Real Time Hybrid Simulation Testing of a Rolling Isolation System

Abstract

Seismic base isolation is a common engineering practice in regions where earthquake activity is frequent. Base isolators can be designed to reduce structural displacement and sustained accelerations, mitigating the effects of an earthquake induced ground acceleration on a structure. Although base isolators are highly effective in reducing the transmission of these accelerations, there exists uncertainty in the dynamic response of base-isolated structural systems under varying frequencies (low- and high-frequency seismic waves). These dynamic response uncertainties can be taken into account with full-scale testing of base isolated structures; however, high costs and lack of resources for full-scale testing limit research in this field. Real-time hybrid simulation (RTHS), which involves numerical modeling of a structure’s dynamic behavior while testing a portion of the structural system, allows researchers to bypass the challenges of full-scaletesting. RTHS allows for an extended scope of testing, cost efficiency, flexibility, adaptability, and enhances the accuracy and precision of numerical modeling techniques in this field. This thesis explores the dynamic response of a superstructure on a ball-n-cone designed rolling isolation systems (RIS). The RIS allows for an increase in displacement capacity while reducing ground acceleration transmission with the use of a rubber rolling element (ball). A RTHS testing framework is developed, in which a state-space numerical model is utilized to model the dynamic behavior of a superstructure while experimentally testing a RIS supporting an idealized mass. A Quanser Shake Table II (STII) was utilized to induce relative displacement across the RIS, while the top of the RIS was help fixed using a brace equipped with a load cell to measure the restoring force. Control and compensation using static-time series compensation (STS) is applied to ensure accurate execution of STII command displacement and to mitigate communication delay during experimental testing at time steps of 0.001 s. Performance of the RTHS testing framework is further validated with a linear elastic structure. The RIS was determined to have high displacement response mitigation for one degree-of-freedom (1DOF) and two degree-of-freedom (2DOF) cases. Impulse loads and band-limited white noise (BLWN) excitations were successfully mitigated. However, high-frequency oscillatory responses (5-8 Hz) were observed at small displacements. These were determined to be an artifact of RTHS, where negative damping within the RTHS testing system is equal to damping within the RIS. This led to zero total damping, resulting in the observed oscillatory displacements after the strong shaking.