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Steel bridge on the roadway bridge,Japan.
Fatigue cracks were found in the sole plate welds at the girder support locations in 1990 after 22 years of service.
The outline of the bridge structure is as follows.
- Bridge length : 114.864m
- Span length : 35.0m+44.0m+35.0m
- Structure : Three spans continuous girder bridge.
- Structural steel : SM490A,SM490B,SS400
Fluctuating loads due to vehicles live load.
The location where the fatigue cracks were found were as follows.
- The fillet welding joint at the front side of the sole plate(Type-1).
- The fillet welding joint between the lower flange and the web(Type-2).
Type-1 crack penetrated the lower flange.The length of type-2 crack was 200mm.
Causes of fatigue cracks were as follows:
- Stress concentration at the front side of sole plate that due to the lost of the rotation function of the bearing support caused by corrosion(Fig.2(a)).
- Stress concentration at the welding between the lower flange and the web plate that was caused by the gap that occurred at the time of fabrication(Fig.2(b)).
Emergency repair
At first, H-steel was inserted just under the lower flange.The main girder was supported by jack up after the partial repair that the temporary brackets and the temporary stiffener were installed to the web plate of the main girder.
Permanent repair
- The cracks were repaired by full penetration welding after gouging.
- The reinforcement plate was bolted with the lower flange to decrease the gap(Fig.3(a)).
- The reinforcement plate with rib plate was bolted with the web to decrease the stress at the location of the crack(Fig.3(b)).
- At the same time, the work to recover the function of the bearing supports was done.
Fig.3 Permanent repair.
Kurokawa et al,A repair case of fatigue damage which occurred at a corner of a steel pier with circular section ,Prc.of Annual Conferenece of JSCE,vol.58,2003.(In Japanese)
