The safety related structures in nuclear power plants often need to be designed to withstand the effects of tornado generated missile impacts. The heaviest missile to consider is often an automobile which is a soft missile due to its large deformations during the impact. Due to the large mass of this missile, it often has the highest kinetic energy which makes the design of the structure to resist such an impact somewhat challenging. The most common approach to evaluate or design of safety related structures for an automobile impact is by estimating the forcing function and checking the structure’s capacity to resist such force. The interface forcing functions that is given in the literature is based on experimental test results on automobile crashes. However, the existing formulation is only applicable to rigid targets since it does not take credit for the energy loss due to the movement of the target mass and the missile together during the impact.

This paper provides a simplified forcing function for evaluating the structures under automobile missile impacts by using the kinematic properties of the missile and the structural dynamic properties of the target structure. For simplification purposes, a justifiable assumption is made in this study, that the peak impact force resulted from the crushable missile is proportional to the missile peak impact velocity. The formulation also utilizes the laws of conservation of linear momentum and conservation of energy to obtain the unknown parameters in the forcing function. An example is given in the paper that consists of a realistic flexible structure in typical nuclear power plants, subjected to impact by a high kinetic energy tornado generated automobile missile. The tornado missile used is similar to the standard automobile missile defined in NRC RG 1.76.