The ground motion induced by close-in underground explosions can be characterised by very short duration (thus high principal frequency) and large peak acceleration. The response of building structures subjected to this type of ground motion is expected to differ significantly from typical seismic responses, due to the contribution of high-frequency local mode vibration. Evaluation based on a simplified analytical model indicates that one of the major effects of the blast ground motion is the unusually high shear force in the beam-column members of the structures, leading potentially to a brittle shear failure under certain circumstances. This paper attempts to provide some insights into such high shear phenomenon, associated with other response characteristics, concerning structural response to high-frequency horizontal ground motions. A preliminary experimental investigation to reproduce the blast ground motion effects on a small-scale model is also described. The test results provided some crucial evidence with regard to the local-mode vibration and the subsequent high shear, low displacement response features.
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