![[PukiWiki]](image/pukiwiki.png "[PukiWiki]")
*Shitoku-Ohashi [#c7a846a5] **1.Field of application [#me7f5eb6] >Shitoku-Ohashi , the Chubu District, Japan.&br; **2.Circumstances of Repair [#x7dd8ca2] >Fatigue cracks were found in the gusset ends at the diagonal member connections in Jul. 1967 after 4 months of service. Therefore a reinforcing measure or a preventive measure of vibration was required immediately. **3.Types of structure [#eb9782d8] >The bridge is Langer bridge like truss structure of which span length is 150m ([[Fig.1>#fig1]]). The diagonal members are composed of steel pipes, which are of 320mm diameter. Thickness of the steel pipes was of 6.9mm and These were fabricated from STK 41 steel. &br; &br; CENTER:&aname(fig1);&attachref(Shitok26.jpg);&br; &br; CENTER:Fig.1 Elevation view.&br; &br; &br; **4.Details of loading [#r23b3522] >Fluctuating loads due to wind load. **5.Description of damage [#y3d740d8] >Fatigue crack was found in the fillet weld at the gusset connection with the diagonal members ([[Fig.2>#fig2]]). As a result of measurement in site, these diagonal members had suffered the vibration of 3.4 Hz and wind blowing of 6.2 meters per second.&br; &br; >Cause of fatigue cracks was as follows: -Vibration of the members which caused by Kerman's vortex. &br; &br; CENTER:&aname(fig2);&attachref(Shitok27.jpg);&br; &br; CENTER:Fig.2 Crack at the gusset connection with the diagonal members.&br; &br; &br; **6.Repair method applied [#i9c5fb67] >Firstly, repair of parts subjected to cracking was performed by stop hole, gouging and re-welding. >In order to lessen stress concentration at the gusset locations, strengthening was performed by connecting the circular plates ([[Fig.3>#fig3]]). As a result, the bridge was in no structural danger no matter how frequent diagonal members suffered vibration. >Secondary, the cracked web was bolt spliced ([[Fig.5>#fig5]],[[6>#fig6]]). >To extinguish Kerman's vortex, however, trip wires of which diameter corresponded to about 10% of steel pipe diameter were additionally spiraled on diagonal pipes ([[Fig.4>#fig4]]). >Beside, the original base mortar under the shoe of the G5 girder were replaced by the new non-shrink mortar after re-installing the shoe.&br; >In other Langer bridges, it was reported that fatigue cracks occurred in the suspended members owing to vibration which caused by Kerman's vortex ([[Fig.5>#fig5]]: fatigue cracking at the suspended member end ,for example ). These suspended members consisted of H-beam steels. >As a result of cracking, there are two or three repair cases in Japan that wind slot were opened or detail were improved or two wires were linked between the vertical members, as a preventive measure of vibration ([[Fig.6>#fig6]]: wind slots for H-beams, for example). &br; &br; CENTER:&aname(fig5);&attachref(Hanko924.jpg);&br; CENTER:&aname(fig3);&attachref(Shitok28.jpg);&br; &br; CENTER:Fig.5 Repair method.&br; CENTER:Fig.3 Strengthening method.&br; &br; &br; CENTER:&aname(fig6);&attachref(Hanko925.jpg);&br; CENTER:&aname(fig4);&attachref(Shitok29.jpg);&br; &br; CENTER:Fig.6 Complete view.&br; CENTER:Fig.4 Final retrofit.&br; &br; &br; CENTER:&aname(fig5);&attachref(Shitok30.jpg);&br; &br; CENTER:Fig.5 Fatigue cracking at the suspended member end.&br; &br; &br; CENTER:&aname(fig6);&attachref(Shitok31.jpg);&br; &br; CENTER:Fig.6 Wind slots for H-beams. &br; &br; &br;
