Recently, studies on seismic energy isolation and damping structures abound and a number of attenuation mechanisms have been proposed. One of them proposes to utilize the elasto-plastic hysteresis of steel, using low yield strength steel as material. This study conducted low-cycle fatigue tests to clarify the low-cycle fatigue characteristics. Hysteresis characteristics and energy absorption characteristics of low yield strength steel will be discussed in the next report. As a result, the following conclusions were obtained concerning low-cycle fatigue characteristics of low yield strength steel. (1) The low-cycle fatigue characteristics (ε-N_f relationship) of low yield strength steel can be expressed by the Manson-Coffin equation. (2) Despite major differences in static ductility and other properties, low-cycle fatigue characteristics vary little by steel type. (3) The effect of strain rate on low-cycle fatigue characteristics is small. (4) The Monson-Coffin equation's coefficient C_1 and m_1 of low yield strength steel deviate from the values obtainable from the conventionally proposed equations. (5) A correlation of C_1=2.1/460^<ml> exists in all types of steel.
