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*The Third line of The Metropolitan Expressway(Part 2) [#a709481a]

*首都高速道路3号線（Part2）[#a709481a]
**1.Field of application [#ne906a3c]

>The third line of the metropolitan expressway, Tokyo.&br;
>首都高速道路3号線.&br;

**2.Circumstances of Repair [#zdd1d09f]

>Fatigue cracks were found in the welded joints which joined the gusset plates of lateral bracings to the web panels of the main girders in 2000 after 28 years of service.
>供用開始から28年が経過した2000年、下横構のガセットとWEBをつなぐ溶接部に疲労き裂が見つかった。

**3.Types of structure [#t01e5b85]
>The outline of the bridge structure is as follows.
>橋梁の構造諸元は次のとおりである。
-Span length : 28.9m
-Structure : Simple composite I-beam girder bridge
-Structural steel : unknown
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-支間長：28.9m
-橋梁形式：単純合成鈑桁橋
-使用鋼材：不明
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**4.Details of loading [#v40db87c]
>Fluctuating loads due to expressway live load.
>活荷重

**5.Description of damage [#b2ae20a6]
>The one of the fatigue cracks is shown in [[Fig.1>#fig1]].[[Fig.2>#fig2]] shows classification of the crack position that occurred in the weld of gusset.These cracks were found from 2000 to 2004.The result in [[Fig.2>#fig2]] indicates that the most cracks is tpye2.
>[[図.1>#fig1]]に疲労き裂のひとつを示す。[[図.2>#fig2]]にガセット周辺に発生した疲労き裂の位置による区分を示す。これらの疲労き裂は2000年から2004年にかけて発見されたものである。[[図.2>#fig2]]から、TYPE-2のき裂が多いことがわかる。
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CENTER:&aname(fig1);&attachref(./lateral_gusset_1.jpg,20%);&br;
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CENTER:Fig.1 Photograph of the crack.
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CENTER:図.1 疲労き裂の写真
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CENTER:&aname(fig2);&attachref(./lateral_gusset_2.jpg,20%);&br;
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CENTER:
|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:Type of crack|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:TYPE1|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:TYPE2|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:TYPE3|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:TYPE4|
|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:Number of crack|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:30|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:54|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:14|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:1|
CENTER:Fig.2 Classification of the crack position that occurred in the weld of gusset. 
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CENTER:図.2 ガセット周辺の疲労き裂の発生位置による区分 
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//>Causes of fatigue cracks were as follows:
>As a result of stress measurement and FEM analysis , the causes of the type1 and type2 to show as follows were estimated.The cause of type1 was the stress concentration in the edge of the gusset which occurred by local bending of the web plates of the main girder.The cause of type2 was the local deformation in the vicinity of the scallop which occurred by axial force of the lateral bracing.
>応力測定とFEM解析の結果から、TYPE-1のき裂の原因は主桁WEBの局部曲げによってガセット端部に発生した応力集中である。TYPE-2の疲労き裂については、下横構の軸力によりスカラップ周辺に生じる局部変形である。

**6.Repair method applied [#gde74152]
>The repair detail is shown [[Fig.3>#fig3]]
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>[[図.3>#fig3]]に補修の詳細を示す。
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CENTER:&aname(fig3);&attachref(./lateral_gusset_3.jpg,40%);&br;
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CENTER:Fig.3 Repaif detail.
CENTER:図.3 補修の詳細

**Reference [#e654779c]
>Chitoshi Miki,Fatigue and destruction of bridge,2011.10(In Japanese)
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