Rolling Isolation Systems to Protect Building Contents from Earthquakes

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Fragile objects and mission-critical building contents such as hospital equipment may be placed on rolling isolation systems in order to protect them from damage during earthquake event. Rolling isolation systems consist of a matched pair of horizontal rectangular frames with rigid shallow dishes fixed to their corners. The dishes in the lower frame are concave up, and those in the upper frame are concave down. A large steel ball located between these dishes allows the upper frame to roll over the lower frame. The intensity of shaking that rolling isolation systems can protect against is determined largely by the diameter of the steel dishes. Currently one of the limiting factors for rolling systems is that they can protect objects only from horizontal shaking. Further, the best bowl shape and the proper amount of energy-damping for a particular application remain open questions. This award supports research to develop rolling isolation systems that can protect fragile building contents from severe horizontal and vertical motions. The resulting systems will incorporate specialized components for vertical isolation and multiple isolation layers. In developing these systems and assessing their promise for earthquake hazard mitigation, this research will lead to a better understanding of the true three-dimensional aspect of earthquake ground motions and their impact on fragile objects and structures. Ultimately, the proper design and implementation of rolling isolation will ensure that irreplaceable objects, critical hospital and telecommunications equipment, and digital infrastructure will remain operational during and after severe earthquakes, thereby mitigating the costs of these potentially disastrous events. Research opportunities for undergraduate and high school students will broaden the participation in this research. An industrial-outreach program will enhance the practical dissemination of the results. The non-holonomic constraints inherent to rolling isolation systems result in nonlinear coupling between lateral and rotational dynamics. Uniaxial and linearized models are therefore not sufficient to predict the response of these systems. The objective of this project is therefore to advance the performance and implementation of high-capacity isolation systems for equipment and components subjected to three-dimensional ground-motions. New mathematical models for the nonlinear dynamics of three-dimensional isolation systems will be derived and validated with experiments on a six degree of freedom shake table. These validated models will accelerate the design of new bowl topologies in order to maximize the effective displacement capacities of these systems. New methods of seismic hazard analysis will be developed that recognize the three-dimensional nature of ground motions and the threshold-sensitive behavior of buildings and contents.