Dynamic Response of Rigid Blocks to Simultaneous Horizontal and Vertical Ground Shock

Abstract

Surface and underground explosions generate ground shock that might result in overturning of equipment housed in nearby structures owing to rocking responses. Comprehensive studies of rigid structure responses to seismic ground excitations have been reported. It was found that the rocking and sliding response of a rigid structure is highly nonlinear. The structure stability depends on the structure slenderness, as well as the ground motion amplitude, frequency and duration. Compared to an earthquake ground motion, a ground shock has a very large amplitude, high frequency contents and short duration. Moreover, vertical component of a ground shock is often higher than the gravitational acceleration g. This will cause the unanchored equipment fly into air. Therefore, the responses and stability regions of a rigid structure to blast induced ground shock will be very different from those under seismic ground motions. No study of rocking response and overturning of rigid structure to ground shock of amplitude more than 1.0 g can be found in the literature. As there might be some important equipment in buildings near a mining or a quarry site, or a military command center subjected to ground shock, understanding rigid structure response to ground shock is essential for protection of such equipment. In this study, theoretical derivation and numerical prediction of rocking and flying responses and overturning of rigid structures to simultaneous horizontal and vertical ground shock are carried out. Numerical results of stability regions of rigid structures to ground shock are derived. Particular attentions are paid to the case when the vertical ground shock is more than 1.0 g and the rigid structure flies into the air. Results are compared to those obtained with earthquake ground motions. Discussions of the rigid structure stability to ground shock are made.