This paper proposes a fatigue damage assessment methodology of a reinforced concrete bridge based on a train bridge coupled dynamic analysis system. This coupling system is composed of a vehicle a ballasted track and a bridge structure to realize a coupled vibration analysis during train passages. This methodology adopts the Palmgren Miner rule to linearly accumulate fatigue damage, and accomplishes fatigue assessment based on recommended SN relationships for reinforced concrete from various criteria. In this paper, the dynamic performances of a bridge structure are analyzed with two different vehicle models, a moving load model (and a moving spring mass damper model). Calculated dynamic stresses areused to evaluate the fatigue damage of critical positions in a reinforced concrete bridge. A case study is carried out of a railway arch bridge with a span of 89 m, Långforsen Bridge. It runs over Kalix River on the railway between Kalix and Morjärv in northern Sweden The fatigue assessment is made by combining the presented methodology with measurements. Furthermore, the effects of train speed and axle load on fatigue damage are investigated. The results indicate that good estimations of the fatigue damage assessment are made for four measured cases based on a train-bridge coupled dynamic analysis. For low speeds and light loads no difference could be seen in the cumulative fatigue damage for the two vehicle models. But high speeds and/or heavy load ssignificantly affect the fatigue damage.

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.

The dynamic response of a concrete railway arch bridge is studied through a case study of the bridge over Kalix River, situated at Långforsen on the railway line between Kalix and Morjärv in northern Sweden. A simplified beam-element model, a spatial grillage-beam model and a refined shell-element model were built to analyze the bridge structure. A methodology was applied where measured static and dynamic responses were used to update finite element models of Långforsen Bridge. A multi-response objective function was presented, and the finite element method was proved feasible by comparison of predicted and measured response. In the paper comparative analyses were made of the time history displacement of three finite element models under three measured load cases. A standard train model from EUROCODE, HSLM-A 1, was applied and the dynamic responses under different speeds were studied. The results showed that a refined shell element model could accurately analyze dynamic responses of the concrete railway arch bridge in a better way than beam element and spatial grillage models. The dynamic analysis based on this type of shell model can give an optimized suggestion for the railway operation as well as for the design of high-speed railway bridges.