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*Dan Ryan Express [#dd02b438] **1.Field of application [#l3ed32eb] >Dan Ryan elevated bridge of the Lake-Dan Ryan express line in Chicago, Illinois. **2.Circumstances of repair [#jdd6e7be] >Fatigue crack was found in the transverse box beam cap of the rigid-frame steel pier in Jan. 1978 after 9 years of service. After finding this crack, repair was immediately recommended. **3.Types of structure [#j83b307a] >This bridge is curved and elevated structure ([[Fig.1>#fig1]],[[2>#fig2]]). The superstructure is composed of four continuous plate-girders and field-placed concrete deck ([[Fig.3>#fig3]]). The transverse beams of the rigid-frame steel pier which support four plate-girders and columns are box sections ([[Fig.4>#fig4]]). The girder bottom flanges pass through the slot-holes, which were formed near the box beam lower web, and is partial penetration groove weld connected to the box beam webs. The welded girder members, which corresponded to 0.9~1.22mm length from both side of the transverse beam, was fabricated with the pier and was pin-link or bolt connected to the adjacent girder members. The structural steel was applied to the quality of A36 steel as a result of the tensile test and so on. &br; CENTER:&aname(fig1);&attachref(i95_ht83.gif);&br; CENTER:&aname(fig1);&attachref(DanRya7.gif);&br; &br; CENTER:Fig.1 Schematic of the exterior web face of fascia girders.&br; CENTER:Fig.1 Complete view. &br; CENTER:&aname(fig2);&attachref(DanRya8.gif);&br; &br; CENTER:Fig.2 Pier and superstructure view. &br; CENTER:&aname(fig3);&attachref(DanRya9.gif);&br; &br; CENTER:Fig.3 Plan and cross section. &br; CENTER:&aname(fig4);&attachref(DanRya10.gif);&br; &br; CENTER:Fig.4 Pier view and crack location. &br; **4.Details of loading [#xf35a68d] >Fluctuating loads due to vehicles live load. >Fluctuating loads due to rail live load. **5.Description of damage [#c8b09665] >The crack occurred in the butt connection groove weld of a continuous tension-side longitudinal stiffener, continued through the web between the stiffener and bottom flanges, and penetrated the bottom flange. &br; >Fatigue cracks was found in the groove weld at the box beam web connection with the girder bottom girder flange ([[Fig.5>#fig5]]). In the fabrication, the slot holes were firstly opened to the box beam webs by frame-cutting in order to permit the penetration of the girder flanges. Secondly , the girder bottom flanges were inserted in the slot hole and were groove weld connected to the box beam webs. >Cause of fatigue crack was as follows: -Separational discontinuities in the butt connection groove weld of the continuous tension longitudinal stiffener. >Causes of fatigue crack were as follows: -Lack of fusion in the groove weld which connected the girder bottom flange to the transverse box beam cap of the pier. -Detail of the weld joint indicating the low fatigue strength. **6.Repair method applied [#m67844b0] >The fatigue cracked girder web and bottom tension flange were bolt spliced ([[Fig2>#fig2]]). &br; CENTER:&aname(fig2);&attachref(i95_ht84.gif);&br; CENTER:&aname(fig5);&attachref(DanRya1.gif);&br; &br; CENTER:Fig.2 Bolt splice repair of fatigue cracked girder web and bottom flange.&br; CENTER:Fig.5 Crack occurred in pier 26. &br; > The possibility existed for fatigue crack growth in the butt connection groove welds of other tension longitudinal stiffeners. Therefore, from the exterior of the fascia girder web, small hole was drilled through the girder web at the top of the fillet weld toe centered over the tension groove weld. **6.Repair method applied [#m67844b0] >A 51mm diameter holes were trepanned from the interior of the fascia girder web centered on the longitudinal stiffener groove weld ([[Fig.3>#fig3]]).The holes extended through the web into the longitudinal stiffener a maximum 3mm past the stiffener fillet weld toe. >After the discovery of the crack, temporary supports were immediately constructed and stop holes were drilled at the crack tips as a emergency repair. >Strengthening was recommended to lessen the high stress concentration and residual stress at the girder flange-box beam web connections where fatigue crack did not initiate yet. Two 64mm diameter holes were drilled on side of the box beam web adjacent to up-and-down girder flange termination. The two holes were connected by a vertical saw cut ([[Fig.6>#fig6]]). &br; CENTER:&aname(fig3);&attachref(i95_ht85.gif);&br; CENTER:&aname(fig6);&attachref(DanRya17.gif);&br; &br; CENTER:Fig.3 Retrofit of tension longitudinal stiffeners.&br; CENTER:Fig.6 Repair method for pier 26.&br; &br; &br;
