UC Berkeley

Seismic isolators, and more specifically, triple friction pendulum (TFP) bearings are ideal earthquake protection technologies for use in performance-based design because they can be designed to achieve multiple performance objectives corresponding to different levels of ground shaking. TFP bearings can limit structure displacement during a design basis (or maximum considered) earthquake while the still effectively isolating the structure under the service level earthquake, reducing seismic demands on the structure and its non-structural components. Furthermore, TFP bearings allow for a gradual transfer of force to the superstructure at ultimate displacement.

This dissertation presents an advanced bidirectional model for the TFP bearing that is based on the kinematic and compatibility relationships of the components of the bearing. To validate the model, experimental characterization tests were conducted on the shake table at the University of California, Berkeley. Two distinct types of experiments were conducted: (a) displacement-controlled tests in which the bearings were cycled through specified orbits and (b) unrestrained tests in which the table replicated ground motions recorded during earthquakes. The bidirectional displacement-controlled tests, which are the first of their kind, generated new knowledge to aid in the development and validation of TFP numerical models. The experimental results provided valuable insight into TFP bearing response and showed that the developed bidirectional model accurately captured the observed behavior of the TFP bearing. The advanced model, which includes translational and rotational degrees of freedom in both horizontal directions, tracks all component displacements as well as the change in bearing height during lateral displacements. The model is general so that no a priori conditions regarding bearing properties are required for the validity of the model. These properties make the advanced TFP model a valuable tool to explore the use TFP technology in novel applications.

To further the use of seismic isolation in more standard applications, simplified methods are needed for design. This dissertation investigates the use of generalized modal response spectrum methods to approximate global responses of isolated buildings without the need for costly non-linear numerical simulations. The advanced nonlinear TFP model is used for evaluation of the simplified methods.

Advanced isolation models are important and necessary for understanding the complex nonlinear dynamic behavior exhibited by seismically isolated structures, and to have confidence that performance goals are achieved under a wide variety of seismic hazards. Such models can, as shown in this dissertation, also be used to assess and improve simplified analysis methods suitable for use in routine design.