Railway Concrete Arch Bridge over Kalix River at Långforsen : Dynamic Properties and Load-Carrying Capacity

The concrete arch bridge over Kalix River at Långforsen was built in 1960 and has a mid-span of 89,5 m and a height of 13,7 m. The bridge owner, Trafikverket, wanted to increase its allowable axle load from 225 to 300 kN. Field tests were carried out under service condition and with ambient vibrations. The test results were used to update and validate Finite Element Models. At last, the refined models were used to check the possibility to increase the axle load. According to earlier assessments, most parts of the bridge is capable of carrying an axle load of 330 kN. The only critical sections are located in the beams carrying the rail on top of the arch in the section where the beams are united with the arch. Here the stresses in the longitudinal bottom reinforcement are slightly too high. These sections have been studied in a FEM model for different loads and results show maximum strains of about 50·10-6 corresponding to stresses of only about 10 MPa in the reinforcement in the critical sections. Live load vertical deflections of the crown of the arch is of the order of only ± 6 mm. Dynamic studies have also been made showing that fatigue is no issue. Altogether the studies show that the bridge is able to carry an increased axle load of 300 kN without problems