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*Allegheny River Br. [#d5061b0c] **1.Field of application [#e71f5e28] >Allegheny River Bridge is Pennsylvania Turnpike over Allegheny River on the outskirts of Pittsburgh, Pennsylvania. **2.Circumstances of repair [#h8755997] >Fatigue crack was found in the tie plate which was rivet connected with the floorbeam top flange and the cantilever bracket top flange in 1971 after 19 years of service. **3.Types of structure [#aeb4ee39] >This bridge consist of four spans of Gerber bridge and five spans of truss bridge ([[Fig.1>#fig1]]). The structure is composed of two main girders, floorbeams, twelve stringers supporting the reinforced concrete deck, cantilever brackets. The plane, elevation views and typical cross section are shown in [[figure 2>#fig2]],[[3>#fig3]]. The top flange of the floorbeams are rivet connected to the top flanges of the brackets by the tie plate ([[Fig.4>#fig4]]). The tie plates were A7 steel. &br; CENTER:&aname(fig1);&attachref(Allegh7.gif);&br; &br; CENTER:Fig.1 Allegheny River Bridge. &br; &br; CENTER:&aname(fig2);&attachref(Allegh8.gif);&br; &br; CENTER:Fig.2 Plan and elevation views. &br; &br; CENTER:&aname(fig3);&attachref(Allegh9.gif);&br; &br; CENTER:Fig.3 Cross section (A-A section shown in figure 2.) &br; &br; CENTER:&aname(fig4);&attachref(Allegh10.gif);&br; &br; CENTER:Fig.4 Detail of the tie plate. &br; **4.Details of loading [#n4f46cf1] >Fluctuating loads due to highway live load. &br; **5.Description of damage [#nb1828be] >Fatigue cracks were found in the tie plate which was rivet connected to the floorbeam top flange and the cantilever bracket top flange (Fig.5). These cracks initiated from the rivet connection holes of the tie plates. >Fatigue cracks were found in the tie plate which was rivet connected to the floorbeam top flange and the cantilever bracket top flange ([[Fig.5>#fig5]]). These cracks initiated from the rivet connection holes of the tie plates. &br; >Cause of fatigue cracks was as follows: -In-plane-distortion of the tie plates which was caused by the longitudinal displacement of the main girder top flanges. &br; CENTER:&aname(fig7);&attachref(I-93_h75.gif);&br; CENTER:&aname(fig8);&attachref(Allegh10.gif);&br; &br; CENTER:Fig.7 Vertical and horizontal fatigue cracks at the bottom web cope.&br; CENTER:Fig.5 Cracked tie plate. &br; CENTER:&aname(fig8);&attachref(I-93_h76.gif);&br; &br; CENTER:Fig.8 Cross-section view of angle with fatigue cracks.&br; &br; CENTER:&aname(fig9);&attachref(I-93_h77.gif);&br; &br; CENTER:Fig.9 Longitudinal girder not bolted full depth to the connection angles.&br; **6.Repair method applied [#l1c3ff99] >Repair of the tie plates subjected to cracking was performed by groove welding. The strengthening plates were bolt connected on the repaired tie plate ([[Fig.6>#fig6]]). However, significant cyclic stresses, which were caused by the displacement, have been acting in the repaired tie plates and the reinforcing plates. Therefore, there was possibility that crack reinitiate after 10 or 20 years. -The 1984 recommended retrofit for fatigue cracking in the web copes of longitudinal girders and the floorbeams was 25mm hole-drilling at the crack tips. >A further retrofit was required. Holes were drilled in the girder web and flange and an angle, 200 by 200 by 29mm, was bolted to the girder inside web and flange and to the connection angle ([[Fig.10>#fig10]],[[11>#fig11]],[[12>#fig12]]). 16mm fill plate was used on the web and the lower bolt holes ware reamed for bolting. &br; CENTER:&aname(fig10);&attachref(I-93_h78.gif);&br; CENTER:&aname(fig6);&attachref(Allegh11.gif);&br; &br; CENTER:Fig.10 1984 retrofit procedure for all of the longitudinal girder bottom web gaps.&br; CENTER:Fig.6 The reinforcing plate. &br; CENTER:&aname(fig11);&attachref(I-93_h79.gif);&br; &br; CENTER:Fig.11 1984 retrofit of a longitudinal girder bottom web gap viewed from girder interior. &br; &br; CENTER:&aname(fig12);&attachref(I-93_h80.gif);&br; &br; CENTER:Fig.12 1984 retrofit of a longitudinal girder bottom web gap viewed from girder exterior. &br; -Removing the lower nine bolt rows in the web connection for relaxing the compression web and moving the bottom flange toward normal alignment. -The 1987 recommended retrofit was the drilling of a retrofit hole, 51mm, through the web thickness at the crack tip. For the lower beam-column connections of the bents, the retrofit was the transfer of the live load force from the lower beam top flange to the column. >Both procedure needed to enable the flanges of the wide-flange to be bolted to the webs of the column ([[Fig.13>#fig13]],[[14>#fig14]]). &br; CENTER:&aname(fig13);&attachref(I-93_h81.gif);&br; &br; CENTER:Fig.13 1987 retrofit procedure for I-section of beam-column connection.&br; &br; CENTER:&aname(fig14);&attachref(I-93_h82.gif);&br; &br; CENTER:Fig.14 1987 retrofit of beam-column connection showing flange of wide-flange bolted to web column. &br; &br;
