Research Activities on Confined Concrete in Japan

A key of seismic design of ductile frame is to provide the adequate flexural ductility to potential plastic hinge regions. This is realized by limiting the amount of tension reinforcement index, providing transverse reinforcement and others. For columns, the application of transverse reinforcement to potential plastic hinge region is essential, that is, the compressive ductility of concrete is improved and results in larger flexural ductility. In the 1980s, a new reinforced concrete (RC) project was carried out as a Japanese National Project to establish the design and construction guidelines for high-rise buildings, up to 200 meters high. For columns at the lower part of high-rise buildings, the use of high-strength (HSC) concrete is required. However, HSC fails in brittle manner and results in small flexural ductility of potential plastic hinges. Therefore the new RC project gave an opportunity to re-recognize the importance of lateral confinement to concrete. This paper presents the recent research works on confined concrete in Japan, mainly for HSC. Some experimental works and idealizations of stress-strain curve of confined concrete are introduced. Maximum compressive strength covered in this paper is 176 MPa.