This paper proposes a simplified method to predict the peak displacement and base shear of a single-degree-of-freedom nonlinear structure subjected to earthquakes. The method considers bilinear hysteresis, and it can express the peak responses as functions of the dynamic property of the structure and the elastic response spectrum. It is based on equivalent linearization as well as spectrum modification and reduction, reflecting increase in equivalent vibration period and damping ratio. The method is validated through numerous time history analyses over a wide range of elastic vibration period, yield strength, post-yield stiffness, ductility, and earthquake type.
