Seismic evaluations of existing reinforced concrete buildings have been extensive in Japan after the 1995 Hyogoken-Nambu earthquake. According to some reports, seismic evaluations found many RC buildings with very low concrete strength, i.e. less than half of the design concrete strength. It is important for retrofitting to clarify the mechanical characteristics of concrete from the existing reinforced concrete buildings. In this report stress strain curves of low strength concrete from the existing buildings constructed in the 1960s were investigated in comparison with concrete manufactured in the laboratory.
