR.

SHIMOTSUI SETO BR.

HITSUISHIJIMA BR.

IWAKUROJIMA BR.

KITA BISAN-SETO BR.

MINAMI BISAN-SETO BR.

SHIN-ONOMICHI BR.

INNOSHIMA BR.

IKUCHI BR.

TATARA BR.

OHSHIMA BR.1ST KURUSHIMA KAIKYO BR.

2ND KURUSHIMA KAIKYO BR.

3RD KURUSHIMA KAIKYO BR.

KOJIMA-SAKAIDE

ONOMICHI-IMABARI

KOBE-NARUTO

OHMISHIMA BR.

CALENDAR YEAR

YOSHIMA BR.

BRIDGEBRIDGE

TYPE

SUSPENSION

SUSPENSION

SUSPENSIONCABLE-STAYED

TRUSS

SPAN LENGTH

(m)(SIDE+CENTER+SIDE)

960+1991+960

330+876+330

230+940+230

185+420+185

185+420+185

175+245+165

SUSPENSION

SUSPENSION

274+990+274

274+1100+274

SUSPENSION

ARCH

SUSPENSION

SUSPENSION

SUSPENSION

SUSPENSION

85+215+85

250+770+250

150+490+150

270+890+320

297

140+560+140

140+600+170

250+1020+245

260+1030+280

CABLE-STAYED

CABLE-STAYED

CABLE-STAYED

CABLE-STAYED

Construction history of Honshu Shikoku Bridges4

Kobe EQ.

Akashi-Kaikyo Bridge5

Main Tower

Stiffening Girder

Side View

3 span, 2 hinged stiffening girder systemNumber of lanes: 6Opened to traffic in 1998

1A 2P 3P 4A

960 9601991

85 80 78 80（unit：m）

T.P.+297.3

46.5

General View of the Akashi-Kaikyo Bridge6

35.5m

T.P.+81.0

T.P.+10.5

Akashi Kaikyo Bridge just after the Earthquake(January 23, 1995)

7

0.8m

0.4m

N

Effects of Kobe earthquake onthe Akashi Kaikyo Bridge

8

Kobe

Awaji Island

Ground movement

Relative deformation of bridge

1990

1990.8m

3910

3911.1m

960.3m960.0m

960960

1A 2P 3P 4A

Kobe Awaji Island

Honshu Island

Dynamic Monitoring and Precise Inspection9

in order to know change of the state with time

Categories Monitoring

or Inspection

Object parts Items measured Intervals

Structural

PreciseInspection Whole bridge

Shape of the whole bridge

5 yearsDisplacement of foundations

Suspender rope tension

DynamicMonitoring Whole bridge

Wind velocity and direction, displacement, velocity,acceleration

always

Material

PreciseInspection

Paint for steel members

Film thickness, glossiness, adhesion

About 5 years

Monitoring Main cablesTemperature and humidity inside of main cables and in spray saddle rooms

always

Precise Inspection

Concrete structures

Chloride ion concentration, neutralization depth 5 years

Others PreciseInspection

Tower foundation

Seabed scour condition around Tower foundation

5 years or more

Outline of Dynamic Monitoring 10

Long-span Bridges in the Honshu-Shikoku Bridges・10 Suspension bridges, 5 Cable-stayed Bridges,1 Truss bridge, 1 Arch bridge (span length > 200m)

Objectives・Evaluation of bridge behavior during extraordinary event・Evaluation of bridge soundness after extraordinary event

Sensors arrangement・Wind characteristics are observed

on the Akashi-Kaikyo Bridge and the Tatara Bridge.・Seismic motions are observed at 2 locations on each route.・Bridge behavior is observed on the representative bridges.

①Akashi-Kaikyo Bridge, ②Ohnaruto Bridge, ③Minami Bisan-Seto Bridge, ④Tatara Bridge, ⑤Kurushima Kaikyo Bridges

Arrangement of Monitorng Sensors on the Akashi Kaikyo Br.11

1A 2P 3P 4A

Earthquake recorder : Accelerometer

: Velocity Gauge: Wind Speed Gauge : Displacement Gauge

: GPS

960m 960m1991m

Kobe Awaji

100km200km300km

Japan Sea

8.0 9.0M

7.5 8.0M

7.0 7.5M

6.5 7.0M

6.0 6.5M

Pacific Ocean

Earthquakes around the Akashi Kaikyo Bridge12

Natural period, T (sec)

Acc

eler

atio

n r

esp

on

se s

pec

tru

m (

gal

)

0.1 0.2 0.3 0.5 0.7 1 2 3

1000

700

500

300

200

100

70

50

30

20

(0.206sec, 800gal) h = 0.05

Standard

acceleration

response

spectrumM=8.5

Distance=150km

TR=150 years

Acceleration response spectrum for the design 13

Epicenter

Awaji Island

M6.3 Earthquake on April 13, 2013

Location of Seismometer

Kobe side

Observation of Seismic Motions14

Akashi Kaikyo Bridge

0.1

1

10

100

1000

0.01 0.1 1 10

Acc

eler

atio

n r

esp

on

se s

pec

tru

m (

gal)

Time (sec.)

h=0.05Longitudinal direction

Transverse direction

Original design

Transverse velocity at the center of the middle span

Acceleration Response Spectrum15

-30m

-50m

-70m

-70m

-50m

-40m

-50m

-20m

-80m

-100m

-80m-60m

-40m

-60m

-110m

Maiko

Awaji Island

KOBE

The Akashi Kaikyo Bridge

1A

2P

3P4A

Akashi Kaikyo waterway

Wind observation tower

80m

Wind Observation Site16

1965 1970 1975 1980 1985

10

20

30

40

50

60

70

Win

d v

eloci

ty (

m/s

)

: Gust wind velocity

: Mean wind velocity

(10 min. average)

65.0m/s

52.2m/s

Year

Typhoon No.20

Typhoon No.23

Lack of data

Wind Observation Data17

Wind

Full-model Wind Tunnel Test (S=1/100)18

VerticalStabilizer

V=60 m/s (at girder)

Transverse direction

Win

d v

elo

city

(m/s

)W

ind

dir

ecti

on

(d

egr

ees)

Observed Wind Data of September 22, 1998 (Typhoon 9807)19

13

:00

14

:00

15

:00

16

:00

E

N

S

W

13:00

14:2016:00

North-east

South-east

Horizontal Displacement

Wind

1A 2P 3P 4A

Arrangement of GPS sensors20

Wind Speed

Time history (Second)

Win

d v

elo

city

(m

/s)

32.0 m/s

Time (Second)

Girder Displacement at the Middle of the Center Span

Observed Horizontal Displacement on the Akashi Kaikyo Bridge21

Gir

der

Dis

pla

cem

ent

(cm

)

Comparison of Observed and Analytical Data22

Observed

displacement (m)

Analytical results (m)

Case 1 Case 2

Average displacement

① 5.17 5.43 5.43

Dynamic displacement

② 0.78 2.62 0.68

Total displacement

（①＋②） 5.95 8.05 6.11

Note : Average wind speed was 32.0 m/sCase 1 was using designed power spectrum and spatial correlationCase 2 was using observed power spectrum and spatial correlation

Horizontal Girder Displacement at the Middle of the Center Span

0

2

4

6

8

10

0 10 20 30 40Average wind speed (m/s)

Ho

rizo

nta

l gir

der

dis

pla

cem

ent

at t

he

mid

dle

of

the

ce

nte

r sp

an(m

)

Designed average displacement

Designed dynamic displacement

Observed average displacement

Observed dynamic displacement

Designed total displacement

Observed total displacement

Relation between Girder Dispalcementand Wind Velocity

23

Dry air flow between galvanized wires

Dehumidifier and blower Air injection cover

Injection mouth

Exhaust opening

Dehumidifier and blower

Supply pipe

Girder

Tower

Cable

Dry-air Injection System developed by HSBA24

■ Keep relative humidity in the cables less than 60%, andthe cable can be protected from corrosion.

■ Dry-air injection system was introduced to keep relativehumidity less than 40% in the cables.

腐食の限界湿度

Relative humidity (%)

Co

rro

sio

n v

olu

me

of

Zn g

alva

niz

ing

(g/m

2)

Attached salt

60

Corrosion of a main cable

Monitoring of Dry-air Injection System25

(Just after a start of operation)

Year, month

40%

0

20

40

60

80

100

19

98

.3

Rel

ativ

e h

um

idit

y (%

)

Outer air Inside cable

19

97

.11

19

98

.7

19

98

.11

19

99

.3

19

99

.7

19

99

.11

20

00

.3

20

00

.7

Monitoring Data of Humidity in Cables26

Temporally suspended

(During normal operation)

40%

0

20

40

60

80

100

Rel

ativ

e h

um

idit

y (%

)

Year, month

20

04

.5

20

04

.9

20

05

.1

20

05

.5

20

05

.9

20

06

.1

20

06

.5

20

06

.9

20

07

.1

20

07

.5

20

07

.9

Outer air Inside cable

Monitoring Data of Humidity in Cables27

Cable Opening Inspection in 2008 and 20189 and 20 years after Completion

28

February, 2008 (9 year)

No rust

Inspectoin Window

Wedge

November, 2018 (20 years)

Inspection Window

No rust くさび

Conclusion

◼ Dynamic monitoring has been conducted on major Honshu Shikoku Bridges

◼ It was confirmed that original design of the bridges is appropriate and proved to be conservative.

◼ Main Cables have been protected against corrosion by the Dry-air Injection System.

◼ It was confirmed that main cables are in proper condition.

◼ In order to improve the Dry-air injection system, more efficient operation has been currently investigated and introduced. (Reduction of operation units, reduction of air pressure, installation of pre-cooling units, etc.)

Conclusion29

30

Thank you very muchfor your attentions !

Akashi Kaikyo Bridge