In the beginning of the 20th century there was an expansion of the infrastructural network due to the evolvement of the industry. This expansion included a series of new railway bridges being built and those bridges were designed according to the traffic situation at the time. Many of the bridges are still in use today and as the traffic volume is continuously increasing, replacing of the bridges due to undercapacity would be expensive. Therefore, it is of interest to investigate the capacity of the bridges to determine their viability. Critical parts in bridges are details which cause stress concentrations and discontinuities in the geometry such as connections. The longitudinal and transversal beams in floor-systems of old bridges are often connected through their webs by double-angle plates. These connections are designed only to take shear forces since the beams are assumed to be simply supported. The longitudinal beams are in fact continuous and the assumption that they are simply supported is therefore wrong. A simply supported beam would mean no support moments but a high field moment whereas a fixed beam would mean that there would exist support moments and lower field moments compared to a simply supported beam. If the field moments are proven to be reduced compared to what the beams are designed for, it would mean that there would be end moments acting on the supports which would indicate that the beams would have a certain level of constraint. End moments mean an extra stress on the connections and it would mean that they would be subjected to forces they are not designed to take. The purpose of this thesis is to investigate if the stringers of an old riveted steel truss bridge are not simply supported by doing a case study. An old railway bridge was monitored during loading with strain gauges, LVDTs and a photometric device, the displacements and strains were measured and analyzed to determine the stresses, moments and as a result of that, the level of restraint. The magnitude of the field moment for the stringers in the bridge proved to be somewhere in between a simply supported and a fixed beam which means that the connections between the floor-beams and the stringers are subjected to both shear forces and moments.