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*I-470 and I-79 tied arch Br. [#m920dc7a] **1.Field of application [#ife5704a] >I-470 spans the Ohio River at Wheeling , West Virginia. &br; >I-79 spans the Ohio River at Neville Island , Ohio. &br; **2.Circumstances of repair [#d53622ca] >In I-470, fatigue cracks were reported at the diaphragm-tie girder web connection and at the tie girder web-flange connection near completion. Upon discovery of the I-470 cracks, I-79 was inspected and fatigue cracks were found in July 1983 at the diaphragm-tie girder web connection and at the tie girder web-flange connection after 7 years of service. Inspection and strain measurements indicated that retrofit was required. **3.Types of structure [#j0bf0407] >I-470 and I-79 are tied arch structures and are similarly designed at the floorbeam-tie girder connection ([[Fig.1>#fig1]],I-470 plan). The framing plane and typical cross section are shown in [[figure 2>#fig2]] and the tie girder elevation is shown in [[figure 3>#fig3]]. The tie girder is a box section containing an internal diaphragm plate at the floorbeam connection. &br; >The diaphragm plate is bevel groove weld connected for I-79 and fillet weld connected for I-470 to both the tie girder webs but does not extend full depth of the webs. The four web-flange connections of the tie girder are groove weld connected using continuous backup bars. &br; >The I-470 floorbeam flange and web plates are A36 steel (or A588) and A572 steel. The tie girder flange and web plates are A588 steel, the diaphragm plate is A36 steel. At the tie girder splice locations, the tie girder flange and web plates are A514 steel and the diaphragm plate is of 13mm thickness A36 steel. The I-79 material is presumed to be similar to the I-470 material. &br; &br; CENTER:&aname(fig1);&attachref(I-79an36.gif);&br; &br; CENTER:Fig.1 Plan and elevation of I-470. &br; CENTER:&aname(fig2);&attachref(I-79an37.gif);&br; &br; CENTER:Fig.2 Typical floorbeam framing of I-470. &br; CENTER:&aname(fig3);&attachref(I-79an38.gif);&br; &br; CENTER:Fig.3 Tie girder elevation of I-470. &br; **4.Details of loading [#u2487adb] >Fluctuating loads due to vehicles live load. **5.Description of damage [#j41c7d50] >In I-470, fatigue cracks were found at the fillet weld terminations of the diaphragm-tie girder web connection and at the groove weld root of the tie girder web-flange connection. In I-79, fatigue cracks were found at the groove weld terminations of the diaphragm-tie girder web connection and at the groove weld root of the tie girder web-flange connection. &br; >Causes of fatigue crack were as follows: -Lack of fusion between the multiple weld passes of 10mm diaphragm-tie girder fillet weld and groove weld. -Lack of fusion planes at diaphragms and backup bars of I-470 and I-79 creating a crack-like defect ([[Fig.4>#fig4]]). -Out-of-plane distortion of the tie girder web gaps due to relative displacement between the tie girders. -High wind loads showed significant cyclic stresses. (I-470) -Large construction loads. (I-470) &br; CENTER:&aname(fig4);&attachref(I-79an39.gif);&br; &br; CENTER:Fig.4 Schematic of lack of fusion planes at diaphragms and backup bars of I-470 and I-79. &br; **6.Repair method applied [#s67c47cd] -Initial retrofit. --The hole-drilling in the diaphragm at the crack tips. -Further retrofit. --Angle 180 by 100 by 13mm (130 by 130 by 13mm, at locations of flange splices.) were used to bolt connect the diaphragm to the top and bottom tie girder flanges (Fig.5,6). --Further retrofit of the inside bottom web gap consisted of a bolted strap between the tie girder bottom flange and the floorbeam bottom flange (Fig.7). --Angle 180 by 100 by 13mm (130 by 130 by 13mm, at locations of flange splices.) were used to bolt connect the diaphragm to the top and bottom tie girder flanges ([[Fig.5>#fig5]],[[6>#fig6]]). --Further retrofit of the inside bottom web gap consisted of a bolted strap between the tie girder bottom flange and the floorbeam bottom flange ([[Fig.7>#fig7]]). -Final retrofit. --The region between backup bars without a full fusion groove weld to provide continuity was ground out and the backup bars shaped to relieve the stress concentration. &br; CENTER:&aname(fig3);&attachref(i95_ht85.gif);&br; CENTER:&aname(fig5);&attachref(I-79an40.gif);&br; &br; CENTER:Fig.3 Retrofit of tension longitudinal stiffeners.&br; CENTER:Fig.5 Retrofit angle (partially shown) bolt connected to I-79 diaphragm and flange. &br; CENTER:&aname(fig6);&attachref(I-79an41.gif);&br; &br; CENTER:Fig.6 I-79 web retrofit procedure. &br; CENTER:&aname(fig7);&attachref(I-79an42.gif);&br; &br; CENTER:Fig.7 I-79 inside bottom web gap retrofit procedure. &br; &br;
