Concrete girder bridges are a commonly used type of bridge which can be reinforced withboth regular and post-tensioned reinforcement. At a certain span length, the use of tensionreinforcement becomes a must because regular reinforcement won’t be enough. To get anidea of where this boundary lies, we studied a bridge in this research which is a half-throughbridge intended for railway traffic with the use of post-tensioned reinforcements. Thisbridge has a span of 22,15 metres and it is compared to bridges at the same span andshorter span using regular reinforcements. The analysis in this thesis is made using the finiteelementsprogram Brigade Standard.Two previously executed projects are used as references. A literature study will be carriedout initially, where Eurocodes, old examination projects and other literature on tensionreinforcement are examined.The acquired result is that the tension-reinforced bridge relates to a bridge with about 3/4span with regards to torque over the middle support. The torque over the support is thelimiting factor which causes an exponential increase in the amount of reinforcement atlonger spans. At about 20 metres the amount of necessary reinforcement starts to increaseexponentially and above this span post-tensioning is the preferred method.Torsion at the end support is also a crucial parameter since a regular-reinforced bridge with20-metre span cannot be reinforced to handle this with the current geometry. At a 20-metrespan, actions are therefore required to improve the torsion capacity, for example, increasingthe girder width. This increased girder width could be considered a saving in materials dueto the avoided increment of concrete in the case of tension-reinforced design, where thisincreased width is unnecessary.The total amount of reinforcement, independent of the reinforcement type, is greater in themiddle support of the regular reinforced bridge than the tension reinforced with the samespan. However, the total amount of reinforcement over the entire bridge is higher in thetension reinforced alternative.The result also shows that the tension reinforcement increases the compression force in thebridge and eliminates tension cracks which were expected according to our literature study.

A significant portion of the reinforced concrete railway bridges in Sweden are reaching their designed lifespan and are scheduled to be demolished and replaced in the upcoming years. To limit the econom-icand environmental impact related to the replacement of existing railway infrastructure, a comprehen-siveevaluation of their capacity is required with the aim of extending its lifespan. In fact, experimental evidence has shown that some of these bridges may have a higher capacity than previously determined due to the conservative assumptions used during their design. The proper stress distribution pattern at the ballast-concrete interface is among the factors that need to be studied, as research on the topic has shown that some of the available guidelines to calculate it can produce conservative results. In this paper, available analytical models for computing the internal forces in concrete bridges due to train axle loads are compared to a numerical model calibrated using the experimental results obtained from the test of ballasted reinforced concrete trough bridge, a typical structural type found in Sweden, and existing research. As a first step, a literature review of existing numerical modeling strategies for ballast-edconcrete railway structures (e.g., finite element models, discrete element models, and their combina-tion)is conducted. Then, the most appropriate numerical modelling strategy is identified and used to develop the numerical model of the bridge, including the ballast. Finally, results of contact pressure and vertical stresses in the numerical model are compared to those obtained analytically.