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Title: Evaluation of Rolling-Type Isolation Systems for Seismic Hazard Mitigation
Nonstructural components within mission-critical facilities such as hospitals and telecommunication facilities are vital to a community's resilience when subjected to a seismic event. Building contents like medical and computer equipment are critical for the response and recovery process following an earthquake. A solution to protecting these systems from seismic hazards is base isolation. Base isolation systems are designed to decouple an entire building structure from destructive ground motions. For other buildings not fitted with base isolation, a practical and economical solution to protect vital building contents from earthquake-induced floor motion is to isolate individual equipment using, for example, rolling-type isolation systems (RISs). RISs are a relatively new innovation for protecting equipment. These systems function as a pendulum-like mechanism to convert horizontal motion into vertical motion. An accompanying change in potential energy creates a restoring force related to the slope of the rolling surface. This study seeks to evaluate the seismic hazard mitigation performance of RISs, as well as propose and test a novel double RIS. A physics-based mathematical model was developed for a single RIS via Lagrange's equation adhering to the kinetic constraint of rolling without slipping. The mathematical model for the single RIS was used to predict the response and characteristics of these systems. A physical model was fabricated with additive manufacturing and tested against multiple earthquakes on a shake table. The system featured a single-degree-of-freedom (SDOF) structure to represent a piece of equipment. The results showed that the RIS effectively reduced accelerations felt by the SDOF compared to a fixed-base SDOF system. The single RIS experienced the most substantial accelerations from the Mendocino record, which contains low-frequency content in the range of the RIS's natural period (1-2 seconds). Earthquakes with these long-period components have the potential to cause impacts within the isolation bearing that would degrade its performance. To accommodate large displacements, a double RIS is proposed. The double RIS has twice the displacement capacity of a single RIS without increasing the size of the bearing components. The mathematical model for the single RIS was extended to the double RIS following a similar procedure. Two approaches were used to evaluate the double RIS's performance: stochastic and deterministic. The stochastic response of the double RIS under stationary white noise excitation was evaluated for relevant system parameters, namely mass ratio and tuning frequency. Both broadband and filtered (Kanai-Tajimi) white noise excitation were considered. The response variances of the double RIS were normalized by a baseline single RIS for a comparative study, from which design parameter maps were drawn. A deterministic analysis was conducted to further evaluate the double RIS in the case of nonstationary excitation. The telecommunication equipment qualification waveform, VERTEQ-II, was used for these numerical simulations. Peak transient responses were compared to the single RIS responses, and optimal design regions were determined. General design guidelines based on the stochastic and deterministic analyses are given. The results aim to provide a framework usable in the preliminary design stage of a double RIS to mitigate seismic responses.  more » « less
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The University of Oklahoma Libraries
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National Science Foundation
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  1. null (Ed.)
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