Pedestrian Bridge, Japan. †

1.Field of application

Tpedestrian bridge across a prefectual road, Japan.

2.Circumstances of Repair

A Serious fracture that extended halfway through the circumference of a steel pipe column was discovered in a pedestrian bridge.

3.Types of structure

The center span of its superstructure is 10.5m and it is supported by two steel pipe columns. The diameter of steel pipes is 609.6mm, its plate thickness is 9.5mm and its height is 4.7m.br;

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Fig.1 Pedestrian bridge

4.Details of loading

Fluctuating loads due to wind load.

5.Description of damage

Fatigue cracks occurred in the joint of the vertical member and tie girder (Fig.2).The vertical members at the middle part of the bridge suffered the vibration due to wind of which speed was about 15 m/s. Cause of fatigue cracks is as follows. Vibration of the vertical members which was caused by Kerman's vortex.

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Fig.2 Crack which occurred in the joint of the vertical member and tie girder.

6.Repair method applied

Emergency repair

Fracture part were pulled back by wire rope. To prevent the vibration of the vertical members, each vertical member were connected to the adjacent members by making use of logs.

Permanent repair

The modification of connection detail was performed so that the stress transfers smoothly to the web plate of the tie girder (Fig.3). The ground areas were checked by dye penetration. It was verified that no the crack tips remained.

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Fig.3 Retrofit work.
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