Reinforced concrete structures are mostly subjected to loads causing the structure to displace laterally some amount of displacement called story drifts. Those loads may be mainly caused by earthquakes, wind or due to eccentricity of loading and unsymmetrical frames. In one or the other way when lateral displacement encountered is significant, it causes sections of a frame member to crack. Therefore, element properties should reflect this condition, and inertias of beams and columns should be reduced accordingly. Previously several procedures were suggested to consider effective flexural rigidity. However, still there is no a uniform criterion, and comparison of demonstrated results is made with ACI-318-08 and EN 1998-2004. Four plane reinforced concrete frame are selected for this study. The peak ground acceleration selected to take earthquake effect is 0.2g. Lateral loads are generated according to EN 1998-2004 using Response Spectrum Analysis method. All sample frames are designed according to requirements of EN 1998-2004. Effective flexural stiffness is determined from secant stiffness of moment vs curvature diagram extracted from critical sections of frames. It is found that effective flexural stiffness determined for beams is in the range of 0.22 to 0.30 of gross stiffness of the sections and for columns effective stiffness is increases from lower to upper Storys and is in wide range of 0.17 to 0.85 of gross stiffness of section. For uniform longitudinal reinforcement ratio, effective flexural stiffness of the section is highly dependent on the amount of normalized axial load. Frame member sections are becoming stiff from lower storys to upper storys i.e. frame member at upper story levels have high effective stiffness than lower storys. Comparison of investigated effective stiffness ratio with ACI318-08 and EN 1998-2004 provisions are made by performing lateral load analysis and top story deflection investigated using investigated effective stiffness ratios is 2.5 times of EN 1998-2004.