Hybrid shake table testing method: Theory, implementation and application to midlevel isolation

A 2 m by 6 m unidirectional shake table was constructed at the University of California, Berkeley and combined with a real‐time hybrid simulation system creating a hybrid shake table. A series of tests were carried out to examine the viability of real‐time hybrid simulation techniques to perform experimental simulations of buildings with midlevel seismic isolation. The isolation system and superstructure were physically tested on the table while the portion of the building below the isolation plane was numerically modeled. OpenFresco was used to interface the numerical model with the control system. The isolated superstructure consisted of a two‐story steel moment frame on six triple friction pendulum bearings, which exhibit significant nonlinear velocity‐dependent behavior, necessitating real‐time testing. Shear building models with a range of periods were used to represent the portion of the building below the isolation plane. Increasing the number of degrees of freedom increased the control difficulty as higher modes were excited in the numerical model because of experimental errors caused predominantly by feedback noise and table tracking. Nonetheless, the results illustrate that hybrid shake table tests are indeed an economical and reasonably accurate method to assess the seismic behavior of midlevel isolation systems installed in a range of building configurations. Results showed that midlevel isolation was beneficial for the superstructure and, to a smaller extent, the substructure. However, to achieve maximum benefits, it is recommended that the effective period of the isolation system be sufficiently longer than the period of the substructure. Copyright © 2016 John Wiley & Sons, Ltd.