Steel bridge on Hanshin Expressway (at gusset end) †

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1.Field of application †

Steel bridge on Hanshin Expressway ,Japan.

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2.Circumstances of Repair †

Fatigue cracks were found in the gusset plate at the lower lateral bracing locations.

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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 Cross section.


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Fig.2 Cantilever bracket which supports a sign pole.


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Fig.3 Cantilever bracket which are connected to the box girder web.


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4.Details of loading †

Fluctuating loads due to highway live load.

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5.Description of damage †

Fatigue crack was found in the interior vertical stiffener end and at the bracket connection with the box girder web (Fig.4). The crack originated from the interior vertical stiffener end and was branched in three directions (Fig.5,6). The interior vertical stiffeners were not fillet weld connected to the box girder tension flanges.


Cause of fatigue cracks was thought as follows:



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Fig.4 Crack location.


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Fig.5 Crack of the vertical stiffener end.


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Fig.6 Girder exterior view of the crack.


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6.Repair method applied †

Repair was performed as follows.

The box girder web of parts subjected to cracking was removed (Fig.7) and the plates were bolt connected from both sides of the box girder web (Fig.8,9). The interior of the box girder was reinforced as shown in figure 10.

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Fig.7 Removal of the box girder web.


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Fig.8 Strengthening of the bracket location.


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Fig.9 Bolt splice.


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Fig.10 Interior view of the internal strengthening.


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