*Steel plate floor of The Metropolitan Expressway [#bcab6f2e]
**1.Field of application [#w10a177d]
>Cable stayed bridge with steel plate floor of The Metropolitan Expressway Bridge, Tokyo.&br;
**2.Circumstances of Repair [#g405fb91]
>Fatigue cracks were found in various connections of the beam bridge members with steel plate floor in 1985 after 14 years of service.&br;
**3.Types of structure [#fb3ee7ff]
>The outline of the bridge structure is as follows.
-Bridge length : 280.8 m
-Span length : 60.3 + 160.0 + 60.3 m
-Structure : Tree spans continuous cable stayed bridge with steel plate floor.
-Deck : Steel plate floor with Y-type ribs (12mm thickness)
-Structural steel : Steel correspond to 40 kgf/mm2 (about 400MPa) steel. Steel correspond to 50 kgf/mm2 (about 500MPa) steel.
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>Elevation and plan views are shown in [[figure 1>#fig1]]. The bridge is composed of the box-girder in the center of the cross section and the I-beam girders on both sides of the box-girder as shown in [[figure 1>#fig1]]. The longitudinal ribs on the steel plate floor are Y-type ribs. The structure with Y-type ribs were few used.
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CENTER:&aname(fig1);&attachref(Steelp32.jpg);&br;
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CENTER:Fig.1 Elevation and plan views.&br;
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**4.Details of loading [#uff93c55]
>Fluctuating loads due to highway live load.
**5.Description of damage [#f45d026b]
>The location and the number of fatigue cracks which were found as a result of the inspection are shown in [[table 1>#table1]]. The cracks were observed at the connections of the members as shown in [[figure 2>#fig2]].
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CENTER:Table.1 Number of cracks and ratio of the occurrence.&br;
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|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:Member|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER: Total location|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER: crack location|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER: Ratio|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: At the weld between the deck plate and vertical stiffener.|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 144|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 143|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 99%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: At the weld between the floorbeam bottom flange and stiffener.|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 76|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 34|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 45%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: At the intersection of the longitudinal rib and transverse rib.|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 3160|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 256|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 8%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: At the boxing of the floorbeam web stiffener.|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 32|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 25|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 78%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: At the manual weld of transverse rib.|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 292|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 2|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 1%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: the gusset at the cross bracing location.|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 152|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 24|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 16%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: the gusset at the diagonal member ( I-girder side)|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 38|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 20|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 53%|
|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: the gusset at the diagonal member (box-girder side)|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 38|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 6|BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 16%|
|BGCOLOR(#FFFFFF):COLOR(#000000):CENTER:Total|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: |BGCOLOR(#FFFFFF):COLOR(#000000):RIGHT: 510|BGCOLOR(#FFFFFF):COLOR(#000000):LEFT: |
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>These cracks showed the characteristic as follows ([[Fig.2>#fig2]]).
>1. The cracks of type A were only observed in the I-beam sections([[Fig.3>#fig3]]). No the cracks of type A occurred in the welds of the vertical stiffener ends, which were connected to the steel plate deck, in the inside webs of the box-girder.
>2. The difference of the tendency in the crack occurrence were not observed in both ways.
>3. Fatigue cracking did not show a tendency in the axial direction of the bridge. The crack at the weld of the vertical stiffener top end.
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>Type A of the cracks were classified in three patterns ([[Fig.4>#fig4]]). However most cracks were crack-1 that originated from the boxing toe at the vertical stiffener side. Some of them propagated into the steel plate deck ([[Fig.4:crack-1'>#fig4]]).
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>Cause of fatigue cracks was thought as follows:
-Localized stress concentration which resulted from the restraint of the deck plate deflection due to the wheel load.
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CENTER:&aname(fig2);&attachref(Steelp33.jpg);&br;
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CENTER:Fig.2 Crack location.&br;
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CENTER:&aname(fig3);&attachref(Steelp34.jpg);&br;
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CENTER:Fig.3 Crack at the weld between the stiffener and deck plate.&br;
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CENTER:&aname(fig4);&attachref(Steelp35.jpg);&br;
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CENTER:Fig.4 Crack location at the weld.&br;
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**6.Repair method applied [#j6b89815]
-The crack at the vertical stiffener top end (type A).
>After frame cutting the vertical stiffener upper parts, the fillet weld terminations exposed by frame cutting (Fig.5:A point) were welded as repair. The finishing of the weld toe was performed by TIG dressing.
>In case of having propagated into the deck plate, 22mm diameter stop holes were drilled at the crack tips. T-type plates were weld connected to the deck plate ([[Fig.5>#fig5]]).
-The cracks from type B to type G.
>Repair was performed by TIG dressing and R process to the locations where the stress concentrated.
-The cracks near the gusset plate.
>The original cross bracings were strengthened to the double warren structure due to the addition of the members.
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>Follow-up inspection have been executed because of confirming the effect of the repair and the strengthening. Periodic inspection will be continued too.
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CENTER:&aname(fig5);&attachref(Steelp36.jpg);&br;
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CENTER:Fig.5 Repair procedure.&br;
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