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*No. 28 County road Br. [#ac1ffc29] **1.Field of application [#v5e5d2b2] >No.28 County road Bridge over I-57 in Fayette County, north of Farina , Illinois. **2.Circumstances of repair [#df397552] >Large fatigue crack was found in the main girder web at the core refilled by welding, which was drilled in the main girder web by mistake, in March 1977 after 9 years of service. These cracks had connected each other and had caused the brittle fracture of the girder flange and web. Therefore, repair was required. **3.Types of structure [#m1872c1a] >This bridge consists of four continuous spans skewed structure. The plane and elevation views are shown in [[figure 1>#fig1]]. A cross section is shown in [[figure 2>#fig2]]. The five main girders are W36×H150 of ASTM A36-97 steel. The reinforced concrete deck forms composite action with girders. &br; CENTER:&aname(fig1);&attachref(DanRya7.gif);&br; CENTER:&aname(fig1);&attachref(No_28B11.gif);&br; &br; CENTER:Fig.1 Complete view. CENTER:Fig.1 Plan and elevation views. &br; CENTER:&aname(fig2);&attachref(DanRya8.gif);&br; CENTER:&aname(fig2);&attachref(No_28B12.gif);&br; &br; CENTER:Fig.2 Pier and superstructure view. CENTER:Fig.2 Cross section. &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 [#qc43cc77] >Fluctuating loads due to rail live load. >Fluctuating loads due to vehicles live load. **5.Description of damage [#vcf973c1] >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. >Fatigue cracks originated from two cores refilled by welding, which were drilled in the main girder web by mistake([[Fig.3>#fig3]]). The sharp cracks due to fatigue connected each other and occurred in the brittle fracture under low temperature. As a result, the girder bottom flange was fractured. >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. >Fatigue cracks horizontally had propagated in the middle girder web([[Fig.4>#fig4]]). &br; >Cause of fatigue cracks was as follows: -Inclusion of slag and void which had existed in the refilling weld. &br; CENTER:&aname(fig5);&attachref(DanRya1.gif);&br; CENTER:&aname(fig3);&attachref(No_28B13.gif);&br; &br; CENTER:Fig.5 Crack occurred in pier 26. CENTER:Fig.3 Crack initiated from the weld-refilling holes. &br; CENTER:&aname(fig4);&attachref(No_28B14.gif);&br; &br; CENTER:Fig.4 Crack propagation in the 2B2 girder web. &br; **6.Repair method applied [#jce9a91e] >After the discovery of the crack, temporary supports were immediately constructed and stop holes were drilled at the crack tips as a emergency repair. >Replacement of the damaged parts ([[Fig.5>#fig5]]). >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]]). >The repair procedure is as follow. >Total length of the girder web between the splice parts was frame-cut below the 254mm from the bottom face of the girder top flange. The T-shaped steel which consisted of the same form as the removal girder was horizontally field-welded. After that, this T-shaped steel was bolt connected to the adjacent girders by using the connection plate which had been used before repair. >As a result of repairing, new weld joint was located near the girder neutral axis. No the outstanding cyclic stress could produced there. Therefore, it was supported that no the crack reinitiate from the repaired member. CENTER:&aname(fig5);&attachref(No_28B15.gif);&br; &br; CENTER:&aname(fig6);&attachref(DanRya17.gif);&br; CENTER:Fig.5 Detail of repair. &br; CENTER:Fig.6 Repair method for pier 26.&br; &br; &br;
