*Steel bridge on roadway bridge(butt wellding of trough rib) [#s0475f78]
*国内の鋼橋（トラフリブの突合せ溶接） [#nb1c4940]

**1.Field of application [#u526442e]

>Steel bridge in Japan.&br;
>国内の鋼橋.&br;

**2.Circumstances of repair [#c864b047]

>The fatigue cracks were found at butt weldings of trough ribs. These cracks were found after 20 years service.
>トラフリブの突合せ溶接部に疲労き裂が見つかった。これらのき裂は供用開始から20年経過してから見つかった。

**3.Types of structure [#o37b2357]
>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 : 418.0m
-Span length :86.550m+3×87.000m+69.550m
-Structure : box girder bridge with orthotropic deck system
-thickness of deck plate : unknown

-橋長　：　418.0m
-支間長：86.550+87.000+69.550m
構造形式：鋼床版箱桁橋
デッキプレート厚：不明　

>Side view,plane view and cross section view of the bridge are shown in [[Fig.1>#fig1]]. 
>橋梁一般図を[[図.1>#fig1]]に示す. 
CENTER:&aname(fig1);&attachref(./butt_wellding_1.jpg,30%);&br;
CENTER:Fig.1 Side view,plane view and cross section viwe of the bridge &br;
CENTER:図.1 橋梁一般図 &br;

**4.Details of loading [#s943973c]
>Fluctuating loads due to vehicles live load. 
>活荷重

**5.Description of damage [#gabe4f96]
>The crack that was found at butt welding of trough rib is shown in ([[Fig.2>#fig2]]). Types of cracks are shown in ([[Fig.3>#fig3]]). 
>見つかった疲労き裂の写真を([[図.2>#fig2]])に示す. また鋼床版の疲労き裂タイプを([[図.3>#fig3]])に示す.

CENTER:&aname(fig2);&attachref(./butt_wellding_2.jpg,20%);&br;
CENTER:Fig.2 Photograph of crack &br;
CENTER:図.2 疲労き裂 &br;

CENTER:&aname(fig3);&attachref(./butt_wellding_3.jpg,50%);&br;
CENTER:Fig.3 Type of cracks &br;
CENTER:図.3 疲労き裂のタイプ &br;

>Causes of fatigue cracks were as follows:&br;
>疲労き裂の原因は次のとおりである。
-Increase of the traffic.
-Upsizing of the vehicle.

-交通量と車両重量の増加

**6.Repair method applied [#e1b093f2]
After removing by gouging, the slightly damaged part was repaired by rewelding([[Fig.4(b)>#fig4]]).
>After removing by gouging, the slightly damaged part was repaired by rewelding([[Fig.4(b)>#fig4]]).
In the case that the crack propagated to the fillet welding between deck plate and trough rib, the part of trough rib which was damaged was replaced to new trough rib([[Fig.4(a)>#fig4]]).
>損傷が軽微な場合は、疲労き裂をガウジングで除去し、再溶接により補修した([[図.4(b)>#fig4]]).き裂がトラフリブとデッキプレートの溶接部まで進展している場合には、損傷部を除去して新しいトラフリブを高力ボルトで取り付けた([[図.4(a)>#fig4]]).

CENTER:&aname(fig4);&attachref(./butt_wellding_4.jpg,40%);&br;
CENTER:Fig.4 Repair method &br;
CENTER:図.4 補修方法 &br;


**Reference [#r61e37c0]
>Casebook of repairs and reinforcements on road bridge(In Japanese)
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