Åby river bridge (case study)

The bridge over Åby River on the main railway line in northern Sweden was built in 1955 with a length of 33 m. A code-based assessment carried out in 1994, indicated that the bridge was damaged because of fatigue. According to the report, it was the overlapping continuous plate in the stringer-to crossbeam connection that had insufficient capacity. There were no visible cracks in this location, Häggström (2016), MAINLINE (2014).

Object description

(No object description available.)

Civil engineering type

:

Railway network Bridge

Year of construction

:

1955

Composed of materials

:

Steel

Location coordinates

:

65° 24' 58.16" N, 20° 22' 25.03" E

Country

:

Sweden

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Object analysis

Measurements of strains and deflections were carried out, while the bridge was in service. Due to the risk for a fatigue failure and bumpy connections it was decided to exchange the bridge. The old bridge was moved to a new site, close to the old one, and loaded to failure.

Case type

:

Research

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Object state

It was found that the bridge could withstand loading corresponding to four times the highest permitted axle-loading, or twice the design load for new bridges, before exhibiting an obvious non-linear behaviour regarding vertical displacement in the mid span. The peak load was achieved at loading approximately 50% higher than the initial non-linear behaviour, where lateral buckling of the top chord limited the structure from carrying more load. The failure can be concluded as being redundant without brittle failure of any of the connections. The results helped save a twin bridge at Rautasjokk on the Iron Ore Line north of Kiruna.

Observed deterioration processes

:

Fatigue

Observed damage types

:

Performance indicators

:

Deformation, Displacement

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