Development of a large scale hybrid shake table and application to testing a friction slider isolated system

A unidirectional hybrid control shake table was constructed at the NEES lab at the University of California Berkeley. The 2 m by 6 m table is controlled using an MTS 493 Real-Time Controller. The control system provides PID closed loop control. The ability to have real-time hybrid shake table control is especially important for systems that have strong rate dependencies, such as friction sliding systems. A series of tests was carried out using a 1/3^rd scale friction pendulum isolated specimen to examine the viability of hybrid simulation techniques to perform experimental simulations of tall 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. Numerical modeling was done using OpenSees, and OpenFresco was used to interface between the numerical model and the control system. The isolated superstructure consisted of a one bay by two bay, two story steel moment frame on six triple friction pendulum bearings. These bearings have significant nonlinear behavior. The superstructure was expected to remain elastic; however, a small amount of yielding occurred. Various models were used to represent the portion of the building below the isolation plane, ranging from one to three degree of freedom models with periods from 0.125 to 1.0 seconds. Increasing the numbers of degrees of freedom increased the control difficulty as higher modes were excited in the numerical model. However, the results illustrate that hybrid shaking table tests are indeed feasible and produce reasonably accurate results.