Keywords: Mechanical behavior. Multi-spherical sliding isolation bearings. Seismic isolation systems. Passive control. Force-displacement relationship. Friction pendulum bearings. Seismic damping.
Abstract: The principles of operation and mechanical behavior of three novel spherical sliding isolation bearings are developed in this report. Their internal construction consists of multiple concave surfaces and behavior is dictated by the different combinations of surfaces upon which sliding can occur over the course of motion. As the surfaces upon which sliding is occurring change, the stiffness and effective friction change accordingly. These bearings are completely passive devices, yet exhibit adaptive stiffness and adaptive damping. That is, the stiffness and damping change to predictable values at calculable and controllable displacement amplitudes. The primary benefit of adaptive behavior is that a given isolation system can be separately optimized for multiple performance objectives and/or multiple levels of ground shaking. With the devices presented here, this is accomplished using technology that is inherently no more complex than what is current used by the civil engineering profession. In this report, the force-displacement relationships are derived based on first principles and by extending basic theories that apply to sliding upon a single concave surface. The theoretical behavior is validated experimentally through extensive component testing of the various devices. It is shown that the forces and displacements at which transitions in stiffness occur are predictable and therefore controllable in design.