Dottorato in INGEGNERIA STRUTTURALE E GEOTECNICA

Titolo della tesi: Seismic Assessment and Protection Strategies Using Multi-Rocking-Body Dynamics

In this thesis, novel multi-rocking-body models are developed to investigate the dynamic response of rigid blocks coupled with flexible elements. The equations governing the problem, characterized by the transition between rocking modes, and the solution algorithm are illustrated for each of the proposed model. The attention is focused on two subjects: a) out-of-plane mechanism of a masonry wall connected to a flexible diaphragm; b) base isolation protection for slender stacked rocking objects. First, a non-linear dynamic model of a two-bodies vertical spanning wall elastically restrained at the top is developed. The dynamic response of specific walls to a given earthquake record highlighted the strong nonlinearity of the numerical model, demonstrating how the motion is characterized by several pattern changes with and without impacts. For these reasons, using a specific optimization algorithm the previous model is validated with experimental data. The calibrated model is then used to carry out a parametric analysis on the mechanical and geometrical characteristics of the wall. The study highlights interesting results, such as the observed reverse scale effect caused from the top spring. Then, a novel multi-body rocking model is developed to investigate the dynamic response of two stacked rigid blocks placed on a linear base isolation device. The model is used to investigate the dynamic response of a realistic statue-pedestal system subject to pulse-like ground motions. The analysis shows that, in general, increasing the period of the base isolation increases the safety level of the rocking system. Further, for large period pulses or small size blocks, the linear isolator can amplify the ground motion, resulting in a lower minimum overturning acceleration than the non-isolated system. This potentially dangerous phenomenon disappears if the pulse period is reduced, or the block size is increased. The analysis also demonstrates how the dynamic response of the two stacked blocks is equivalent to that of a single block configuration coincident with the whole system assumed monolithic or the upper block alone, whichever is more slender. Finally, simplified displacement based design strategies for isolated rocking rigid blocks are proposed.