Researchers load test the bridges of Malmbanan

The Iron Ore Line (Malmbanan) is Sweden's most heavily trafficked railway with passenger trains, freight trains and ore trains. Ore is transported from the mining towns of Malmberget, Svappavaara and Kiruna to the ports of Narvik and Luleå and further out into Europe. There are now plans to increase the permitted axle load for the trains along the 500 km long Malmbanan to be able to load more into the wagons. Luleå University of Technology therefore performs a unique test program on a full-scale trough bridge in the university's laboratory in collaboration with Trafikverket.

"This bridge is a fantastic and unique opportunity to test railway bridges, as there is no similar test facility in Sweden. We will gain better knowledge of how bridges can be loaded and how long they last, so we can plan the right maintenance measures well in advance," says Lars-Olof Andersson, Section Manager for Construction Maintenance at Trafikverket.

In the unique research project in Sweden, which is now starting in Luleå University of Technology's largest laboratory, advanced load tests are performed on a full-scale trough bridge for about three months ahead. Various monitoring sensors have been mounted at strategic points on the train bridge that make it possible to track and analyse various parameters such as forces, strains, and displacements. The experiments will subject the bridge to static and dynamic loads with different axle load levels. The loads are representative of the traffic that has passed through Malmbanan over the past 50 years. The results will be used to calibrate analytical and numerical models as well as advanced computer models with which the capacity and service life of existing bridges on Malmbanan can be forecast. The tests will ensure that the Malmbanan's bridges can cope with the plans for increased loads.

Determining the final load-bearing capacity of the bridges

"Our primary objectives are to reduce uncertainties about the structural behaviour, identify critical sections and determine the final load-bearing capacity of the trough bridges. In addition, we strive to gain an increased understanding of how the load is transferred from the railway sleepers through the ballast and into the bridge structure itself,” says Gabriel Sas, Professor and Head of Subject in Structural Engineering at Luleå University of Technology.

Two years ago, Luleå University of Technology initiated a comprehensive evaluation of the condition of the bridges on Malmbanan in collaboration with Trafikverket and LKAB, focusing on the specific type of bridge that is representative of Malmbanan, a so-called trough bridge. This type of bridge makes up about 50 per cent of the bridges on Malmbanan (about 60 in number).

"The project can save money, carbon dioxide emissions and the environment. By being able to determine more safely and probably further increase the load capacity on Malmbanan, the bridges can be retained for a longer period of time and perhaps being strengthened instead of being replaced with new ones," says Gabriel Sas.