The softening response properties of plain concrete, which directly affect the structural capacity of the concrete containment building of nuclear power plants, were studied via direct tension tests using large-size concrete specimens with two notches. A variation of two and three levels of the concrete strength and the maximum size of coarse aggregate, respectively, was considered. Two independently controlled actuators were used to ensure a homogeneous increase of crack mouth opening displacement (CMOD) on the top and bottom notches of the specimen and to avoid secondary flexural stresses. From the tests, the complete load-CMOD responses with stable post-peak descending curves were obtained for each specimen. The fracture energy data obtained using the complete load-CMOD responses and one evaluated using a classical prediction equation were compared. The results, owing to size effect, indicated that the fracture energy obtained in the current investigation is larger on average than that obtained using a classical prediction equation. The direct tensile strength of the large-size specimens was, however, about half the splitting tensile strength of the cylindrical specimens.
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