Damage-based yield point spectra for sequence-type ground motions

Structural damage caused by mainshock can further be aggravated by aftershocks, which can lead to structural collapse. The current practices on the seismic design of structures generally only consider mainshock effects. This manuscript therefore presents the investigation on damage-based yield point spectra (YPS) of a single-degree-of-freedom (SDOF) system under sequential earthquakes. The collected sequence-type ground motions are recorded from 16 earthquake events and classified to four classes. The aftershocks in sequence are scaled according to different relative intensity levels. The modified Park-Ang model, which consists of maximum displacement and hysteretic energy dissipation, is employed to calculate YPS. The effects of period, ductility factor, damage index, site category, aftershock intensity, and structural damping are statistically studied. The results prove that the strong aftershock ground motion has more distinct influences on the YPS. In particular, the yield strength coefficient demand under seismic sequence increases by 10%-50%. The yield strength coefficient demand determined by the damage-based YPS is greater than that determined by the ductility-based YPS-the former is 10%-40% higher than the latter. Finally, the empirical expression of damage-based YPS is established by statistical mean method and regression analysis.