New Seismic Testing Method. I: Fundamental Concepts

A new hybrid testing method is presented, which is based on separating the ground motion components into two arbitrary additive parts. The simulation of the first part is accomplished with a conventional shaking table, whereas the second is carried out with actuators acting directly onto the structure. The concept is demonstrated here by means of a simple one-degree-of-freedom system, but a companion paper in this issue shows that it is also valid for a system with many degrees of freedom, including those that exhibit material and/or geometric nonlinearities. The hybrid strategy presented here could offer several advantages in the design of a seismic testing device, particularly when the action of multiple ground motion components must be considered simultaneously. Among the potential benefits one could cite: considerable reductions in the total power and energy requirements; substantial decrease in stroke and thrust of the actuators needed to move the table or exert forces on the structural masses; simplification of the support mechanisms needed to shore up the structure and resist overturning moments when vertical and rotational components are simulated; and the possibility of using novel, low-frequency force actuators (such as jet engines or unbalanced flywheels), which need not have the capacity of rapidly changing the thrust.