Bridges are one part of the Road Infrastructures which needs care during design stages,rnamong which include analysis. The most common Bridge superstructures forms widely usedrnare RC T- and Box Girder types. To analyze such forms the most widely used method ofrnanalysis is Approximate Method based on Distribution Factor concept. This method isrnpreferred due to its simplicity for use. This method has limitation for not considering stiffnessrnof components sufficiently and effect of provision of diaphragm on load distribution; thesernparameters have great impact on load distribution between Girders. The result of this methodrnis also considered conservative as compared to more refined method of analysis. In this study,rnthe result obtained by this method and refined method of analysis (Grillage Analogy Method)rnare investigated.rnUsing these methods, RC T- and Box Girder superstructures are analyzed, consideringrndifferent Traffic lanes and span length. This task involves examining the maximum BendingrnMoment and Shear Force using the two numerical models. Furthermore, the effect ofrnDiaphragm on load distribution is also investigated.rnThis study provided useful information about the variation of Bending Moment, Shear Forcernwith respect to change in Traffic Lanes, Span Length and arrangement of Diaphragm. It isrnconcluded that the results obtained from Grillage analogy method are smaller thanrnapproximate method, except for shear force of Interior Girder of T-Girder Bridge, whichrngives slightly higher result where, the percentage differences varies from case to case. For allrnother cases considered, approximate method gives conservative values. In addition, sincernapproximate method does not consider effect of diaphragm, provision of more number ofrndiaphragms has effect on load distribution is observed for T-Girder than Box Girder inrnGrillage Analogy method.rnKey words: T-Girder; Box Girder; Approximate Method (Distribution Factor Method);rnGrillage Analogy Method; Flexural Moment of Inertia; Torsional Moment of Inertia;rnBending Moment; Shear Force; Vehicular Live Load; Traffic Lanes; Span Length