Case Studies

Story Isolation

Our story isolation system uses stiffness control and passive damping to achieve high performance during earthquakes. The system consists of a building's floors and columns (the gravity frame), which are connected to the lateral load resisting elements (the reaction frames) via a unique assembly of springs and passive dampers located at each floor. The gravity frame is laterally isolated from the base by slide bearings. Seismic resistance is gained through spring and damper forces that are developed by the relative displacement and velocity between the gravity frame and the reaction frames.

Because these forces are resisted independently at each level by direct connections to the reaction frames, unusually high levels of damping can be achieved in comparison to buildings that use traditional passive control systems. With this direct-load path, uplift limitations associated with some base-isolated structures can be avoided, and the system can be incorporated in taller, more slender structures. The system also excels with lightweight structures, which may be problematic with some base-isolation applications. Ultimately, the story isolation system provides the design engineer unprecedented control of the building’s response by setting the period, level of damping, and drift.