Section L-2C
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開始行:
*Section L-2C [#n4672e7c]
**1.Field of application [#cb022eba]
>Washington Metropolitan Authority's metrorail near new Carrollton, Washington, D.C.
>The area is section L-2c.
**2.Circumstances of repair [#y20e2529]
>The structure was built in the late 1970's. Fatigue cracking was found in the back-up bar welds in 1987. A site inspection indicated that retrofit was required.
**3.Types of structure [#m4b5fbb4]
>The structure is composed of multiple simple spans. Each span consists of a steel box girder supporting a reinforced concrete deck. The plan and elevation views are shown in [[figure 1>#fig1]]. Within the box girder, X-type diaphragms are bolt connected to transverse connection plates which are fillet weld connected to the box girder webs and to the tension and compression flanges. The web-flange welds of the box girder are full penetration groove welds with a back-up bar ([[Fig.2>#fig2]]). The back-up bar is continuous and the butt splice of the back-up bar is a groove weld ([[Fig.2>#fig2]]).
>The structural steel is ASTM A588.
&br;
CENTER:&aname(fig1);&attachref(Sectio40.gif);&br;
&br;
CENTER:Fig.1 Plan and elevation views.
&br;
CENTER:&aname(fig2);&attachref(Sectio41.gif);&br;
&br;
CENTER:Fig.2 Schematic of the groove-weld butt-splice connection and the web-flange groove weld.
&br;
**4.Details of loading [#ae259d81]
>Fluctuating loads due to train (Metrorail) live load.
**5.Description of damage [#ca65640a]
>Fatigue cracking was found in the groove-weld butt-splice connections of the back-up bars.
>Cracking occurred adjacent to the tension and compression flange. The crack had propagated into the box girder web-flange groove weld.
>Cause of fatigue crack was as follows:
-Lack of fusion in the groove-weld butt-splice connections of the back-up bars.
**6.Repair method applied [#u225a865]
>The retrofit was to remove all of the groove-weld butt-splice connections adjacent to the tension flange. The procedure was to use a hole saw and to remove a 38mm hole encompassing the groove-weld butt-splice connection and the crack tip. The crack tips which remained in the web-flange welds were to be ground out.
>The fatigue cracking adjacent to the compression flange was not critical and did not require retrofit.
&br;
&br;
終了行:
*Section L-2C [#n4672e7c]
**1.Field of application [#cb022eba]
>Washington Metropolitan Authority's metrorail near new Carrollton, Washington, D.C.
>The area is section L-2c.
**2.Circumstances of repair [#y20e2529]
>The structure was built in the late 1970's. Fatigue cracking was found in the back-up bar welds in 1987. A site inspection indicated that retrofit was required.
**3.Types of structure [#m4b5fbb4]
>The structure is composed of multiple simple spans. Each span consists of a steel box girder supporting a reinforced concrete deck. The plan and elevation views are shown in [[figure 1>#fig1]]. Within the box girder, X-type diaphragms are bolt connected to transverse connection plates which are fillet weld connected to the box girder webs and to the tension and compression flanges. The web-flange welds of the box girder are full penetration groove welds with a back-up bar ([[Fig.2>#fig2]]). The back-up bar is continuous and the butt splice of the back-up bar is a groove weld ([[Fig.2>#fig2]]).
>The structural steel is ASTM A588.
&br;
CENTER:&aname(fig1);&attachref(Sectio40.gif);&br;
&br;
CENTER:Fig.1 Plan and elevation views.
&br;
CENTER:&aname(fig2);&attachref(Sectio41.gif);&br;
&br;
CENTER:Fig.2 Schematic of the groove-weld butt-splice connection and the web-flange groove weld.
&br;
**4.Details of loading [#ae259d81]
>Fluctuating loads due to train (Metrorail) live load.
**5.Description of damage [#ca65640a]
>Fatigue cracking was found in the groove-weld butt-splice connections of the back-up bars.
>Cracking occurred adjacent to the tension and compression flange. The crack had propagated into the box girder web-flange groove weld.
>Cause of fatigue crack was as follows:
-Lack of fusion in the groove-weld butt-splice connections of the back-up bars.
**6.Repair method applied [#u225a865]
>The retrofit was to remove all of the groove-weld butt-splice connections adjacent to the tension flange. The procedure was to use a hole saw and to remove a 38mm hole encompassing the groove-weld butt-splice connection and the crack tip. The crack tips which remained in the web-flange welds were to be ground out.
>The fatigue cracking adjacent to the compression flange was not critical and did not require retrofit.
&br;
&br;
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