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M Bridge in Tokyo, Japan.
The fatigue crack ,that length was 245mm, was found at the web panel of the end of the girder in the A2 support.
The outline of the bridge structure is as follows.
- Bridge length : 250.0 m
- Span length : 43.0m + 52.0m + 60.0m + 52.0m + 43.0m
- Structure : Five spans continuous box girder bridge with orthotropic deck system
- Structural steel : SM41
Elevation,plan and cross section of M bridge is shown in Fig.1.
Fluctuating loads due to vehicles live load.
The location and the detail of the crack are shown in Fig.2.Fig.3 shows the part which was surrounded in the lower flange,the end of diaphragm and the horizontal stiffener.This part corroded remarkably.The stagnant water was thought as the cause of the localized corrosion like this.As a result of having measured a residual thickness with a ultrasonic thickness gauge, it was revealed that the thinnest part was 1.8mm.
Fig.2 Location and detail of crack.Fig.3 Corrosion in the box girder.
Causes of the fatigue crack were thought as follows:
- Fatigue due to repeated high support reaction.
- Repeated out-of-plane deformation of the web plate at the welded joints of the web plate and the lower flange.
Bolted splice plates were installed(Fig.4,Fig.5).
Fig.4 Detail of the repair.Fig.5 Photograph of the repair((a):The part of support.(b):Outer surface of the girder.(c):Inner surface of the girder.)
Chitoshi Miki,Fatigue and destruction of bridge,2011.10(In Japanese)
