It is reported that huge impulsive forces are acting repeatedly on such port structures as breakwaters consisting of concrete caissons, resulting in ultimate failure of concrete members. In the present design of such concrete structures, impulsive forces, which have large variations with regard to time and space, are converted equivalently to simple distribution of static loads in order to compare to load carrying capacity of structures in static conditions. Therefore, it is one of the problems that scatters of impulsive forces and dynamic behavior of structures is not taken into account. It is necessary to establish an integrated design method of port concrete structures subjected to repeated impact loads. And it is necessary to examine measures to improve impact resistant capacity that is applicable to port structures.
　In this study, the target was impact loading of concrete blocks acting to the wall of concrete caissons for breakwaters. A part of the wall of typical concrete caissons was modeled to one-way slabs. And, structural behavior of the slabs subjected to repeated impact loads was investigated through falling-weight impact loading tests. As the result of the tests, it was confirmed that the test slabs showed punching shear failure after yield of reinforcement. It was examined how the repeated impact loads affected dynamic responses of reinforced concrete slabs, reaction forces and deflection of the slabs. And, it was confirmed that the number of repetition of impact loading until failure was increased in case of the slabs with PVA short fiber and in case of the slabs with higher reinforcement ratio. Furthermore, the method to calculate the maximum reaction force and the maximum deflection of the beams was confirmed applicable to the slabs.