Artificial Specimen Damping for Substructure Real-Time Hybrid Simulation

Damping plays an important role in structural dynamics by absorbing energy and reducing structural responses. The inherent damping in a building ranges from approximately 2 to 10% critical damping in the first mode; even greater levels of damping are achieved when including supplemental damping devices such as viscous oil dampers. When creating laboratory scale structures, it is difficult to achieve the target level of damping in the specimen. Solutions such as adding discrete damping devices are costly, while solutions such as adding foam or other dissipative materials may add undesired nonlinear behavior or increase the stiffness. This paper proposes a novel technique to introduce artificial damping to a dynamic specimen through shake table control. Artificial damping (AD) is introduced by designing a feedforward (FF) shake table controller that compensates for both shake table dynamics and achieves target specimen performance; that is, with larger damping than the original specimen. The performance of the proposed artificial damping by FF (AD-FF) is investigated for both traditional shake table testing and shake table real-time hybrid simulation (RTHS) through a uniaxial shake table and a two-story shear building specimen with very low damping. The target level of structural damping is accurately realized through the proposed AD-FF in both traditional shake table testing and RTHS. Moreover, damping can be introduced to specific modes of the structure, a feature that cannot be realized by using physical damping devices. In RTHS, the proposed AD-FF gives researches the ability to increase stability without changing the dominant structural response by adding damping to higher modes, even if they appear in the specimen.