Ikitsuki Bridge の変更点

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*Ikitsuki Bridge [#m976cbec]
*生月大橋　[#m976cbec]

**1.Field of application [#u891c745]

>Ikituki Br. in Nagasaki, Japan.&br;
>生月大橋（長崎県）.&br;

**2.Circumstances of Repair [#bd6ac31d]

>Fatigue crack was found at the panel point of the diagonal member in Dec.2009 after 19 years of service.
>供用開始から19年が経過した2009年、斜材のボルト継手近傍で疲労き裂が見つかった。

**3.Types of structure [#m6e7a5fd]

>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。
-Bridge length : 800.0 m
-Span length : 200.0 + 400.0 + 200.0 m
-Structure : Tree spans continuous througy-type truss bridge
-Structure : Tree spans continuous through-type truss bridge
-Structural steel : SS400,SM490Y,SM520,SM570

-橋長：800.0m
-支間長：200+400+200m
-橋梁形式：3径間連続下路トラス橋
-使用鋼材：SS400、SM490Y、SM520、SM570


>Photograph of Ikitsuki Br. is shown in [[Fig.1>#fig1]].
>[[図.1>#fig1]]に生月大橋の写真を示す。

CENTER:&aname(fig1);&attachref(./ikitsuki_1.jpg,30%);&br;
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CENTER:Fig.1 Ikitusuki Br.&br;
CENTER:図.1 生月大橋.&br;

**4.Details of loading [#tf497e6d]

>Fluctuating loads due to wind load.
>風荷重

**5.Description of damage [#ua572d2b]

>The fatigue crack was found by the visual inspection.The crack location and detail are shown in [[Fig.2>#fig2]],[[Fig.3>#fig3]].
&br;
>目視点検により疲労き裂が見つかった。き裂の位置と詳細をそれぞれ[[図.2>#fig2]]、[[図.3>#fig3]]に示す.
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CENTER:&aname(fig2);&attachref(./ikitsuki_2.jpg,30%);&br;
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CENTER:Fig.2 Crack location.
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CENTER:図.2 疲労き裂の位置
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CENTER:&aname(fig3);&attachref(./ikitsuki_3.jpg,30%);&br;
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CENTER:Fig.3 Crack detail.
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CENTER:図.3 き裂の詳細
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>Cause of fatigue cracks was as follows:&br;
>疲労き裂の原因は以下のとおりである:&br;
-Vibration of the diagonal member which was caused by wind.
-風による斜材の振動

**6.Repair method applied [#vace2b9b]
-Emergency repair

-応急的処置
>Firstly,stop-holes(φ=20mm)were drilled at the crack tips([[Fig.4>#fig4]]).
&br;
>最初に、[[Fig.4>#fig4]]に示すとおり、疲労き裂の先端部にストップホール（φ=20mm）を施工した。
&br;
CENTER:&aname(fig4);&attachref(./ikitsuki_4.jpg,30%);&br;
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CENTER:Fig.4 Stop hole.
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CENTER:図.4 ストップホール
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>Secondaty,bolted splice plates was installed on the web plat of the diagonal member([[Fig.5>#fig5]]).
&br;
>次に[[図.5>#fig5]]に示すとおり、斜材にWEBに当て板補強を行い高力ボルトで固定した。
&br;

CENTER:&aname(fig5);&attachref(./ikitsuki_5.jpg,30%);&br;
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CENTER:Fig.5 Bolted splice plates.
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CENTER:図.5 当て板補強
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>Finaly,steel bars were tightened to moderate stresses([[Fig.6>#fig6]]).
&br;
>最後に鋼棒に張力を導入した([[図.6>#fig6]]).
&br;

CENTER:&aname(fig6);&attachref(./ikitsuki_6.jpg,30%);&br;
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CENTER:Fig.6 Moderate stresses by tightened steel bar.
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CENTER:図.6 鋼棒への張力導入
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-Permanent repair

-恒久的処置
>The original diagonal member was replaced with new one in May 2010. ([[Fig.7>#fig7]]).
&br;
>2010年5月、損傷した斜材は新しいものに取り替えられた。
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CENTER:&aname(fig7);&attachref(./ikitsuki_7.jpg,30%);&br;
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CENTER:Fig.7 Completion view.
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CENTER:図.7 取替えが完了した状態
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**Reference [#jfcdb670]
>Kaneko Tetsuya,A study on the Retrofits of Ikitsuki Bridge,'''Kyushu Gihou''',vol.48,2011.01(In Japanese)
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