Torsionally coupled primary-secondary systems

Critical equipment in lifeline installations such as power plants, hospitals, refineries and hazardous chemical plants are designed to remain functional during and after an earthquake. The equipment and non-structural components or Secondary systems (S-system) are subjected to dynamic loads that depend on the dynamic interaction with the main supporting structure or Primary system (Psystem). Whenever the equipment or the structure has eccentricity, further dynamic interaction is introduced. Limited studies have been attempted to characterize the response of the secondary systems attached to torsionally coupled primary system. In addition, the experimental verification for any of the analytical approaches is still lacking. The objective of the present investigation is to experimentally characterize the response of torsionally coupled nonlinear PSsystem and to evaluate the effect of the S-system eccentricity with respect to the P-system's Centre of Mass and Centre of Rigidity. The tested PS-systems are subjected to earthquake records using a small shake table. The degree of torsional coupling of the modelled P-system is adjusted by changing the location of masses eccentricity. The model parameters were selected to represent a practical range of cases. From this experimental investigation it was found that the yielding of the primary system has significant implications on the deamplification of near tuned secondary system response. The location of the secondary system mounted on the primary system affects the peak response amplification, and interaction with the coupled primary system.