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*Steel bridge on Hanshin Expressway [#mdf6f0c2] **1.Field of application [#hef1bd8c] >Steel bridge on Hanshin Expressway, Japan &br; **2.Circumstances of Repair [#c188edf0] >Fatigue cracks were found in the web gap plates at the floorbeam and the lateral cross bracing locations in Aug. 1983 after 14 years of service.&br; **3.Types of structure [#c9813d6a] >The outline of the bridge structure is as follows.&br; -Bridge length : 30.0 m ( 29.0 m ~ 37.0 m ) -Span length : 29.4 m ( 28.4 m ~ 36.4 m ) -Structure : steel simple composite I-beam girder -Deck : Reinforced concrete deck ( 18 cm thickness ) -Structural steel : SM50 , SM41 , SS41 >The side view and cross section are shown in [[figure 1>#fig1]]. The number of the main girders is five and the depth is 1.7m. The floor system is composed of the floorbeams and the sway bracings which are spaced at 4.9m.&br; Web gap plates of 9mm thickness were weld connected between the floorbeam flanges and the girder flanges. &br; &br; CENTER:&aname(fig1);&attachref(Hanshi1.gif);&br; CENTER:Fig.1 Side view and cross section &br; &br; &br; **4.Details of loading [#k46ab9bb] >Fluctuating loads due to highway live load. **5.Description of damage [#s01706fc] >Fatigue cracks were found in the welds of the web gap plates at the floorbeam and sway bracing locations. Fatigue cracks were classified in four types as follows ([[Fig.2>#fig2]],[[3>#fig3]]).&br; >(A) Fatigue cracking which occurred in the web gap plate welds at the connection with the girder top flanges. >(B) Fatigue cracking which occurred in the scallop of the web gap plates. >(C) Fatigue cracking which occurred in the web gap plate welds at the connection with the girder webs. >(D) Fatigue cracking which occurred in the girder web-flange weld at the scallop location. >Type A cracks are reported that were the most frequent observed in four types of the cracks.&br; >Cause of fatigue cracks was as follows:&br; - Out-of-plane distortion of the girder web gap resulted from the differential rotation between the deck and the floorbeam. &br; &br; CENTER:&aname(fig2);&attachref(Hanshi2.gif);&br; &br; CENTER:Fig.2 Types of crack..&br; &br; &br; CENTER:&aname(fig3);&attachref(Hanshi3.gif);&br; CENTER:Fig.3 Types of crack..&br; **6.Repair method applied [#e81628fd] >Repair of parts subjected to cracking was performed by welding and replacement of the web gap plates.&br; >The repair procedure is as follows. >The original web gap plates were removed and the new plates of 19mm thickness were weld connected at the web gap locations ([[Fig.4>#fig4]]). The additional rib plates were installed on the outside web face of the exterior girders ([[Fig.4(a)>#fig5]]). Gouging out, crack area was full penetration welded. >The original web gap plates were removed and the new plates of 19mm thickness were weld connected at the web gap locations ([[Fig.4>#fig5]]). The additional rib plates were installed on the outside web face of the exterior girders ([[Fig.4(a)>#fig4]]). Gouging out, crack area was full penetration welded. &br; &br; CENTER:&aname(fig4);&attachref(Hanshi4.gif);&br; CENTER:(a)Repair for the exterior girder.&br; &br; &br; CENTER:&aname(fig5);&attachref(Hanshi5.gif);&br; CENTER:(b)Repair for the interior girder.&br; &br; CENTER:Fig.4 Repair method.&br; &br;
