Critical response of free-standing rocking blocks to the intense phase of an earthquake

The paper deals with a simplified approach to assess the critical response of slender rigid blocks to the intense phase of an earthquake. First, an artificial limit accelerogram is proposed to represent the most unfavorable effects of this phase. It consists of a sequence of instantaneous impulses, all applied right after the impact of the blocks on the ground, that continuously add energy to the system and cause rocking resonance. The results highlight 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. It is shown that the intermediate impulses have a stabilizing effect, increasing with their amplitude. Numerical analyses are performed to highlight the most significant aspects of the proposed approach.