Originally dedicated in 1928, the Los Angeles City Hall underwent a major historical and life safety renovation begun in 1999. During this renovation, the structure was outfitted with over 500 isolator/sliders which were inserted between the columns/walls and the foundations below the existing basement. This state of the art seismic retro-fit utilizing base isolation permits the building to move up to 22 inches in any direction during a seismic event. In the event of an earthquake, these dampers will allow the structure to “float” as the earth moves around the building. In addition to the base isolators, 52 viscous dampers were installed in the basement with an additional 12 located in the building tower.
As the structure moves 22 inches in each direction, utilities, parking, and pedestrian connections to “fixed” earth must be capable of similar movement for the building to remain operational during and after future seismic events. This movement is accommodated by a “moat” with garage ramps connected to one side of the “moat” by sliding connections similar to bridge structures, and gas, electrical, communications, and sewer/water mains to move laterally utilizing special flexible and ball joint connections.
