Development and implementation of the effective force testing method for seismic simulation of large–scale structures

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This paper describes the development and experimental implementation of a real–time earthquake simulation test method for large–scale structures. The method, effective force testing (EFT), is based on a transformation of coordinates, in which case the structure is fixed at the base (similar to the set–up for the pseudo–dynamic (PsD) test method); however, in the case of EFT, the method is based on a force–control algorithm rather than a displacement–control algorithm. Effective forces, equivalent to the mass of each storey level multiplied by the ground acceleration, are applied at each respective storey. As such, the EFT forces are known a priori for any ground acceleration record. As opposed to the PsD test method in which the ground displacements to be imposed are affected by the measured structural response as the stiffness changes. As in the case of the PsD test method, the EFT method is suitable for testing any type of structural system that can be idealized as a series of lumped masses (e.g. building or bridge structures). Research has been conducted on a linear elastic single–degree–of–freedom system at the University of Minnesota to develop and investigate implementation of the EFT method. A direct application of the EFT method was found to be ineffective because of a natural velocity feedback phenomenon between the actuator and the structure to which it is attached. A detailed model of the control, hydraulic and structural systems was developed to study the interaction problem and other nonlinear responses in the system. The implementation of an additional feedback loop using the measured velocity of the test structure was shown to be successful at overcoming the problems associated with actuator–ndash;control–ndash;structure interaction, indicating that EFT is a viable real–time method for seismic simulation studies.