Investigation of story ductility demands of inelastic concrete frames subjected to repeated earthquakes

The present study focuses on the influence of repeated earthquakes on the maximum story ductility demands of three-dimensional inelastic concrete frames. A comprehensive assessment is conducted using generic frames with 3-, 6-, 12-, and 18-story structures. Each is assumed to have behaviour factors of 1.5, 2, 4, and 6 referring to Eurocode 8. Stiffness and strength degrading hysteresis rule to represent reinforced concrete structure is considered in the plastic hinge of members. Twenty ground motions are selected, and single, double, and triple events of synthetic repeated earthquakes are considered. Some interesting findings are provided showing that repeated earthquakes significantly increase the story ductility demand of inelastic concrete frames. On average, relative increment of maximum story ductility demand is experienced 1.4 and 1.3 times when double and triple events of repeated earthquakes are induced, respectively. Empirical relationships are also provided to predict these increments where their efficiency is presented examining characteristic 3- and 8-story reinforced concrete buildings.

► We simulate 48 RC frames designed according EC8 excited by 60 seismic sequences.
► The frames have 4 periods, 4 behaviour factors, and 3 rotation capacities of member.
► The DCM frames exhibit larger increment of story ductility than the DCH frames.
► The formulas to predict the increment of maximum story ductility is proposed.