2682 Br. in I-79
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*2682 Br. in I-79 [#web91f68]
**1.Field of application [#yee61c60]
>The 2682 bridges in I-79 cross Big Sandy Creek 48km north of Charleston, West Virginia.
**2.Circumstances of repair [#q2d5a776]
-Fatigue cracks were found in the girder bottom web gap in May 1984 after 12 years of service.
-Fatigue cracks were found in the structure at the other locations in August 1984.
>Therefore, all the cracking locations required retrofit.
**3.Types of structure [#r6153526]
>A typical portion of the framing plan and the longitudinal girder elevation are shown in [[Fig.1>#fig1]]. The structure is comprised of two longitudinal girders, hunched at the piers, and four longitudinal stringers which are supported by transverse floorbeams. The floorbeam webs are bolt connected to the transverse connection plates which are fillet weld connected to the girder webs. The transverse connection plates and intermediate web stiffeners are fitted to the girder compression flange and cut short of the girder tension flange. Lateral cross bracing exists between the girder([[Fig.2>#fig2]]). The structural steel is ASTM A36 steel.
&br;
CENTER:&aname(fig1);&attachref(i79_2_27.gif);&br;
&br;
CENTER:Fig.1 Girder elevation and framing plan.&br;
&br;
CENTER:&aname(fig2);&attachref(i79_2_28.gif);&br;
&br;
CENTER:Fig.2 Floorbeam and lateral cross bracing connections.&br;
**4.Details of loading [#afd6344a]
>Fluctuating loads due to vehicles live load.
&br;
**5.Description of damage [#s6ec2a7b]
>Ⅰ.Fatigue cracks were found in the girder web at the cut short ends of the intermediate web stiffeners([[Fig.3>#fig3]]). These cracks were parallel to the girder principle stress. Therefore, only the cracked locations required retrofit.
&br;
&br;
CENTER:&aname(fig3);&attachref(i79_2_30.gif);&br;
&br;
CENTER:Fig.3 Fatigue cracking of the girder web gap.&br;
>Ⅱ.In negative and positive moment regions, vertical fatigue cracks were found on the girder outside web face along the stiffener weld toe which corresponded to the web gap locations created by the lateral gusset plates and transverse connection plates ([[Fig.4>#fig4]]). These cracks were also perpendicular to the girder principle stress and had the potential for unstable growth. Therefore, all the girder web gap locations created by the lateral gusset plates and transverse connection plates required retrofit.
&br;
CENTER:&aname(fig4);&attachref(i79_2_31.gif);&br;
&br;
CENTER:Fig.4 Fatigue cracking of the girder outside web face.&br;
>Ⅲ.Fatigue cracks were found in the floorbeam web copes at the floorbeam top flange termination([[Fig.5>#fig5]]). All the floorbeam coped webs at the top and bottom flange terminations required retrofit.
&br;
CENTER:&aname(fig5);&attachref(i79_2_32.gif);&br;
&br;
CENTER:Fig.5 Fatigue cracking of the floorbeam web cope.
&br;
>Causes of fatigue crack were as follows:
>Ⅰ.Minimal lateral bending displayed by the strain measurements on the girder bottom flange at floorbeam location.
>Ⅱ.A time lag which existed between the maximum stresses in two laterals framing into a lateral gusset plate. This represented the tendency of the laterals to rotate the gusset plate which increased the distortion of the web gap between the lateral gusset plate and the transverse connection plate.
>Ⅲ.The in-plane cyclic stress in the floorbeam top coped web which was greater than the fatigue limit at the floorbeam web-flange fillet weld termination.
**6.Repair method applied [#x34bdc12]
>Ⅰ.The drilling of retrofit holes,19 or 25mm,st the crack tips.
>Ⅱ.Drilled retrofit holes ,51mm,through the girder web along the web stiffener weld toes from the girder outside face([[Fig.6>#fig6]]) and a positive attachment by using a bolted angle connection between the lateral gusset plate and transverse connection plates([[Fig.7>#fig7]]).
>Ⅲ.Drilling of retrofit holes,25mm,centered on the floorbeam web-flange weld termination and saw cutting from the web edge into the hole.
>Ⅳ.Other case
>For the girder top web gaps at the floorbeam-girder connections required retrofit in order to lessen the severity of the out-of-plane distortion. The positive attachment of the transverse connection plate to the girder top flange([[Fig.8>#fig8]]).
&br;
CENTER:&aname(fig6);&attachref(i79_2_33.gif);&br;
&br;
CENTER:Fig.6 Retrofit procedure for girder web gap. (View from Girder Outside Face.)
&br;
CENTER:&aname(fig7);&attachref(i79_2_34.gif);&br;
&br;
CENTER:Fig.7 Retrofit procedure for web gap. (View from Girder Inside Face.)
&br;
&br;
CENTER:&aname(fig8);&attachref(i79_2_35.gif);&br;
&br;
CENTER:Fig.8 Girder top web gap retrofit.
&br;
終了行:
*2682 Br. in I-79 [#web91f68]
**1.Field of application [#yee61c60]
>The 2682 bridges in I-79 cross Big Sandy Creek 48km north of Charleston, West Virginia.
**2.Circumstances of repair [#q2d5a776]
-Fatigue cracks were found in the girder bottom web gap in May 1984 after 12 years of service.
-Fatigue cracks were found in the structure at the other locations in August 1984.
>Therefore, all the cracking locations required retrofit.
**3.Types of structure [#r6153526]
>A typical portion of the framing plan and the longitudinal girder elevation are shown in [[Fig.1>#fig1]]. The structure is comprised of two longitudinal girders, hunched at the piers, and four longitudinal stringers which are supported by transverse floorbeams. The floorbeam webs are bolt connected to the transverse connection plates which are fillet weld connected to the girder webs. The transverse connection plates and intermediate web stiffeners are fitted to the girder compression flange and cut short of the girder tension flange. Lateral cross bracing exists between the girder([[Fig.2>#fig2]]). The structural steel is ASTM A36 steel.
&br;
CENTER:&aname(fig1);&attachref(i79_2_27.gif);&br;
&br;
CENTER:Fig.1 Girder elevation and framing plan.&br;
&br;
CENTER:&aname(fig2);&attachref(i79_2_28.gif);&br;
&br;
CENTER:Fig.2 Floorbeam and lateral cross bracing connections.&br;
**4.Details of loading [#afd6344a]
>Fluctuating loads due to vehicles live load.
&br;
**5.Description of damage [#s6ec2a7b]
>Ⅰ.Fatigue cracks were found in the girder web at the cut short ends of the intermediate web stiffeners([[Fig.3>#fig3]]). These cracks were parallel to the girder principle stress. Therefore, only the cracked locations required retrofit.
&br;
&br;
CENTER:&aname(fig3);&attachref(i79_2_30.gif);&br;
&br;
CENTER:Fig.3 Fatigue cracking of the girder web gap.&br;
>Ⅱ.In negative and positive moment regions, vertical fatigue cracks were found on the girder outside web face along the stiffener weld toe which corresponded to the web gap locations created by the lateral gusset plates and transverse connection plates ([[Fig.4>#fig4]]). These cracks were also perpendicular to the girder principle stress and had the potential for unstable growth. Therefore, all the girder web gap locations created by the lateral gusset plates and transverse connection plates required retrofit.
&br;
CENTER:&aname(fig4);&attachref(i79_2_31.gif);&br;
&br;
CENTER:Fig.4 Fatigue cracking of the girder outside web face.&br;
>Ⅲ.Fatigue cracks were found in the floorbeam web copes at the floorbeam top flange termination([[Fig.5>#fig5]]). All the floorbeam coped webs at the top and bottom flange terminations required retrofit.
&br;
CENTER:&aname(fig5);&attachref(i79_2_32.gif);&br;
&br;
CENTER:Fig.5 Fatigue cracking of the floorbeam web cope.
&br;
>Causes of fatigue crack were as follows:
>Ⅰ.Minimal lateral bending displayed by the strain measurements on the girder bottom flange at floorbeam location.
>Ⅱ.A time lag which existed between the maximum stresses in two laterals framing into a lateral gusset plate. This represented the tendency of the laterals to rotate the gusset plate which increased the distortion of the web gap between the lateral gusset plate and the transverse connection plate.
>Ⅲ.The in-plane cyclic stress in the floorbeam top coped web which was greater than the fatigue limit at the floorbeam web-flange fillet weld termination.
**6.Repair method applied [#x34bdc12]
>Ⅰ.The drilling of retrofit holes,19 or 25mm,st the crack tips.
>Ⅱ.Drilled retrofit holes ,51mm,through the girder web along the web stiffener weld toes from the girder outside face([[Fig.6>#fig6]]) and a positive attachment by using a bolted angle connection between the lateral gusset plate and transverse connection plates([[Fig.7>#fig7]]).
>Ⅲ.Drilling of retrofit holes,25mm,centered on the floorbeam web-flange weld termination and saw cutting from the web edge into the hole.
>Ⅳ.Other case
>For the girder top web gaps at the floorbeam-girder connections required retrofit in order to lessen the severity of the out-of-plane distortion. The positive attachment of the transverse connection plate to the girder top flange([[Fig.8>#fig8]]).
&br;
CENTER:&aname(fig6);&attachref(i79_2_33.gif);&br;
&br;
CENTER:Fig.6 Retrofit procedure for girder web gap. (View from Girder Outside Face.)
&br;
CENTER:&aname(fig7);&attachref(i79_2_34.gif);&br;
&br;
CENTER:Fig.7 Retrofit procedure for web gap. (View from Girder Inside Face.)
&br;
&br;
CENTER:&aname(fig8);&attachref(i79_2_35.gif);&br;
&br;
CENTER:Fig.8 Girder top web gap retrofit.
&br;
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