Response spectra of rigid blocks with uncertain behavior

The dynamic behavior of rigid blocks can effectively describe a wide variety of structural problems. The seismic behavior of art objects, the out-of-plane response of masonry façades, the foundation uplift of stiff structures, the rocking response of bridges’ piers (often adopted as seismic isolation strategy), represent only few examples of how the concepts behind dynamic rigid body motion govern problems with very different features. There is a wide literature on the topic aiming at understanding the dynamic behavior of rigid blocks and at proposing strategies to employ the basic principles of rocking motion to assess and seismically protect buildings and objects. In this paper an experimental survey on the seismic response of rigid blocks, characterized by different aspect ratios and scale factors, is presented. The results are reported in terms of response spectra considering the maximum rotation of the blocks. The experimental research is focused on small rigid blocks. However, the experimental results are also numerically simulated showing that widely used numerical models can fail in the prediction of the actual dynamic response of rigid blocks leading to wrong safety considerations. A marked uncertainty in the response of the blocks is identified under specific conditions that the author tried to identify and discuss. The conclusive remarks could be of help to assess the risk with respect to the overturning of rigid blocks under seismic excitation and to provide some considerations with respect to seismic protection strategies.