*Canoe Creek Br. [#j5338350]
**1.Field of application [#a4b5ed0b]
>The Canoe Creek Bridge on I-80 located in Clarion Country, Pennsylvania.
**2.Circumstances of repair [#k0f4bdf9]
>As a first, in 1983, cracking was observed in the girder top web gaps at the negative moment regions and retrofit holes were drilled at the crack tips([[Fig.3>#fig3]]) after approximately 14 years over of service. In a following year, cracking in the girder webs at various locations was observed in addition to re-initiation of the web cracks from the retrofit holes.
>In a following site inspection of the other structure , vertical crack indications were observed on the outside girder web face along the transverse stiffener weld toe at the level of the lateral gusset plate.
**3.Types of structure [#o285cb3b]
>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 plate girders which are hunched at the piers, multiple longitudinal stringers, and transverse floorbeams([[Fig.2>#fig2]]). The floorbeam webs are bolt connected to transverse connection plates which are fillet weld connected to the girder webs. The transverse connection plates are fillet weld connected to the girder compression flanges and cut short of the girder tension flanges. The floorbeam bottom flange is bolt connected to two lateral gusset plates which are bolt connected to lateral tabs. The lateral tabs ,100 by 19 by 559mm,are fillet weld connected to the girder web. The lateral gusset plates and transverse connection plate are not positively connected. The girder depth at the piers (center span) is 4m(2m) and the web is of 13mm(10mm) thickness ASTM A36 steel.
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CENTER:Fig.1 Plan and girder elevation views.&br;
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CENTER:Fig.2 Cross section at center span and at piers.&br;
**4.Details of loading [#kd651bd0]
>Fluctuating loads due to vehicles live load.&br;
**5.Description of damage [#a60293c4]
-Fatigue cracking was found in the girder top web gaps between the girder web-flange fillet weld and the cut short and of the transverse connection plate. The cracking was located at the floorbeam-girder connections of the negative moment regions.&br;
>Causes of fatigue crack were as follows:
--Large cyclic stress and stress concentration.
--Cause of re-initiation from the retrofit hole edges was out-of-plan distortion.
-Fatigue cracking was found in the girder horizontal web gap between the lateral tab and the transverse connection plate at the lateral tab weld toe.&br;
>At nearly every floorbeam-girder connection, vertical cracking was found on the outside girder web face along the web stiffener weld toe. The vertical cracking corresponded to the inside face horizontal web gap location.
>Causes of fatigue crack were as follows.
--The floorbeam end rotation and the out-of-phase action of the lateral bracing caused the out-of-plane displacement of the girder web.
--Slag and lack of fusion.
**6.Repair method applied [#e75de9ef]
-The preliminary retrofits of the girder top web gap were 19mm hole-drilling and Channel connection ([[Fig.3>#fig3]]). However, the fatigue cracks reinitiated from the retrofit holes. Additional retrofits were recommended.
--hole-drilling at the crack tips.
--An angle, 200 by 200 by 19mm, connection with an equal number of high strength bolts for the transverse connection plate and flange connection (four bolts per shear plane.) ([[Fig.4>#fig4]]).
-The preliminary retrofit was to replacing the welded lateral tab connection with a bolted angle connection([[Fig.5>#fig5]]). However, this retrofit procedure did not change the horizontal web gap geometry. Therefore, the revised retrofit for the horizontal web gap was to increase the gap to 100mm ([[Fig.6>#fig6]]).
>The recommended retrofit for the vertical fatigue cracks was the drilling of holes on each side of the stiffener and lateral gusset plates([[Fig.7>#fig7]]).
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CENTER:Fig.3 Preliminary retrofit of longitudinal girder top web gap.&br;
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CENTER:Fig.4 Final retrofit of longitudinal girder top web gap.&br;
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CENTER:Fig.5 Preliminary retrofit of lateral gusset plates.&br;
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CENTER:Fig.6 Revised retrofit of lateral gusset plate with Increased horizontal web gap length.
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CENTER:Fig.7 Recommended retrofit for vertical cracks.
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