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*Quinnipiac River (Defects in the butt welds of horizontal stiffener) [#ba944424] **1.Field of application [#g4a1f522] **2.Circumstances of repair [#q4c0d071] >First fatigue cracking was found in the girder web in Nov. 1973 after 9 years of service. The following fatigue cracking was found in the butt connection groove weld of the longitudinal stiffeners which are fillet weld connected to the girder webs. At the time of discovery, the first crack had propagated in the depth of the web and had gone into the bottom flange. Therefore, repair was required immediately. **3.Types of structure [#j539ae9d] >This bridge is continuous for four spans and is non-composite Gerber bridge, which consist of suspended span on center, except for span 1. The complete and elevation views are shown in [[figure 1>#fig1]]. The structure is composed of nine main girders on half side lane. Transverse cross bracings of X-type exist between the main girders. >Longitudinal stiffeners are fillet welded to the girder web ([[Fig.2>#fig2]]). &br; CENTER:&aname(fig1);&attachref(quinni15.jpg);&br; &br; CENTER:&aname(fig1);&attachref(quinni16.jpg);&br; &br; CENTER:Fig.1 Complete and elevation views.&br; &br; CENTER:&aname(fig2);&attachref(quinni17.gif);&br; &br; CENTER:Fig.2 Typical cross section.&br; **4.Details of loading [#m824d451] > **5.Description of damage [#w3e33ff2] >Fatigue cracks were found in the coped end of the main girder and the swells of the girder webs also occurred in the girder ends due to buckling ([[Fig.2>#fig2]]).&br; >Cause of fatigue cracks was as follows:&br; -Concentration of stress unforeseen in design. -Functional disorder of the movable support. >Fluctuating loads due to vehicles live load. **5.Description of damage and Repair method applied [#keedc255] -Detail of transformation >Fatigue cracking which was found in the girder web originated from the butt connection groove weld of the longitudinal stiffeners ([[Fig.3>#fig3]],[[4>#fig4]]). The fracture in the girder web resulted from a fatigue crack ([[Fig.3>#fig3]]). &br; CENTER:&aname(fig3);&attachref(quinni18.jpg);&br; &br; CENTER:&aname(fig2);&attachref(Copede2.jpg);&br; CENTER:Fig.2 Crack location and swell range of the girder web.&br; CENTER:Fig.3 Crack originated from the butt connection groove weld of the longitudinal stiffeners. &br; CENTER:&aname(fig4);&attachref(quinni19.jpg);&br; &br; CENTER:Fig.4 Crack propagated in the girder web.&br; **6.Repair method applied [#b040e829] > Repair of parts subjected to cracking had been performed by stop hole and bolt connection as shown in [[figure 3>#fig3]]. After completion of repair, inspection indicated that fatigue crack re-initiated from the stop hole. Therefore, additional repair and strengthening were required. -Cause >From thorough investigation of fracture, it turned that non-deposited part of butt weld of horizontal stiffener caused and crack were originated at intersection of web plate and stiffener. It is probable that cracks in non-deposited part propagated during transportation and erection. >Web plate was brittle-fractured from the first fatigue crack. The crack became unstable and propagated rapidly and stopped around the center of flange or web plate. It is found there are some stages in which cracks propagates. -Maintenance and reinforcement >The portion crack appeared was cut off and splice plate was attached by bolts([[Fig.5>#fig5]]). For cracks which did not propagate so much, drill holes were opened on web plate and cracks were separated from the girder([[Fig.6>#fig6]]). CENTER:&aname(fig5);&attachref(quinni20.jpg);&br; &br; CENTER:Fig.5 Bolt splice repair of fatigue cracked girder web.&br; CENTER:&aname(fig6);&attachref(quinni21.jpg);&br; &br; > New plates with the rib plates were bolt connected to both sides of the girder webs ([[Fig.4>#fig4]]). This repair made the swell of the girder web reform. These new plates of 9mm thickness played the role of transmitting the load. CENTER:Fig.6 Hole-drilling repair.&br; &br; &br; CENTER:&aname(fig3);&attachref(Copede3.gif);&br; CENTER:Fig.3 Primary repair.&br; &br; &br; CENTER:&aname(fig4);&attachref(Copede4.gif);&br; CENTER:Fig.4 Final repair&br; &br; &br;
