Monitoring and enhanced fatigue evaluation of a steel railway bridge

During routine inspections of the Söderström Bridge in central Stockholm, one of Sweden’s most important railway bridges, cracks were found in the web of the main steel beams. The finding initiated theoretical studies which showed that the cracks developed mainly due to poorly designed connections of the cross beams and out-of-plane bending of the web. The studies also showed an alarming result regarding the remaining fatigue life of the stringers and the cross beams. However, no cracks or other damage have been found on these components during the inspections. To explore the differences between the theoretical indications and the inspected reality, an extensive monitoring program has been performed. This article describes the monitoring program and the analysis methods used. Some results regarding the remaining fatigue life based on measured and theoretical values are presented.