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*Ft. Duquesne Bridge, Pennsylvania. [#x1939e31] **1.Field of application [#m4d52fe1] >Northern approach Ramp of Ft Duquesne Bridge in Pittsburgh, Pennsylvania. **2.Circumstances of Repair [#adbfef04] >Fatigue cracks were found in the welds ,which connected the lower transverse beam to the column in the rigid -frame piers, in Sep. 1978 after 10 years of service. **3.Types of structure [#l5c1bd2d] >Approach Ramp is the double-deck structure which is composed of the composite box girders, which are continuous for two and three spans, supported by the steel rigid-frame piers ([[Fig.1>#fig1]]). Plan and side views are shown in [[figure2>#fig2]]. The box girders and piers were individually fabricated by shop welding. >The box girders were connected to the piers by field welding. Center parts of the transverse beam of the pier were bolt connected on site. The differential cross sections of the box girders depended on span length. Typical cross sections of the box girder with the internal diaphragms are shown in [[figure 3>#fig3]]. Typical detail of the rigid-frame pier is shown in [[figure 4>#fig4]]. >The transverse beam flanges were continuous and had penetrated the column. The column inside flanges were groove weld connected to the transverse beam flanges at the web corner. Most of piers were fabricated from A36 and A441 steel. Piers with the relative long span were from S517 steel.&br; &aname(fig1); CENTER:&attachref(Ft_Duq1.gif);&br; CENTER:Fig.1 Rigid-frame pier and box-beam girder.&br;&br; &aname(fig2); CENTER:&attachref(Ft_Duq2.gif);&br; CENTER:Fig.2 Plan and side views.&br;&br; &aname(fig3); CENTER:&attachref(Ft_Duq3.gif);&br; CENTER:Fig.3 Typical cross section.&br;&br; &aname(fig4); CENTER:&attachref(Ft_Duq4.gif);&br; CENTER:Fig.4 Detail of the rigid-frame pier&br; **4.Details of loading [#f44ca7c3] >Fluctuating loads due to vehicles live load. **5.Description of damage [#i40392ef] >Fatigue cracks were found in the weld joint which connected the box-section transverse beam flanges to the box-section column flanges in the rigid -frame piers.&br; >There were two types of the fatigue cracks ([[Fig.5>#fig5]], [[Fig.6>#fig6]])&br; -Fatigue cracking like lamellar tearing which occurred in the transverse beam flange plate center at the penetrating locations.&br; (Fatigue cracking was observed in A517 built-up members.)&br; -Fatigue cracking which occurred in the groove weld toe which connected the column flange to the transverse beam flange. (Fatigue cracking was observed in both A517 and A 441 built-up members.)&br; >The cracks occurred in both the transverse beam tension flange and the compression flanges. The cracks which occurred in the transverse beam tension flanges indicated the trace of the fatigue crack growth.&br; >Cause of fatigue cracks was as follows:&br; -Lamellar tearing which had initiated during fabrication. &aname(fig5); CENTER:&attachref(Ft_Duq5.gif);&br; CENTER:(a) Cracks before removing the paint.&br;&br; &aname(fig5); CENTER:&attachref(Ft_Duq6.gif);&br; CENTER:(b) Cracks after removing the paint.&br; CENTER:Fig.5 Crack occurred in the transverse beam top flange at the transverse beam connection with the column. &br;&br; &aname(fig6); CENTER:&attachref(Ft_Duq7.gif);&br; CENTER:Fig.6 Crack occurred in the transverse beam compression flange. &br;&br; **6.Repair method applied [#i846b2a9] >Primary repair was performed by 25mm slot-holes at the transverse beam tension flanges connection with the columns ([[Fig.7>#fig7]]). >Final repair was performed by bolt splice of the plates which connected the box-section transverse beams web with the box-section column webs top flanges ([[Fig.8>#fig8]],[[9>#fig9]],[[10>#fig10]]). Flanges with partial width were groove weld connected to the web in order to help the load transmit at the column-beam corners. >Because lamellar tearing of the transverse beam compression flanges did not indicate the fatigue crack growth, repair was not performed. &aname(fig7); CENTER:&attachref(Ft_Duq8.gif);&br; CENTER:Fig.7 Slot hole location in the transverse beam web. &br;&br; &aname(fig8); CENTER:&attachref(Ft_Duq9.gif);&br; CENTER:Fig.8 Final repair at the column-beam corner. &br;&br; &aname(fig9); CENTER:&attachref(Ft_Duq10.gif);&br; CENTER:Fig.9 Splice plates used by repairing. &br;&br; &aname(fig10); CENTER:&attachref(Ft_Duq11.gif);&br; CENTER:Fig.10 Final repair. &br;&br;
