Simplified methods for evaluating the uplift of buildings with raft foundation

The uplift of the raft foundation of reinforced concrete buildings, and the consequent partial loss of contact between soil and foundation, is a possible effect of an earthquake. Actually, reinforced concrete buildings with raft foundation are commonly used in nuclear power plants. In this context, some simplified approaches for uplift evaluation have been proposed in the past and are still used for many practical applications. In particular, the so-called energy equivalence method is studied here. The classical form of this method can be applied to rectangular foundations with earthquake direction parallel to one of the rectangle sides and to circular foundations. A generalization of classical equations to the case of generic foundation shape and generic earthquake direction is proposed in this paper. Then, uplift assessments from energy equivalence method, pushover and non-linear time history analyses are compared, with reference to the specific situation of a nuclear power plant building.