  This paper aims to investigate the effects of motion duration on the
structural seismic demands, seeking potential correlations between motion
durations and structural responses at several seismic intensity levels. Three
seismic intensity levels with 100years, 475years, and 2475years earthquake
return periods (RPs) are first considered for correlation computations.
Spectrally matched ground motions are employed to isolate the contribution of
duration from the effects of ground motion amplitudes and response spectral
shape. Four single degree of freedom systems derived from four real reinforced
concrete structures are studied, where both degrading and non-degrading
equivalent SDOF systems are included for structural modeling. Results show a
low positive correlation between motion duration and structural displacement
demand, but this correlation increases with an increase in earthquake RP. It is
also investigated whether or not this insignificant positive correlation has an
impact on the incremental dynamic analysis curves. The spectrally matched
ground motions are divided into two distinct groups in this case: short and
long duration ground motions. The comparison of incremental dynamic analysis of
these two groups at the collapse limit reveals that long-duration ground
motions can cause up to a 20 percent decrease in the spectral acceleration
demand of considered structural systems.
