High strength concrete (HSC) has been used widely in the world in recent years for construction technology due to its preferable strength and workability. However, in Ethiopia, normal strength concrete (NSC) has been commonly practiced in design and construction of RC T-Girder bridges. The application of NSC for RC T-Girder bridges, resulted large designed section or increased concrete volume which devours much construction time and labor during casting. One of the reasons for the application of NSC instead of HSC is resulted from inadequate investigation of structural behavior of RC T-Girder bridges made of high strength concrete. Even standard typical drawings have not been prepared for HSC bridges in ERA bridge design manual while for NSC up to C-30 MPa bridges prepared. Thus, continues investigations regarding to HSC structures are necessary to bring HSC into application. So, analytical study was conducted to investigate the structural behavior of HSC RC T-girder bridges subject to vehicular live loads in addition to permanent gravity loads. Sample RC T-girder bridges with clear span length of 12m, 16m, 20m and 24m were modeled and analyzed using structural analysis program CSIBRIDGE. Each span length bridge had 4 models with concrete grade of C-30, C-50, C-70 and C-90 and a total of 16 models for all sample RC T-girder bridges were modeled, analyzed and designed. Validation of CSIBRIDGE models were performed in comparison with conventional beam line method of analysis. The girders were designed based on AASTHO 2010. The results obtained from the study showed that flexural and shear strength of the designed girder section was reduced as concrete strength increased but sufficient to resist action effects. Girders sectional ductility based on curvature enhanced with higher concrete strength of the girders. Maximum deflection, fatigue stress, stress for service loads and crack width parameters for service loads were within the limit and slightly higher for HSC girders comparison to NSC. The application of HSC for girder reduced significantly the concrete quantity. Economical comparisons were also made and it was found that girders with HSC was cost-effective. Generally, the application of HSC for girders led to ductile, reduced and economical section.