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*Gerber bridge on roadway bridge (Part 2) [#r0ec368d] **1.Field of application [#q80821f6] >Gerber bridge on the roadway bridge, Japan.&br; **2.Circumstances of Repair [#v379ccd1] >The fracture of the girder web was found at the coped end of the Gerber hinge in 1991 after 29 years of service.&br; >After the detection of the fracture, the traffic was closed and repair was required immediately.&br; **3.Types of structure [#e260106e] >The outline of the bridge structure is as follows. -Bridge length : 460.2 m -Structure : Deck-type two span continuous warren truss -Deck : Reinforced concrete deck ( 16.0 cm thickness ) -Structural steel : SS 41 &br; &br; >Elevation and cross section are shown in [[figure 1>#fig1]]. The main girders are spaced at 8.6m and deep at 8.0m. The number of the stringers are four and three stringers were added later due to the strengthening of the concrete deck. [[Figure 2>#fig2]] shows the structure of the Gerber hinge. &br; &br; &br; CENTER:&aname(fig1);&attachref(Gerber31.jpg);&br; &br; CENTER:Fig.1 Elevation and cross section.&br; &br; &br; CENTER:&aname(fig2);&attachref(Gerber32.jpg);&br; &br; CENTER:Fig.2 Structural detail of the Gerber hinge.&br; &br; &br; **4.Details of loading [#y7516deb] >Fluctuating loads due to vehicles live load. **5.Description of damage [#o5ac620b] >Fatigue cracks were found in the coped corner at the hinge locations of Gerber bridge ([[Fig.2>#fig2]]). The fatigue cracks occurred along the fillet weld beads at the coped corners ([[Fig.2>#fig2]],[[3>#fig3]]). There were some cracks that propagated into the girder webs from the corner ends.&br; >The fracture of the girder web were found at the Gerber hinge location([[Fig.3>#fig3]]). Because the base plate of support had been weld connected to the girder top flange, the crack initiated from the weld toe of the base plate ([[Fig.4>#fig4]]). Fracturing the girder web, the crack stopped over the bottom flange weld. The crack also initiated from the girder coped end ([[Fig.5>#fig5]]).&br; &br; &br; >Cause of fatigue cracks was thought as follows: -Stress concentration due to the cope. &br; &br; CENTER:&aname(fig2);&attachref(Gerber25.jpg);&br; CENTER:&aname(fig3);&attachref(Gerber33.jpg);&br; &br; CENTER:Fig.2 Crack location.&br; CENTER:Fig.3 View of the fractured web.&br; &br; &br; CENTER:&aname(fig3);&attachref(Gerber26.jpg);&br; CENTER:&aname(fig4);&attachref(Gerber34.jpg);&br; &br; CENTER:Fig.3 Crack along the weld root of the coped corner.&br; CENTER:Fig.4 Crack which initiated from the weld toe of the base plate.&br; &br; &br; CENTER:&aname(fig5);&attachref(Gerber35.jpg);&br; &br; CENTER:Fig.5 Crack which initiated from the coped end.&br; &br; &br; **6.Repair method applied [#p9694bf7] -Emergency repair >Repair of parts subjected to cracking was performed by 24mm diameter stop holes at the crack tips. >High strength bolts (M22,F10T) were fastened there ([[Fig.4>#fig4]]). >Because it was thought that the cracks initiated from the fillet weld root at the coped corner, all the fillet weld parts at the coped corners were gouged out and full penetration welded ([[Fig.5>#fig5]],[[6>#fig6]]). >In order to prevent the drop of the bridge, the connection plate was installed between the stringers. The suspended girder was supported by making use of the diagonal member which were constructed at the truss chord member. -Permanent repair >After the completion of the repair weld, Strengthening was performed by bolt connection with the rib plates ([[Fig.7>#fig7]]). >The crack in the girder web were repaired by welding. CENTER:&aname(fig4);&attachref(Gerber27.jpg);&br; >The original girder top flange was replaced with new plates. The new plates with the rib plates were bolt connected to the girder web ([[Fig.6>#fig6]]). CENTER:&aname(fig6);&attachref(Gerber36.jpg);&br; &br; CENTER:Fig.4 Emergency repair.&br; &br; CENTER:&aname(fig6);&attachref(Gerber37.jpg);&br; &br; CENTER:&aname(fig5);&attachref(Gerber28.jpg);&br; &br; CENTER:Fig.6 Permanent repair.&br; &br; CENTER:Fig.5 Range of the full penetration weld.&br; &br; &br; CENTER:&aname(fig6);&attachref(Gerber29.jpg);&br; &br; &br; CENTER:Fig.6 Repair weld (Full penetration weld.)&br; &br; &br; CENTER:&aname(fig7);&attachref(Gerber30.jpg);&br; &br; &br; CENTER:Fig.7 Permanent repair.&br; &br; &br;
