This thesis focuses on the structural behaviour of prestressed concrete girder beams with a particular emphasis on stiffness degradation near intermediate supports due to cracking, in inverted-T girders. Despite advancements in bridge engineering, there is still a lack of understanding regarding crack development along the length of the beam and its impact on stiffness, including the redistribution of forces. The thesis aims to analyse the implications of these structural changes by utilizing methodologies such as the moment-curvature diagram and Finite Element Method (FEM) models. The unique properties of the moment-curvature diagram are leveraged to accurately reproduce changes in stiffness caused by cracking. Two case studies are conducted to achieve these objectives. Case Study 1 involves comparing actual tests with FEM models, it revealed a disparity between the FEM models and actual test results. Particularly in load-deformation behaviour and stiffness variation due to crack development, this case study highlights the necessity to accurately calculate the moment regions, especially the cracking moment, which defines the moment-curvature diagram. While Case Study 2 evaluates the performance of FEM models to realistic loading conditions, including traffic loads, with some models surpassing expected performance while others failed to withstand traffic loads. Overall, the study underscores the importance of a proper methodology to accurately translate the material parameters and complex behaviours into a FEM environment.