Studying of foundation behaviour under different loading cases is one the most important topics that has occupied a great deal of interest. Foundation closely correlated with factors and surrounding conditions such as type of active load and type of soil bearing foundation. Non-static load (dynamic) is one of the most dangerous types of loads that affect the foundations such as earthquakes, which in turn depends heavily on the weight of the building, which depend on the number of floors, as well as the type of soil bearing foundations. To study the effect of variable load on the foundations, a model of two different types of foundations was presented (Raft – Raft with inverted beam) and exposed to El_centro earthquake with constant soil type and changing the number of floors (5, 10 and 15). From analysis results, it showed that:- 1-   Raft and raft with inverted beam have almost equal stresses and deformations. 2-   Raft with inverted beam is better in resisting H.Z displacement resulting of dynamic loads than raft. 3-   Raft with inverted beam improved results although it is equal to 70 % of raft inertia, so that it is better to use it with dynamic loads.