Collaborative Research: Seismic Isolation of Embedded Foundations Using Periodic Meta-material Barriers to Create Resilient Structures

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The severity of damage caused by earthquakes over the past decades underscores the need for improvements to reduce the associated threat to America's economy and the safety of its citizens. Evidence in more recent earthquakes shows that conventional seismic isolation systems are effective in reducing the damage from horizontal components of earthquake shaking. However, conventional isolation systems are not well suited for protection against the vertical components of earthquake shaking, nor can they be readily used for embedded or underground structures. To overcome the disadvantages in the conventional seismic isolation systems, we have developed innovative periodic material-based seismic isolators. Periodic material-based seismic isolators possess distinct frequency band gaps which block, filter, and reflect incoming ground vibrations with frequencies falling between these gaps. These frequency band gaps can be designed to block ground motions that are harmful to structures. Previous studies have shown periodic foundations, made of periodic material-based seismic isolators, to be effective in isolating ground motions for structures built on the ground surface. This project will investigate periodic material-based seismic isolation systems of embedded or underground structures. The knowledge gained from this research will have broad and far-reaching significance that goes beyond conventional commercial and residential buildings and extends to all types of structures located in seismic zones. Results from this research can impact the development of seismic design codes on a universal basis.This project involves the investigation of periodic meta-material barriers-based seismic isolation systems for development of resilient structures. The periodic meta-material barriers-based seismic isolation system is a complementary system to be applied together with periodic foundations. Both periodic barriers and periodic foundations are inspired by phononic crystal, which can isolate the seismic waves using the frequency band gap mechanism. With this mechanism, the incoming seismic waves falling within the frequency band gaps of the properly designed periodic foundations or barriers will be filtered out regardless of the direction of wave propagation. The periodic foundations, which also act as the foundation of the superstructure, can isolate seismic waves coming from the soil beneath the embedded foundations. Periodic barriers, on the other hand, will isolate the embedded structures from the incoming lateral seismic waves. The combination of periodic barriers and periodic foundation will form an isolation envelope for the embedded foundations. This project will study the effectiveness of the combined periodic barriers and the periodic foundation systems through numerical simulation and field studies. The field studies will examine how seismic waves propagate in soil with and without periodic barriers. The main objective of this project is to develop periodic barriers that can effectively attenuate incoming seismic waves. This project will also generate a set of simplified design guidelines for practicing engineers to design periodic barriers that will attenuate seismic shaking.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.