[en] In LWR plants etc. the reinforced concrete structures are used under high-temperature environment. In order to grasp their high-temperature behavior, experimental studies have been conducted at temperatures from 100 deg C up to 500 deg C, allowing the moisture in concrete to dissipate freely. In strength and elastic modulus of the concrete there is evident temperature dependence, but the data scatter considerably depending on the experimental conditions; their quantitative evaluation is impossible. Concerning mechanical properties of reinforcing bars, the temperature dependence of their yield-point strength and the stress-strain characteristic following the yield have influences on the yield point and the ultimate yield point of the reinforced concrete beam, respectively. In high-temperature behavior of the reinforced concrete beam, the difference in thermal expansion coefficient between reinforcing bars and concrete has also influence. (Mori, K.)