Due to modernization of the railway transportation sector, as high speed railway lines have become morerncommon, nowadays researches are being been carried to assess and analyse the properties of the trackrnand its component besides its effect on the overall bridge dynamics.rnDynamic responses of the railway track and its elements are key parameters to measure the structuralrncapability of railway track and its elements. If a dynamic loading resonates the railway trackâ€™s dynamicrnresponses, its elements tend to possess damage from excessive dynamic stresses. for instance, a railrnvibration leads to defects in rails or wheels. The track vibrations will cause the crack harm in railwayrnsleepers or fasteners, or maybe the breakage of ballast support. Therefore, the identification of dynamicrnproperties of ballasted railway track and its elements is very essential, so as to avoid any train operationrnwhich may trigger such resonances.rnIn this thesis,3D FEM models that represent the ballast as a solid part were modelled. Such systems ofrnmodeling take sensible advantage of the capability of contemporary FEM package (Abaqus) in modelingrnthe continuity of the track beyond the bridge by imposing applicable boundary conditions on the railwayrnline. And a static load test was conducted on one tracked Prestressed T-girder railway bridge to check itsrnstiffness. Data from the tests was processed, and modeling the prestressed tendon like embedded elementrngive more realistic result compared to assuming it like cohesive element with concrete girder.rnThe objective of this thesis is to investigate the effect of ballast the dynamic behavior of T-girder RailwayrnBridge. Hence its effect on the dynamic properties of the bridge was assessed in this thesis byrnimplementing and comparing different 3D FEM models of the bridge that describe different structure andrntrack configurations. Model that included the ballast alone showed a drop by (2.09-17.63)% in the naturalrnfrequency for vibration mode 1-4Th and 10th and a rise by (3.07-16.52)% in the natural frequency for 5-rn9th mode of vibration were observed as compared to the model that accounted for the mass of the T-girderrnbridge only. In addition, different parameters influencing the natural frequencies and modes shapes of thernbridge were tested and it appears that the ballast introduces considerable additional stiffness for 5-9thrnmode of vibration. Density, stiffness, depth of ballast and support condition parameters as well was foundrnto affect the dynamic properties of the bridge.