Originally built in 1911, Oakland City Hall was the first high rise building of the American Beaux Arts style, west of the Mississippi. Overaa performed $36 million of this major reconstruction effort, including the installation of the first base isolators in a seismic retrofit of an historical building in California.
To insert the 119 - 2000 pound steel and rubber base isolators, Overaa first built a 3 foot mote around the structure to prevent it from slamming laterally into an adjacent structure from a seismic event. Overaa actually "jacked up" the 19 story building with massive steel work in the basement in order to transfer the load to the isolators.
Reinforcing was installed throughout the entire building. A steel frame was added to the tower walls of terra cotta tile and brick infill. A historic clock tower sits on top of a truss system that extends to the outside walls and then transfers the weight to the columns below. The biggest challenge, perhaps, was getting the concrete up throughout the building. The concrete was pumped through elevator shafts to form shear walls without disrupting other work.
Overaa also restored or replaced the interior finishes in the lobby and lower levels. Today, visitors to the beautiful national landmark will still see the walnut paneled Mayor's Office, silver leaf colonnades in the council chambers, granite, terra cotta and marble throughout the structure.
- protection of and matching of historic architectural finishes - interior and exterior finishes - marble, wood, plaster, etc.
- addition of a state-of-the-art Oakland City Council public auditorium with balconies, theater seating, communication system, historic lighting, and podium
- high acoustical ceilings for greater sound carry.
- life safety upgrades were installed throughout the building and included new fire sprinklers and renovation of the power generator system.