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*U.S.51 Br. [#o2ba021f] **1.Field of application [#b350c7bd] >U.S. 51 Bridge over Illinois River in Peru. **2.Circumstances of repair [#wed63b03] >Fatigue cracks were found in the butt connection groove weld of a cover plate in July 1980 after 22 years of service. The fractured cover plates were also observed. The following inspection indicated that repair was required. **3.Types of structure [#t18fcb0d] >This bridge is the thirteen span continuous structure having the three span Gerber truss in center. Approach spans is composed of simple girder bridge and either 2 or 3 span continuous girder bridge. The structure is composed of six main girders in span 1 and five main girders in span 2 and 3 ([[Fig.1>#fig1]]). The cover plates were weld connected to the rivet girder at the center span and piers. Derail of the welded cover plates is shown in [[figure 2>#fig2]]. The main girder which is composed of flange angles,203 by 152 by 22mm, and the cover plates were fabricated from A373 steel. >The girder webs were of 11mm thickness A7 steel. &br; CENTER:&aname(fig1);&attachref(U_S_514.gif);&br; &br; CENTER:Fig.1 Plan and Side view of span 1 and 2. &br; &br; CENTER:&aname(fig2);&attachref(U_S_515.gif);&br; &br; CENTER:Fig.2 Detail of the welded cover plate. &br; **4.Details of loading [#qa3e3f6e] >Fluctuating loads due to vehicles live load. &br; **5.Description of damage [#e9538d19] >Many fatigue cracks were found in the butt connection groove welds of the cover plates which is a transforming locations of the cover plate thickness ([[Fig.3>#fig3]]). the cover plate had fractured at the two locations. In one of these two locations, an outside leg of the flange angle had fractured ([[Fig.4>#fig4]]). &br; >Cause of fatigue cracks was as follows: -Large internal defects, such as luck of fusion and inclusion of slag, of the butt connection groove weld of the cover plates. -Large internal defects, such as lack of fusion and inclusion of slag, of the butt connection groove weld of the cover plates. &br; CENTER:&aname(fig3);&attachref(U_S_512.gif);&br; &br; CENTER:Fig.3 Crack occurred in the groove weld of the cover plate. &br; &br; CENTER:&aname(fig4);&attachref(U_S_513.gif);&br; &br; CENTER:Fig.3 Crack propagated in the flange angle. CENTER:Fig.4 Crack propagated in the flange angle. &br; **6.Repair method applied [#bc139ff5] >At all the cracked locations and all the butt connection groove welds locations where the crack was supposed to initiate, The repair and strengthening were performed by bolt-splice ([[Fig.5>#fig5]]). >In the passed butt connection groove weld joints by non-destructive testing, the weld surfaces were only ground smooth and repair was not required. &br; CENTER:&aname(fig5);&attachref(U_S_520.gif);&br; &br; CENTER:Fig.5 Bolt splice repair and remove of the fillet weld. &br; &br;
