Ductility demand spectra for multiple near- and far-fault earthquakes

This study presents ductility demand spectra for single degree of freedom (SDOF) systems under multiple near- and far-fault seismic ground motions. The main innovation has to do with the quantification of the seismic sequence effect directly into ductility demands, a phenomenon which has not been studied in the past. Due to lack of real seismic sequences records, this paper examines only artificial sequences, where they have been generated by a rational and random combination of real single events. A statistical investigation of more than 120 millions dynamic inelastic analyses is conducted to obtain expressions for the ductility demands, in terms of the period of vibration, the viscous damping, the post-yield stiffness and the force reduction factor. It is found that due to the seismic sequence effect, it is certainly insufficient to consider only the ‘design earthquake’, since this traditional hypothesis leads to underestimated ductility demands and therefore to underestimated structural damage.