Steel bridge on Hanshin Expressway (at sole plate) †

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1.Field of application †

Steel bridge on Hanshin Expressway ,Kobe, Japan.

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2.Circumstances of Repair †

In box girder, fatigue cracks were found in welds of the sole plate in Aug. 1982 after 12 years of service.

In I-section girder, fatigue cracks were found in the welds of the sole plate in Aug. 1984 after 14 years of service.

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3.Types of structure †

The bridge is composite I-section girder bridge of which span length is 34.3m (Fig.1). There are two kinds of joints in the cross bracings as shown in figure 2. The lower lateral bracings were fillet weld connected to the gusset plates.


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Fig.1 Framing plan.


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Fig.2 Two kinds of lateral joints.


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4.Details of loading †

Fluctuating loads due to highway live load.

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5.Description of damage †

Fatigue cracks originated from the contact locations between the gusset plates and the vertical stiffeners (Fig.3,4). The occurrence of fatigue cracking was limited to type-2 structure of the lateral bracings.


Cause of fatigue cracks was thought as follows:

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6.Repair method applied †

In order to relieve high stress concentration, parts of the original gusset plates were removed and new gusset plates were bolt connected to the lower lateral bracings. Angles, which were installed under the gusset plates, were bolt connected to the lower lateral bracings (Fig.5). As a result, the structure of this repair became similar to type-1 detail of the lateral bracing which included no cracks (Fig.6).

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Fig.5 Replacement of the gusset plate and angle connection.


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Fig.9 Strengthening method.


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