Section D10
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*Section D10 [#hd6d01d7]
**1.Field of application [#hec2d4a8]
>Washington Metropolitan Transit Authority's metrorail near new Carrollton, Washington, D.C.
>The area is section D10.
**2.Circumstances of repair [#m8e72951]
>The Metro was built in the late 1970's. In Aug. 1984,fatigue cracking was found at the transverse connection plate ends at the diaphragm locations. Between 1984 and 1985, retrofits were produced. In Dec. 1987, re-initiation of fatigue cracking and new fatigue cracks were found. The strain measurements indicated that retrofit was required.
**3.Types of structure [#c1a7bb27]
>The structure is composed of multiple simple spans. Each span consists of two steel box girders which support a reinforced concrete deck ([[Fig.1>#fig1]],[[2>#fig2]]). Within each box girder, K-type diaphragms are weld connected to transverse connection plates which are fillet weld connected (with tapered ends) to the box girder webs ([[Fig.3>#fig3]]). The transverse connection plates are fitted to the tension and the compression flanges of the box girder. No positive attachment exists between the transverse connection plates and the box girder flanges (top or bottom). No positive attachment also exists between the K-type diaphragm and the box girder bottom flange. The structural steel is ASTM A588.
&br;
CENTER:&aname(fig1);&attachref(Sectio38.gif);&br;
&br;
CENTER:Fig.1 Plane and elevation view.&br;
&br;
CENTER:&aname(fig2);&attachref(Sectio29.gif);&br;
&br;
CENTER:Fig.2 Washington Metropolitan Transit , section D10.&br;
&br;
CENTER:&aname(fig3);&attachref(Sectio39.gif);&br;
&br;
CENTER:Fig.3 Internal view of box girder.&br;
&br;
**4.Details of loading [#wbab46b5]
>Fluctuating loads due to train (Metro-rail) live load.
**5.Description of damage [#p08e0b38]
>Fatigue cracking was found in the box girder bottom web gaps at the weld toe of the transverse connection plates ([[Fig.4>#fig4]])
>Causes of fatigue crack were as follows:
-Vertical movement of the bottom flange under train passage which resulted in the end rotation and out-of-plane distortion of the bottom web gaps ([[Fig.5>#fig5]]).
-Vibrations at a frequency of 20Hz related to the bottom flange movement.
CENTER:&aname(fig4);&attachref(Sectio30.gif);&br;
&br;
CENTER:Fig.4 Cracked weld toe of transverse connection plate with crack tip into box girder web.
&br;
CENTER:&aname(fig5);&attachref(Sectio31.gif);&br;
&br;
CENTER:Fig.5 Bottom web gap distortion.
&br;
**6.Repair method applied [#re485fea]
-Retrofit Between 1984 and 1985
--Retrofit holes were drilled at the crack tips as a temporary retrofit ([[Fig.6>#fig6]]).
--A trial retrofit was made between the bottom channel of a K-diaphragm and the box girder bottom flange ([[Fig.7>#fig7]]). The retrofit consisted of a positive attachment using a T-stub.
>The retrofit holes without the T-stub retrofits were not sufficient to arrest the crack growth. Therefore, re-initiation of fatigue cracking and new fatigue cracks were reported.
&br;
CENTER:&aname(fig6);&attachref(Sectio32.gif);&br;
&br;
CENTER:Fig.6 Retrofit holes and crack profile viewed from the box girder outside web face.
&br;
CENTER:&aname(fig7);&attachref(Sectio33.gif);&br;
&br;
CENTER:Fig.7 1984 trial retrofit using a T-stub.
&br;
-1988 retrofit
--The final retrofit was positive attachment between the bottom channel of the K-diaphragm and the box girder bottom flange. The retrofit consisted of a T-stub with friction joints. Therefore, the installed retrofit contained four 22mm A325 bolts between the T-stub web and the channel and two bolts between the T-stub flange and the box girder flange ([[Fig.8>#fig8]]).
--The drilling of retrofit 19mm holes at all of the crack tips was recommended in addition to the T-stub retrofit to arrest the fatigue crack growth. Because it was indicated that the stress gradients in the bottom web gaps were reduced up to 75 percent as composed to the 1984 gradients. At locations of the crack re-initiation, additional angles were installed ([[Fig.9>#fig9]]).
&br;
CENTER:&aname(fig8);&attachref(Sectio34.gif);&br;
&br;
CENTER:Fig.8 1988 retrofit T-stub.
&br;
CENTER:&aname(fig9);&attachref(Sectio35.gif);&br;
&br;
CENTER:Fig.9 Angle installed near web gap with fatigue cracks reinitiating from retrofit holes.
&br;
&br;
終了行:
*Section D10 [#hd6d01d7]
**1.Field of application [#hec2d4a8]
>Washington Metropolitan Transit Authority's metrorail near new Carrollton, Washington, D.C.
>The area is section D10.
**2.Circumstances of repair [#m8e72951]
>The Metro was built in the late 1970's. In Aug. 1984,fatigue cracking was found at the transverse connection plate ends at the diaphragm locations. Between 1984 and 1985, retrofits were produced. In Dec. 1987, re-initiation of fatigue cracking and new fatigue cracks were found. The strain measurements indicated that retrofit was required.
**3.Types of structure [#c1a7bb27]
>The structure is composed of multiple simple spans. Each span consists of two steel box girders which support a reinforced concrete deck ([[Fig.1>#fig1]],[[2>#fig2]]). Within each box girder, K-type diaphragms are weld connected to transverse connection plates which are fillet weld connected (with tapered ends) to the box girder webs ([[Fig.3>#fig3]]). The transverse connection plates are fitted to the tension and the compression flanges of the box girder. No positive attachment exists between the transverse connection plates and the box girder flanges (top or bottom). No positive attachment also exists between the K-type diaphragm and the box girder bottom flange. The structural steel is ASTM A588.
&br;
CENTER:&aname(fig1);&attachref(Sectio38.gif);&br;
&br;
CENTER:Fig.1 Plane and elevation view.&br;
&br;
CENTER:&aname(fig2);&attachref(Sectio29.gif);&br;
&br;
CENTER:Fig.2 Washington Metropolitan Transit , section D10.&br;
&br;
CENTER:&aname(fig3);&attachref(Sectio39.gif);&br;
&br;
CENTER:Fig.3 Internal view of box girder.&br;
&br;
**4.Details of loading [#wbab46b5]
>Fluctuating loads due to train (Metro-rail) live load.
**5.Description of damage [#p08e0b38]
>Fatigue cracking was found in the box girder bottom web gaps at the weld toe of the transverse connection plates ([[Fig.4>#fig4]])
>Causes of fatigue crack were as follows:
-Vertical movement of the bottom flange under train passage which resulted in the end rotation and out-of-plane distortion of the bottom web gaps ([[Fig.5>#fig5]]).
-Vibrations at a frequency of 20Hz related to the bottom flange movement.
CENTER:&aname(fig4);&attachref(Sectio30.gif);&br;
&br;
CENTER:Fig.4 Cracked weld toe of transverse connection plate with crack tip into box girder web.
&br;
CENTER:&aname(fig5);&attachref(Sectio31.gif);&br;
&br;
CENTER:Fig.5 Bottom web gap distortion.
&br;
**6.Repair method applied [#re485fea]
-Retrofit Between 1984 and 1985
--Retrofit holes were drilled at the crack tips as a temporary retrofit ([[Fig.6>#fig6]]).
--A trial retrofit was made between the bottom channel of a K-diaphragm and the box girder bottom flange ([[Fig.7>#fig7]]). The retrofit consisted of a positive attachment using a T-stub.
>The retrofit holes without the T-stub retrofits were not sufficient to arrest the crack growth. Therefore, re-initiation of fatigue cracking and new fatigue cracks were reported.
&br;
CENTER:&aname(fig6);&attachref(Sectio32.gif);&br;
&br;
CENTER:Fig.6 Retrofit holes and crack profile viewed from the box girder outside web face.
&br;
CENTER:&aname(fig7);&attachref(Sectio33.gif);&br;
&br;
CENTER:Fig.7 1984 trial retrofit using a T-stub.
&br;
-1988 retrofit
--The final retrofit was positive attachment between the bottom channel of the K-diaphragm and the box girder bottom flange. The retrofit consisted of a T-stub with friction joints. Therefore, the installed retrofit contained four 22mm A325 bolts between the T-stub web and the channel and two bolts between the T-stub flange and the box girder flange ([[Fig.8>#fig8]]).
--The drilling of retrofit 19mm holes at all of the crack tips was recommended in addition to the T-stub retrofit to arrest the fatigue crack growth. Because it was indicated that the stress gradients in the bottom web gaps were reduced up to 75 percent as composed to the 1984 gradients. At locations of the crack re-initiation, additional angles were installed ([[Fig.9>#fig9]]).
&br;
CENTER:&aname(fig8);&attachref(Sectio34.gif);&br;
&br;
CENTER:Fig.8 1988 retrofit T-stub.
&br;
CENTER:&aname(fig9);&attachref(Sectio35.gif);&br;
&br;
CENTER:Fig.9 Angle installed near web gap with fatigue cracks reinitiating from retrofit holes.
&br;
&br;
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