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Steel bridge of Route 43, Japan.
Fatigue cracks at intersection of bulb ribs and transverse ribs were found.
The outline of the bridge structure is as follows.
- Bridge length : 211.0m
- Span length : 60.0m+91.0m+60.0m
- Structure : Box girder bridge with orthotropic deck system
Fluctuating loads due to vehicles live load.
Fatigue cracks were detected on boxing weld joints between bottom of bulb ribs and web plates of transverse ribs .Cracks initiated from the toe of the boxing weld joints and propagated at the web plates of the transverse ribs (Fig.1).
Fig.1 Crack location
Cause of fatigue cracks was as follows:
- Localized stress concentration which resulted from the restraint of the deck plate deflection due to the wheel load.
Retrofitting procedures for the cracks were positive attachments by using bolted angle connections between the bulb ribs and the web plates of the transverse ribs(Fig.2).
Fig.2 Bolted angle connections between the bulb ribs and the web plates of transverse ribs.
