ROCKING RESONANCE CONDITIONS OF LARGE AND SLENDER RIGID BLOCKS UNDER THE INTENSE PHASE OF AN EARTHQUAKE

A simplified approach is proposed in this paper for assessing the safety levels of the seismic response of large and slender rigid masonry blocks. The dynamic behavior of rigid free-standing blocks subjected to earthquake ground motions is highly non-linear and sensitive to small perturbations of various parameters. Many difficulties arise in defining reliable response spectra for such systems and these are well known in the literature. An artificial limit accelerogram is herein proposed to represent the most unfavorable effects of the intense phase of an earthquake. This consists of a sequence of instantaneous impulses, all applied right after the impact of the blocks on the ground. The resonance conditions also aim at highlighting to what extent the ground motion details and the system parameters can influence the rocking response. A secondary sequence of intermediate impulses is then introduced to reduce the resonance effects and to cover a broad range of conditions. Approximate equations of motion of the rocking blocks are also proposed and numerical analyses are performed to highlight the most significant aspects of the proposed approach.