Lafayette Street Br.
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開始行:
*Lafayette Street Br. [#l42366aa]
**1.Field of application [#j702dd68]
>Lafayette Street Bridge over Mississippi River located in St. Paul , Minnesota.
**2.Circumstances of repair [#ye2247cb]
>This bridge was opened in Nov. 1968. In May 1975, fatigue cracking was found in the girder web.
**3.Types of structure [#n977ffd5]
>The structure is continuous for three spans consisting of two longitudinal main girders ([[Fig.1>#fig1]]). The floorbeam frames into two main girders and the transverse cross bracings exist between the girders as shown in cross section of [[figure 1>#fig1]]. Two stringers with the wide-flanges are supported by the transverse floorbeam. The structural steel of the girder flanges and webs was ASTM A441.
&br;
CENTER:&aname(fig1);&attachref(Lafaye87.gif);&br;
&br;
CENTER:Fig.1 Elevation view and cross section.&br;
**4.Details of loading [#ie997659]
>Fluctuating loads due to vehicles live load.
&br;
**5.Description of damage [#t1dbed76]
>Fatigue crack initiated from the weld intersection which connected the web gusset plate to the vertical stiffener ([[Fig.2>#fig2]]).
&br;
>Cause of fatigue crack was as follows:
-The lack of fusion which had included in the one-side ?-type groove weld that connected the web gusset plate to the vertical stiffener.&br;
&br;
CENTER:&aname(fig2);&attachref(Lafaye88.gif);&br;
&br;
CENTER:Fig.2 Crack initiated from the girder web gusset plate weld.
&br;
**6.Repair method applied [#rfc5e1c0]
>At the time of discovery, the crack had propagated part way up the web and the bottom flange had completely fractured ([[Fig.2>#fig2]]). The repair of parts subjected to cracking was the bolted splice.
-For the other bridges which had suffered the same cracking.
>Strengthening was carried out for the other bridges in which the same damages were observed in the weld intersection connected the web gusset plate to the vertical stiffener.
>Two 32mm diameter vertical holes were drilled through the gusset plate at the intersection of girder web, vertical stiffener, and gusset plate ([[Fig.3>#fig3]],[[4>#fig4]]). The hole edges were ground smooth.
Two vertical holes which are smaller than those holes were drilled through the gusset plate at the intersection of the gusset plate and the vertical stiffener. The exposed toes of the groove weld, which connected the gusset plate to the vertical stiffener, was ground smooth.
>At the locations where the crack propagated in the girder web, Two 32mm diameter holes were drilled at the angle from the web opposite faces through the girder web thickness ([[Fig.5>#fig5]]).
&br;
CENTER:&aname(fig3);&attachref(Lafaye89.gif);&br;
&br;
CENTER:Fig.3 The retrofit procedures.
&br;
&br;
CENTER:&aname(fig4);&attachref(Lafaye90.gif);&br;
&br;
CENTER:Fig.4 Retrofit hole at the gusset plate.
&br;
&br;
CENTER:&aname(fig5);&attachref(Lafaye91.gif);&br;
&br;
CENTER:Fig.5 Retrofit hole through the girder web.
&br;
&br;
終了行:
*Lafayette Street Br. [#l42366aa]
**1.Field of application [#j702dd68]
>Lafayette Street Bridge over Mississippi River located in St. Paul , Minnesota.
**2.Circumstances of repair [#ye2247cb]
>This bridge was opened in Nov. 1968. In May 1975, fatigue cracking was found in the girder web.
**3.Types of structure [#n977ffd5]
>The structure is continuous for three spans consisting of two longitudinal main girders ([[Fig.1>#fig1]]). The floorbeam frames into two main girders and the transverse cross bracings exist between the girders as shown in cross section of [[figure 1>#fig1]]. Two stringers with the wide-flanges are supported by the transverse floorbeam. The structural steel of the girder flanges and webs was ASTM A441.
&br;
CENTER:&aname(fig1);&attachref(Lafaye87.gif);&br;
&br;
CENTER:Fig.1 Elevation view and cross section.&br;
**4.Details of loading [#ie997659]
>Fluctuating loads due to vehicles live load.
&br;
**5.Description of damage [#t1dbed76]
>Fatigue crack initiated from the weld intersection which connected the web gusset plate to the vertical stiffener ([[Fig.2>#fig2]]).
&br;
>Cause of fatigue crack was as follows:
-The lack of fusion which had included in the one-side ?-type groove weld that connected the web gusset plate to the vertical stiffener.&br;
&br;
CENTER:&aname(fig2);&attachref(Lafaye88.gif);&br;
&br;
CENTER:Fig.2 Crack initiated from the girder web gusset plate weld.
&br;
**6.Repair method applied [#rfc5e1c0]
>At the time of discovery, the crack had propagated part way up the web and the bottom flange had completely fractured ([[Fig.2>#fig2]]). The repair of parts subjected to cracking was the bolted splice.
-For the other bridges which had suffered the same cracking.
>Strengthening was carried out for the other bridges in which the same damages were observed in the weld intersection connected the web gusset plate to the vertical stiffener.
>Two 32mm diameter vertical holes were drilled through the gusset plate at the intersection of girder web, vertical stiffener, and gusset plate ([[Fig.3>#fig3]],[[4>#fig4]]). The hole edges were ground smooth.
Two vertical holes which are smaller than those holes were drilled through the gusset plate at the intersection of the gusset plate and the vertical stiffener. The exposed toes of the groove weld, which connected the gusset plate to the vertical stiffener, was ground smooth.
>At the locations where the crack propagated in the girder web, Two 32mm diameter holes were drilled at the angle from the web opposite faces through the girder web thickness ([[Fig.5>#fig5]]).
&br;
CENTER:&aname(fig3);&attachref(Lafaye89.gif);&br;
&br;
CENTER:Fig.3 The retrofit procedures.
&br;
&br;
CENTER:&aname(fig4);&attachref(Lafaye90.gif);&br;
&br;
CENTER:Fig.4 Retrofit hole at the gusset plate.
&br;
&br;
CENTER:&aname(fig5);&attachref(Lafaye91.gif);&br;
&br;
CENTER:Fig.5 Retrofit hole through the girder web.
&br;
&br;
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