Seismic Mitigation by Targeted Energy Transfer

In this chapter we examine the application of NESs to the problem of seismic pro¬tection of frame structures, though other infrastructural systems such as towers, bridges, and so forth will likely benefit from this technology. As has often been noted, infrastructure in the United States alone constitutes a societal investment counted in the trillions of dollars. While the fraction of infrastructure vulnerable to large-scale earthquakes is relatively limited by geography (i.e., the west coast, midwest and southeast, in addition to Alaska and Hawaii, are historically the most vulnerable areas), seismic activity capable of causing property damage has been recorded throughout the country and around the world. This provides the impetus to develop effective strategies to protect not only new construction but also existing structures likely to be subjected to seismic effects.

Various passive methods for mitigating the effects of earthquakes have been ap¬plied to large scale structures, including auxiliary dampers, base isolation systems, tuned mass dampers, as well as active, semi-active and hybrid systems. Detailed de¬scriptions and a comparision of the performance and limitations of each of these are beyond the scope of this chapter. Rather, the interested reader should refer to several excellent monographs, including Soong and Constantinou (1994), Soong (1990), Skinner et al. (1993), Chu et al. (2005), and recent review articles (Housner et al., 1997; Spencer and Sain, 1997; Soong and Spencer, 2002; Spencer and Nagarajaiah, 2003), as well as references therein for details. It seems clear, given the recent exten¬sive body of literature and burgeoning number of isolated structures,1 that the need exists for a fully passive isolation strategy, lightweight and inexpensive but capable of high performance over an extensive range of earthquakes of different properties.