Abstract | This paper contributes a pioneering numerical study to assess statistically, within the performance based earthquake engineering framework, the effect of the evolutionary frequency content observed in field recorded earthquake induced ground motions (GMs) to peak seismic structural response of yielding multi-degree-of-freedom structures. To this aim, the average rate of change of the mean GM frequency content, termed alpha, α, is used as a proxy to quantify the time-varying attributes of recorded GMs. The α index is invariable to GM scaling and is herein computed by wavelet-transforming of GMs using Morlet wavelets. Further, the concept of spectrally equivalent GMs is used in conjunction with a large database of 1222 far-field GMs to construct two sets of 50 GMs each having significantly different median α values but closely matching mean response spectral shapes, as well as effective duration and mean period distributions. Numerical results obtained from applying incremental dynamics analysis (IDA) to a lumped-mass plasticity model of a benchmark 7-storey code-compliant reinforced concrete frame demonstrate that median peak inter-storey drift ratio demand posed by the GM set with high a values is significantly larger from the GM set with low α values having negligible time-variation of mean frequency content. It is further found that the evolving mean GM frequency content introduces significant discrepancy to the median IDA curves irrespective of the quality of the intensity measure used for GM scaling. These findings suggest that the evolutionary GM frequency content should be accounted for in GM record selection used for seismic performance evaluation of structures. To this aim, the a index can serve as a potent record selection criterion.