  This study proposes a new approach to incorporate motion duration in
incremental dynamic assessments. In the proposed methodology, at each intensity
level, a simulation-based approach, which is verified with actual data, is
employed to determine the median duration and the median acceleration spectra
of ground motions expected to occur at the site. Afterward, at each intensity
level, artificial or spectrally matched motions are produced based on the
median acceleration spectra and the median duration, indicating that different
intensity levels are directly covered by the generated artificial or adjusted
motions rather than just scaling up and down a set of recorded ground motions.
In the proposed methodology, duration and acceleration spectral shape changes
against intensity level while they remain the same for different intensity
levels in approach where responses are derived by scaling up and down of a set
of ground motions. The functional relationship between duration and seismic
intensity level, which is vital for the estimation of median duration at each
intensity level, is firstly investigated for the sites with different soil
conditions and rupture distances. Not only is it demonstrated that the data can
fit into exponential functions, but the sensitivity of the functions against
different parameters is also explored as well. The proposed duration-consistent
incremental seismic assessment is used in nonlinear seismic assessment of two
single degree of freedom structures, with and without a degrading behavior
capability. It is revealed that when changes in duration and spectral shape of
the motions at different intensity levels are considered in the nonlinear
dynamic analysis, an impactful influence that cannot be easily ignored is
witnessed in the structural responses of incremental analyses.
