Confined Concrete with High-Strength Materials

The first purpose of this report is to introduce experiments on 91 square confined concrete specimens and 59 circular ones with high strength materials subjected to monotonic and concentric axial loading conducted in Japan recently. The concrete strength of specimens ranged from 27 MPa to 132 MPa and the strength of transverse reinforcement ranged from 173 MPa to 1360 MPa. Small size specimens with section dimension of about 200 mm have been conducted mainly but it is notable that four quasi-real size specimens with 470 mm square section were tested through the New RC Projects. The second purpose of this report is to introduce the recent research works on models, examining their feasibility. Conclusions included the following: (1) Regarding the maximum strength of the square confined specimens, the predictions with the models proposed by Sakino et al. and Watanabe et al. were accurate enough especially for quasi-real size specimens. However, the accuracy of the prediction for the axial strain became much worse compared with that for maximum strength in each model. (2) Regarding the stress-strain curves, the relations of the model by Sakino were quite similar to the observed curves until the end of the loading of quasi-real size specimens. (3) Regarding the effects of the material strengths, assuming that the model by Sakino was true, it was concluded that the stress increase was independent of the concrete strength and proportional to the strength of transverse reinforcement as far as it reached 687 MPa. On the other hand, the strain increase depended on the concrete strength: it decreased with the increasing value of the concrete strength.