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*Third St. Viaduct [#n87f65ca] **1.Field of application [#s8768f1c] >The Third Street Viaduct spans Conrail tracks in Franklin Country near Columbus, Ohio. **2.Circumstances of repair [#e00c8c9b] >The Viaduct was completed in 1960. In March 1978,Conrail notified the city of Columbus of a crack in the fascia girder >The Viaduct was completed in 1960. In March 1978,Conrail notified the city of Columbus of a crack in the fascia girder. >At the time of discovery, the bottom tension flange had fractured and the crack had propagated part way up the web. Upon notification to the City of Columbus a few days later, the web crack had propagated to within a few inches of the top flange. Therefore, repair which is hole-drilling in the web at the crack tip was required immediately. **3.Types of structure [#v1876597] >The structure consists of five welded steel girders at 3m spacing which support a reinforced concrete deck >The structure consists of five welded steel girders at 3m spacing which support a reinforced concrete deck. >The five main girders are connected by transverse cross bracing at 4.3m spacing([[Fig.1>#fig1]]). >The web plate of the cracking main girder was of 11mm thickness and bottom flange plate was of 32mm thickness ASTM A373 steel. &br; CENTER:&aname(fig1);&attachref(Third_42.gif);&br; &br; CENTER:Fig.1 Typical transverse and lateral cross bracing.&br; **4.Details of loading [#e8231b21] >Fluctuating loads due to Conrail tracks live load. **5.Description of damage [#j80dc7a0] >Fatigue cracks were found in the fascia girder web. The fracture in the fascia girder resulted from a fatigue crack in the girder web(Fig.2). This fatigue crack originated from cold lap which was created by the weld intersection of the groove weld connecting lateral gusset plate to the girder web and the fillet weld connecting transverse stiffener to the girder web. >Fatigue cracks were found in the fascia girder web. The fracture in the fascia girder resulted from a fatigue crack in the girder web([[Fig.2>#fig2]]). This fatigue crack originated from cold lap which was created by the weld intersection of the groove weld connecting lateral gusset plate to the girder web and the fillet weld connecting transverse stiffener to the girder web. &br; >Causes of fatigue crack were as follows: -Discontinuities introduced by welding clip angles to the girder web. (the primary cause for fatigue crack initiation) -The lack of fusion created by the weld intersection of the groove weld connecting lateral gusset plate to girder web and fillet weld connecting transverse stiffener to girder web. (the primary cause of failure) -The condition of cold lap accentuated by local buckling of the transverse gusset plate which resulted from weld shrinkage during cooling of the groove weld connecting lateral gusset plate to transverse gusset plate. &br; CENTER:&aname(fig2);&attachref(Third_43.gif);&br; &br; CENTER:Fig.2 Schematic of crack path.&br; **6.Repair method applied [#l5e1e436] >Repair used for the cracked girder web and the fractured bottom flange was the bolted web splice (Fig.3). At the repaired location, the lateral gusset plate was welded directly to the transverse web stiffener. The transverse gusset plate contained a cut out, of 13mm end radius, for the lateral gusset plate to frame through(Fig.4,Type II). >Repair used for the cracked girder web and the fractured bottom flange was the bolted web splice ([[Fig.3>#fig3]]). At the repaired location, the lateral gusset plate was welded directly to the transverse web stiffener. The transverse gusset plate contained a cut out, of 13mm end radius, for the lateral gusset plate to frame through([[Fig.4>#fig4]],Type II). >All lateral gusset plates located in regions of cyclic or tensile stress range were properly retrofitted to prevent fatigue crack growth in the girder web. Two types of repairs were used. -Type I : Trepanning a 76mm diameter slot at the intersection of girder web, transverse stiffener, and lateral gusset plate. The slots extended through the web and through 13mm of the lateral gusset plate and transverse web stiffener leaving the plug in place(Fig.4). A stiffener plate was fillet welded to the girder web in the same direction and directly opposite the lateral gusset plate(Fig.4). -Type II : Drilling vertical holes through the lateral gusset plate at the intersection of girder web, transverse stiffener and lateral gusset plate(Fig.4) -Type I : Trepanning a 76mm diameter slot at the intersection of girder web, transverse stiffener, and lateral gusset plate. The slots extended through the web and through 13mm of the lateral gusset plate and transverse web stiffener leaving the plug in place([[Fig.4>#fig4]]). A stiffener plate was fillet welded to the girder web in the same direction and directly opposite the lateral gusset plate([[Fig.4>#fig4]]). -Type II : Drilling vertical holes through the lateral gusset plate at the intersection of girder web, transverse stiffener and lateral gusset plate([[Fig.4>#fig4]]) &br; CENTER:&aname(fig3);&attachref(Third_44.gif);&br; &br; CENTER:Fig.3 Repair procedure for fractured web and bottom flange.&br; &br; &br; CENTER:&aname(fig4);&attachref(Third_45.gif);&br; &br; CENTER:Fig.4 Type I and II retrofit for lateral gusset plates located in regions of cyclic or tensile stress range. &br; &br; &br;
