Steel bridge on Hanshin Expressway (at cantilever bracket) †

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1.Field of application †

Steel bridge on Osaka-Kobe line of Hanshin Expressway, Japan.

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2.Circumstances of Repair †

Fatigue cracks were found in the flange-web welds of the cantilever brackets, which were used as a support of the sign poles, in Jul. 1984. The cracks was thought that had occurred after one to one and half years of service, because the cracked regions had exhibited significant corrosion.

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3.Types of structure †

The cross section is shown in figure 1. The base plates of the sign poles were directly bolt connected to the bracket flanges (Fig.2) and no bed plates existed on the bracket. The thickness of the bracket flange plates was 9mm.


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Fig.1 Cross section.


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Fig.2 Detail of the connection between the sign pole and the bracket.


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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 occurred in the flange-web fillet welds of the cantilever brackets, which supported the sign poles (Fig.3,4). The cracks propagated along the bracket flange-web welds and reached the diaphragm locations. Some of them propagated into the bracket top flanges (Fig.5).


Cause of fatigue cracks was as follows:

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6.Repair method applied †

The original brackets were replaced with the new brackets of which the top flanges were full penetration groove weld connected with the webs (Fig.6). The new brackets had the bed plates, which were of 19mm thickness, on the flanges themselves (Fig.7). Also for the uncracked brackets, similar bed plates were inserted between the base plates of the sign poles and the bracket top flange plates.


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Fig.6 Detail of the bracket flange-web connection.


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Fig.7 Completion view.


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