IN-PLANE MULTI-DIRECTIONAL CHARACTERIZATION, MODELING, AND REAL-TIME HYBRID SIMULATION TESTING OF ROLLING PENDULUM SEISMIC ISOLATION SYSTEMS FOR SENSITIVE EQUIPMENT

Abstract

<p>Earthquakes, which are inherently multi-directional in nature, can significantly damage the built environment and cause loss of life. These catastrophic consequences can be alleviated through seismic isolation to protect the building and/or its contents. Rolling pendulum (RP) isolation systems are used to protect sensitive and critical equipment, providing functional post-earthquake recovery for community resilience. However, their behavior and performance under multi-directional loading conditions have not been thoroughly studied. Therefore, to address this need, this dissertation aims to characterize, model, and test RP seismic isolation systems under in-plane multi-directional demands, as a key step for their safe and cost-effective implementation in practice.</p> <p>First, the general concept of seismic response modification strategies (SRMS) is introduced from a historical perspective, using Japan as a reference, and making a comparison with the U.S. Then, the specific SRMS (seismic isolation) and experiment technique (hybrid simulation) considered in this dissertation are further studied. A thorough literature review of research and advances in seismic isolation through hybrid simulation is conducted. It is found that the number of tests performed at full-scale, incorporating nonlinearities, using real-time loading rate, and applying multi-directional demands is limited. Moreover, RP bearings have been studied using hybrid simulation a few times in the past, but using uni-directional tests.</p> <p>Next, the behavior of RP seismic isolation systems under multi-directional displacement-controlled characterization protocols is studied. A full-scale RP isolation system was tested at the NSF-funded NHERI Lehigh EF. For the experimental campaign, 22 characterization tests are defined, which are a combination of different planar orbits, amplitudes, frequencies, and velocities. The experiments investigate the effects of the rolling surface treatment, different tributary weights, and loading rate, as well as isotropy and repeatability. A physics-based mathematical model of a single RP isolation bearing is developed, which is subsequently extended to RP isolation systems comprised of multiple RP bearings. The mathematical model and the experimental results are compared. It is concluded that the theoretical results were able to effectively and consistently predict the main features of the RP seismic isolation system exhibited during the experimental tests. Therefore, the theoretical model has the potential to be used by researchers and designers as a reliable way to simulate the behavior of RP bearings subject to in-plane multi-directional demands.</p> <p>Finally, a real-time hybrid simulation (RTHS) framework for the multi-directional testing of RP seismic isolation systems under bi-directional ground motions is developed. The goal is to evaluate the performance of RP bearings under conditions as closely resembling practical use as possible and considering most of the parameters influencing the response of nonstructural building contents subject to seismic demands. The experimental substructure is the same setup as used for the characterization tests, and the analytical substructure is a three-dimensional, nonlinear finite element model of the supporting building and the isolated object. Based on these results, it is concluded that the RTHS framework is capable of effectively simulating the behavior of three-dimensional structural systems coupled with RP isolated building contents subject to multi-directional demands in the plane.</p>