ABSTRACT
This chapter analyses the behaviour of a rigid body excited into a rocking motion upon a rigid horizontal base, on which unilateral contacts, impacts and sliding can occur, causing a dissipation of the Kinetic Energy. An overturning condition defines the failure that occurs when the seismic acceleration reaches a value for which the moment due to self-weight equals the overturning moment. The analysis of the dynamic problem of a rocking element acquires fundamental importance in order to define a realistic "seismic strength reduction factor" which takes account of the ultimate inelastic response of a masonry structure. In order to evaluate the influence of the masonry elastic strains on the strength reduction factor, parametric analyses are performed considering the group of the seven spectrum-compatible time histories artificially derived by the spectrum A. The main vulnerabilities of existing unreinforced masonry buildings with poor connections are associated to the local out-of-plane response.
