The Influence of Strong-Motion Duration

Abstract. The influence of strong-motion duration on the response of saturated soils is clearly recognised
and accounted for in the assessment of liquefaction potential. The degree to which duration
of shaking influences damage to structures, however, remains a topic of debate, with resolution of the
issue complicated by the variety of definitions of duration and the variety of structural behaviours, as
well as the difficulty of decoupling the specific effect of duration from other features of the ground
motion. A suite of seven structural models with strength and stiffness degrading characteristics,
designed to reflect the seismic behaviour of masonry structures commonly encountered in many parts
of Europe, are analysed using a suite of almost 500 strong-motion accelerograms. Correlations are
explored between the damage, measured in terms of the strength degradation, and a range of strongmotion
parameters, demonstrating that Arias intensity and spectral acceleration at the fundamental
initial period of the structure are both reasonably good damage indicators for such structures. A
significantly improved correlation is obtained by using the elastic spectral accelerations averaged
over a period range from the initial period of the structure to a value approximately three times
greater, reflecting the stiffness degradation as the shaking progresses. The scatter in the correlation
is shown to be partially explained by differences in duration