Rocking Response and Overturning of Anchored Equipment under Seismic Excitations

iii This report investigates the transient rocking response of anchored electrical equipment and other anchored structures that can be approximated as rigid blocks. Practical issues that control over-turning, such as the effect of the vertical component of ground accelerations and the effect of the coefficient of restitution during impact, are also addressed. The anchorages of equipment are assumed to have a pre-yielding linear behavior, a finite post-yielding strength, and some ductility. The nonlinear behavior of the restrainers in conjunc-tion with the nonlinear dynamics of a rocking block yield a set of highly nonlinear equations which are solved numerically using a state-space formulation. The study uncovers that while for most of the frequency range, anchored blocks survive higher accelerations than free-standing blocks, there is a short frequency range where the opposite happens. This counterintuitive behav-ior is the result of the many ways that a block might overturn. It is shown that under a one-sine (Type-A) pulse or one-cosine (Type-B) pulse with frequency, a free-standing block with fre-quency parameter has two modes of overturning; one with impact (mode 1), and one withou