An Innovative Application of Base Isolation Technology

The first application of seismic isolation in the world that permits the vertical expansion of an existing structure by introducing isolation bearings between the existing structure and the addition is presented. In essence, the isolated addition acts more like a tuned mass damper than an isolated structure. The existing building which serves as the base for the isolated addition is about 825 ft long and 110 ft wide with two expansion joints at approximately the third of the length. The new addition is a continuous structure that bridges over the expansion joints and utilizes concentric braced frames for its lateral strength. This is truly a unique application of the base isolation technology where the plane of isolation has been moved from the base of the building to the roof of an existing building. A 3D non linear analysis using site specific time histories was used to demonstrate the adequacy of the base structure and extract the design parameters for the new addition.