Railway bridges with masonry abutments represent a significant portion of aging infrastructure in north Sweden. The assessment of their structural integrity is crucial to ensure safe and efficient railway operations. This paper presents the development of a proof loading method tailored specifically for railway bridges with masonry abuments.

Before conducting the tests, the bridge condition was assessed through visual inspections using ground-based photogrammetry and Ground Penetration Radar (GPR). Realistic loads were simulated using a carefully chosen train fleet during the tests to evaluate load-carrying capacity and structural integrity. Comprehensive data, including strains, displacements, temperature, and acceleration measurements, were collected to gain insights into the bridges' behavior under real-life loading conditions. This data played a crucial role in making predictions and guiding maintenance decisions for targeted rehabilitation efforts. 

To enhance capacity assessments, finite element models were calibrated using test results, enabling predictions of how the bridges would respond to varioius loads. 

The IronOre line between Narvik in Norway and Luleå in Sweden faces challenges with aging bridges and an increase in allowable axle loads. In this line, reinforced concrete trough bridges constitute about 50% of the bridge population; therefore, they are crucial for the country’s economy. An essential factor of trough bridge design is how traffic loads are distributed on the concrete surface. Thus, in this study, a laboratory campaign was implemented by monitoring the pressure on the slab and beams of a new full-scale trough bridge. The monitoring was made using load cells placed on the slab and beam surfaces at points of interest. The pressure was measured for different axle load levels and static and cycling loads. This study belongs to a more extensive experimental campaign where further tests on load distribution are planned. The results show how the loads are distributed among the sleepers and the final transversal and longitudinal distribution shapes on the bridge.

Railway noise barriers should provide excellent sound insulation and sufficient load-bearing capacity. High-speed railway noise barriers experience significant and transient aerodynamic loads from passing trains, resulting in noticeable dynamic responses. In this study, three simplified load models were applied to a noise barrier to compare the dynamic responses to those obtained under a reference load from computational fluid dynamics (CFD) simulations, Results show that the natural frequency of target noise barriers exceeds 10 Hz, significantly surpassing the excitation frequency of the train-induced areodynamic load, thereby minimizing the likelhood of resonance. The displacement or stress evolution closely correlatesd with the variation of pressure over time. Along the longitudinal direction of the noise barrier, the stress range initially increases, stabilizes, and eventually decreases, reaching its maximum at the penultimate post. Compared to the two simplified rectangular load models, the triangular load model with a distribution load length of 12 m better represents the detailed time-varying aerodynamic load.

Die Erzbahnlinie wurde um 1900 gebaut und überquert in ihrem Verlauf über 100 Brücken. Sie ist mehr als 500 km lang und verläuft von den Minen in Nordschweden zu den Häfen am Atlantik und an der Ostsee. Die ursprüngliche Achslast betrug 14 Tonnen. Zur Senkung der Transportkosten wurde die Achslast kontinuierlich erhöht, 1955 auf 25 Tonnen, 1998 auf 30 Tonnen und schliesslich auf 32,5 Tonnen im Jahr 2017 bzw. 2019. Der Erhöhung der Achslast ging jeweils ein Monitoring und eine Begutachtung der Brücken voraus. Dabei zeigte sich, dass viele dieser Brücken eine höhere Last tragen können, als ursprünglich beim Entwurf vorgesehen. Es werden Erfahrungen aus Studien vorgestellt, die zeigen ,dass durch gut geplante Erhaltungs- und Instalthaltungsprogramme/Ersatzneubauten viel Geld gespart werden kann. 

The Iron Ore Railway Line was built around 1900 and has more than 100 bridges. It has a length of ca 500 km and runs from the mines in northern Sweden to harbours on the Atlantic and on the Baltic. The original axle load was 14 ton. In order to lower freight costs, the axle loads has gradually been increased to 25 ton in 1955, to 30 ton in 1998,  and to 32.5 ton in 2017-2019. The increases in axle loads have been proceeded by monitoring and assessment studies of the bridges. Many of the bridges could carry a higher load than what it was designed for. Experiences from studies are presented showing that much money can be saved by a well planned maintenance and retrofitting/replacement program.

The bond failure is studied of a reinforced concrete trough bridge strengthened with near surface mounted reinforcement of carbon fibre reinforced polymer (CFRP) bars. The bars were embedded in epoxy resin in pre-sawed groves in the soffit of the bridge edge beams. The failure was modelled with 3D nonlinear finite elements, and it was possible to study the process from initiation to final collapse. A local bond failure in the interface between the concrete and the epoxy resin initiated a redistribution of forces in the bridge leading to yielding in the longitudinal and vertical steel reinforcement, rupture of stirrups and finally a full failure of the bridge. The bridge was a 50-year-old typical concrete railway trough bridge in Örnsköldsvik, in northern Sweden. It was going to be dismantled due to a relocation of the railway line. The aim of the loading test was to get detailed information of the bridge behaviour all the way up to the final failure. The test was a part of the European Research Project “Sustainable Bridges” regarding assessment and strengthening of existing bridges. The bridge was strengthened in bending before the loading test to avoid an uninteresting flexural failure. Failure was reached for an applied load of 11,7 MN by pulling downwards a steel beam placed in the middle of one of the two spans.  The FE calculations presented here show the effect of the strengthening with CFRP, the effect of the epoxy when using the Near Surface Mounted Reinforcement (NSMR) strengthening method and the high load-carrying capacity of this bridge type

In this paper, experiences on the development of an assessment method for existing bridges are presented. The method is calibrated using the results of full-scale testing to failure of a prestressed bridge in Sweden. To evaluate the key parameters for the structural response, measured by deflections, strains in tendons and stirrups and crack openings, a sensitivity study based on the concept of fractional factorial design is incorporated to the assessment. Results showed that the most significant parameters are related to the tensile properties of the concrete (tensile strength and fracture energy) and the boundary conditions. A finite element (FE) model in which the results of the sensitivity analysis were applied, was able to predict accurately the load-carrying capacity of the bridge and its failure mode. Two additional existing prestressed concrete bridges, that will be used to improve further the method, are also described, and discussed.

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.

A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the loadcarrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Örnsköldsvik in northern Sweden. It was tested in situ as the bridge had been closed following the construction of a new section of the Railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European research project called Sustainable bridges. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion, and bond failures at an applied load of 11.7 MN (2,630 kips). A computer model was developed using specialized software to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over six times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe, and the United States.

A 55 year-old, 121.5 m long, five span prestressed bridge was situated in the deformation zone close to a mine in Kiruna in northern Sweden. There was a risk for uneven ground deformations so the bridge was analyzed and monitored. Results and measures taken to ascertain the robustness of the bridge are presented.The analysis resulted in an estimate that the bridge could sustain 24 mm in uneven horizontal and 83 mm in uneven vertical displacement of the two supports of a span. To be able to sustain larger deformations, the columns of the bridge were provided with joints, where shims could be inserted to counteract the settlements. To accomplish this, each one of the 18 columns of the bridge was unloaded by help of provisional steel supports. The column was then cut and a new foot was mounted to it. This made it possible to lift each individual column with two jacks, when needed, and to adjust its height by inserting or taking away shim plates.The deformations of the bridge and the surrounding ground were monitored. The eigenmodes of the bridge were studied with accelerometers and by analysis with finite elements (FE) models. Comparison indicated good agreement between the model and the actual bridge, with calculated eigenfrequencies of 2.17, 4.15 and 4.67 Hz, for the first transversal, vertical and torsional modes, respectively. Measurements during winter resulted in higher values due to increased stiffness caused by frozen materials.