Flat plate structures are commonly used in moderate and low seismic zones as lateral force resisting systems. The study on flat plates showed that under seismic loading entire width and stiffness is not effective. There is difference of opinion as to what should be the stiffness of the beam slab for the analysis of equivalent frame for horizontal loads. In this paper attempt has been made to study the efficiency of the equivalent frame methods proposed by various researchers and carry out finite element analysis using computer program. The equivalent frame method proposed by various scientists has found suitable for approximate lateral load analysis; which results in conservative design. The study showed that under lateral load, the larger width of the slab participating in resisting the lateral loads and hence contributes larger stiffness to the structure. Hence finite element modelling is the good approach for the lateral load analysis. In equivalent frame method, Hwang and Moehle method found suitable for the analysis of lateral loads; comparing to British code, Grossman and Wallace method.