Steel bridge on Hanshin Expressway (at corner plate weld) のバックアップ(No.1)

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  • 1 (2013-08-03 (土) 12:18:57)

Steel bridge on Hanshin Expressway (at corner plate weld) †

1.Field of application †

Steel bridge on Hanshin Expressway ,Kobe, Japan.

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.

3.Types of structure †

Simple I-section girder bridge is composite with the deck. The framing plan and cross section are shown in figure 1,2. Box girder bridge, which is located on the other location of the Hanshin Expressway line, is continuous of three spans. In both girders, sole plates were fillet weld connected to the girder bottom flanges at the support locations.

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Fig.1 Framing plan.

File not found: "Hanko517.jpg" at page "Steel bridge on Hanshin Expressway (at corner plate weld)"[ź��]

Fig.2 Cross section.

4.Details of loading †

Fluctuating loads due to highway live load.

5.Description of damage †

Fatigue cracks initiated from the fillet weld toes of the sole plates under the girder webs. The cracks propagated along the fillet weld toes of the sole plates. After penetrating through the girder bottom flanges, some of the cracks propagated into the girder webs (Fig.3,4:I-section girder, Fig.5:Box girder). No the occurrence of the cracks depended on types of the supports, movable support or fixed bearing. The longest crack reached about 200mm length.

Causes of fatigue cracks were as follows:

• Stress concentration due to the subsidence of the support and the lost of the support function.
• Stress concentration due to sudden change of the girder section at the support location.
  
  
  File not found: "Hanko518.gif" at page "Steel bridge on Hanshin Expressway (at corner plate weld)"[ź��]
  
  
  (I-section girder)　　　　　　　　　　　(Box section girder)
  
  Fig.3 Crack location.
  
  
  
  File not found: "Hanko519.jpg" at page "Steel bridge on Hanshin Expressway (at corner plate weld)"[ź��]
  
  
  (Girder outside flange)　　　　　　　　　　　(Girder inside flange)
  
  Fig.4 Crack which propagated into the girder web and flange ( In case of I section girder ).
  
  
  File not found: "Hanko520.jpg" at page "Steel bridge on Hanshin Expressway (at corner plate weld)"[ź��]
  
  
  Fig.5 Crack which propagated into the girder web and flange ( In case of Box section girder ).
  
  
  

6.Repair method applied †

• In case of I-section girder.

Because it was difficult to replace the sole plate, repair was performed by gouging, groove welding and plate welding.

Retrofit procedure is as follows.

1.16mm diameter stop hole were drilled at the crack tip.

2.After jacking up the girder, a scallop was constructed in the girder web.

3.After gouging the crack and groove welding (Fig.6), the new plates were weld connected on the girder flange and were bolt spliced at the scallop area which corresponded to the stop hole location of the girder web (Fig.7,8).

• In case of box girder.

The original sole plate was replaced with a new one by bolting (Fig.9,10).

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