Tokyo Gate Bridge †

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1.Field of application †

Tokyo Gate Bridge in Tokyo, Japan.

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2.Circumstances of Repair †

The large block of the bridge(Length=113.3m,weight=2500t) was assembled at the fabricator of the order receiver.Then the large block was carried by a barge.Finaly the large block was erected by large block erection method.The transport by sea was carried out from Sakae in Osaka to Ichihara in Chiba from May 11th to May 13th 2010.The circumstances of towing is shown in Fig.1.The projecting length of the block from the barge was 22.5m,and the cantilever length from the support point of the block to top of it was 38.5m.

Tokyo_Gate_Bridge_4.jpg
Fig.1 The circumstances of towing
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3.Types of structure †

The outline of the bridge structure is as follows.

Photograph of Tokyo Gate Bridge is shown in Fig.2.

Tokyo_Gate_Bridge_1.jpg
Fig.2 Tokyo Gate Bridge (Photograph by Wikipedia)
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4.Details of loading †

Repeated loads of waves while the large block was carried by a barge.

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5.Description of damage †

The deformed parts were found by inspection when the barge arrived in Ichihara on May 13th at 15:00.Then the visual inspection was carried out over 7:00 on the next morning from 16:00 of the day.Fig.3 shows the placement of the diaphragms in the box of the truss girder.The damages due to buckling and the peeling of coating were found in the diagonal members and the bottom lateral ribs at R92,R93 and R94(Fig.4).Under the assumption that detailed investigation and examining repair method were carried out after the large block was erected,it was erected on schedule at May 16th 2010. The visual inspection was carried out for all of the large bolck from May 24th 2010.The most important failures which were found by the inspection were some fatigue cracks.The fatigue cracks which were found at R92 and R93 were found in the welded joints of bottom lateral rib and lower flange and the welded joints of bottom lateral rib and longitudinal rib(Fig.5).The fatigue cracks were generated from the both sides of toes of the boxing welded joints of the tips of the members.The fatigue cracks developed and coalesced into the penetrating cracks.The fracture surfaces of the fatigue cracks were flat,but they showed the aspect that a dimple was crushed.Therefore,those cracks were regarded as a fatigue crack by the repetition of high stress.

Tokyo_Gate_Bridge_5.jpg

Fig.3 The placement of the diaphragms in the box of the truss girder(In Japanese).

File not found: "ikitsuki_3.jpg" at page "Tokyo Gate Bridge"[ź]

Fig.3 Crack detail.

Cause of fatigue cracks was as follows:

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6.Repair method applied †

Firstly,stop-holes(φ=20mm)were drilled at the crack tips(Fig.4).

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Fig.4 Stop hole.

Secondaty,bolted splice plates was installed on the web plat of the diagonal member(Fig.5).

File not found: "ikitsuki_5.jpg" at page "Tokyo Gate Bridge"[ź]

Fig.5 Bolted splice plates.

Finaly,steel bars were tightened to moderate stresses(Fig.6).

File not found: "ikitsuki_6.jpg" at page "Tokyo Gate Bridge"[ź]

Fig.6 Moderate stresses by tightened steel bar.

The original diagonal member was replaced with new one in May 2010. (Fig.7).

File not found: "ikitsuki_7.jpg" at page "Tokyo Gate Bridge"[ź]

Fig.7 Completion view.

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Reference †

Kaneko Tetsuya,A study on the Retrofits of Ikitsuki Bridge,Kyushu Gihou,vol.48,2011.01(In Japanese)

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