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Tokyo Gate Bridge in Tokyo, Japan.
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.
Fig.1 The circumstances of towing
The outline of the bridge structure is as follows.
- ridge length : 760.0m
- Span length : 160.0 + 440.0 + 160.0 m
- Structure : Tree spans continuous composite truss-box bridge
- Structural steel : SBHS
Photograph of Tokyo Gate Bridge is shown in Fig.2.
Fig.2 Tokyo Gate Bridge (Photograph by Wikipedia)
Repeated loads of waves while the large block was carried by a barge.
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.
Fig.3 The placement of the diaphragms in the box of the truss girder(In Japanese).
Fig.4 The buckling of the bottom lateral rib and diagonal members.(a) (b)Fig.5 The fatigue cracks which were found at R92.((a):The fatigue crack at the welded joint of bottom lateral rib and longitudinal rib.(b):The fatigue crack at the welded joint of bottom lateral rib and lower flange.)
The damaged block which was from J32 to J34 was replaced to new block.The damaged block was removed at Jan 9th 2011,and the new block was erected at Jan 23th 2011(Fig.6).
(a) (b)Fig.6 Replacement of the damaged block((a):Removal of the damaged block.(b):Erection of the new block.)
Chitoshi Miki:The damage of the truss girder that occurred during marine transportation,Journal of the Japan Society of Civil Engineers,vol.97,No.4.April.2012(In Japanese)
