This paper derives equations to predict hysteresis energy of SDOF systems for a wide range of damping ratio. In order to confirm the effectiveness of the proposed equations, time domain analyses under recorded earthquakes are conducted for a lot of SDOF systems with various yield strengths and damping ratios. Concluding remarks are as follows.
1. For 2 % damping ratio, not only the proposed equations but also almost previous equations show good corresponding to time domain analyses.
2. For 5% or 15% damping ratio, the proposed equations show good corresponding to time domain analyses while almost previous equations overestimate hysteresis energy.
