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Constant-ductility energy factors of SDOF systems subjected to mainshock–aftershock sequences

This article focuses on the energy factor of single-degree-of-freedom (SDOF) systems subjected to mainshock–aftershock (MSAS) sequences, of which 163 and 143 are collected from crustal and subduction regions, respectively. The recorded MSAS sequences are divided into four groups based on the relative intensity that is defined as the ratio of the peak ground acceleration (PGA) of an aftershock to the PGA of the corresponding mainshock. Constant-ductility inelastic spectra are calculated to assess the energy factor, γ, defined as the ratio of the covered area of the skeleton load-deformation curve of the inelastic structural system to that of the corresponding elastic system with identical elastic properties, by considering various levels of structural inelasticity. Moreover, the effect of the hysteresis law, damping ratio, post-yield stiffness ratio, soil condition, and relative intensity on the energy factor is thoroughly analyzed. A predictive model is also developed as a function of the ductility factor, vibration period, damping ratio, and post-yield stiffness ratio. Such a model is expected to facilitate the energy-based seismic design of structures.