Super long span cable-suspended bridges in Japan

11 

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Autor(en):

Ito, Manabu

Objekttyp:

Article

Zeitschrift:

IABSE congress report = Rapport du congrès AIPC = IVBH

Kongressbericht

Band (Jahr): 15 (1996)

Persistenter Link: http://dx.doi.org/10.5169/seals-875

PDF erstellt am:

18.06.2016

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1009

Super Long

Span Cable-Suspended

Bridges

in

Japan

Manabu

ITO

M-It0 hasbeen engaged

Prof

Emeritus in'«chingand research

~e

t

tc onbridges and structural

The University

of

dynamicsat the

Tokyo UniversityofTokyofrom

Japan 1959 to 1991, andthenat

SaitamaUniversityuntil 1995.Hehasalso been

involvedinmany cable-suspendedbridge projects, andiscurrently

aVice-Presidentof

IABSE.

Summary

Thestate-of-the-art

of

long spancable-suspended bridgesin Japan is presented

After

describing some

of

their specific features, special mentionismade

ofthe

Akashi-Kaikyo Bridge

ofthe

Suspensiontype andthe TataraBridge

ofthe

cable-stayed type,both

of

which

will

respectively havethe world's longestspanswhen completed in afewyears. Finallyseveral other projects

of

straits crossings under consideration, which containfurther long spanbridges, are referred to.

1.

Introduction

Japan consists

of

four major islands and many othersmall islands, whereas it has afairlylarge

population inthelimited flat area. Never-the-less, any largebridge, thespan

of

which exceeds 200m, had not beenbuiltbefore the middle

of

thisCentury.

It

might bedueto such reasonsthat road networkswere in poor condition;that rivers in thiscountry did not requirewide

navigation Channel, andthat the bull-headed militaryauthorities did not like large bridge construction.

Thereconstruction

of

devastatedfacilities started afterthe Second World War, and

with

the development

of

vigoroussocio-economic activities thereafter, the improvement

of

transportation networks hasbeenpromoted. Since 1960's many longspanbridge projects to cross straitsand river mouths in urban areas, orsometimes toconnect areas

of

reclaimed land in coastal cities, have beenundertaken. Aboveall, theHonshu-Shikoku linking project across the Seto Inland Seaatthree differentroutes (cf. Fig 1)gavean impetus tothe rapid progress

of

largebridge construction in Japan.

When very long span is required, the leadis taken by cable-suspended bridges, namely Suspension orcable-stayed types It can be recognised from Fig2 and Tables 1 and 2 that the

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threedecades. The effect

of

earthquake loading onJapanese bridges has ledtothe extensive use

of

steel ascompared

with

other countries. Inaddition, avariety

of

steelmaterials are availableat areasonable priceinthis country

Tsugaru

St.

Kyushu

Hokk

Honshu

Sh

Tokyo

Bay Mouth

/se

Bay Mouth

Kitan

St.

Ho-vo

St.

Figure 1 Strait Crossing projects in Japan

2000 i n 1000 1500 1000 500 OVERSEAS JAPAN—> 500 I r I OVERSEAS

f

i

J i i J I

K

ee"JT

r

I-

r

¦«-JAPAN 1900 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000

(a) Suspension (b) Cable-Slayed

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M. ITO 1011

On the otherhand, quite high designwind speeds arerequired

for

Japanesebridgesbecause

of

frequent attack

of

strong typhoons. The state-of-the-art

of

Japanesecable-suspended bridges in general is reviewed in thepapers by A. R. Bürden [1,2] and theauthor

ofthe

present article

[3,4],

name max. span (m) year remarks

Kanmon 712 1973 truss-stiffened

In-no-shima 770 1983 truss-stiffened

Ohnaruto 876 1985 truss-stiffened, designed

for

highway+railway

Ohshima 560 1988 twin-trapezoidal box girder

Shimotsui 940 1988 continuous double-deck truss, road

&

rail

North

Bisan 990 1988 continuous double-deck truss, road

&

rail South Bisan 1100 1988 continuous double-decktruss, road

&

rail Tokyo Port 570 1993 double-deck truss

Hakucho 720 * streamlined boxgirder, snowydistrict

Kurushima

I

600 *

Kurushima

II

1020 * boxsection, three 3-span bridges linked

Kurushima

III

1030 *

with

two shared anchorages

E\kashi 1991 * truss-stiffened

Table 1

Major

Suspension bridges in Japan (as

of

1995), note: * under construction

name max. span (m) year remarks

Yamato River 355 1982 trapezoidalboxgirder,very skew

Meikoh-West 405 1985 hexagonalbox

with

fairingtruss-stiffened Katsushika 220 1987 S-shape curved, box girder

with

fairing

Katsushika 250 1988 twinbox, R/C tower, snowy district

Iwakuro Is. 420 1988 double deck truss (highway

&

railway), Hitsuishi Is 420 1988 standing in line

YokohamaBay 460 1989 doubledeck truss

with

shallowboxupperchord Tempozan 350 1990 flathexagonal box

with

Splitter plate

EastKobe 485 1993 double deck truss

Ikuchi 490 1991

twin

hexagonal box, P/C girder in side spans Tsurumi 510 1994 streamlined boxgirder

Meikoh-Central 590 $ trapezoidalbox girder

Meikoh-East 410 $ trapezoidal box

Tatara 890 * streamlinedboxgirder, P/C girderin sidespans Table 2

Major

cable-stayed steel bridges in Japan (as

of

1995), note: * under construction

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2.

Specific

Features

In

Design

And Construction

2.1 Designand

Construction

Process

Very longspan bridgesinJapanareusuallybuiltby thepublic corporations invested by the central and local governments, andput touse as

toll

bridges after completion. The

organisationswhichcommission theproject control its design

work

and have aleadingrolein

the main decisionprocess, although Consultingfirmsundertake the substantial

work.

The

authority hasexpertise in-house to evaluate designand supervise constructionas well.

Another feature in the designand constructionprocess

for

large projectsinJapanis theuse

of

committees comprisingacademics and experiencedengineers, thoughthe members

of

private enterprisesare rarelyincluded there. Theydiscuss particular issues on theprojectand give advices uponconsultation

ofthe

owner. Therearesometimes more thanone committees in parallel, such astechnical and aesthetic.

Sofarbig projectshave been not tendered on a competitivedesign-and-builtbasis in Japan, andseveral Joint ventures areformed

for

theconstruction stages

of

substructuresand superstructures, respectively.

2.2 Effects

of Environmental Actions

Earthquakes and strong windsarefrequentlythe dominant actions in designing longspan bridges. Generally speaking, earthquakes govern theproportioning

of

substructuresand towers, while windaffects the design

of

superstructures. Dynamic analysis isnowthe routine

procedure in designingflexiblestructures[5].

A

feature

worthy

of

special mention on long span Japanesecable-stayed bridges is theuse

of

elasticconstraint in the longitudinal direction by connecting thegirderandthetower, the piers orthe abutmentwith steel bars, layeredplate Springs, shear-type rubber shoes, or links,in order to control seismic forces appliedtothe substructures and optimise the sectional forces dueto notonlyseismic but alsotemperature effects [6].

Designwind speeds fortheJapanesecable-suspended bridgesare quite high (between about 50 to 75 m/s atdeck level), and thecritical wind speed

for

aerodynamicinstabilitypredicted from windtunnel model tests is requiredto be above 1 2 timesthese

designwind speeds.

Accordingly, many

ofthe

longspanbridges areprovided

with

means suppressingwind-induced vibrations [7]. Thefirst choiee isto selectan aerodynamically stablecross sectionand,

if

necessary, fairings, flapsorother aerodynamic appendages areattached. Withthegrowth

of

scale

of

structuresthese days,the use

of

variousdamping devices on towers, girders and stay cäbles has also increased.

2.3 Cäbles

Parallel wirecäbles consisted

of

galvanised steelwires

of

about5 mm in diameter have been exclusivelyused onlong span Suspensionbridges inJapan. The type

of

cableformation usedon them hasbeen mostlythe prefabricated parallel wireStrand (PPWS) methodevenon the

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M. ITO 1013

Akashi-KaikyoBridge, the cable length

of

whichexceeds 4 km.

A

recentexception was the Shimotsui-Seto Bridge (main span

of

920m) where the airspinning method wasused because

ofthe

limitation

of

space at the north anchorage.

As shown inFig.3, the tensile strength

ofthe

steel wires used in Suspensionbridge cäbles has not changed drastically in thepast seven decades, but high-strength steelwire

with

the tensile strength

of

1,800 MPawas developed by adding appropriate amount

of

Silicontouse onthe main cäbles

ofthe

Akashi-Kaikyo Bridge. Its motivation

will

be discussed in the next chapter.

The most prevailing stay cäblesin longspan cable-stayed bridges in Japan arethe so-called non-grout-typeStrandinwhich each wire isbundled

with

alay angle

of

not more than 4

degreesto enablethe reeling

ofthe

Strand and ensurethe mechanical properties

of

parallel wire Strand. The Polyethylene sheathiscompletely shop-fabricated bya directlyextrudedjacket

aftercorrosion protection measures aretaken. The coloured surface

for

aesthetic requirement andthe notchedordimpled surface

for

aerodynamic stability arenow available on the

Polyethylene covering.

2.4 Bridge Decks

Truss girder hasbeenemployed on double-deck bridges inJapan, in both Suspension and cable-stayedbridges.

Mhough

thestiffening truss was also adopted

for

the

Mashi-Kaikyo

Suspension bridge, whichisasingle-deck road bridge, asmentioned later, theuse

of

shallow

box-section is now prevailingon thegirder

of

Japanese cable-suspended bridges. Thetype

of

steelgirders in these cases hasbeen based on generallysimilar concepts: single or twinboxes

with orthotropicdecksformingtrapezoidalorhexagonal crosssections mainly foraerodynamic reasons. Even

if

a trussgirder is used, aerodynamic appendages have beenattached onsome bridges.

2.5 Towers

Combination

of

steelgirderand concretetowers has been seenin Japan

for

onlya few

cable-stayed bridgeswith amain span

of

less than250m. What follows is, therefore, all concerned

with

steeltowers.

Suspension bridgetowers areusually classified into X-braced typeand rigid frame type In Japanesebridges where earthquake andwind effects are large, the former hasbeen

conventional

for

long span. Although thelatter hasbeen increasingly adoptedfromthe aesthetic preference, it isnot yet used ontheSuspension bridge larger than 1,030mspan On theother hand, towers

of

cable-stayed bridgeshave more varied forms. In casethat span length

isverylarge, however, A-shapedor inverse Y-shaped typesareusuallyselected

for

the reasons

of

structural stabilityand higher torsional rigidity

ofthe

whole system.

Since the towers

of

cable-suspended bridges are noticeable, theirvisual design ishighly put

stress. Sometimes industrial designersand architects areinvolved in it Forexample, theuse

of

curved elements appears tobea developing trend inJapanese designs. The position

of

bracing

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design. The general softening

of

form isalso apparentinthe design

of

gravitycable

anchorages. There hasbeen increasinguse

of

strongly texturedsurfaces ontheirmassivebody. 200 Akashi 80 Kanmon G.Washinqtön 160 Seto bü NewPort

M

Manhattan xs W)140

wllliamsburg

oo 20 Brooklyn 110 -1880 1900 1920 1940 1960

Fig

3 Tensile Slrength

of

steel wire

for

Suspension bridge cable

1980 2000

Year

2.6 Large

Block

Erection

When steelbridge isbuilt atthe sites whereanarea

of

open and deepwateris available, large

block erectionbyfloating cranes isveryfrequentlyused inJapan. The advantages

ofthe

method are shortening

of

construction period, reduction

of

labour atthesite, betterand easier control

of

erection, increasing safetyby reducing

work

at high positions. However, the

restrictions maybe associated

with

compromises

with

navigational

traffic

andfisheries, and caused byerection scheme andrapid waterflow. Cost saving may not always attainedbecause

of

additional facilities andtemporary or local reinforcement

ofthe

structure during erection. The number

of

largefloating cranes with lifting capacities

of

3,000

tonf

ormoreis nowsix in Japan, andthe biggest hasamaximum liftingcapacity

of

4,100tonf. The maximum erection

weight

of

one structural block ever experienced is7,300 tonf.

In

this case, threefloating cranes

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M. ITO 1015

3.

World's

Longest

Cable-Suspended

Bridges

3.1 The

Akashi-Kaikyo Bridge

TheAkashi-Kaikyo Bridge,which

will

cross the Akashi Straits

with

a shore to shore distance

of

about 4 km, is part

ofthe

Honshu-Shikoku Bridge project that includesten Suspension and fivecable-stayed bridges.

It

is athreespan Suspension bridgeasseeninFig4. Carrying six

lanes

of

highwaytraffic. the bridge isscheduled to be completedin 1998 after aten-year

construction period.

Despite itsworld's longest span

of

1,990m, the foundations

ofthe

tower piersreachas deep as 70m below seasurface under thesevere marine conditions

ofa

seadepth

of

40manda

maximumtidalcurrent speed

of

4.5m/s. The foundations are placed on the granitebedrock and were constructed by thelaying-down caissonmethod which used steelcylindrical caisson

with

double walls. 3,910 Awaji Island 960 990 960 Kobe

3J_l-4-^

4A 3P 2P A 36.5

(a)

General View

ZS

35.50 Road Level 2£5 : 2.50 10.75 10.752.50 3.50 46.5 14.8

Main

Tower

Fig

4 TheAkashi Kaikyo Bridge

Stiffening

Girder

(b)

Main

Tower

and

Stiffening

Girder

At

the 1995 Hyogoken-NanbuEarthquakewhich devastatedKobe andits vicinity, the

construction stage

of

this bridge wasduring the squeezing

of

main cäbles afterfinishingcable erection. Although the epicentrewas nearly under the bridge site, no damage was foundon the

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structures.

It

was observed, however, that the foundations showed permanent displacements, and in its consequence, the mainspan and one side spanexpanded 0.8m and 0.3m,

respectively The resultant verticality

ofthe

main towersremained withinthe allowance

of

construction, thoughthe maximumvelocity response

ofthe

tower top exceeded 100Kines. Therefore, the erection

ofthe

bridge could be continuedby slight modification

of

sometruss membersbefore fabrication, and thebridge

will

becompleted nearly on schedule.

iMterthewind tunnel tests

with

various alternative section modelsincluding streamlined boxes

withopening, atrussgirder with high torsional stiffness was selected This decision was made also fromthe erection constraints atthe site High-strengthtempered steel

of

780 MPaclass

of

the reduced preheated typeisused forhighlystressed membersin the regions where bending moments arelarge.

Asmentioned previously the newly developed high-strength steel wires wereusedon the

Mashi-Kaikyo

Bridge Theprimary motivationwasto reduce thedead weight becausemore than90 percent

ofthe

cross section

ofthe

maincäbles is usedto carry the bridge's ownweight. Secondary advantages

of

itsuse wereto simplifythestructural details by usingtwo main cäbles instead

of

fourin the original design and toreduce theheight

of

main towers by decreasing the sag to span ratio

ofthe

main cäbles. As a consequence, each main cablewith a diameter

of

1.1 m consists

of

approximately37thousand parallel wires

of

5.2 mmin diameter. Thetwo towers supporting the main cäbleshave height

of

about 300m abovewaterlevel. The steeltowershafts havea constantwidth

of

6.6m in thetower plane and avarying width

of

14.8mto 10 0m inthe direction

of

bridge axis. High-strength, quenched and tempered steel

was mainlyused on the 40 to48 mm thickplates composing thetower shafts. Onthese tall slendertowers, tuned-mass dampersare installed inaddition to the corner eut as one

ofthe

aerodynamic means.

3.2 The

Tatara Bridge

The TataraBridge is alsoone

ofthe

Honshu-Shikoku linking bridges on the most western route

ofthe

Island Sea. Theoriginal schemewas naturallya Suspensionbridge

for

suchlong span as nearly 900m. However, theexecution

for

a massiveanchorage on the Ikuchijimaside would haveforced seriouschangeto theground configuration and the road alignment on the same sidehas a sharp curve nearthe end

ofthe

bridge. As a result, the alternative cable-stayed bridge design wasadopted.

The mainspan length

ofthe

bridge was decided to be 890m, which

will

betheworld's longest incable-stayed bridges, because

ofthe

topographical features and geological conditions at the site and

for

navigational requirement. Since theboth side spans arerelativelyshort and have different lengths as shownin Fig. 5, intermediate piersare provided in the side spans andthe continuousgirderconsists

ofa

steel box portion throughoutmost

ofthe

girder lengthand prestressed concreteportions on certain length

of

both girder endsinorder to avoid theuplift

at theend supports and to improve thebehaviour

ofthe

bridge. In addition,the shear-type

aibber shoeswiththe spring constant

of

3.9

MN/m

per bridgearegoingto be used considering the distribution

of

seismicforce, theeffect

of

temperature change, the longitudinal

displacement

ofthe

girder, and theelasto-plastic stability

ofthe

whole structural system [8].

(10)

M. ITO 1017

Ikuchi Island Omishima Island

480 320 390 270 l

ower

220.0

Girder

Cross Section

20.0

75 7.0

,2.5,

7.0 1.75

^

TZIilZ"^^

(unit

Im)

Fig. 5 The Tatara Bridge

4.

Future

Projects

It

is important to handdownthe developed technology to successors. Nowadays printed documents andComputer disc records can beleft to give the necessary information But some parts

ofthe

essential techniques or know-howmaybekept inthe engineerswhohavebeen engaged themselves in the actual project.

New straits crossing projects after thecompletion

ofthe

Honshu-Shikoku Bridge project are fortunatelycontemplated inJapan. Althoughthe realisation

will

be in the nextCentury, the committees concerned arenowdiscussingthe schemes

of

theseprojects. Referring

to

Figl, the projects under investigation are listedin Table3. Super long Suspension bridges having centre span

of

more than 2,000m

will

beneededto realise theseprojects Marine conditions to build substructures and designrequirements

for

strong wind and earthquakes

will

be moresevere as comparedwith theHonshu-Shikokubridges. Cost saving is alsorequired fromtheviewpoint

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location shore to shore distance

(km)

max water depth

(m)

expected water depth

atpier

(m)

Tsugaru St 270 east 13 270 west 19 140

Tokyo

Bay 15 80 50 Ise Bay 20 100 53 Kitan St 11 120 70

Ho-yo

St 14 200 100

Table3

Future slraits

crossing

projects

in

Japan

Therefore,

further

innovations in design and construction

of

theseprojects shall be pursued Concerted studies are underway thatare aimed at imparting higher

reliability

to higher strength

steel

wire with

the

ultimate

goal

of

realising such super long Suspension bridges as

above-mentioned In

order

to clear up the aerodynamic issues, the use

of

auxiliary cable System, a

variety

of

damper Systems, open

grating floor

and so

forth

are also now investigated

5.

References

1 Bürden,

A

R

Modern

Japanese Suspension bridgedesign, Proc ICE, Part 1,

Vol

90, Feb 1991

2 Bürden,

A R

Japanesecable-stayed bridge design, Proc ICE, Part 1,

Vol

90, Oct 1991 3

Ito, M

Cable-stayed bridges in Japan, "Cable-Stayed Bndges-Recent Developments and

their

Future".

M

Ito

et al(ed Elsevier, 1991

4

Ito, M

Long span steel bridges in Japan, Rep

IABSE

Symposium, Leningrad, 1991.

5 Ito,

M

Design practices

of

Japanesecable-stayed bridges against wind and earthquake

effects, Proc

Intl

Conf

Cable-Stayed Bridges,

AIT,

November 1987

6

Ito, M, Supporting

devices

of

long span cabie-stayed bridge girder, Innovative Large Span

7 Structures,

Vol

l,

Canadian Soc

Civil

Engr,

1992

8 Ito,

M

Measures against wind-inducedvibrations

of

bridges, Proc Structures Congress '87, ASCE, August 1987

9 Ito,

M

and Endo,

T

The Tatara

Bridge-World's

longest cable-stayed span, Proc Structures Congress'94

Vol

1

ASCE

1994

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