A set of 4620 single-degree-of-freedom oscillators have been taken into consideration which has different natural periods, different critical damping ratios and different backbone curves. The initial concrete cracking phenomenon was taken into account in the considered backbone curves. Two sets of ground motion records were also selected to be representatives of free-field and near-field events. The incremental dynamic analysis was performed in order to quantify the seismic demand in different intensity levels. Then, the relationship between natural period, ductility factor and strength reduction factor was derived versus intensity measure. Influence of each input variable was also studied in which revealed that the natural period and the concrete initial cracking have significant influence on the seismic demand of oscillators.
