Structural Response to High Frequency and Short Duration Impulsive Ground Motions
This paper presents a conceptual discussion on structural response to high frequency and short duration impulsive ground motion based on numerical analysis of a single degree of freedom system subjected to explosion-induced ground motion. Parametric study is performed to investigate the effect of impulse duration to natural period ratio on the maximum response of a single degree of freedom system to different types of impulsive loadings. As the loading duration of explosion-induced ground motion is smaller than half of the natural period of most civil engineering structures, maximum displacement response to underground explosion increases with the increase in total impulse, and it generally occurs in the free vibration phase. It is, therefore, necessary to consider longer time domain than the loading duration in the analytical prediction of structural damage due to high frequency and short duration loading. Numerical analyses are carried out on single degree of freedom systems with different natural periods to simulate and investigate the contribution of vibration modes on the overall displacement, velocity and acceleration responses. High frequency vibration modes, which are activated within the forced vibration phase, cause smaller displacement and larger acceleration response. However, free-vibration response is dominated by lower frequency fundamental mode that yields larger displacement and smaller acceleration response. Hence, structures are more likely to undergo displacement-induced damage in the free vibration phase, but relatively larger inertia force due primarily to high acceleration might be detrimental in the forced vibration phase.