The Third line of The Metropolitan Expressway †

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1.Field of application †

The third line of the metropolitan expressway, Tokyo.

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2.Circumstances of Repair †

Fatigue cracks were found in the sole plate welds at the girder support locations in 1986 after 15 years of service.

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3.Types of structure †

The outline of the bridge structure is as follows.

Plan and cross section were shown in figure 1. The interior of the box girders contains the diaphragms. Two pin supports are constructed per a box girder.


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Fig.1 Elevation plan and cross section.


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4.Details of loading †

Fluctuating loads due to vehicles live load.

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5.Description of damage †

Fatigue cracking were found in the sole plate front welds at the girder supports.

Most of the cracks initiated from the weld in front of the sole plate. Only a few cracks which initiated from the girder web-flange weld are observed. After penetrating through the girder bottom flange, the cracks which initiated from the welds in front of the sole plate had propagated at an angle in the girder web(Fig.2). At the time of discovery, Both the movable supports and the fixed bearings lost the function as supports and the subsidence of the shoe base was also observed.

Cause of fatigue cracks was as follows:

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6.Repair method applied †

As an emergency repair, temporary support bent was constructed for the cracks which propagated to the girder web.


As a permanent repair, strengthening was as follow (Fig.3,4).

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