To improve the earthquake resistance of antiseismic cylindrical walls of existing nuclear power plants, new seismic retrofitting method is planned in which concrete is poured on one side of the wall after installing additional rebars and shear connectors, to produce a monolithic structure with increased thickness. The loading tests were carried out to verify the validity of this reinforcement method. The specimens consisted of two types: one in which the amounts of inner and outer reinforcements of the doubly arranged wall reinforcements were varied, simulating the retrofitted condition, and one for comparison, in which the inner and outer steel reinforcements were evenly distributed. The experimental results showed no substantial differences in the behaviors of the two specimens up to the ultimate state, each displaying roughly equivalent shear strength.

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