New Seismic Testing Method. II: Proof for MDOF Systems

Abstract

This paper deals with the theory of a new seismic testing method based on a separation of the ground motion components into two arbitrary parts; the simulation of the first part is accomplished with a conventional shaking table, while the second part is carried out with actuators acting directly onto the structure. A demonstration is presented of the method's validity for systems with many degrees of freedom, including those that are subjected to inelastic deformations, large displacements, material and/or geometric nonlinearities, and/or the effects of gravity (i.e., the so-called Π-Δ effects). The motivation for the proposed method lies in the possibility of optimizing the two ground motion components from the point of view of the power or force demands on the table and actuators or the mechanical characteristics of these devices. This strategy could offer significant advantages, among which are a considerable reduction in the total power required to drive the combined system, a potential simplification of the support mechanisms needed to shore up the structure when vertical and rotational seismic components are simulated, the opportunity for expanding the capabilities of existing shaking tables, or the possibility of employing novel low-frequency force actuators (such as jet engines or unbalanced flywheels), which need not have the capacity of rapidly changing the effective thrust.