Existing buildings or individual supporting structures must undergo reassessments of bearing and serviceability capacities according to up-to-date technical standards if investments are made to improve the building structure, if current actions are higher than the original actions, if bigger constructional measures are made, if constructive defects are detected, etc. Because of the first two points the 50 years old prestressed girder which is analysed in this thesis needs to be reassessed by way of calculation. The girder has variable cross section heights and a kink in the axis of symmetry. Chapter 2 describes the general approach of reassessing the bearing capacity of existing buildings in Austria. Also, the difficulties of reassessing the shear capacity are explained. A large part of the existing buildings are not able to fulfil the demanded shear capacities. The actual shear capacity is thereby often underestimated. This is due to a, in certain cases, more conservative approach in current standards compared to former generations of standards. Furthermore, deviation forces in concrete structures are theoretically discussed because of the girder-s kink. Chapter 3 comprises the reassessment of the existing prestressed girder by way of calculation in accordance with current standards. The demanded shear capacities are not met. Also, there is not enough stirrup reinforcement to take the deviation force in the middle of the girder. Even though they don-t fulfil verifications in current standards many existing buildings might have a sufficient shear capacity. This is why the existing prestressed girder was replicated at a scale of 1:1 and with equivalent materials in order to carry out tests. The tests were designed to determine the actual shear and deviation force bearing capacities- these are described and interpreted in chapters 4 and 5. The tests show that the girder has in fact a sufficient shear and deviation force bearing capacity.