Softening response properties of plain concrete by large-scale direct tension tests

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.